Strange idle

[TAlber8]

Trying to dial in tune on fresh rebuild of 74 with stock bore. About 120mikes on build now.

VM34 - PJ:25. MJ:180
Air screw only .5 turn but it already doesn’t really like choke; so I didn’t try 27.5

Pamco ignition and advance - timing looks good. Single coil.

Idle ~ 1200 rpm
New plugs, good battery, charging seems ok.

This is all when bike is fully warm:

Aside from the occasional ‘hiccup stall’.... I have one where when I come to a stop the idle drops very low. If I blip it, it’ll usually correct itself. If I don’t god chance it’ll stall. It’ll drop to about 800. So assuming one cylinder drops.

now if I’m idling in driveway, I can’t recreate it. Only after riding down the road.

I’m tempted to think it’s an electrical connection. But also still think it could be carb. They are synched, which was headache. I rerouted throttle cables to make sure they don’t pinch (I was thinking maybe that was case throwing out of synch but again I can’t recreate in driveway). No missing at speed either.

I’m thinking possible needle position could affect but chopping throttle vs rolling out seem to have the same effect.

many ideas on next step?

 

[grizld1]

Idle drop or stalling when coming to a stop could be caused by high fuel level. Try this: On a downhill grade, close the throttle, pull in the clutch, let the motor drop to idle, and apply the front brake. If the idle falls or the motor stalls, check fuel level and float valve function.

 

[TAlber8]

...and being smart, I left electric start out (it was out before rebuild and I left it that way)

I never notice clutch slip unless I’m trying to bump it while it’s rolling downhill! Ha!

il try this though to look for a difference

 

[TAlber8]

Hmm not really sure what happened but I got myself in left field.

now I’m having considerable trouble getting the bike to idle. It’s difficult to start, and now once warm it stalls almost immediately when I pull in the clutch or stop. Then it’s very difficult to re-start.

I tried quickly grabbing choke on the warm bike When slowing but that Made it promptly die.

quick movements of brakes etc don’t seem to effect it.

I was concerned my fuel hoses were pinching the way they were routed with the filter so I removed them and made new tubes directly to the carb (no filter)

lights don’t seem to matter, battery appears good.

i think I may remove them and fully go through them on the bench. Recheck float height etc.

Question: The cover of the barb for vacuum tube, ever have one leak?

 

[grizld1]

Answer: commonly!

 

[TAlber8]

Plot thickens.... I ve been having a lot of trouble keeping it running now period, and very hard to start (kick only)

retested batter and now was only 11.7

maybe battery was getting weak without me realizing it. I had checked recently and was charging ok but something may have changed

 

[TAlber8]

With battery fresh and charged I’m still has having issue. The right cylinder Seems not to be firing.

the ignition is firing, hooked up a test light. Timing was dbl checked very recently.

on top of that, I had carbs out to try 22.5 Pilots. I have no reason to think it’s not getting fuel. I even tried starter fluid. Hmm... maybe I’ll swap plugs left to right to See if Moves (single
Coil dual output)

 

[TAlber8]

Swapped plugs (which were new 120 miles ago), and problem moved sides.

put in old plug I had laying around fires right up. Wtf

how does that happen??

 

[5twins]

It's rare but occasionally you get a bad plug right out of the box. This may have been your whole problem right from the start.

 

[TwoManyXS1Bs]

Do a Google search on "Counterfeit spark plugs".

The market is infested with them...

 

[TAlber8]

Ahh shoot must have been coincidence. Started today but cylinder quickly started to miss and then completely stopped firing.

Noticed it doesn’t charge at 1k rpm (one cylinder) but it’s 14.4v at 1600 rpm. Seems about normal.

I swapped out for a diff, charged , known good battery. It fired right up on 2 cylinder, but after about 2 min riding up the road it started popping out of one cylinder and then that cylinder failed.

i tried playing with spark cap, this is a MP coil from a Honda, no change though.

I might go through and clean up wiring from the ignition and grounds.

any other suggestions?
I can try swapping coil but it’s not running g long enough that it would get hot

 

[TwoManyXS1Bs]

Swapped plugs (which were new 120 miles ago), and problem moved sides.

put in old plug I had laying around fires right up. Wtf

how does that happen??

Sounds like this is the area of concern.

I'd be inspecting, checking, and changing plugs...

 

[TAlber8]

I bought new plugs and going to try today to rule out but....

I was doing some searching and found my own post from 2017 with some issues that I think are related. I had Honestly forgot about them and the bike sat for quite a bit the last few years. It had really excessive pop-stalls at idle, intermittent cylinder mis-fires then too.

Since the motor is new except for generator assembly, battery, plugs, coil,wires... all those have been swapped or replaced between then and now, I think by default it has to lie in:

• Wiring harness/switches
• Possibly the pamco ignition

Generator seems to charge when I put meter on it, and even if it missed sometimes it has a decent sized Charged good battery in there that should keep running for a while I would think