Author Topic: Hesitation on Acceleration plus Excessive Backfire on Deacceleration  (Read 8148 times)

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Offline YoungBlood

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I had another thread asking about hesitation problems. I solved the 15A fuse problem by swapping a new condenser with an older one on 2/3 point plate. Since then, the hesitation returned, and swapped it with another old condenser once again. I was swapping condensers because I was seeing an excessive amount of zapping on the contact point, yet I know there is supposed to be some.

I am still not blowing the 15A fuse, but today when pushing 70 the bike started hesitating. This started after riding the bike 50 miles today. Then shortly after the hesitation started it started hesitating whenever I gave it a solid amount of throttle whether in 1st or 5th gear. I would appreciate a straight diagnostic step by step from you all. I am starting to lose my cool not knowing where to go testing electrical problems, or whether this is even an electrical problem. Is this fuel/air, electrical (coil related), ignition (do I need new contact points?) I will gladly report back whatever info/testing I need to do.
Here is what has been done in the interim:
Point gapping 1/4 is at .012
Point gapping 2/3 is at .016
Timing on 1/4 is dead on with F mark
Timing on 2/3 is just a tad retarded because I cannot adjust my plate any more
New coils off of 4into1.com
New caps (all are very close to 5okm)
Adjusted float height on 4th carb to richen condition (tried to eyeball it with #1 carb)
New ignition starter button housing - Starter works again
Voltage on hot side (closest to battery terminal) of fuse 15A is 12.12
Voltage on other side is 12.18
All spark plugs are new (#4 and #1 are sooty rich, #2/#3 are rich)
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Offline kerryb

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Several places to address your symptoms...
1.  Swapping the condenser should have little to no effect on the 15amp fuse.  The condenser is on the high coltage output of the coils.  It seems you have some high resistance in the wiring harness.  Have you cleaned all the connectors yet?
2.  The ignition FAQ has two places discussed that you should consider.  It is here. http://forums.sohc4.net/index.php/topic,5752.0.html.  specifically the parts about feeding the coils directly (I use a relay off the kill switch) and post #8 by twotired about shimming the points plate to get rid of the slop that prevents you from getting 4-1 & 2-3 to match in gap and fire.
3.  Have you used the clear tube method of checking float height/ bowl level?  It is the only way to really know where the fuel level is in the bowls (see photo ).
4. Do you have Keihin jets and needles in your carbs?, or something of lesser quality.
5. While proving to myself that pods are the problem on a 76 550f,  I also discovered that Timing  and ignition are vitally important to getting the engine to run smooth and burn clean.  So you seem to have two fronts to address; electrical for timing and enough spark, and carbs for right mixture.
Good luck, don't give up, it can be done.
intrigued by the wail...seduced by the scream.

Offline TwoTired

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The condenser is on the high coltage output of the coils.
Sorry, no.  Condensers are on the primary side of coils.

To the issue at hand:
Sooty plugs will all by themselves cause erratic spark.  The carbon coating creates an electrical pathway that shunts spark energy away from the spark gap.  But, “electrical” problem is actually an artifact of the engine getting more fuel than can be burned cleanly, ie too rich.

I don’t know how “stock” your bike is.  If it is, make sure your air filter is clean and for correctional tuning purposes, make it a new one.
 Have carbs been altered since new?
Have they been cleaned?
are emulsion tubes all clean?
What heat range are the plugs you are using?

If you put new plugs in, does it run ok until the plugs get sooty?  If so it’s pretty certain to be a carb mixture issue.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #3 on: June 01, 2021, 12:18:51 AM »
I am going to pull that airbox and check out the filter. Can this issue also be related to the breather element? I believe mine is disconnected, partially.

After pulling all four plugs, 1/2/4 were sooty and carbon deposited. Plugs are NGK D8EA. I wire brushed them off, and I also set all four floats to 26mm using a float tool while mounted to the bike. The hesitation issue became worse.

