Topic: Tuning problem

[Donzon]

Hey All:
            I am once again forced to ask for ideas\opinions as I have wracked my brain, exhausted all archived posts, etc.

CB750K4  Stock airbox, paper filter, 4into2 exhaust.
 
  I am experiencing what seems to be an intermittent ignition miss from idle through low and midrange RPMs, after that I can't tell.  Not sure that it's ignition, but it feels like it.  Kind of a quick, irregular surging.  It started a few weeks ago (I think) and has since become worse, now to the point I parked the bike. 

  Bit of background.  Bought it 18 months ago in very poor, not runable condition.  Did lots of repair, cleaning , tuning and managed to get it up and running, but never really quite right.  Was down alot for continual repairs further tuning, carb cleaning etc.  There were parts that were not the best but I was trying to spread the cost over time.  Read lots of posts and kept learning.  Every time I went to check something it was bad, so I kept replacing things hoping I would eventually win the game.

This year my goal was to keep working on getting it running properly so I tore the carbs down again for cleaning and rebuild.  The carbs are 657B,  so I replaced the main jets with the recommended 105, replaced the slow jets 40, and the needle valves and seats.  Set the floats to exactly 26mm with a gauge, and made sure the emulsion tubes and every passage was clean. Set air screws one turn out.  New manifold boots from airbox, and carb to engine.  Filter is new paper. New fuel lines and filter screen in petcock.  Synched carbs with vacuum gauges (several times).

 Replaced the points, condensers, plugs (NGK D8EA), resistor caps, trimmed wire ends.  Tested coils with OHM meter as per FAQ, cleaned and checked bullet connectors etc.  Set point gap to .015, timed with timing light.  Checked battery voltage and condition.

 To my great joy, the bike ran worse! 

  Checked the compression both wet and dry and all was well.  Set my valves, again, this time I set them to .003 and .004 to make sure they weren't too tight. Read some more posts on ignition stuff so I aligned the ignition cam shaft, and shimmed the point plate to remove all slop.  Tried setting the points to .012 and re-installed the old condensers, re-timed.  No improvement. 

   After all this time I'm running out of ideas.  Despite my best intentions and efforts this bike has never run properly and I've put only 1000 miles on this machine since I've had it.  It's become quite the joke around work how I ride one day and tear it apart for a week.  Hell this thing is getting more maintenance per hour than the space shuttle!

  Don

[Gordon]

Sorry you're still having trouble after all that work.

What do the spark plugs look like, and is your battery holding a full charge? 

[TwoTired]

I agree.  A note about the spark plug deposits would be helpful.

Some other things to check. 
Look at your ignition leads in the dark, to see if spark is escaping through insulation cracks.
If you can, run the motor with the fuel tank off, so you can see near the coil mounts, too.
Check the mechanical advance mechanism for free movement.

Cheers,

[Donzon]

  No cracks in the insulation and I have checked for arcing but haven't noticed any: I always run with the tank off to do carb synch. I'm wondering about cross firing since the wires do touch each other near the coils, so I'll check into that when I can run at night again, and will try to separate the wires better.  I've tried holding them apart at idle and haven't been able to find any problem.  Checked the plugs a few times and they are the typical sooty black from idling.  The headers do all get hot,so if it's a misfire it's very intermittent.  I've tried to determine misfire with my inductive timing light but it is very unreliable.  I could only ever pick up a signal from 3 and 4 wires and since I replaced the caps, 4 has become a very difficult signal as well: I just get enough sparse signals to determine the timing.

  I had the advancer off and it was free and working fine.  I did lube it and the springs were a tiny bit loose so I clipped half a coil off of each.  That cured my timing from floating around at idle and still advanced properly.  I may order new springs since I seem to be at Honda every damned week anyway.  Gotta love Honda for stocking parts for these bikes! 

  I suppose a plug chop is in order, but I was under the impression that it was more of  a tool to fine tune mixture and since the bike is running poorly I didn't figure it would tell me much until I get this particular problem under control.


Don

[Donzon]

Hey, me again.

  Still having problems.  Checked some more stuff and everything appears to be fine.  Even installed a Hondaman module today but no luck yet.

