Tri-Z Fuel Pump Problem

[christph]

I've got a mystery problem with my Tri-Z and am hoping for ideas on what could be causing it. First, I replaced the all the gaskets in the fuel pump so it shouldn't be a matter of replacing them, and it also has all new hoses with clamps. Second, my Z runs like a champ for 15 to 20 minutes, but then the pump seems to stop working, the carb goes lean, and then the machine shuts off due to lack of fuel. After I kick it about 30 times, it starts flowing fuel again. It tends to do it after a long hard runs at full throttle, which led me to think a vacuum was developing in the tank. The vent hose is clear, however, so I don't think that's it. I'm starting to think the pump is less efficient at high rpms (the membrane just barely flutters and it's drawing lots of fuel), which is why it goes into a lean condition. In this case the problem is inherent in the design. Then again, I can pin the throttle the first 15 minutes or so and not see the problem. It only seems to show up when the engine is hot. Any ideas on what's causing this?

[jonolanracin]

Have you ch3cked to make sure that the vent hose from tank is clear open and not kinked or clogged up sometime after thaey get old they will suck together take it off tank and try that

[El Camexican]

If the pump was put together correctly it is highly unlikely it is the problem.

You say the engine shuts off due to a lack of fuel. Does it rev to the moon prior to shutting off or does it sputter and lose rpm before it dies?

Also, is the carb stock?

[muthey]

also have you checked the hose going from the crank to the fuel pump that creates vacuum? I had to replace mine as it developed cracks and mine would start to run out of fuel

[YTZ drew]

Have you ever done a leak down test on this engine? I wonder if you're developing an air leak somewhere when its hot. That would make it lean, and also cause you to lose some of the crankcase "pulse" needed to run the fuel pump.

[christph]

If the pump was put together correctly it is highly unlikely it is the problem.

You say the engine shuts off due to a lack of fuel. Does it rev to the moon prior to shutting off or does it sputter and lose rpm before it dies?

Also, is the carb stock?

Thanks for the advice guys. It sputters and loses rpm before it dies. The carb is not stock; it's a Keihin 38mm A/S. I'm thinking it is somehow heat related because it doesn't do it until it heats up and I'm really hard on the throttle. I haven't done a leak down test yet. I'm starting with the simplest problems and going from there. The vacuum hose is new, so that shouldn't be it. I've checked the vent hose and it's clear. It just occurred to me that I haven't checked the fitting on the cylinder. Since aluminum expands more than steal, perhaps it develops an air leak at the fitting when it is hot. Hmm... I'll have to check.

[El Camexican]

Based on what's been posted so far I don't think you're running out of fuel. I would assume that if you were starved for fuel the motor would lean out and rev up before it died. Same with an air leak. Do check that elbow though. Some soap and water while its running should do it, no bubbles, no problem.

Regarding the 38AS there are threads in here about what happens if the pump pushes the float needle seat off a none stock carb on here. Try to search them, but that never stalled my trike when I went through it, it just leaked out the overflow tube and varied the idle speed. You're problem seems like it might be electrical.

[RIDE-RED 250r]

I know it's not a Tri-Z fuel related problem, but one of my 250r would act up much the way you describe. After 15 minutes of riding, especially when riding it hard, it would all of the sudden stop taking throttle. It would just go totally flat almost like a chainsaw when you run out of fuel. After checking my reeds, carb for cleanliness, flywheel magnet and pulse generator for corrosion, and then swapping coils, all of which did not fix the problem, I then replaced the stator and pulse generator and so far it seems to have cured my problem. Sometimes ignition/electrical problems can mimic a fuel problem like an SOB! Initially, I swore up and down I had a fuel delivery issue.

Are you 100% positive it is a fuel issue??? If not, the next time this problem occurs I would let it die and then without kicking it over, pull the plug out of the carb bowl and check for fuel. If the fuel level in the bowl is low enough that it won't stay running, you will only have a small amount drain out after pulling the plug.

If you have fuel in the normal amount, I would start swapping out your ignition components for known functional units if you have them available to you.

[christph]

I'm pretty sure it is a fuel problem. When it stops I pull the fuel hose off the petcock and there is no fuel in it. Then, I kick it over until fuel starts flowing again, which can take as many as 30 kicks. I checked the fitting on the cylinder and it seems fine. I'm going to disassemble the pump, clean out the tank, recheck the hoses, etc. and see if that works. If it doesn't I'll focus on the electrical system.