As to stock: there is the stock airbox, but aftermarket exhaust (a kind of can like exhaust, similar to what crotch rocket bikes have)...I can post a pic if needed. PO installed it.
Carbs were cleaned approximately 1500mi. ago when the PO flipped the bike. How often do I need to clean the carbs?
When setting the floats I noticed the gasket sealant I used to make the gasket stop leaking on the float bowl was corroded inside the bowl. I will definitely pull the main jets and emulsion tubes for a thorough cleaning while leaving them on the bike.
The hesitation problem did not leave when I put new spark plugs in. It appeared nearly right away, I'd say less than .25 miles it started hesitating.
Carb note: I have not messed with the carbs significantly other than vacuum syncing, putting all air screws 1 full turn out from fully seated, and messing with #4 float because it was too lean. This problem creeped up within the past 100-200 miles, sometimes I can drive 50 miles with no hesitation, then it becomes unbearable.

Thank you for the feedback, is a full carb pull and cleaning called for? Kerryb, ignition timing was spot on until this problem slowly creeped in. I double checked timing and point gapping, bike was running good early yesterday for 50 miles (pushing up to 85mph). Then hesitation started and progressively got worse.
« Last Edit: June 01, 2021, 12:23:43 AM by YoungBlood »
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Online pjlogue

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #4 on: June 01, 2021, 05:07:23 AM »
Adjusting the float height with a float gauge while the carbs are mounted on the bike, it's impossible to get a good setting.  Your best approach is to remove the carbs and do a complete cleaning of ALL internal passages and jets and always keep the same fuel valves and seats with their respective carbs!  Upon reassembly you can then adjust the float height with the float gauge.  This is done while the carb is sideways and the floats are hanging down from the pivot.  You tilt the carb so the float tang just touches the float needle pin.  At that point you check with the gauge.  Double check this with the clear tube fuel level in the float bowl.  Easier to do this on the bench.

Also, with the non CV carbs you need to lead the engine RPM with the throttle.  You can't just whip the throttle open. 

-P.

-P.

 

Offline TwoTired

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #5 on: June 01, 2021, 07:22:51 AM »
I am going to pull that airbox and check out the filter. Can this issue also be related to the breather element? I believe mine is disconnected, partially.

I don’t see a correlation here.  But, there are plenty of other reasons have that system functional.


After pulling all four plugs, 1/2/4 were sooty and carbon deposited. Plugs are NGK D8EA. I wire brushed them off, and I also set all four floats to 26mm using a float tool while mounted to the bike. The hesitation issue became worse.

Its the center electrode insulator that concerns me.  Coated with carbon makes it no longer an insulator.  Further, the porcelain is a bit abrasive and will remove metal from your wire brush a leave those conductive deposits on the insulator, giving the same effect as a carbon deposit.  So, either verify the problem exists with brand new plugs, or used a cleaning method that won’t replace carbon with metal deposits.  I don’t know a good way to burn off metal deposits, but an abrasive blaster using nonconducting media could work.

As to stock: there is the stock airbox, but aftermarket exhaust (a kind of can like exhaust, similar to what crotch rocket bikes have)...I can post a pic if needed. PO installed it.
Carbs were cleaned approximately 1500mi. ago when the PO flipped the bike. How often do I need to clean the carbs?

Answer: Whenever they get dirty or don’t provide the proper mixtures for your bike.

As to your exhaust, the back pressure profile is unknown then.  If your exhaust provides more back pressure than did the stock one, it will make the carbs appear to be more rich, as there is reduced scavenging effect with high pressure exhaust.

The carbs being “ cleaned” by the PO leaves much concern over the quality of the “cleaning”, and the parts that may have been replaced during the process.  Aftermarket parts are not always made to keihin specs. And that nearly always results in poor carburetor effects.  The engine still runs for the prospective buyer.  But seldom as well as using stock / proper components.  And sooty plugs are a delivered mixture issue, not an electrical one
.


When setting the floats I noticed the gasket sealant I used to make the gasket stop leaking on the float bowl was corroded inside the bowl. rb note: I have not messed with the carbs significantly other than vacuum syncing, putting all air screws 1 full turn out from fully seated, and messing with #4 float because it was too lean. This problem creeped up within the past 100-200 miles, sometimes I can drive 50 miles with no hesitation, then it becomes unbearable.

