Topic: How Do These Plugs Look? New Movie - Much Better Throttle Response Off Idle!

[TwoTired]

I watched the video.
Sure looks like faulty accel pump to me.  Check it, and make sure the acell pump actuator clearance is set per book.

Also, you are supposed to vacuum balance carbs AFTER the valve clearances, timing etc. is set, as this can change how the engine breathes and the vacuum it produces on a per cylinder basis.  The IMS  would normally all be set the same.  However, there is a procedure that sets them individually for highest idle speed and then resetting the big idle knob after each tweak.

Fastest idle from IMS adjusting would be the leanest mixture setting and lowest exhaust hydrocarbons at idle.   The accel pump is responsible for enrichment with throttle advance.  The PD carbs are quite different in this regard compared to earlier CB750 carbs.

Cheers,

[Frostyboy]

Now forgive me if I'm way off here, but listening to the sound on the vid gives me the impression that you might be suffering a misfire there.
The fact that it improves with the choke may simply be that the richer mixture masks the fact because it takes less high tension spark to fire it.
I'd be checking the resistance of the plug caps & also repeating what you were doing in the video with the tank off & checking for H/T leakage to the engine from the leads. Do it in the dark & see if you witness any "lightning strikes".
In my work I've been led up the carburettor path many a time only to find a shortfall in the ignition system.
Just sayin'.

Cheers.

[Imago]

I watched the video.
Sure looks like faulty accel pump to me.  Check it, and make sure the acell pump actuator clearance is set per book.

Also, you are supposed to vacuum balance carbs AFTER the valve clearances, timing etc. is set, as this can change how the engine breathes and the vacuum it produces on a per cylinder basis.  The IMS  would normally all be set the same.  However, there is a procedure that sets them individually for highest idle speed and then resetting the big idle knob after each tweak.

Fastest idle from IMS adjusting would be the leanest mixture setting and lowest exhaust hydrocarbons at idle.   The accel pump is responsible for enrichment with throttle advance.  The PD carbs are quite different in this regard compared to earlier CB750 carbs.

Cheers,

Thanks... The manual is also a bit unclear about which to adjust first, the cam chain adjuster of the valves. I noticed when I backed off the lock nut and opened the cam chain adjuster bolt a 1/2 turn as per the manual while the bike was running, things got VERY noisy so I shut it down and adjusted as per the earlier 15 degrees past TDC (although there are no 15 degree marks as on earlier engines, I aligned it at the back of the spring post as in the manual photo). Does the order in which these two procedures are done make a difference?

[lucky]

Well, I adjusted the valves, adjusted the cam chain tensioner, (at first I tred doing it while running as per the Honda shop manual but it got rattling/noisy fast, so I shut it down and did it the original way @ 15 degrees past top center). I also adjusted the points, they were a bit too wide. It also appears the PO had set the valves a bit more open than I have, I'd say perhaps at least .003 intake and .004 exhaust as I mentioned that I might try earlier, however I did end up setting them @ .002 and .003 as per Two Tired's advice.

My thoughts are is that nothing much has changed, if anything the valve train and cam chain is noisier than before. Perhaps a function of the tighter tolerance on the valves. I took it out on the highway and it pulls hard at anything above about 3000 RPM but as you can see in the video while it idles well @ 1000 RPM, it bogs as the throttle is applied, unless choked.

Take a look at the video... I'm thinking I need to pull and repair the accelerator pump on #2 carb as Two Tired suggested, and/or clean the carbs again. When I had the carbs apart last time, I did clean out some gunk from in there, although the jets were spraying on all four when the throttle was advanced and the diaphram looked fine. I haven't checked the timing as yet, could that be part the problem?
 

Cam chain tension MUST be adjusted BEFORE the valves are adjusted. That is why cam chain tension instructions come first in the manual.

You keep asking....Should I recheck this or that / Or could it be this or that.

The reason this is happening is because you need to do one thing at a time and make absolutely sure it is correct before doing something else.

[lucky]

Mixture screws were also found to be unevenly adjusted.