  It appears to be idling better, and also accelerates fine but when I run at steady speed I can feel it surging.  Since it's most apparent at low throttle I figured air screws, but I've adjusted them all over the place and I can't get rid of it.

  I'm still not sure if it's ignition or carburetion but I can't seem to get past this problem.  It gets worse the hotter the engine gets.  My usual 15 minute highway run to work is no problem but if I go for a longer ride it begins to  happen more and more until it becomes really bad.  I know the next step is a plug chop but I wonder if anyone has experienced this problem before so I can check some other stuff first?  I keep trying different things and it always seems to be fine afterwards, so I figure I've finally got it licked, but as soon as I have a chance to take a longer run, there it is again! 

  Please give me some help, I'm really running out of ideas now. 

  Don

 

[bender01]

Is it vapor locking from a poor gas cap vent? I dont think the plugs should be sooty from idling. Is the petcock clean and working properly? Do You have an inline fuel filter and is everything going downhill to the carbs? Seems you have a clue but just trying to help. I had to clean my carbs 3 times on both mine til I got it right. Are thse o-rings in the carbs in good shape? Are you sure the jets are the right size?

[rshelbert]

My last project was doing exactly the same thing.  After a wide range of plug chops I determined it was running extremely rich until it got to around 4k rpms.  At 4k it would lean up to normal.  When it got hot it would get sluggish and sputter at these rpms and hesitate slightly off idle.

It ended up being my float on carb 1 and 2  snagging up and letting to much gas in.

I found it purely by accident really,  I was riding around with it warmed up and running crappy as usual when my float stuck on number 1 carb pouring gas all over the ground..  I decide I would turn the gas off so the bowl would run some of the gas out and let the float drop freeing it.  When I turned the gas off it stoped leaking and the bike started running perfect.  I turned it back on, it ran good for about 10 seconds then back to crappy. Turned it off and back to good. 

I am not sure why exactly it did this , but when I took the carbs apart the bowl gaskets were kinda mushy like they were always in gas.  I adjusted then to spec and noticed that float 1 and 2 were hitting the side of the bowl like they had been bent or something.  I bent them slightly and they run great now.

Now if I can get my current project to run right, does it ever end?

[joeb]

Is your problem a surge or a ( stutter) at a held throttle posistion??? I had a stutter or stumble with my motor at steady throttle it ended up being my float jet needles were sticking closed (not getting enough fuel ).  Just a thought .  Not sure about your motor but .03and .04 is a little open for your valves.

[chrislib]

I was having a very similar problem with my bike. I did all the usual stuff, O/H carbs, set valves (@ .03&.04 better a lil loose than tight) &cam chain etc. Bike has elec ign (Martek) and Accell 3.4 ohm coils & wires.  Carbs are 120 mains 40 pilots(IIRC), needles 3rd slot. Exh is a Kerker with a homefab baffle/tip, stock airbox w/paper filer. Bike ran awesome when cold and as it warmed it did the off idle/midthrottle breakup/chug 8 stroke thing. What I did was dropped the needles another notch (leaner) and air bleeds at 1 1/8 turn out. A big help but still a little soggy. I took the bleeds out to 1 1/2 and it`s 95% to my satisfaction. Yours sounds fat as well, try making small changes at a time and see what it does.

[number13]

My usual 15 minute highway run to work is no problem but if I go for a longer ride it begins to  happen more and more until it becomes really bad.

I am betting on an electrical issue. In my experience, 20 minutes or so is the
typically the amount of time it takes for weak electrical parts to begin
breaking down, especially those parts exposed to heat, which is basically
every part on a motorcycle. Double check your coils,coil connections, plug leads,
battery cables and connections and main fuse holder.

[Gordon]

Why are you avoiding looking at the spark plugs?  It's easy to do and can really help narrow down your problem. 

You also never said what condition your battery is in. 

[RRRToolSolutions]

The other Gordon here. Hi.

Surging comes from too lean. It it's starting, idling, and will accelerate ok - but is surging (seems to be wandering at a steady throttle setting) then it's too lean. Like these guys said early on - pull your plugs.

This ain't rocket science (even I can do it). Get the bike warmed up and take it for a ride. Set the throttle and repeat the surging. After 30~60 seconds - pull the clutch in and kill the engine at the handle. Don't use engine braking because you want to see the plugs at their "as-ran" condition. Pull them all and keep up with which hole each came from because you want to compare them.