Thank you for the feedback, is a full carb pull and cleaning called for? Kerryb, ignition timing was spot on until this problem slowly creeped in. I double checked timing and point gapping, bike was running good early yesterday for 50 miles (pushing up to 85mph). Then hesitation started and progressively got worse.

Do you think chunks of sealant made its way to block tiny passages inside the carb?
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #6 on: June 01, 2021, 10:20:29 AM »
Thanks everyone, PJ I am hesitant to pull the carbs and clean them precisely because I rent an apartment in a city. I am trying to get creative in thinking how I can get away with cleaning and rebuilding it on my shared stairway porch. Yesterday I believe I got pretty darn close to 26mm where the float just started to push in the valve's safety pin when using the tool. I don't know the technical term, but once that valve rises to the seated close position, there is a very small button like pin that gets pressed in. As to not cracking the throttle, thank you, I have been wondering in the past if that was an indication of an issue with the bike or not. Either way, 1/2/4 were rich and sooty, all three of these carbs I bent the tab up a hair making them a bit leaner, they are now closer to 26mm then they were before. The tabs were seated downward, on #2 it seemed the valve was going to fall out. 
Twotired, I'm going to clean the plugs using some carb cleaner and without brushing them off. I also have some older plugs, at the moment I'm a bit strapped waiting on work to resume.
As to the debris, yes I unfortunately do think that the #2 carb has been plugged up with the gasket goop. In the gasoline of the bowl I could see it floating around like a sludge or thick crap (miniscule pieces too). I am going to remove all four mains and emulsions with carb on to clean them up and reinstall.
I'll take a picture of the exhaust, I have had no idea what type of exhaust it is. Other motorcyclists I've asked also had no clue.

Side note, I do know that #4 had 105 mains, the stock size for my 75' CB750F. I'll double check all sizes.
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Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #7 on: June 01, 2021, 10:52:29 AM »
Twotired, I realized after thinking about what you said that it would not make sense for the plugs to be rich if the emuslion/main jet was plugged up with gasket residue. I then got to wondering, what will cause this rich condition from the carb. I know float height, jet sizes, but what else?
Lastly, I also errored in saying that when I replaced the plugs with new ones the problem went away. I was blowing fuses left and right that was also causing a hesitation issue. Once that was resolved, the bike stopped hesitating, which then leads to the thought that those new plugs gradually became deposited causing the erratic spark theory.
About to clean the plugs and see what happens. Thank!
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Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #8 on: June 01, 2021, 02:17:20 PM »
I used some carb cleaner and a toothbrush to clean up all four spark plugs. I pulled the air filter, washed it in water, and then brushed motor oil onto it. I also pulled all four jets and emulsion tubes and carb cleaned. None were clogged up, and they are all 105s. Lastly I realized the float on #3, the only spark plug that was marshmellow colored was seated higher than 1/2/4, I eyed balled and adjusted them all to match where #3 sits and where the tab hits the valve.

However, the problem remains, it actually seems to have gotten worse. I'm at a loss, TwoTired, what next? New plugs? I'd like to avoid that at all costs given I own two sets of plugs (all are fouled, but I'd really like to try to reuse them). The first set was only used for two months. Pull the carbs and rebuild them? I have four rebuild kits lying around.
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Offline TwoTired

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #9 on: June 01, 2021, 03:40:34 PM »
Twotired, I realized after thinking about what you said that it would not make sense for the plugs to be rich if the emuslion/main jet was plugged up with gasket residue. I then got to wondering, what will cause this rich condition from the carb. I know float height, jet sizes, but what else?

The main jet and throttle jet are unlikely to clog.  However the emulsion tube mixes air with the fuel flow before entering the carb throat.  Plug the emulsion tube holes, and you'll get a richer mix of fuel.

