Viper fuel issue

R

rlbock

Member
Joined
Apr 9, 2006
Messages
118
Age
70
Location
Saline, MI
Need some incite, over the past 5 days the sled sat in heated garage with track elevated about 6 inches off the cement. Came home to a fuel smell in garage, noticed stain on cardboard I had under it. Appears that fuel leaked into cylinder and out the exhaust manifold, (pipe was off). Pulled it over and 12 ounces of fuel was pushed out of manifold.
Of course I’m not going to try to start. Pulled plugs and mag cylinder had fuel on top of piston, so I’m assuming the fuel is coming from that carb,
Has anyone ever seen this? I’m thinking the float and shut off needle is the problem,
Why is the fuel pump allowing the gas to flow past without running?
Any and all incite would be greatly appreciated
 

rlbock said:
Need some incite, over the past 5 days the sled sat in heated garage with track elevated about 6 inches off the cement. Came home to a fuel smell in garage, noticed stain on cardboard I had under it. Appears that fuel leaked into cylinder and out the exhaust manifold, (pipe was off). Pulled it over and 12 ounces of fuel was pushed out of manifold.
Of course I’m not going to try to start. Pulled plugs and mag cylinder had fuel on top of piston, so I’m assuming the fuel is coming from that carb,
Has anyone ever seen this? I’m thinking the float and shut off needle is the problem,
Why is the fuel pump allowing the gas to flow past without running?
Any and all incite would be greatly appreciated
Click to expand...
This was a real problem on my old 650 Polaris Indy under exactly the same conditions. Usually if the fuel is leaking into the cylinders its because the needles and seats are leaking but having the rear of the sled raised can cause the float to allow fuel to continue to flow and not cut it off. I haven't had this issue on the Yamaha triples but the way I cured it on my Polaris was to install a fuel shut off valve between the fuel tank and the fuel pump...this is especially important when trailering on many sleds.
 
Thanks for the advise, the issue seems to be still happening, I was away for a week, turned it over with plugs out and it spit gas out of all 3 cylinders, originally I thought it was just the mag side cylinder. It’s like all 3 floats aren’t shutting off the fuel, and the fuel pump is letting gas flow right through when it’s just sitting. I’ve owned a lot of Yamaha 2 strokes and have never experienced anything like this.
Is the fuel pump designed to let the fuel flow right through it without the engine running/turning over?
 
I will have to check, but I doubt it is as it was in all 3 cylinder, I’m thinking the needles are wore, I’ll check the hose and needles next. Sled ran and idled good. First noticed fuel in mag side cylinder only. Then all 3 had fuel
 
I would say your guess is pretty good. The Float is the usual culprit. you see it alot in go karts. Ive had it happen to me on motorcycles but they only leaked when i ran them.
 
Fuel is not entering the pulse line, I’ve checked 4 different fuel pumps, if you blow air into the fuel line inlet it blows air out through all 3 carb lines. I discovered what I think is letting fuel into each cylinder. The float needle seat has a o-ring seal on it and all are showing their age. My thinking is these old o-rings are letting fuel past and slowly filling each cylinder. I’ve replaced the o-rings and will install carbs and see if the issue is solved.
 
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