[misterguitar]

I just put my bike back together. Got the timeing balls on for once with points! (checked with strobe), sync is spot on, tappets are spot on, and mixture I think is close. I just ran it 50 miles to pull the plugs and see.

But my problem since the rebuild is as I'm riding in ever single gear the fastest the engine will rev is 7k. Then it sputters and slips a bit and just hangs at 7k rpm. WOT. I tried this in all 6 gears! It never did this before! Occasionally at idle it will speed up randomly and then slow down. I thought it may be the sync, so I put my motion pro 4 tube sync checker on and both are exactly equal! So I'm kind of at a loss about why this would be happening!

I just recently had to tear the whole engine apart to replace the head as my intake valves where mushromming at the ends. (Check the engine forum here) This head had a new valve job. I lapped the valves.

Mixture off maybe?

 

[J-T]

It helps when you specify exactly what bike you're working on but your hints suggest it's a 360.

Sounds to me like the most likely cause is the points floating.

 

[misterguitar]

Yep! CB360!

What is points floating? I don't think I have ever heard of that.

 

[doode]

Same concept as valve float.

What's your air box and bike setup?

 

[Boomer343]

I just went through this with a CB350. Turned out to be low voltage at the coils. Wasn't any one thing unfortunately. Cleaned the kill switch, cleaned ALL the connections, replaced the ignition switch and just to be sure replaced the feed wire from the headlight bundle to the coils.

Check the voltage at the coils when it is running and under load.

 

[JamesPal]

How many miles the the bike have and what did the engine overhaul consist of?

 

[misterguitar]

The bike had about 20k on it when bought a few years ago. I completely rebuilt the engine last year. Put about 2k miles on it. Rebuild included, new rings, overbore to .25, new pistons (art), new valves, new valve guides, deck the head and jugs, new gaskets, new plugs. Ran great for about 2k miles and then recently when riding one of my exhaust studs snapped in two while riding leaving a remnant in the head. So I took the engine apart and took the head to the shop and had the stud drilled out. Upon picking it up and getting ready to put it on I noticed the intake valve ends had mushroomed due to metallurgy problems with the new valves. They were not honda brand. I had a good head at home that had just had a valve job done I was keeping on the shelf as a spare. So I lapped the valves, put on new seals and used it to put it all back together again. While I had it apart, the engine got a thorough cleaning, new oil seals, new gaskets, and new exhaust studs. (Wanted to avoid that problem again!) Put it all back together again. Put a set of brand new plugs in and tuned the bike per the honda manual. Tappets, points/timing, carbs, cables. Tappets were correct. Timing was spot on. On both sides. As close to perfect as I have ever gotten it. Checked with a strobe timing gun. Including full advance. (rev throttle watch timing advance with strobe to the other markers). Did mixture and also did sync with my motion pro liquid tube sync gauge. Sync was perfect. Took it for a 50 mile ride. ran well. Just wont rev up past 7k RPM! In any gear! and while idling ocasionaly it will rev up to 2k, then in a few seconds settle back down to 1200 RPM. Its a 1974 Honda CB360.

 

[J-T]

Points floating is what happens when the points never quite close. It can happen when the points are adjusted excessively wide or if the spring is too weak to close the points quickly enough at higher rpm.

 

[misterguitar]

Must have been it. So I did the timing again today. This time I used static with a light. Found out my strobe timing light seems to be WAY off! Timing was WAYY too advanced! So I set it statistically. hit it with my timing light and light was showing it being half way advanced to top of the mechanical advance mark! After setting it statistically took it for a ride and it went to 10k easy on all 6 gears. So it was a points issue. Need to just buy that pamco and get it over with!

So it;s down to tuning carbs now. Trying to get the mixture right. These are the plugs yesterday after 40 miles. Looked a bit lean. But I'm new to looking for this on plugs

So I riched both sides a bit and got this which looks too black!

Performance was better today. Idle was a bit erratic at times. But it never sputtered out at idle. Till I touched the throttle to take off. Then it would die. Restart and it would roar to life. Too rich maybe?

 

[frogman79]

That's way to rich, Pilot settings are very simple, start them 1 1/2 turns out from a soft bottom. Get the bike to operating temp. Start on one side and adjust the pilot (screw in or out) for the HIGHEST idle on that side. Once you find it reset the IDLE screw knob back to 1200. Then do the other PILOT screw. Again reset the idle back to 1200. Top picture was very close.

I've never used a timing gun to set the timing on my 360, Static time always seems to do just fine, just make sure your gaps are in the measurement range. Also make sure to lube the point cam felt lightly, I use just a small amount of lithium grease.

The idling up and down thing, that can be a few things, sync is off, timing is off or you have one of your sides that is going slightly advanced when the bike is running which drag the other one along for a bit. Can be an air leak at the carb boots to the head, If that bike had that many miles and you are using the advance unit that came with the bike it can be worn out. I had this issue on mine, there is supposed to be a spacer that takes up the space behind the cam on the advance unit. Mine had disappeared which allowed the cam to bounce in and out which will cause the gap to change on the Right side timing while the bike is running. Fix is to make or find a spacer that brings that gap out where it needs to be. There is no spec for this but I filed a copper spacer down until I got about .005" end gap between the cam and the washer on the end. I think the gap without was around .020" which is quite a lot of movement when you think about it.

 

[misterguitar]

OK I started at 1 1/2 turns out. Problem was the idel was still a bit erratic. up and down. making change son the screws didn't seem to really make much difference in RPM except at the extremes when it would start conking out.

Does the mixture screw affect mixture at all throttle positions? Or only at idle? That is something I am confused about. I know this carb has several circuits.

Would any changes in mixture lead to the need to resync or make timing changes?

There are days I wish I had a modern bike with fuel injection. lol

 

[J-T]

The effect of the mixture screws diminishes as the throttle is opened until it is negligible at cruising speeds. Not likely the cause of your original problem. Adjusting the mixtures won't result in the need for syncing the carbs but your issues with the screws not affecting idle speed could be caused by the carbs not being properly synced, again, not the cause of your original problem. Not responding to mixture screw changes can also be cased by vacuum leaks between the carbs and the head, restricted/plugged carb passages, improper float levels, etc. Mixtures, and the carbs for that matter, don't have any effect on ignition including timing.

 

[misterguitar]

So after reading a spark plug does one need to clean it (get all the oil and soot off) or can you just pop it back in adjust, run hard for a while, then pull and check again? If it is run too rich doe sthe carbon just burn up after it is leaned out?

 

[Yendor]

No you need to use new plugs for each plug chop.
It takes too long for them to burn off and show the current condition.
BUT ...
They aren't that expensive and you can re-use them after you get things worked out.