Plug chops aren't just for top-end, WFO runs - these can be done safely and at speeds I'm guessing will not exceed 50~60 mph.

That's where surging is most often hits comuters. I'm willing to bet it's the slide needle is too low. Look at the plugs first and if they are white around the insulator as I suspect, you'll need to raise those needles 1 or 2 notches.

Bookmark this link. It will save your life (well not really, but will make life a lot easier to understand)

Regards,
Gordon

http://www.4secondsflat.com/plug_chart.html

[Donzon]

Hey All:
          Many thanks for the replies, it helps a lot.

I finally was able to get the plug chops done.  What follows are the results:

First pic is at wide open throttle, uphill, top gear for about 10 seconds.

Second pic is cruising at 4000 rpm top gear

Third is low rpm, low gear slow speed .

[Donzon]

The photos don't show that well, but by comparison to the sparkplug chart I am on the lean side of normal, about #22.  I only have one clip position left on these jets, do you think it would be enough or do I need to go up one size?

I didn't have as much trouble today as yesterday though it might have been because I stopped to do the chops and the bike cooled down a bit.  To answer some previous questions, it wasn't that I was avoiding the plug chops, it was just that I have checked so many things lately and every time I do, there is a problem that needs to be fixed!  I just wanted to make sure that I had everything covered before I did the chops so I could trust the result and make changes accordingly.  I still wonder why the problem is so intermittent and is worse some days than others, so I still haven't discounted electrical problems.  I have cleaned and checked the connections and tested everything I can think of (including battery)  but might have missed something.

As for the last pic, usually all the plugs are sooty after low speed operation, I don't know what happened to #1 there?  I didn't idle the bike though, I just treated it as another plug chop and killed it.


Don

[RRRToolSolutions]

Don,

1) The low-speed is too fat/rich - it's either the pilot jets are too large or you've got the floats set too high in the bowls - and you're sloshing/over-filling the bowls (remember the floats are measured as distance away from gasket surface - more = less fuel and earlier shut-off). Unless someone has drilled them out, I assume the pilots would be exactly the same size (are they?). If so, then I would guess too much fuel and it's puddling into the venturi and causing the way too rich fuel issue.

2) You're dangerously lean (piston melting, ring-land area will soon start coming apart lean). Whe you say you're near the top, are you referring to the clip being in the upper grooves? Remember, the clip in the bottom groove would translate to the needle being up (as rich as it will go). Confirm this - I've known some to get this part confused. You want the clip in the middle or one below it.

3) If you are in fact set with the needle in the lower 1 or 2 grroves (needle raised), then you have too small a main jet. You are not getting enough fuel at 4,000 rpm or at full throttle.

A few things to consider -

A) The mains should have no effect on your low-speed problems, so just because she is crazy-rich down low, she can still need the needles raised or the main swapped for larger.

B) I don't think the pilot could make that big of a difference from 2-3,000 rpm to mid-range. I think the culprit is fuel level too high. #4 is really fat and blubbering at low speeds. I don't like setting floats with a gauge. The "fuel level" method is actually much better, but it can be a pain in the butt since it's measuring fuel level in the bowls where a special tool/adapter is needed and several cycles of bowl removal and settings are required. This fuel puddling is exactly what I went through recently on my KZ900.

Best Regards,
Grodon

[Donzon]

1) The low-speed is too fat/rich - it's either the pilot jets are too large or you've got the floats set too high in the bowls - and you're sloshing/over-filling the bowls (remember the floats are measured as distance away from gasket surface - more = less fuel and earlier shut-off). Unless someone has drilled them out, I assume the pilots would be exactly the same size (are they?). If so, then I would guess too much fuel and it's puddling into the venturi and causing the way too rich fuel issue.

The slow speed jets are stock #40 and brand new from Honda.  I did set the floats very carefully with a gauge but it would seem I had better rig something up to check the actual gas level.  This rich condition has screwed me up for a long time, I made many changes to compensate for it but I assumed the float levels would be accurate.  The bike has always started first kick, but I never needed much/any choke and always had to open it as soon as the engine fired up.  I've pissed around with the mixture screws a zillion times but the float thing never occurred to me.  Everything I know about bikes I have learned from this forum over the last year and a half.  I've had other bikes but I never had to work much on them, they just ran.

