300 fourtrax runs good higher rpm, but dies when warms up

6361 Views 14 Replies 6 Participants Last post by howols, Nov 1, 2019

Johnz12321

Discussion Starter · Oct 30, 2019

I'll get the year in a bit. 2wd 300 fourtrax. I tinkered with it all day yesterday and got nowhere. Things I've done:
Rebuilt carb.
New oil, oil filter, air filter.
New cdi.
New plug, wire, coil.
Compression is 95-100.
It will start right up cold, after 10 seconds at most will die without choke. Soon after have to give it gas to keep it running. Once fully warmed up, will run worse and worse until it dies. I thought it was possibly electrical or fuel delivery related, but I'm just mechanically inclined enough to get myself in trouble. Never messed with valves, and only rebuilt top end on a 2 strokes. But I have tore 4 strokes apart before, I am thinking rings, or possibly valves need adjusted. If someone could point me in the right direction thatd be great, not sure what else it could be. Bought the machine at an estate sale for cheap and it's in almost showroom quality cosmetically, and from what I could gather it had been sitting for a long, long time. -John

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BruceHill

· #2 · Oct 30, 2019

Hi John
I am struggling with a similar issue but on a TRX 420. Mine runs fine for about 5 km then dies and wont start up at all till it cools right down.
Reading your post makes me think you may have fuel starvation. It could be that the fuel filter is blocked or there is severe dirt/rust in the tank/fuel line. I replaced my fuel pump, filter and cleaned out plenty dirt in my tank.The more things you do the sooner you find the problem.

I suspect my problem is now electrical so I will try coil, plug etc next.

Good luck!

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