RMX Cutting out on long pulls.

[Studboy]

Our RMX is cutting out, but only on long long pulls at the sand dunes, it does fine at the track and on the trails.

Here are the specs:
It is a 91 RMX250, with a 94 Eric Gorr RM 265 cylinder, with a RM head that has been modified for the cylinder.
The bike has a fresh topend and reeds, etc.

At first I thought that the petcock was starving the engine for fuel, but I took it off to see how fast it would flow, and it seems to be plenty fast, so I don't think that is the problem any more.

What else could it be? Weird air leak? Cooling (The hose coming out of the top of the head is a little pinched by the gas tank.) Float level?

I have tried richening the jets, and it really doesn't help any.
Right now I'm leaning towards cooling or fuel starvation because it runs awesome everywhere until it bogs out.

Any suggestions would be appreciated!

 

[JasonJ]

Check any fuel filter in the line for dirt and proper flow direction. Check gas tank vent, it may be clogged causing a vacume in the fuel tank at high flow conditions. check this out next time your pulling hard and it starts to sputter, crack the fuel cap open like 1/2 turn and see if it recovers. You may have spooge in your carb too that is limiting the fuel flow, cheap gas has been know to put a redish rust color spooge in the carb. Thats my $.02

 

[Studboy]

Thanks for the tips Jason, The gas tank vent is clear, I've checked that already. The carb is also clean, I'm leaning more towards a cooling problem than anything right now, all of the fuel stuff seems to check out OK, I am measuring the float height tonight.

 

[JasonJ]

Yeah, running fast in the sand is alot of work for a 250.