If/when I take the carbs out again, would it be recommended to set these mixture screws all the same? The first time I had them out I cleaned and reset them exactly as I found them.

YES...of course. They should all be the same -LUCKY

[Imago]

Cam chain tension MUST be adjusted BEFORE the valves are adjusted. That is why cam chain tension instructions come first in the manual.

You keep asking....Should I recheck this or that / Or could it be this or that.

The reason this is happening is because you need to do one thing at a time and make absolutely sure it is correct before doing something else.

OK, but in both the Official Honda Shop Manual as well as the Clymer Honda Manual the valve adjusting procedure comes prior to the cam chain adjusting procedure. That's why I asked. But now I know.

[TwoTired]

Small Cam chain tension variance wouldn't effect valve lash gap.  There might be some possible impact on chain tensioning from valve clearance variance.  But, that is pretty hard to analyze.  During a tune up, I hardly think it matters which comes first regarding these.  Upon engine reassembly, I'd do the cam chain tension first.

FWIW

Cheers,

[lucky]

Now forgive me if I'm way off here, but listening to the sound on the vid gives me the impression that you might be suffering a misfire there.
The fact that it improves with the choke may simply be that the richer mixture masks the fact because it takes less high tension spark to fire it.
I'd be checking the resistance of the plug caps & also repeating what you were doing in the video with the tank off & checking for H/T leakage to the engine from the leads. Do it in the dark & see if you witness any "lightning strikes".
In my work I've been led up the carburettor path many a time only to find a shortfall in the ignition system.
Just sayin'.

Cheers.

I agree that adjustment of the carbs is the last step in the tuning process.
The mixture is too lean with the #35 idle jet.
IF the mixture screw will not take care of the problem, it WILL need a larger idle jet.

[lucky]

Cam chain tension MUST be adjusted BEFORE the valves are adjusted. That is why cam chain tension instructions come first in the manual.

You keep asking....Should I recheck this or that / Or could it be this or that.

The reason this is happening is because you need to do one thing at a time and make absolutely sure it is correct before doing something else.

OK, but in both the Official Honda Shop Manual as well as the Clymer Honda Manual the valve adjusting procedure comes prior to the cam chain adjusting procedure. That's why I asked. But now I know.

 

Sorry imago I was wrong on that.
BUT... on page 48 Clymers' manual at the bottom of the page it says....

NOTE:
If cam chain is to be adjusted(next procedure),do not install the tappet caps for #1 cylinder or the breaker point cover.

Then it says CAM CHAIN ADJUSTMENT:
The cam chain tensioner bears against the cam chain to absorb shock while a chain guide damps vibration.A loose cam chain is noisy and can change valve timing.
So I guess you can do it afterwards. You are right.

[Imago]

Short new movie... MUCH better throttle response off idle thanks to the great advice found here!

Bike stock except for MAC 4 into 1 exhaust.

Slow jets #35
Main jets #105 (odd, thought it would be larger)

Re-cleaned carbs paying particular attention to the "mickey mouse" ears in the accelerator pump diaphram. The one that passes gas was was nearly swollen shut. Opened them both with a small drill bit and also ensured the two tiny one way gas valves (ball, spring and brass block) were functioning properly. All mixture screws adjusted out from seated exactly 1.5 turns.

P1050204

Next, timing check followed by syncing carbs with manometer, both new procedures to me...

[Imago]

Timing done... first time doing it. Seems to be set up just about perfectly, was actually out about 10 to 12 degrees, perhaps as a result of the cam chain and valve adjustments. Had to advance the 1-4 and retard the 2-3.

The bike's running better and better with each 3000 mile tuneup procedure.

Tomorrow morning... carb sync, if I have enough tubing for the old mercury manometer I received with the bike.

My experience with this '78F SS is giving me more confidence to tear into this '74K I picked up, with a stuck motor.

[Imago]

Quick question... when I was adjusting the timing in near darkness this evening I noticed a small spark occasionally between the 2-3 points. Is this normal?

I haven't installed my Hondaman ignition module as yet.