2) You're dangerously lean (piston melting, ring-land area will soon start coming apart lean). Whe you say you're near the top, are you referring to the clip being in the upper grooves? Remember, the clip in the bottom groove would translate to the needle being up (as rich as it will go). Confirm this - I've known some to get this part confused. You want the clip in the middle or one below it.

I installed the 105 jets at the fourth groove from the top (dull end)  as per the chart of carb settings referred to in the FAQ.  I can raise the needle only one more notch.  The chart only specifies 105 jets for this specific carb, I wonder if it is correct as most others use 110.  I guess I will have to order some so I have some room for adjustment.  The bike had 110 in when I got it but they were in very pitted condition so I replaced them.  Since I was having so many carb problems I replaced the needle valves, slow jets and mains with the chart recommended sizes and figured I could work from there.  If I went to 110 should I start in the middle clip position?  I don't know how much difference these adjustments make so I'm not sure how much of a jump I should take.

3) If you are in fact set with the needle in the lower 1 or 2 grroves (needle raised), then you have too small a main jet. You are not getting enough fuel at 4,000 rpm or at full throttle.

A few things to consider -

A) The mains should have no effect on your low-speed problems, so just because she is crazy-rich down low, she can still need the needles raised or the main swapped for larger.

Ya, it took me awhile to get this whole thing figured out.  Kinda steep learning curve for this carb stuff.  I keep reading the posts, faqs over and over but some things just take a while to wrap my head around 

B) I don't think the pilot could make that big of a difference from 2-3,000 rpm to mid-range. I think the culprit is fuel level too high. #4 is really fat and blubbering at low speeds. I don't like setting floats with a gauge. The "fuel level" method is actually much better, but it can be a pain in the butt since it's measuring fuel level in the bowls where a special tool/adapter is needed and several cycles of bowl removal and settings are required. This fuel puddling is exactly what I went through recently on my KZ900.

I seem to remember a thread on this method posted some months ago, I guess I will have to see if I can find it again.  At least I can tweak float levels without pulling the carbs off.  I've had them off a LOT of times now!

Best Regards,
Gordon

Thanks a million Gordon, this has helped clarify some things for me, and thanks to everyone else who has replied as well!  At least I have a direction to go.  Now back to bashing my head against the beast.

Don

[Hush]

Ah and there lies the clue....."I don't have to use much choke" these beasts love choke, at least 5 minutes of it on my beastie.
So if you don't need choke then something is running not according to Honda logic.
Even worse if you can start from cold without the choke, if this happens check the side of the tank it will probably say SUZUKI.

[andy750]

Ah and there lies the clue....."I don't have to use much choke" these beasts love choke, at least 5 minutes of it on my beastie.

Even worse if you can start from cold without the choke, if this happens check the side of the tank it will probably say SUZUKI.

I can sometimes start my CB750K2 with no choke - 120 mains/40 pilot, HM300 exhaust, stock engine, 51,000 miles. Bike runs great. For my K4 I use choke for only 5-10secs and again stock - 110 mains/40 pilot, stock HM341 exhaust. Bike runs good but compared to the K2 could use some tweaking. I know the later bike (77/78) were more cold blooded but I the early ones are better in my experience.

cheers
Andy

[Donzon]

OK, here we go again 

Changed to the 110 mains, but I left the needle position the same for quick diagnosis, and did a WOT plug chop.  Things are virtually the same.

I guess I have to look again at the float levels, meaning I have to search out and buy a float bowl to destroy.  Yay.

Question is once I have this rigged up, how in the hell do I know where the gas level is supposed to be, now that I'm basically eyeballing it, and it doesn't appear that any of the plugs are the right colour yet?


Don

[Donzon]

Dammit, pics don't show very well.  Guess I'm a worse photographer than bike wrencher!  Plugs were pretty much identical to last chop.

Plug one had a snow white insulator, others were basically white with a bit of soot, likely because I was too slow on the kill switch.

Don

[upperlake04]

  Sorry, no advice from here Don - hang in there, with your stick-to-it attitude, its only a matter of finding more things to eliminate before you nail it. 

