Warm bike won't start

So, my 1984 VF750F starts right up when it's cold. The starter turns it over great and . . . . VROOOOM!

Sadly, it's a different story when the bike is warm. A couple of grinds and it's done. Like a dead battery, but when the bike cools a bit it starts right up again.

Troubleshooting tips, anyone?

 

test battery with your multimeter for proper VOLTAGE and, additionally, take battery to a motorcycle shop for a LOAD TEST to determine its true health .

Or just replace the miscreant bastard!

 

If it is the original starter motor, it might need new brushes and a good cleaning. Small block Chevy starters used to suffer from "heat saturation", as in when they got hot, they would not crank the motor.

If the battery is more than three years old, it might be giving it up slowly. Typically, a warm battery will put out more energy than a cold battery, but a hot starter motor requires more energy to operate.

I would start by checking/cleaning all the large cable connections, positive and negative. If it were me, I would replace the battery if it was older, just because they seem to give it up halfway between point A and point B, and I hate being stranded.

If the connections are good and the battery is good, the only other possibility is the starting relay and the starter motor. Relays are usually good or bad, with little middle ground.

Do you smell gas when it won't start hot? If so, it could be a leaky carb(s) causing some slight hydraulic lock, and might not be the starter circuit.

 

No pronounced gas smell.

I will start with the connections and go from there. I hope that will take care of it.

 

Lgn001 makes a good post. Check the basics first. Look for signs of heat damage on that starter magnetic relay. I've also come across many starters of that vintage that have failed in just this manner. A simple rebuild (brushes and possibly a commutator refinish) might fix it...but just as often the problem seems to be the armature shorting to ground under heat, in which case a rebuild is a waste of time. I can give you more detail if you need it.

 

Thanks, guys. Would the problem get progressively worse if it's the starter? This is something that has creeped up on the bike rather than something that occurred suddenly one day.

 

Yes. The starter will usually give you warning signs, as opposed to relays that just stop working or work intermittently . I have had automotive batteries give me warning signs, but every bike battery I have had just suddenly stop due to a shorted cell.

If any body out there has had a bike battery slowly fail, please add your two cents. Education is a good thing...

 

Batteries are a weird thing. They can die suddenly, or just get weak. Up here in MN Winters take out a lot of batteries. Batteries are one of the few things that last longer the more you use them. About three years ago I finally had to replace the original battery in my ST1100. It was over ten years old. I bought new, original equipment, serviced it properly, kept it charged when not in use. It lasted one year!! Meanwhile...a coworker had replaced a battery in a newly purchased TRX450ES (same as ST) in deference to a customer's insistence it went dead all the time, even though my comrade suspected the battery was fine. He donated it to me and it's worked perfectly for two years. Go figure?

 

Hello, dizzy. Welcome to the club! Have you ever heard of a problematic battery losing power as it heats up, per Alaskan's problem?

By the way, did you post an "Introduction" thread? I missed it, if you did.

 

next time the problem happens try jumping the bike battery with a car battery and see if the starter spins then.....

 

Thanx Lgn. I did post an intro thread 4/6. As to your battery question...well...heat can destroy a battery, warp plates, usually from overcharging, and I've seen batteries freeze solid, which is only possible (even here in the Neolithic climate of MN) if they are discharged to begin with. However, I think the way you mean that question...that is...can a battery fail in the upper reaches of normal operating temperature but work fine otherwise? I can't think of a time, but I could see where it is possible. Countless times I've seen components fail under thermal loads, so that's what I would look for in a case like Alaskan's.

 

Sounds like a heat-soaked starter to me. I'd order the rebuild kit and get to work, before the starter is ruined.

 

Well, it's definitely not the battery and it's not the ground connections. Must be the starter. Time to get my hands dirty - again!