[crazypj]

Plugs look good but I think they look warm because they were not tightened properly.
The crush washers look like new so may not be transferring heat from shell into head?

That is getting very exotic.
I have been involved in motorcycle racing for 40 years and never heard
anyone looking at plug color to tell if the plugs are loose or too tight. Usually that is checked with a torque wench. I think some torque wrenches need to be calibrated.
Many times people are using torque wrenches that have not been calibrated since new.

Never trust a racer, they are more interested in flat out performance than why something works
I've studied and experimented with this stuff for as long as I can remember, over 40 years
It's a good picture so simple observation shows washers are not crushed.
Things have changed a LOT since the 50's~60's, you can't use generic terms/'readings' any longer

[lucky]

Now forgive me if I'm way off here, but listening to the sound on the vid gives me the impression that you might be suffering a misfire there.
The fact that it improves with the choke may simply be that the richer mixture masks the fact because it takes less high tension spark to fire it.
I'd be checking the resistance of the plug caps & also repeating what you were doing in the video with the tank off & checking for H/T leakage to the engine from the leads. Do it in the dark & see if you witness any "lightning strikes".
In my work I've been led up the carburettor path many a time only to find a shortfall in the ignition system.
Just sayin'.

Cheers.

It is not an electrical problem because if it was, it would be misfiring all the time not just at one particular point. The OP has already gone over the basics including the accelerator pump and nozzles. Another thread.

I know it does not make sense but on three other motorcycles 77-78's with similar set ups the answer is a larger idle jet.

A mixture adjustment would be the first remedy but after that would be a larger idle jet.

[lucky]

Now forgive me if I'm way off here, but listening to the sound on the vid gives me the impression that you might be suffering a misfire there.
The fact that it improves with the choke may simply be that the richer mixture masks the fact because it takes less high tension spark to fire it.
I'd be checking the resistance of the plug caps & also repeating what you were doing in the video with the tank off & checking for H/T leakage to the engine from the leads. Do it in the dark & see if you witness any "lightning strikes".
In my work I've been led up the carburettor path many a time only to find a shortfall in the ignition system.
Just sayin'.

Cheers.

Please go to the Thread titled "78 CB750 Slow jets" and see jetting solutions for three other bikes including IMAGO's.

[lucky]

I watched the video.
Sure looks like faulty accel pump to me.  Check it, and make sure the acell pump actuator clearance is set per book.

Also, you are supposed to vacuum balance carbs AFTER the valve clearances, timing etc. is set, as this can change how the engine breathes and the vacuum it produces on a per cylinder basis.  The IMS  would normally all be set the same.  However, there is a procedure that sets them individually for highest idle speed and then resetting the big idle knob after each tweak.

Fastest idle from IMS adjusting would be the leanest mixture setting and lowest exhaust hydrocarbons at idle.   The accel pump is responsible for enrichment with throttle advance.  The PD carbs are quite different in this regard compared to earlier CB750 carbs.

Cheers,

I agree but... He has gone over the accelerator pump system and has reported that it is functioning.

Mine had the same problem too, and my accelerator pump and nozzles work very well.
Brand new OEM accelerator pump and check ball.
It still had the same hesitation until I increased the idle jets.

I tried a #45 immediate excellent throttle response. running rich.
I tried a #42 immediate excellent throttle response. running rich.
I tried a #40 throttle response OK but not as good as with the #42.
Went back to the #42 and it works better.

#40 idle jet-(1-1/4 turns mixture)
#42 idle jet-(3/4 turns mixture)

My set up:

1978 CB750 PD carbs.
Intake -stock air box and stock filter.
Exhaust 4 into 2 into 1 with internal metal baffle(Cycle Shack).
idle jet #42.
Main jet #120.
needle non adjustable ,no shims added.
mixture screws-3/4 turn open.

[lucky]

I watched the video.
Sure looks like faulty accel pump to me.  Check it, and make sure the acell pump actuator clearance is set per book.

