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1989 Yamaha 350 Big Bear Carb problems

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I rebuilt the carb on a 1989 350 Big Bear. This is a Gen 1 carb ( 2 cables running to throttle).

Quad starts and runs but I have fuel leaking from the air intake.

Is the float set to high / low?

Does the needle for the main jet need adjusting? I have it on the center groove ( 2 groves above and 2 groves below).

All jets are new, float and needle and seat are new.


Thanks for your help


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It’s possible that the float is set to low but that would also result in the overflow also leaking.  The small hose that’s attached to the bottom on the carburetor would have gas coming out. 

If you made any adjustments to the needle my guess would be you need to lower it.  

When you put the slide back in the carburetor did it go in properly? And is it sitting all the way down when the throttle is not pressed ? 

Latlsy did you reassemble the carb properly? I’ve made mistakes. The main jet I didn’t tighten it when I rebuilt one of my carbs.  Shit happens.   Double back and re check everything.   

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Thanks for the tips, I will go through it again and double check everything.

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Took carb apart and reset the float, it was set to high, had to change out the main jet as it wasn't the right one when I compared it to the old one.

Quad starts nice and idles great. Throttles up nice but when reaching higher rpm's it starts to spray a gas mist out of the air intake and does some small backfires through the air intake. When you throttle back down there is a couple of drops of gas comes out the overflow at the bottom of the carb.

Tried adjusting the air / gas screw but didn't seem to make a difference at high rpm's.

Does the needle on the main jet slide need to be lowered some more?

Looking for where to look next.




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Did you adjust the float enough? In my last post I said set it was set to low, I meant high.  Is it possable that it still needs a slight adjustment ? It might need a hair more.  Also be careful with the back fires and that fuel in the air box.  A back fire can easily lead to the leftover  gas in the air box to ignite and catch fire.  Have you messed around with main jet needle at all? If anything maybe you can lower the needle one notch but if it was in that position prior to working on it then I would leave  it.

lastly have you pulled the spark plug to see what the color looks like ? It’s a good indicator on how the bike is running. 


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Thanks, I will adjust the float a little more. I think I will lower the main jet needle one notch as this carb had been played with before they brought it to me.


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This one certainly has been a pain in the ass.

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Sorry, I thought I had updated this post a while back but obviously I hadn't.

After getting taking this carb apart several times and getting frustrated, I walked away and went fishing for the summer, When I looked at it again I took the carb apart and checked everything, mounted it back on the quad and just hooked up the gas line. Quad fired up right away and throttled up nice and idled nice. I then started hooking everything else up on the carb, vent lines throttle cables air box and filter. Quad ran good until I hooked up the line off the bottom of the carb (overflow line). As soon as I hooked this line up quad started blowing gas out the air intake. I removed the line and it ran great. This line has what Yamaha calls a pipe in it. It looks like it may be a oneway valve of some sort. I removed this "pipe" and the quad ran great. 

I looked at a few other Yamaha quads that have has carb jobs done at dealerships and noticed none of then had this "pipe" on them so I just ran a length of gas line off the bottom of the carb.

Quad has ran great ever since. Owner took it hunter last fall and it didn't miss a beat and is still running great.

Still not a hundred present sure what the purpose of the "pipe" is but that was my problem all along.

Thanks to everyone that responded to this request.


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