1985 VF500F Won't Idle Or Start When Warm

My '85 VF500F starts right up when cold - no problem. The choke operates properly and I can bring the bike to idle with the choke in the up position and let it run until it starts to warm and then take off. The problem occurs when the bike is fully warmed up after about 10 minutes of riding. If I pull over and turn off the engine it will not restart (sounds like a weak battery - it cranks slowly but won't turn over, and then it won't crank at all). If I wait until it cools off it starts right up. Also, when the bike is warm I have to be very careful about let the idle drop below 1200 or so, because it will stall and then I'll have to wait until the block cools before re-starting. If I'm riding along and depress the clutch and come off the throttle it'll die right away, and then I have to let it cool again (or pop it at high speed, then it'll start).

Carbs were synched about 10 months ago and the mechanic felt that they were in great shape. I ran some Sea Foam through and that didn't make a difference. I don't think is fuel related or carb related.

Any ideas? Overheated rectifier?

This thing is killing me...I hope you guys can help.

 

may be a problem with your starter motor and/or battery....compression is higher in a hot motor, and your stuff won't pull the load needed to start

look at the condition of your sparkplugs too

 

For the stalling issue: make sure your choke valves are all the way closed. If you can push them in manually AT ALL, then they are not completely closed.

 

Hmmm. Spooky. I don't know if I have an answer to that one. It sure makes me curious. Check the tightness of the carbs boots/manifolds. An air leak that opens with heat expansion will kill it unless you are opening the throttle. I am not sure that is the problem though. The thing that spooks me out is the slow turning starter and the weak sounding battery. Check your charging system and make sure that it is charging. Make sure that you have ample voltage. Check it by revving the engine up to about 5000 rpm and holing the volt meter ton your battery terminals for about 10-15 seconds. Do it cold and if you can get it started and revving do it hot. You may have a "temperature" sensitive charging problem. or just a charging problem in general. The other thing that spooks me is that it will start when you cool down. Usually batteries do recover voltage somewhat when time passes but to do it repeatedly is not normal. Dead is dead.
This lead me to think the horrible thought that something in your engine is heating up and expanding and.....dare I say it?......seizing! Eliminate all of the others possibilities before you assume that you are f---ed.
My girlfriend, who I just talked to, suggested that if you have a charging problem, to take apart all of your electrical connections and switches and spray them with contact cleaner or WD-40. This makes sure that all of those pesky connections don't have corrosion thus inhibiting your continuity. Yes, she is the bomb. She can cook,too. Good luck and I'll keep thinking on this.
PS: What does your temperature gauge say after ten minutes of riding?
Please don't say that it's pegged.

 

I had the same problem with my 85 VF500, I was told that compression problems are a cause of this. I was also told that the VF500's are known for hard starts when it is hot.

Bad news is when I tore my bike down, I had a hole in the top of a piston and a lot of valve problems...

You may want to do a leakdown and/or just to make sure, past that maybe check the valve clearance...

Probably doesn't help much, but thats my words

 

It sounds like your starter is "heat soaked" and will need to be rebuilt. It's an easy job you can do yourself. As for the dieing, I too would check to make sure the choke is going all the way off. I'd also check for a tight valve or two.