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Nero's Govenor? Petcock, or maybe fuel line problems?

Nerobro

Nerobro

Forum Mentor
So... My bike has an issue.

I think my petcock is doing the copierguy thing. Wide open throttle causes so little vacuum that my petcock closes.

Here's the symptom. Wide open throttle. Aproxamately 1 mile down the road my engine cuts out. (30-45 secconds) it's a fuel cutout. If I close the throttle, and coast to the side of the road. By the time the bike has ceased it's coast down..... it's idling normally, and revving normally.

If I'm at 3/4 throttle, it won't cut out.

Yeah, there's an easy answer. "don't use full throttle for more than 30 secconds" Yeah easy for your to say. :-)

Here are my thoughts. I'm going to rebuild my petcock, because my "prime" function doesn't work. I am also going to reduce the length of my fuel hose. I can probally trim 3" off of it without making it to difficult to remove my gas tank.

Or... Gutting my petcock to make it on/res/off, instead of on/res/prime. Just getting rid of the whole vacuum thing.
 
If you can't get prime, yes you do have a prob with the fuel tap,have not heard that one before!
Do a practical check, take your fuel tank off,turn it to prime and see if you have flow.
Then turn it to on and suck on the vac hose , see if you get flow.
You can try running you bike with the fuel cap open(NOT WITH A FULL TANK)
This will tell you if it's a tank vent prob.
 
I KNOW prime doesn't work on this petcock. I've tested it several times. :-)

My carbs already dont' have vent lines on them. Thanks for the suggestion though. :-)

I have already tested the tank cap thing. that's what I thought it was at first. That is what I thougth the problem was last season. Becuase stopping, opening the tank, and restarting would work. it doesn't work anymore. (I've even had the engine die this way with the tank cap off)

I'll admit my fuel line is a bit long. So it "loops" up a little. I'm going to trim it shorter tonight. And I suppose it's time to order a petcock rebuild kit.
 
The float levels are fine. (if that's what you mean by fuel level) In fact, they are better than they used to be. The cylinders cut out at almost the same time now when fuel cuts off ;-) They used to cut out over the course of a 1/4 of a mile.

If anything the main jets are to large. At 130 I'd get a rich cut out and even a severe backfire if I played with the throttle right. With 125's the engine runs strongly at full throttle.

This is DEFINTELY a fuel flow issue. not a carburation issue. Especially given that as long as I don't maintain full throttle for more than 30-45 secconds the carbs never empty, and the engine runs just fine.

Course my jetting is a completely seperate concern ;-)
 
Also, make sure you are using 8mm (5/16") fuel line, and NOT 1/4". if you have a filter inline, make sure it is the free-flowing type, not the paper cartridge type. Let us know what you find
 
That is exactly what I"m using. I'm using 1/4" for the vacuum line. And larger hose for the fuel line. I haven't had time to play with it this week.... #1 it works. #2 I'be been busy :-)
 
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