Engine won't start when hot after sitting a few minutes

[stubone278]

Man I hate to start a new thread, but I've looked all over and can't find anything with what I'm dealing with here.

I have a Honda clone 6.5 on a minibike. It starts up cold on the first pull and runs great. If I shut it off after it's hot it will start right back up again a few seconds later. The problem is when I get it running hot and shut it down and wait 5-10 minutes. If I wait those 5-10 minutes it won't start back up at all, and I have to wait for it to cool back off again. Once it cools off it starts on the first pull again.


Could it be vapor lock? I'm going to pull the spark plug and see if it looks bad.

 

[mymumisaman]

Warm up the engine do what you do to make it not start then take the plug out and put no more than a teaspoon of motor oil into the spark plug hole. Put plug back in and see if it starts then report back

 

[Doc Sprocket]

Might be vapor lock, might not. When it won't start, verify the presence of spark. Either use a spark tester, or put a teaspoon of fuel in the spark plug hole and try again. If it pops or runs for a second, it's a fuel delivery issue. If there's no fire, the problem lies elsewhere.

 

[mymumisaman]

I'm thinking the piston rings as it starts and runs but fails to start when its partly cooled down and has to be fully cooled before starting again

 

[kendelrk]

When its hot after you shut it off, try starting it with the choke closed and then pushing it immediately to no choke after you pull it. I remember having a clone that wouldn't start without the choke regardless of how hot it was.

 

[devino246]

I'm thinking the piston rings as it starts and runs but fails to start when its partly cooled down and has to be fully cooled before starting again

Since when is a no-start condition a symptom of worn piston rings? Worn rings would result in excessive blow-by and oil consumption, and potentially, hard cold-starting and poor performance.

 

[mymumisaman]

Since when is a no-start condition a symptom of worn piston rings? Worn rings would result in excessive blow-by and oil consumption, and potentially, hard cold-starting and poor performance.

I've had the same symptoms before where the engine would start and run from cold, then when turned off would start back up again, but given 10min to cool down the engine failed to start, after checking everything and re-checking I ended up re-building the engine to find the only problem was slightly worn piston rings hence my 1St post, of putting a teaspoon of oil in the cylinder, (as a test )
What was basically happening was the piston rings lost their seal in the 10min the engine had to cool down, resulting in a no start situation as there was no compression, given time to cool down fully the engine would start right up again.
I'm not saying this is most definitely the problem hence the test just voicing my opinion based on my experience

 

[devino246]

I've had the same symptoms before where the engine would start and run from cold, then when turned off would start back up again, but given 10min to cool down the engine failed to start, after checking everything and re-checking I ended up re-building the engine to find the only problem was slightly worn piston rings hence my 1St post, of putting a teaspoon of oil in the cylinder, (as a test )
What was basically happening was the piston rings lost their seal in the 10min the engine had to cool down, resulting in a no start situation as there was no compression, given time to cool down fully the engine would start right up again.
I'm not saying this is most definitely the problem hence the test just voicing my opinion based on my experience

Hmm, that's interesting.

 

[OzFab]

I had this exact problem just yesterday; from cold, started on first pull, ran fine for a few minutes then was shut down. When I tried to restart 10 minutes later, the only way it would start was on partial choke... Once it's running, you can knock the choke off...

 

[stubone278]

I'm thinking it may actually be the cylinder like you said. I changed out the plug, completely cleaned out the carburetor, and blew out the fuel lines. I ruled out the valves because it starts when still very hot.

I checked the oil level just to see it and found my float valve had been stuck a little and there was lots of gasoline in the crankcase. It was flowing out of the oil check plug. Drained and changed the oil.

I guess the piston cools faster than the engine block and allows that slight gap to form if the rings are shot. I also want to say it feels like the compression is not as high when pulling the pull start (after the 10 minutes).

 

[mymumisaman]

Try what I said in my 1St post as that teaspoon of oil should allow the engine to start

 

[mymumisaman]

Might even fix the problem for a short time