Stalling at Operating Temp.

[MadHatter16]

I bought a 1988 Vmax only 9k miles. After tending to the charging system and installing the Odyssey PC680 I'm getting the recommended charging voltages. It runs and idles like a champ when cold, but after reaching operating temp(just past halfway on the temp gauge) the bike stutters and stalls. After it dies, it will crank but won't start until it cools off. I did notice the fuel pumps are getting very hot. Any ideas where to start?

 

[user 16790]

mine ran crap at idle when hot, it turned out to be the original sparkplug caps arcing, maybe you could check yours

 

[MadHatter16]

Thanks for the tip. I will definitely look for that next time I get in the garage.

 

[user 16790]

do you have original caps

 

[MadHatter16]

Yeah, they're OEM.

 

[MaxMidnight]

Does it run without choke before it cuts out?
Will it continue to run if the revs are held at (say) 2500+?
Once it has cut out try opening the float bowl drained to see how much fuel comes out.
When it cuts out have you checked for a spark when attempting to re-start?

If the HT system was the issue then I would have expected that it would affect the running regardless of operating temperature but still worth checking.
Stating the obvious I know but checking for arcing is best done in the dark.

 

[user 16790]

the rubber at the bottom of the caps will look burnt or melted if that is your problem but there are many that are more knowledgeable than me to give other ideas, just giving a suggestion

 

[MadHatter16]

It runs and idles normal without the choke. I can go and ride short distances without much worry as long as I'm not idling in place for an extended amount of time.
I have held the throttle down around 2500rpms to help combat the stall. It will keep it running, but not very well.
I haven't checked the spark nor the float bowl after the stall.

 

[MaxMidnight]

It runs and idles normal without the choke. I can go and ride short distances without much worry as long as I'm not idling in place for an extended amount of time.
I have held the throttle down around 2500rpms to help combat the stall. It will keep it running, but not very well.
I haven't checked the spark nor the float bowl after the stall.

As it runs without choke then I would doubt that it is an idle jet problem.

If you are getting a good spark after the 'shut down' it would suggest a fueling issue.
What I can't reconcile is why it would still run, albeit poorly, at higher revs.
If it were a fuel pump issue I would have expected that as demand for fuel went up then it is there that you would get the problem.
Unless you can substitute the pump it may be worthwhile feeding the cabs from a gravity fed header? That would, at least, rule in or out the pump as the causal problem.

I have also read of ignition control units working OK during the initial start and warm-up but failing once they get hot. Substitution is easiest for diagnosis.

 

[Fire-medic]

Twice in 28 years of owning VMaxes, I've had the ignition pick-up go-bad, it starts, but shuts-off when it gets warm. Let it cool-down, the bike starts again. Check pickup resistance when it happens. It should be ~90-120 ohms. If it's not, you found your issue.

 

[MadHatter16]

Twice in 28 years of owning VMaxes, I've had the ignition pick-up go-bad, it starts, but shuts-off when it gets warm. Let it cool-down, the bike starts again. Check pickup resistance when it happens. It should be ~90-120 ohms. If it's not, you found your issue.

View attachment 76411
You are referring to the "pulsar" pick ups right? Runs from the crank case to a plug under the seat?

 

[Fire-medic]

Here you go. You have two coils on the 1985-'89 bikes, 1990-2007 use a single pick-up coil.

 

[MadHatter16]

Thanks for the tips guys. I was at a loss as to where to start. I'm going to do some digging and I'll post what I find out.

 

[Fire-medic]

Where are you again? Add it under your screen name/avatar, if you wish, perhaps someone by you can lend a hand.

 

[MadHatter16]

Massachusetts

 

[Fire-medic]

East-side or west-side? I think RaWarrior was from the Hudson River Valley. He has a lot of experience w/these, though I believe he's been on an Indian Scout the last few years.

 

[MadHatter16]

I'm in Agawam. It's western Massachusetts

 

[desert_max]

Motorcycle Heaven. (I went to UMass Amherst)

 

[MadHatter16]

After doing some testing and looking around, I have a few observations.
1. The problems(drop in voltage and sputtering) occur when the cooling fan kicks on.
2. The pick up coil resistance was within the recommended range.
3. The primary and secondary omh readings on the rear ignition coils were high after the "shut off." Primary(3.8) Secondary(13.9k)
4. The front ignition coil nearest the left scoop has a hairline crack along the bottom.

 

[Traumahawk]

If the voltage drops when the fan kicks on, I would say that it might be time for the R/R to be replaced (or atleast check the grounds.....clean wires.....etc). Its not putting out enough voltage to keep up with demands.

The below thread should help.

https://www.vmaxforum.net/threads/how-to-fix-your-vmaxs-low-voltage-or-charging-problems.19108/