[hapsh]

It is hard to tell from the pic but they do seem to look a bit better.  Remember you only changed one step 105-110, its hard to see a difference with such a small increment.  I would go with 120 and try again.  I would also figure out your float level.  You don't need to destroy a float bowl to check your fuel level.  I would just drain the floats into measuring cups and compare them.  Then decrease you level by increasing the float level from the gasket 1-2mm and measure again.  Then once they are all the same do your plug chops again.  I agree with the others, you are way rich at idle and pretty lean on WOT.  Get your float level set even and then verify that your idle mixture circuits are not clogged, if your air-jets are clogged it could make your idle mixture rich.

[Donzon]

It is hard to tell from the pic but they do seem to look a bit better.  Remember you only changed one step 105-110, its hard to see a difference with such a small increment.  I would go with 120 and try again.  I would also figure out your float level.  You don't need to destroy a float bowl to check your fuel level.  I would just drain the floats into measuring cups and compare them.  Then decrease you level by increasing the float level from the gasket 1-2mm and measure again.  Then once they are all the same do your plug chops again.  I agree with the others, you are way rich at idle and pretty lean on WOT.  Get your float level set even and then verify that your idle mixture circuits are not clogged, if your air-jets are clogged it could make your idle mixture rich.

  Ya, the pics are deceiving, the plugs are almost identical to the previous chop.  Gotta figure out how to get better pics too.

  Problem with simply draining the bowls is that you also drain the feed lines at the same time so you don't get an accurate reading.  At the moment I'm not concerned about the crappy idle stuff, but the lean running scares the crap out of me so I'm (again) not riding the bike till I get this worked out.  Great to watch yet another summer pass by while I swear at this hellspawn bastard machine! 

  I'm not planning to rejet again till I'm positive I have the  (presumed) float issue under control as the bike has so far not responded to me throwing money at it, and I imagine it should run at least somewhat decently on the stock settings.

  If anyone posts about digging some bike out from under a manure pile, filling it with gas and riding it for 5 years without a problem, I'm coming to your house and burning mine on your front lawn 

  Will keep you all posted when I have something worth posting

  Owner of the Black Lemon
  Don

 

 

[RRRToolSolutions]

Don, check your PM.

No, no guys - you don't have to do all of that. To make a fuel-level gauge, you want the bowls in their as-fit position. The gauge simply replaces the drain screw with clear tubing. That tubing is held-up next to the carb bowl and a reference is made to it's internal level. As we all know, all fluid/liquids find their own level.

All you need to do is get an extra brass bowl drain screw. I drilled mine in the center to accept a Lowes brass fitting, then filled around it with JB Weld. Trust me, I have a $75 dollar tool and one I made for less than $3 - one works as good as the other. Give me a little while to finish work and I'll scan the instructions and post of picture of my expensive tool beside my handmade one - you're going to be shocked at how easy this is.

Now, the pain in the butt is the on/off bowls dance you'll make to get them right. The rewards are sweet and well worth the time.

I learned this the hard way just a few months back trying to get my 900 Kaw worked out. Those have composite floats and I was simply amazed at how much different the bouyancy those floats were from carb to carb. My plugs looked exactly like yours do. I wish I had a copy of them - identical. I got my floats set-up correctly, stopped the sloshing, and she ran flawlessly.

Regards,
Gordon

[RRRToolSolutions]

As promised -

The first photo is obviously the $75 tool that Kawasaki uses in their manual. I like tools so I bought it, but while I was waiting for it to be shipped, I made the one in the 2nd photo - using the tip from the brass T you see cut. I carefully drilled a hole large enough in the brass drain plug (hand drill - no space-age stuff, not even a drillpress). Once I filed and got the fit I wanted, I inserted a nail down the center to hold it while the JB Weld epoxy cured over night. The next day I had a level gauge that cost me less than $3 to make.

Yes, it works perfectly and it's actually easier to install on the 2 inside carbs than the factory tool. With the homemade one, I simply start and finish the threads with the tubing. On the factory tool - you have to reach up in there and turn the thumb screw knob all the while my fat hand blocks the visibility....dummies those engineers are.....real dummies. I guess you could say the same for the foll who buys it too. $72 would have bought several cases of beer and some good steaks for the grill.

Regards,
Gordon