Also, you are supposed to vacuum balance carbs AFTER the valve clearances, timing etc. is set, as this can change how the engine breathes and the vacuum it produces on a per cylinder basis.  The IMS  would normally all be set the same.  However, there is a procedure that sets them individually for highest idle speed and then resetting the big idle knob after each tweak.

Fastest idle from IMS adjusting would be the leanest mixture setting and lowest exhaust hydrocarbons at idle.   The accel pump is responsible for enrichment with throttle advance.  The PD carbs are quite different in this regard compared to earlier CB750 carbs.

Cheers,

Thanks... The manual is also a bit unclear about which to adjust first, the cam chain adjuster of the valves. I noticed when I backed off the lock nut and opened the cam chain adjuster bolt a 1/2 turn as per the manual while the bike was running, things got VERY noisy so I shut it down and adjusted as per the earlier 15 degrees past TDC (although there are no 15 degree marks as on earlier engines, I aligned it at the back of the spring post as in the manual photo). Does the order in which these two procedures are done make a difference?

I think it is better to get the slack out of the cam chain first before you adjust the valves because the the cam could be turned a slightly. but really since the valves are adjusted at overlap (low side of the cam), it probably makes very little difference.

SEE REPLY #33 on this page.

[lucky]

Quick question... when I was adjusting the timing in near darkness this evening I noticed a small spark occasionally between the 2-3 points. Is this normal?

I haven't installed my Hondaman ignition module as yet.

Yes that is normal.
 Matter of fact that is why you do not want to leave the ignition key in the ON position with a points ignition. It burns the points surface and can cause pitting. The points surface starts out a mirror polished surface but after many sparks the surface gets pitted then the points cannot be adjusted with a thickness gauge because one side of the points has pitted holes and the other side has built mounds of metal . then the points can fire between the top of the mound and the bottom of the pitted hole which is a greater distance than from the original surface of the new points which was .012-.014

That is WHY it is better to use a volt/ohm meter(ohms X 1000 scale) to set the timing because you can leave the ignition key off. Points do not get zapped.
Using a timing light (12V key on) takes a certain amount of resistance before the light is visible and then the timing is late.

If you do not believe me, try both methods and you will see just what I mean.

The fact that you saw the spark means you were using a timing light with the key in the ON position.

When I was a dealership mechanic I had to do as may as 6 bikes a day. That did not include other repairs. After a few years you get very good and these things.

I took my Ford van to a dealership and they replaced the serpentine belt on it so fast it made my had spin.  They do them every day. They put the van on a lift and had the proper tools and EXPERIENCE.  Bang... bang done.

[Imago]

Quick question... when I was adjusting the timing in near darkness this evening I noticed a small spark occasionally between the 2-3 points. Is this normal?

I haven't installed my Hondaman ignition module as yet.

Yes that is normal.
 Matter of fact that is why you do not want to leave the ignition key in the ON position with a points ignition. It burns the points surface and can cause pitting. The points surface starts out a mirror polished surface but after many sparks the surface gets pitted then the points cannot be adjusted with a thickness gauge because one side of the points has pitted holes and the other side has built mounds of metal . then the points can fire between the top of the mound and the bottom of the pitted hole which is a greater distance than from the original surface of the new points which was .012-.014

That is WHY it is better to use a volt/ohm meter(ohms X 1000 scale) to set the timing because you can leave the ignition key off. Points do not get zapped.
Using a timing light (12V key on) takes a certain amount of resistance before the light is visible and then the timing is late.

If you do not believe me, try both methods and you will see just what I mean.

The fact that you saw the spark means you were using a timing light with the key in the ON position.

When I was a dealership mechanic I had to do as may as 6 bikes a day. That did not include other repairs. After a few years you get very good and these things.

I took my Ford van to a dealership and they replaced the serpentine belt on it so fast it made my had spin.  They do them every day. They put the van on a lift and had the proper tools and EXPERIENCE.  Bang... bang done.

I set the timing with a timing light while the engine was running in accordance with the dynamic procedure specified here: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
I thought the dynamic method (running) was more accurate than the static method (not running). Are you saying the dynamic method is not optimal?