Be aware that the idle/pilot jet has its own emulsion tube.  Many aftermarket suppliers have made design changes to this part resulting in rich mixtures.  The jets unscrew in your model carb, I believe.  So, they can be examined without carb bank removal.  Not saying it's easy, but possible.  Anyway, the original pilot jets should have a K stamped on them.  The pilot jet system is just that, it supplies the minimum fuel mix to allow the engine to run at idle and can be tweaked somewhat by the air bleed screw.  That system supplies fuel over the entire operating range of the motor, with the throttle valve and main jet adding to the fuel mix as the engine winds and the throttle is twisted.   So, if the pilot system gets rich, it will tend to make other operating ranges richer, too.  As you probably know, the fuel level in the bowl can affect mixture, too, as the further the fuel needs to be drawn up the less tends to make it into the carb's distribution systems.  Note that float mechanical height, while related, is not the final word on actual fuel level, as it has been noted that aftermarket float valves can have a different spring pin tension affecting stock float height settings.   I say all this because flippers will buy a "kit" to rebuild all the carbs and use the kit's hard parts instead of the original parts that have proven to work for 40+ years.  And many times those replacement parts are dimensioned or designed differently.

Lastly, I also errored in saying that when I replaced the plugs with new ones the problem went away. I was blowing fuses left and right that was also causing a hesitation issue. Once that was resolved, the bike stopped hesitating, which then leads to the thought that those new plugs gradually became deposited causing the erratic spark theory.
About to clean the plugs and see what happens. Thank!
When the fuel mixtures are correct, the plugs will self clean whenever the engine revved under power. The combustion heat cleans them.  Some simulate this heat by using a torch to burn off the deposits.  I prefer the media blast technique, myself.  As I have found today's offered chemicals don't do a very good job of removing carbon soot deposits.   Be aware the idling and use of choke tends to build up soot deposits.  Wailing on the throttle can be the answer to keeping plugs clean, which may be tough to do in city environments.  While you sort out fuel mixture issues, you might get a set of D7 heat range plugs, as they run hotter.  Probably not good to use those in summer heat on the freeway, though.  They won't take enough heat out of the chambers like D8 will.  But, until you get the mixtures sorted, they might reduce your time cleaning plugs.

About your air filter.  The stock ones are paper.  You don't oil these ever.  So, I expect you have an aftermarket filter.  The K&N filters have a kit of both cleaner and spray oil of the proper viscosity.  Over oiling and/or using oil too thick can create enough restriction to effectively enrich carb mixtures similar to when the filter is blocked with filtered particles.  As a test, remove the filter element temporarily, to see if it is in fact making your mixtures too rich.  Either buy new plugs for the test or go out and wail on the motor to see if the plugs will self clean.  A test track or area without police presence would be most helpful for this.

Cheers,

Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Online pjlogue

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #10 on: June 01, 2021, 04:35:16 PM »
You should also check your carb rubbers for air leaks.  Easy to do.  Get the bike up to temp and let it idle and spray carb cleaner around each rubber joint on the carb side and the head side.  If the engine rpm changes you know you have a air leak.  Air leaks here can cause a rich burn.  Opposite conventional thought but these are pulse feed carbs.  The rubbers (at 40 + years of age) are hard and usually cracked.  The clamps can also become stretched and not give a good tight squish on the hard rubber.

-P.

Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #11 on: June 01, 2021, 05:26:16 PM »
Thanks everyone, a bit busy atm. Carbs are completely disassembled and I am cleaning/rebuilding with replacement parts. Twotired, the kit I received does not seem to vary at all from the Keihin parts, mine have original K stamps (or something that looks like K, but more scattered like).
Please let me know where the right position should be for the jet needle clips. If I am experiencing rich condition, should I not move the jet needle up/down to lean?
Lastly, how do I do a bench synch? Do I need tools to do that? So far everything looks really clean, I'm kinda pissed off. I was hoping to find something blatantly wrong with them. They are clean to begin with, but I am doing a thorough job. Please let me know how to make this a leaner condition.
Twotired, thank you for the wonderful info. I will be sure to be cracking the throttle soon. I also sacked up and got 4 new D8EA plugs, I read your post late from leaving the store about the other hotter plugs.
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Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #12 on: June 01, 2021, 05:37:50 PM »
I have pulled the jet needle, it is currented slotted in the middle of the 5 groove locations. Should I move it up a slot from the middle towards the top to achieve leaning?
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Online pjlogue

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #13 on: June 02, 2021, 03:15:05 AM »
For a bench sync all you need is a small drill bit.  #55 should work.  The drill diameter isn't really important as long as it is small.  The idea is to get all four carb slides at the same height.  Before you begin, make sure your carb carb adjusting rod feet (T end of the adjusting rod where they engage the carb slides) are clean and a dab of grease is applied so the feet articulate smoothly with the carb slides.  This is important because if they are dirty/rusted it will make your final syncing with the manometer difficult.

