02 Kawasaki kvf 650 back fire through carb

[taggart]

Well I need some help, my 650 is back fireing through the carbs, but ONLY when its cold. If you rev it up, it gets worse, but if you pull the choke on while doing that it gets better. I've gone through everthing in the carbs and everthing is to spec. I thought maybe it's electrical, but what is stumping me is that it's fine when it is warm. HELP ME I'm going crazy!

 

[AreWeThereYet]

When was the last time you did a valve set

 

[taggart]

About a mounth ago? but if it was the valves you would think it would get worse with the heat and expansion?

 

[AreWeThereYet]

Just covering some basics

 

[AreWeThereYet]

Sry was in the midst of eating supper,..

I know when I was too lean with my rhino it was backfiring through the carb. When it's cold though and get's better as warm it all doesn't sound that abnormal.

 

[taggart]

Really, well it was jetted for sea level when I got it, but then I rejetted it, but the jet range for sizes are 1600-4900, and 4900-8100 ft we're at about 3400 but I ride between 3400 and 7000 ft, so went with the 4900-8100 jet range, maybe thats what it is? Thanks for your input, I would love any more ideas you might have. Thanks

 

[AreWeThereYet]

Not sure if you are able,.. but I bought an air/fuel wideband to monitor my mixture so I new for sure if I was running lean or rich. If you don't want to spend the $300, you might be able to find a tuning shop that will install a bung and use theirs.

You could also do the old spark plug color trick, that will get you in the ballpark, but its not as accurate as a wideband.

Myself I jetted for 0-2500, but I am still running too rich, so will have to jet down this spring

 

[KVF 700]

the valves go out of wack pretty quickly sometimes on those machines. unless you have made some recent engine changes (ex pipe, air filter etc) nothing should need to be changed in the carbs if it has run good before. just my .02

 

[taggart]

Well I just put a K&N filter into it. Maybe I'll rejet it a little richer, and recheck the valves at the same time. Thanks!

 

[AreWeThereYet]

Well I just put a K&N filter into it. Maybe I'll rejet it a little richer, and recheck the valves at the same time. Thanks!

Try putting your hand over the intake to choke the incoming air rather than full fuel choking it and see what happens.

 

[taggart]

Well I just rejetted, and am now checking the valves, I'll let you know how it turns out. Cheers thanks again.

 

[taggart]

Well, have new jets in for 1600-4900 ft everything on the carbs is set to spec and all my valve clearances are good, it's better, but will still fart out of the carbs when it's cold, but, only if you try to rev it up a little, if you just let it idle till it's warm it's fine. Maybe it's just the nature of the beast? I would love to talk to some one with the same quad.

 

[ekw60]

I'm new to the forum . I read your post and had to butt in. I bought a kawie 650 4X4 in 03. It was back firing when i loaded it on th trailer to take it home, i though it was because the engine was cold. No big deal. Well when i took it in later to get it fixed. The dealer in Rolla MO. said tough, fuel related problems are not covered. Est. cost to repair $250-$300.I never could get a dealer fix it under the warranty. Well after $1000+ and two dealers in AZ. i got it fixed in Santa Barbara CA. YUP $375 but they fixed it and told me to never leave fuel in the carbs for more than a few days in high temp days. And in AZ to never leave any fuel in the carbs in the summer. That is my story,even with all the problems i still love that kawie. Its great to take out in desert on long rides.

 

[teeroy]

I would bet that it is the "low speed" circuit in the carb is plugged. in front of the mainjet in the bottom of the carb there is a small tube, when that plugs it will do the backfire thing. had it happen to a few of my 4 strokes from fuel sitting in the bowl too long.

 

[ekw60]

I bought a set of carbs from e-bay yesterday for $100. I'm going to use them as a back up if they are any good. No dought they will need to be rebuilt. There are two more out there. I hope it's ok to post this url. Here is one of then.