I have a 15 hp lifan stock electric start long tail that I built. It has 2hrs on it and no mods. It will not start after running under load. It pushes my boat 17mph at 3800 RPM with a 8x4 prop and restarts great in the yard. I have a tiny tach on it so I am sure it is sparking good around 500 RPM when trying to start. I am thinking it maybe getting too hot causing a vapor lock or valve problem. Is there any way to fix vapor lock or keep the engine cooler? Anyone had problems with similar engines? Please help any advice welcome.

I would check the valves first. Those things are notorious for being set too tight from the factory. As the valve gets hot it expands (grows if you will) and then the valve is no longer closing all the way. Properly set valves will make for easier starts, and more power.
Check clearances, and post back what you find out.

I checked the valve lash and the intake was tight at .150 mm so I changed that to .200 mm. I ran it wot 3500 rpm with no load for about five minutes to get it hot and tried to restart. It started after spitting a fire ball thru the muffler. I am guessing that it will be worse after pushing a load and getting hot. Any thoughts?

My problems continue. Can an oversized prop cause a longtail to overheat? I am thinking I am getting a vapor lock or a weak spark. I need to get a spark tester because the spark looks much weaker than what I an use to seeing with larger engines. Any ideas please help. Thanks.

My problems continue. Can an oversized prop cause a long-tail to overheat? I am thinking I am getting a vapor lock or a weak spark. I need to get a spark tester because the spark looks much weaker than what I an use to seeing with larger engines. Any ideas please help. Thanks.

My problems continue. Can an oversized prop cause a long-tail to overheat? I am thinking I am getting a vapor lock or a weak spark. I need to get a spark tester because the spark looks much weaker than what I an use to seeing with larger engines. Any ideas please help. Thanks.

Oops sorry about the triple post. Tapa talk said it wasn't going thru.

are you running cheap gas?

Set your valves to .005

Lifans run a different gap even though they are honda clones. my 9hp is .015'' and .020". I know this might sound silly but mine wont start without me chokeing it hot or cold. have you tried choking it when its hot?

always had to choke mine hot or cold.

It starts good with out choke in warm weather. But i have choked it and found the plug wet. Are you sure about the .015" and .020? I can't find my manual but the predator engines call for .015mm and .020mm which is about .006" and .008"

oh shoot you are right. it is metric. damn i'm sorry. I glanced it and bout messed somebody up. My apologies...

No worries. I am thankful for any help I get.