With the carbs mounted on the carb rack, turn your idle adjustment screw in so you have at least ~2 turns of engagement where the slides are held up.  Now proceed to adjust each slide so the chuck end of the drill bit just fits under the slide on the air filter side (upstream side) of the carb.  Be very careful not to scratch the carb slides!  The cut off face (slide bottom) is a precision part.  Adjust each rod at the top so each carb slide has the exact same opening height using the drill bit as a feeler gauge.  When done you should have about two threads showing above each lock nut on the adjusting rods. 

Once properly adjusted you should be able to use the idle adjustment screw to close all slides.  If all slides don't fully close using the idle adjust screw you will not be able to lower your idle. 

Your main jet needle height should be ~4th position from the bottom.  With these pulse, non pumper (no accelerator pump) carbs it is important to understand how they work in order to set them up properly.  Two main things will effect your throttle response assuming your float height is set properly.  Idle mixture screw setting and main jet needle height.  The leaner things are the more "throttle lead" you will need.  The proper way to see how your carbs are set up for the different throttle openings is to do what is called a "plug chop"  This is where you run the engine after it is fully warmed up at a constant throttle opening and then flip the kill switch while at the same time pulling in the clutch and coast to a stop.  You want the engine to stop turning at the moment you his the kill switch.  You then pull each plug (at the side of the road) and inspect it to see the plug condition.  This plug chop is impossible to do in a city situation.  (except idle)  You need back roads with little traffic and a long stretch of open road for anything above 60 mph where police are few and far between.  ;)  Engine needs to fun for several minutes at a specific load/throttle opening and then chop it to get a good reading.

-P.

Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #14 on: June 02, 2021, 11:21:34 AM »
Thanks PJ, I followed your directions and used this website from another thread for float height: http://www.hondachopper.com/garage/carb_info/float_levels/float_levels.html. Floats are at 26mm. Needle jets are set one groove below the 5th top slot. So as you said, four up from the bottom slot (4th slot going up). All jets are 105s. I did the bench sync as you prescribed, however I set the idle screw 1.5 turns in because I was unable to get the carb slide far enough down for a 1/8 inch bit (round side, not threaded/sharp). All of the lock nuts are approximately two threads exposed. I also think I may have unearthed what my rich condition was being caused from. I believe, I am not sure, but the choke flaps disengaged from the lever that hooks into the side that then runs to the master lever. Thus, I think the choke was "shut" for at least 2 or 3 of the cylinders. My thinking follows this because when reassembling the choke I f***** up where the nut was not tight enough, allowing the little lever to disengage and leaving the choke flap closed. When I removed the choke I recall all the nuts were barely threaded on, they now show atleast 1-2 threads and operate with a touch of resistance.
 About to mount the #$%*, put new plugs in, and try out the "plug chop" too make sure we're all marsh-mellow. 8)
Thanks everyone, it was fun so far.
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Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #15 on: June 02, 2021, 01:54:34 PM »
Problem perists, I pulled the air filter, it helped a little, but the hesitation is there. There is also a terrible backfire every 4/5 seconds. Hesitates like crazy. I'm going to pull the bull#$%* exhaust can off and just run it without a muffler. I am also going to sync the carbs with a vacuum and take a look at the timing again. I sprayed carb cleaner around and found no leak. Ideas?? Those new plugs are in there, and no I was not able to "plug chop" because the bike is running so poorly I didn't want to get onto the express way.
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Offline ANDREAS MILKE

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #16 on: June 02, 2021, 04:06:55 PM »
I had similar problems on my cb500k, the biggest problem was a slack in the centrifugal advance system, there was wear on the advance system, did you check if there is excessive slack in your mechanic advancer system or do you use electronic ignition with programmable advance?
Andreas Milke

Offline Alan F.

