Total Motorcycle Community Forums

I have a 1997 Kawasaki Vulcan 800 Classic. Bought used, had been setting for a while. I cleaned out the tank and coated with POR15. I have also replaced some of the carburator parts, the two small pumps (they were worn). I cleaned out the carburator and got all of the little bits of dirt and rust out of the bowls and other parts of the caburator, but did not touch the jets. The motorcylce will start right up and run great for awhile and then die and then it will run but will back fire. You can tell when it is going to run okay, the idle is higher and it has a good solid sound. When idling it will run bad and either die when you give it gas or backfire, and sometimes it will flaten out and run real good for awhile. I put some new gaskets and seals in the pit stick. When you turn to prime it does alow gas out, however not a steady stream (not sure if this is what it should or should not do). What do you recommend?

sounds like your petcock and/or petcock filter is gummed up.

take the petcock off, take it apart and give it a thorough cleaning.

The erratic flow of fuel when switched to prime is a dead give away that it's gummed up.

Thanks Chris, should the flow from prim be very solid?

glarkin wrote:Thanks Chris, should the flow from prim be very solid?

When the petcock is in Prime, the flow of fuel should be constant, with no bubbles or changes in flow rate.

Owen

(Chris DeBurgh is the man who wrote the song lyric in my sig)

Sorry Owen about the name, I see that now. I did take the pitcock apart, however the does not seem steady. Is there anything else it could be? Especially when it runs good and then bad or not at all. Would I need to replace the pitcock? I did put a new gasket in it, but maybe more to it than that.

You may have some grit in your fuel tank that is intermittantly blocking the screen on the petcock.

are there any deposits in the petcock or around the screen anywhere?

You might be getting some residue from the tank lining coming off and plugging things up.

My first thought is that it may be developing a vacuum inside the tank. You might try opening the gas cap slightly to see if it helps, but of course, don't ride it this way! With the cap open, try blowing through the vacuum relief tube. If you can't, then maybe it got plugged when you did the POR treatment. Also, the routing of the vacuum relief tube is critical - make sure it's routed just the same as it came from the factory and isn't kinked.

Good luck!

Does this bike have hydraulic valve adjusters or do they need manual adjustment? Running for a while then backfiring sounds like valve clearances getting tight. It runs until its warm then things go too far out of tolerance and the slightly open valve/s cause poor compression and unburned fuel to ignite and backfire. Is it backfiring through the exhaust or intake?

It backfires through the exhaust, and some spitting through the intake. I started it today and it ran fine, and then I couldn't give it any gas without it staling. I tried the suggestion about the vent tube and it is clear and I don't believe it has a restriction, did the same with gas tank open or close, vent tube on or off. I also looked at the stream of gas and it trinkles out and is not all that steady. How should the flow be, should it fill the tube with gas when it comes out?

Ideally it should be a full tube of fuel flowing fairly constantly. However, since you do have a reasonable flow of fuel through the petcock, I think maybe you should investigate the carb again. I'm thinking either the jets are clogged at least partially or the float level may be low, and when you open the throttle it leans it out too much and stalls. There may still be some crud floating around in there. I think I'd also give it a good dose of SeaFoam in the fuel. The stuff has worked great for me at cleaning out fuel systems.

Ron made a good point about the valve clearances, though, but it would depend on how many miles the bike has on it and whether an adjustment had ever been done. The Vulcan 800s have a shim type adjustment system which, if neglected long enough, could prevent the valve(s) from seating. I believe the recommended interval is 6,000 miles. With this system, the clearances get tighter as you ride, so Ron's theory may have a bearing on the backfiring.