85 Tri-Z fuel pump issues

[KXtecate3]

OK, what we have here is an 85 Tri-z with a drag ported Alcohol-burning YZ250 engine in it. we have all the lines hooked up how we believe to be correct, following the flow arrows stamped on it. Now, we fired it up and it ran for a few seconds and then it blew that snap-close gas cap lid wide open and spewed alky everywhere...as the engine revved to the moon. I need to know what the heck is going on. please help

[Billy Golightly]

The fuel tank pressurized and blew the cap off? Thats pretty weird, never heard of that. If it did somehow pressurize, it should have went out the vent tube that connects on top of the tank near the back. There is a small nipple that a hose connects to and runs up by the handle bars. Did it instantly rev high as soon as it cranked? Sounds like you might have an airleak. Check your intake boot, and gasket inbetween the intake boot and intake itself.

[TimSr]

The tank vent hose has a check valve (one way valve) about halfway between the tank and the front of the machine where it ends.

When you cut off fuel flow on any two stoke, it will begin to rev really high until whats in the float bowl is gone.

[KXtecate3]

it didn't instantly rev high, it ran like a top for about 30 seconds or so, then it revved to the moon, which was pretty scary sounding when its an alcohol powered engine running thru an ESR drag pipe. =)

I was thinking that somehow the fuel pump is working backwards and is pressurizing the tank instead of making it flow into the carb.

[Dads]

Like TimSr said,
The carb quit getting fuel and it ran the float bowl dry.
and run out of control till bowl is dry.

[Jeroboam7]

You may need different internals for your fuel pump! Check with LRD they should have the correct pieces. Methanol eats rubber and some plastic, it also cleans a fuel system up in a hurry so you may just have a plugged pump! Check the return setup maybe you can't run it with alcohol, you need twice as much alky to run the engine as you did before.

[KXtecate3]

that fuel pump has a return system? I didn't know that! the bike was in pieces when I got it, so I had no idea how it was hooked up, we just ran from the tank to the pump to the carb, and all the other vents on the tank are plugged off...is there some place on the net where I can see the CORRECT way to set up all the lines and what-not?

[MTS]

Kxtecate3 check out the OEM parts diagrams over at www.bikebandit.com
and www.partsfish.com
they should help you figure out what you are missing :)

[mywifeknowseverything]

why not just go to Yamaha and check it out...
http://www.yamaha-motor.com/
Click Parts and service
click parts Catalog and go from there...

Your problem is one Ive never heard of before...Please let us know when you get it hashed out....
Good luck....Post some Pics of the Trike!!!

[TimSr]

that fuel pump has a return system? I didn't know that! the bike was in pieces when I got it, so I had no idea how it was hooked up, we just ran from the tank to the pump to the carb, and all the other vents on the tank are plugged off...is there some place on the net where I can see the CORRECT way to set up all the lines and what-not?

Holy Crap! Until you get this setup right, dont even worry about"fixing" anything. The fuel pump moves enough fuel to run about 10 carbs, and output from the fuel pump is T'ed with the majority going back into the gas tank, and a small line going to the carb input. If you plugged the return line to the tank, I surprised your not blowing off the fuel line, because it will build a huge amount of pressure, which you do NOT want to happen. And if the tank vent line is not open, the tank will pressurize.

[3Razors]

Did you set up you carb for alcohol? Or was is it already converted?

[370banshee]

ok well you all hav seen theis trike beacause i posted the pics of it. it;s my trike and KX is helping me here an there with the small things that are left. ok about the pump it's an alky pump that i got with the engine. i took off the regualer tri-z pump and put thin one on beacuse i know they use different seals and such. the carb also came with the engine. i saw a return on teh stock system but i didn't pu tit back on with the new pump setup (brain fart i guess) ii can just T that line from pump to carb right?? i took the old petcock off because the handle seemed way way way to loose it seemed like it was gonna leak and maybe it was already bad. so i ditched it. this is the only thing keeping me from running it. oh yeah the carb is an alky carb already actually i have 2 of em. this engine came out of a mirco sprint race car. so i got everything involved and alot of extra stuff too