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #17 on: June 02, 2021, 04:29:09 PM »
Problem perists, I pulled the air filter, it helped a little, but the hesitation is there. There is also a terrible backfire every 4/5 seconds. Hesitates like crazy. I'm going to pull the bull#$%* exhaust can off and just run it without a muffler. I am also going to sync the carbs with a vacuum and take a look at the timing again. I sprayed carb cleaner around and found no leak. Ideas?? Those new plugs are in there, and no I was not able to "plug chop" because the bike is running so poorly I didn't want to get onto the express way.

pulling the air filter added more air to the mix, this would prove that you're running rich as would the backfire you mentioned (exhaust backfire correct?) Is this backfire happening at idle? are you quite sure you moved the needle clips in the right direction? It can be confusing when we're frustrated.

yes verify timing and advancer function.


I had similar problems on my cb500k, the biggest problem was a slack in the centrifugal advance system, there was wear on the advance system, did you check if there is excessive slack in your mechanic advancer system or do you use electronic ignition with programmable advance?

Edit: It's not a CB650 sorry I was acting as if it was, instead of the 75 CB750F that he has, stock is points with a mechanical advancer, like all SOHC 750s

« Last Edit: June 03, 2021, 10:47:56 AM by Alan F. »

Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #18 on: June 02, 2021, 07:07:44 PM »
Update: I carb synced and checked the timing. Timing was off, which is weird because it wasn't a few days ago. I reset it, both 1/4 and 2/3 are perfect when static timing on F mark.


Alan, thanks for the feedback. In response there's alot...
Most importantly, the needle jets. If the needle was up and down like this | with the slots on the top, then I put it on the 2nd slot from the top. So the needle hangs lower when installed into the slide and into the jet which is fed from the 105 main jet.
I don't know what you mean by the "advancer function". I only know about the timing plate, contact points, and the fire/timing plate behind the window. Is that plate the advancer function? What is slack in the advancer mechanism, I'm at a lost here on understanding.
I also have noticed the breather element is disconnected from the air filter's top nipple. There is no rubber hose, there never was. Can a dirty breather element cause all this trouble? I've never pulled it out, and I assume the PO never touched the thing and it originally was disconnected.
Also, I have had a gasket head leak for sometime. It doesn't weep oil, it barely leaks oil. But I've never done a compression test b/c the autoparts store didn't have the right rental tool. The red oil light is off when running, wouldn't it kick on if the head gasket has caused a compression issue?
Before the carb sync it was backfiring at idle (no air filter). After the carb sync, the hesitation has improved and the backfire is not there at idle. About the location of the backfire, it is coming from the exhaust, but when I pulled the can and shimmy union off, the backfire still existed. The throttle is also a lot toucher, with barely any rotation of the handle it is moving faster but obviously still hesitating with backfire.
When I was carb syncing a strange problem kept happening, whenever I blipped the throttle to get the vacuum gauge to reread, the push cable would snap back after letting go of the handle. However, the rpms would stay high. After messing around with the nut adjusters, the problem got better, and I got all the carbs dialed together. I believe this is why the bike doesn't return to a low rpm quickly without giving the throttle handle and extra push. I know I'm getting off track, I'm just thinking of everything going on with the bike.
Also, the bike will not start without the choke, even when hot. Which is odd and a new problem.
About the contact plate mechanism, I'll send a picture, but the 2/3 contact point that mounts on the crankshaft sometimes rubs against the crankshaft nut. At times it'll even spark, I don't know why it is out of position, but I always have to push it away with a flat head to stop the side sparking. Also 2/3 has noticeable blue sparks, not excessive, but they are there. 1/4 does not. Both are set at .012.


« Last Edit: June 02, 2021, 07:09:21 PM by YoungBlood »
When you're going through hell, give it some more gas.

Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #19 on: June 02, 2021, 07:21:11 PM »
This is exactly where I set the one I installed.
When you're going through hell, give it some more gas.

Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #20 on: June 02, 2021, 07:26:48 PM »
Should I throw the old coils back on the thing and see if the problem goes away? I'd like to fully rule out whether I am not getting a hot enough spark. All four cylinders are hot hot at idle, but my mind wonders if the new coils I got are "weaker" or perhaps faulty??
When you're going through hell, give it some more gas.

Offline Deltarider

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #21 on: June 02, 2021, 10:15:58 PM »
This is exactly where I set the one I installed.
That's 2nd from top.
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Offline YoungBlood

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #22 on: June 02, 2021, 10:52:52 PM »
Thus 4th from the bottom. So I don’t see how a rich condition is still my problem, nor the carbs now that they’re rebuilt and sync’d. I’ll do a clear tube check, pull the breather element clean it and hook it up properly. If that still doesn’t do it I feel I’ve ruled out fuel/air, and it must be ignition.
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Online pjlogue

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #23 on: June 03, 2021, 03:57:18 AM »
YoungBlood,  You had posted:  "I don't know what you mean by the "advancer function". I only know about the timing plate, contact points, and the fire/timing plate behind the window. Is that plate the advancer function? What is slack in the advancer mechanism, I'm at a lost here on understanding."

Check your spark advance mechanism.  It and the centrifugal weight arms should move freely.  A sticking advance mechanism can give a slow to return to idle or hanging idle.  The advance mechanism consists of a center "collar" that has a timing lobe on it and the points cam follower rides on, the centrifugal weight arms and counter weight springs.  As the engine rpm increases the weights try to fling out and pull on the springs.  The "ears" on the weights engage the center collar (cam) and twist the collar to advance the ignition timing.  The majority of the advance mechanism sits behind the points plate.  Only the cam lobe "collar" protrudes from behind the points plate.  You can check if it is moving freely by twisting the collar.  A strobe timing light is best for testing to see if you get full advance and return to idle settings. 

Your throttle cables should have just a slight bit of slack in them.  The wee bit of slack should be there when the handlebars are fully turned left-right as well.  Throttle cable routing is very important for smooth operation.

If your hesitation is at low speeds or from stops try adjusting your idle mixture air screws.  After my restoration on my '76 750K i had the "hesitation" from a stop and low speeds.  I richened the idle air circuit a little at a time.  Made a huge difference.  This will also help with needing choke when the engine is warmed up.  This tells me that your idle air circuit is very lean.  Thoughts about which direction to turn the screws varies by person.  What I have found is turning the idle air screw in richens the idle mix.  Turning it out leans the mix.  The ends of these needles should not be chewed up.  If they are, you should get new ones.  The holes in the ends of the needle should be clean as well.  They can get quite gummed up.  For my '76K I ended up using #38 slow speed jets and enrichening (turning in) the idle air screws ~1/4 turn.  This gave me the best cold/warm start and proper rideability I wanted. 

There is a LOT of information given in this thread.  My suggestion is to only make ONE adjustment at a time, test it and then either put it back to where it was and make another adjustment some place else.  You don't want to start making multiple adjustments all over the place because you will invariable introduce other problems where there were none and never know it. 

-P.

Offline Alan F.

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Re: Hesitation on Acceleration plus Excessive Backfire on Deacceleration
« Reply #24 on: June 03, 2021, 04:33:02 AM »
Yes, what he says, all of it.

Well written Pjlogue.

Advancer location, #1:



Don't swap back to your old coils.

"About the contact plate mechanism, I'll send a picture, but the 2/3 contact point that mounts on the crankshaft sometimes rubs against the crankshaft nut. At times it'll even spark, I don't know why it is out of position, but I always have to push it away with a flat head to stop the side sparking. Also 2/3 has noticeable blue sparks, not excessive, but they are there. 1/4 does not. Both are set at .012."

I'm doubtful there should be any contact here at all, did you download a manual from the forums here? It should have detailed info on how to set up and gap your points.

I wonder if your advanced shaft #3 in the diagram has a wobble to it?
« Last Edit: June 03, 2021, 10:45:31 AM by Alan F. »