Hi,


So this quad sat for years. I installed a good rebuild kit in the carb, but the diaphragm had a small tear in it. I patched the tear, and cleaned out the carb.

It starts easily, and idles fine. Once it warms up, however, it sputters and backfires constantly mid throttle. If I apply the choke, it runs better, and doesnt backfire, but then bogs slightly.

It idles good, and it even flies during full throttle. Also the exhaust manifold glows cherry red after just a few minutes of riding it.

Any suggestions?

 

Float level set right? Are you sure there are no air leaks into the carb? I know there are a lot of hoses on that carb and maybe one is disconnected or dry rotted with a hole in it.

Assuming no air leaks, then it's a fuel supply problem. Either the float is set wrong and there isn't enough gas in the bowl or the fuel pump isn't strong enough. Maybe take the pump apart and clean the chunks of stuff out of it, since it sat for years and all.

 

Alright so I did what you said. I reset the float height to exactly half an inch.

I took the fuel pump apart, and it wasn't really too dirty inside at all. The diaphragm material looked fairly good.

When I started it, and disconnected the output, it would sputter and kind of spit fuel. Is this normal?

The manual I have says that the vacuum line is supposed to connect to a port on the cylinder head. But I think it connects to a port on the carburetor. There's no port on the cylinder head...

 

What would sputter and spit fuel? The output line from the pump would spit and the engine would sputter because you removed the line?

The pump doesn't flow a lot. It works from engine vacuum. Every time there is a vacuum pulse, the pump should spit fuel. It also depends how much gas is in the tank. On mine, when I have the tank full, the gas level is higher than the pump so the gas flows right past the pump and into the carb (and sometimes over-flows into the engine).

How off was the float height?

 

Here is what mine looked like:





Short of buying a new pump or rebuilding with new parts, I think all we can do is clean everything and hope it seals well enough to supply the carb with an adequate amount of fuel.

 

Could it be a valve adjustment?

 

I wouldn't think so. An intake valve that doesn't close would produce very difficult starting, and then, in my experience, would run just fine once started. I haven't had much trouble out of exhaust valves over the years and can't speak to what would happen if the exhaust valve didn't close.

My friend and I set the floats wrong on a 660 raptor one night. I took it out for testing and was doing donuts while he was jumping up n down and screaming at me. I rode over to see what the hysteria was about and he said "look at the pipes!" They were cherry red... almost translucent. We set the floats properly and that solved the problem. The interesting thing is while the floats were set wrong, the engine seemed to run great. It had lots of power.

 

Well, I hooked a facet (electric fuel pump) and fitted it with a battery, and it solved a lot of the issues. The mechanical fuel pump looked very good inside, and there wasn't any corrosion that I could see. very little debris. It is obviously running much better with the electric fuel pump, though. It's a 1-2 PSI pump, not very much.

The floats were not off that much at all. Maybe a MM or two.

If I am riding it over rough terrain, it will still begin to sputter and die.

The pipe still glow red, not super hot red, but red.

It idles fine, and the top end is great, but mid throttle, it acts strange, bogging down sometimes like it's not got enough fuel. I have to keep it revved sometimes to keep it going, it has no middle end.

I want to buy a diaphragm for it, checking to see if I can get one, in case my patch didn't work as good as I thought. I also have a UNI filter and no airbox on it, and a filter skin. So it must be pulling in a lot of air, maybe it needs to be jetted richer? But I can't see how it would cause this much trouble for me. Sometimes it stalls out and takes a while to start again.

I did a valve adjustment on it about 23 miles ago.

It also sucks down the gas. It will hit 50 MPH though, which I hear is good. Sometimes when it begins to sputter, if I pull the choke, it will run fine, but a little boggy.

 

Try adjusting the float such that there would be more gas in the bowl and then see if the pipes get red. Make a big change so you know for sure.

If there is no change, then I'm thinking the fuel pump is the problem. Try filling the tank to the tippy top and see if there is a change with the pipe-glowing.

My assumption was you fixed the diaprahm adequately. If the diapragm is leaking, maybe that is leaning the mixture.