Suzuki 1989 DT 40 cutting out at high speeds- fixed!

[winsarah]

It is a 1989 Suzuki DT40. Motor starts, idles and runs up to 3/4 speed great. When at full throttle, it seems to de-throttle, cut-out and surge after 15-20 seconds. When pumping the primer bulb, it picks up.
I have replaced everything from the gas tank to a carb rebuild, including new primer bulb and new fuel pump. I have cut what I think are the water flow sensor terminal and then I cleaned the screen and then cut the oil flow/sensor terminal in hopes that might be the problem. Nothing has changed.
Are there specific wires for sensors that I may be missing? Or does anyone have other ideas surrounding this issue?
Thanks in advance,
Win

 

[James R]

Re: Suzuki 1989 DT 40 cutting out at high speeds

Re: Suzuki 1989 DT 40 cutting out at high speeds

Picking up when squeezing the primer bulb says the fuel pump needs attention.

 

[winsarah]

Re: Suzuki 1989 DT 40 cutting out at high speeds

Re: Suzuki 1989 DT 40 cutting out at high speeds

Thanks for the reply!
The fuel pump has been replaced- brand new. Any other input? This is really stumping me.
Best,
Win

 

[jafa]

Re: Suzuki 1989 DT 40 cutting out at high speeds

Re: Suzuki 1989 DT 40 cutting out at high speeds

Mine surges as it runs the bowl dry, as the mixture leans out. I would look for a blockage in the lines or the tank air vent blocked causing a vacuum. If the primer bulb is not being sucked in , then my guess is the fault is after the bulb. Cos its a single carb I dont think its a carb issue as it runs at 3/4 and your on the main jets by then.
Just rambling but perhaps its not fuel flow restriction , I'm thinking air leaking in around the connector breaking the vacuum drawing it from the tank.

 

[winsarah]

Re: Suzuki 1989 DT 40 cutting out at high speeds

Re: Suzuki 1989 DT 40 cutting out at high speeds

I have checked all the fuel lines and have used different tanks, loosened the caps, etc. I replaced the bulb and hose with a brand new one. I have not replaced or bypassed the hose connector at the engine cowling- will try that today. After that, all the fuel lines, hoses and everything to the carb will have been replaced.
I really appreciate the help!
Win

 

[winsarah]

Re: Suzuki 1989 DT 40 cutting out at high speeds

Re: Suzuki 1989 DT 40 cutting out at high speeds

So....after spending time(4 weeks) and money trying to find the problem, the easy fix came today. I am quite embarrassed but ultimately happy.
The fuel filter sleeve has been upside down this whole time.
I figured I would close-out this thread with the news(wish more people would do that).
Thanks everyone for the input!
Best,
Win