Hard start when hot

I think you have a weak spark situation, probably caused by the heat. A maintenance free higher CCA battery might solve your problem. You said your battery is relatively new? Have you checked the water levels?

It's always a good thing to check the valve clearances on a used bike anyway, and now you will know that they are good to go.

I think you have a weak spark situation, probably caused by the heat. A maintenance free higher CCA battery might solve your problem. You said your battery is relatively new? Have you checked the water levels?

It's always a good thing to check the valve clearances on a used bike anyway, and now you will know that they are good to go.

RoMoMoTo wrote:

Loudhvx:
Thanks for another perspective. Worse case scenario, I get the valve clearances in line and still have a hot start problem due to another cause. In any event, I won't burn valves out of neglect.

When I have trouble starting the bike hot, it will crank over for maybe 7-10 seconds, then start to catch, suddenly clear out and run great. I first thought it was carbs percolating dry in the heat and not refilling until the suction from the cranking engine drew enough gas into the float bowls (which is why I posted the problem in the carb forum.) But I started leaving the petcock in the prime position, and it made no difference.

RoMoMoTo

It does sound like a fuel issue. But it's a stumper alright.

The above two posts remind me of the old adage: If it seems like a fuel problem, it's ignition. If it seems like an ignition problem, it's fuel.
I've been swamped with high-priority projects and haven't been able to get beyond removing the existing shims to figure out what I need to buy to bring them into spec.
The battery is new this spring. Haven't checked the charging system; I guess I should do that. But I assume it's working fine, as the bike runs fine once started; no electronic ignition-related stumbling or slow blinkers etc.
But I'll check that out when I can and report back.
RoMoMoTo

RoMoMoTo wrote:

The above two posts remind me of the old adage: If it seems like a fuel problem, it's ignition. If it seems like an ignition problem, it's fuel.

....RoMoMoTo

Ain't that the truth!

On hot days, when the engine is hot, your battery can't produce enough juice to give you a good spark and turn the starter motor. It's a known issue with underpowered motorcycle batteries. Can be a bran new battery, but if it's borderline on what is required to do the job, then on hot days with a hot engine, it is just weak enough to give you problems. I see it all the time, literally every day on the Vulcan 750 forum, where someone complains of hot starting problems, especially now. All the experts will chime in asking what kind of battery they have and recommend a MF battery with more cold cranking amps, and once they try it, it works every time. Of course, if your wiring is old and corroded, you might be adding to the problem. You probably have already checked your voltage at the coils compared to at the battery with key turned on, bike not running. If not, you should check that. It should be at least 12 volts at the coils. If it is less, then when the bike is hot, it will add to the problem.

I don't remember the battery specs offhand, but I know I bought one with the CCA or amp-hour rating the book called for.
As far as voltage to the coils is concerned, I have large-gauge wires running from a relay, with all old connectors and switches removed from the circuit.

That said, I will recheck voltage readings. Thanks for the tip.

RoMoMoTo

By the way, Garden of the Gods is a cool place to visit. Cool avitar!

Yes, Garden of the Gods is a cool place. But the avitar is a photo from Arches National Park in Utah. This is NOT a commercial plug, but for other photos of cool rides, check out the gallery pages at my website, www.RockyMountainMotorcycleTours.com
RoMoMoTo

Wow, close similarities to some of my pics of Garden of the Gods. Anyhow, cool site and business. Is that your business?

Yes, that's my business. Probably should discuss this stuff on a different forum, as we're getting pretty far from carbs! Or email me at
bob@rockymountainmotorcycletours.com

Did you ever find the solution to this? I'm having the exact same problem.