wont start when hot

[b2kvapor]

Hello. I have a 78 xs1100 and recently it won't start when it gets hot... Let it cool off for a day fires right up.

[jwhughes3]

Check battery voltage under load - when the bike is hot the battery may not be carrying the 10.71 volts necessary when the starter is running to fire the TCI. If voltage dips lower it will crank and crank but never start.

John

[BigRed]

Do you ever have misfires under hard acceleration? One symptom of my bad pick-up coil wires was that it didn't like to start when hot.

I'm starting to think that my main contribution here is to tell people to check their pick-up coil wires. So, check your pick-up coil wires

[b2kvapor]

Bike starts easy first thing in the am. Hit the store, gas station and work on prob... But I take it for a 50-60 mile ride she runs great.. no lag, skips or pops... Turn it off try starting ten minutes later just cranks, and cranks. Don't even spit or sputter.

[skids]

I have one like that (maybe two). I found that if you pull out the "choke" lever and give it just a tiny bit of throttle, it will fire.

[BA80]

I would try just the opposite of what skids said. A lot of people (including me sometimes) experience a similar issue when on long rides most particularly when it's hot outside.

We found that just holding the throttle wide open when cranking clears out the fuel vapor that collects in the air filter (air box) because of the heat causing evaporation of the fuel.

You might give that a try. That's what it sounds like to me.

[BigRed]

Have you cleaned up your ground connections? The negative strap from the battery and underneath the voltage regulator are a couple spots that could get crudded up. After running for a long time, a dirty connection will heat up and get worse than when it's cold.

Have you checked the voltage while cranking?

My bike has pod filters, so I don't seem to get the fuel vapor problem mentioned above, but I do get a better start if I just crack the throttle a little bit (no choke) when it's hot.

[ViperRon]

The other suggestions by members are more than likely the issue but next time before you do anything open the gas tank lid and give it a minute. I have seen vapor lock cause this condition before. The gas tank cap vent can get clogged and cause vapor lock.

[BA80]

The other suggestions by members are more than likely the issue but next time before you do anything open the gas tank lid and give it a minute. I have seen vapor lock cause this condition before. The gas tank cap vent can get clogged and cause vapor lock.

+1 Excellent point Ron. Except usually the bike will start running bad and quit. Turning it off and letting it sit a few minutes will usually keep this from happening.

[James England]

Is it possible that heat has caused all of the fuel in the float bowls to evaporate? If so, then putting the petcock onto 'prime' would fill the bowls without the engine needing to be turned over to activate the vacuum switch and get the bowls full again.....

I had a car that did exactly the same thing..le heat from the exhaust manifold caused the float bowl to empty by evaporate and hot starting was a nightmare!

[MPittma100]

Hot Fuel

Is it possible that heat has caused all of the fuel in the float bowls to evaporate? If so, then putting the petcock onto 'prime' would fill the bowls without the engine needing to be turned over to activate the vacuum switch and get the bowls full again.....

I had a car that did exactly the same thing..le heat from the exhaust manifold caused the float bowl to empty by evaporate and hot starting was a nightmare!

This is a normal occurrence in carbureted engines. When shut off, the fuel in the carburetor(s) can actually boil. This can cause a hard start condition. The fix is to hold the throttle partly open to allow more air in when restarting.

This may not be the cause of your (b2kvapor) problem, but is to be considered. Try this to see if it will start when hot.

Mike

[b2kvapor]

I tried chock , looked in gas tank to see if I was out of gas. I took the drain bowl plugs out to make sure there was gas in the bowls...and there was... Iam thinkin electrical...

[jwhughes3]

Check battery voltage under load - when the bike is hot the battery may not be carrying the 10.71 volts necessary when the starter is running to fire the TCI. If voltage dips lower it will crank and crank but never start.

John

BTDT. Still recommend checking battery cranking voltage (not voltage at rest).

JW

[skids]

I would try just the opposite of what skids said. A lot of people (including me sometimes) experience a similar issue when on long rides most particularly when it's hot outside.

We found that just holding the throttle wide open when cranking clears out the fuel vapor that collects in the air filter (air box) because of the heat causing evaporation of the fuel.
.

I know that cracking the throttle open while using the choke seems counter-productive, but it seems to work.

[ViperRon]

In checking the electrical measure the OMS threw the spark plug caps. With some of the plug caps they internally have spring loaded resister. All I have seen have a screw end that makes connection with the wire. Both of these places can build up corrosion and cause a weak spark. The corrosion ends up increasing resistance when hot and the little bit of condensation when cooling makes contact again. Just measure from plug wire to plug wire on the same coil and look for 15K much more than 20K and the circuit starts to fail. Non resister Champion plugs have similar issues at times also because of cheap construction.