I posted this over in the Yamaha forum, since the carb came off a Beartracker, but got no response. I hope someone over here can help since so many quads use a Mikuni.


The problem - I came in from a ride Sat. on my Arctic Cat and decided to add some fuel stabilizer to it and my Beartracker. Fired up the BT, pulled it out of the garage. Added the stabilizer and toped off the tank. Decided to let it idle to warm up to burn of the fuel in the lines and carb. After a few minutes it just shut down like I turned the key off.

The diagnosis - I could not get it to restart. Good spark, good fuel flow out of the tank. I even drained the tank and filled back up with fresh fuel. I opened the float bowl drain, no gas came out. Humm, looks like no fuel. I pulled the air filter and shot some starting fluid in, she fired up till the starting fluid was used up.

Where I am now - I guessed the floats were stuck or the valve was hung closed. I pulled the carb and removed the float bowl. If I try to blow through the fuel inlet port with the carb right side up (floats down) I can not get air in. I figure I should as this would be where the valve was opened to let fuel in the bowl. I take a look at the valve tip and see it only moves through about 1/4 of the travel of the little metal contact pad on the float. I appears to be sticking closed.

The question - How do I get that bugger out? I see a screw next to the valve body but there is no clear shot at it past the platic bits attaching the 2 floats together. The pin that the float pivots on looks to be staked in or is is just pressed in? Can I drive it out with a drift so that I can get the float out and have access to the valve for removal and cleaning?

Thanks,

Brent

 

On my rappy 350 the way to pull the neddle out was through the top part of the carb, under the rubber boot thing. There was this white plastic piece and you just pull it out. Hope that helps, i know my description sucks

 

I think I have it figured out. I figure I should update this as someone may find it in a search should they have a similar problem.

Anyway, the problem looked to be the fill valve for the float bowl. With the floats down I could not blow through the fuel inlet. On my carb there are 2 floats interconnected with a plastic "super structure" that linked them together. Where this structure crossed float to float there is a small metal tab attached over which wraped a bit a wire that, as I discovered, actuated the needle in the valve. At first I thought this was some sort of range of motion limiter as the needle had a small stud projecting from it that would stay out, aparently under spring tension, and push in when the float assembly contacted it. I thought this stud was the valve needle. The question was how to get the valve out as the float assebly blocked it from direct removal. The float pivoted on a pin I was unsure as to how to remove. After looking it over I wraped the carb in a towel, gently secured it in a vice, and drove the pivot pin out with a slight hammer tap and a small drift. The pin looked staked in so I was unsure if I could drive it out. Any way, with it out the float came out and I could get to the valve. I poped the valve out, removed the screen at the end and could see no obstruction. As a side note the rest of the carb was spotless. I soon discovered the center of the valve was removable. This was the actual needle, not the little stud sticking out of it. I still don't understand the little spring load stud in the center of the needle. The previously mentioned wire from the float to the valve (needle) is actually used to actuate the needle in and out of the seat. The needle is basicly an aluminum cylinder with a "rubber-ish" tip. It has 4 raised veins around its outside running the lenght of the needle. These veins look to center the needle in the valve body. Well there was some black crud on each of veins. I took some 400 grit, wet, and polished the crud off. I carb cleaned the seat and swabed it out with a q-tip. Now the needle moves in and out with ease. I but it all back together and can blow through the inlet. If I lift the floats the needle seals off the inlet, no air. It will now open the valve on its own if I let the floats drop.

I think I will be OK now. Still have yet to throw it back on the quad but I don't see a problem.

brent

 

Sand paper may have been a little harsh on that piece, just some carburator cleaner would have done the trick.

 

Check out item #6 in this article, it explains the sping loaded pin in the needle. You did a good job explaining what you did, and sounds like youve got it fixed.

#6

 

Great info, my Yamaha Grizzly 660 had the same problem. I did the exact same thing you did and it's running like a champ now!

 

DKNARND

Tried carb cleaner, have tons of it. Use it all the time to clean parts, tools, etc. Did not phase what ever this junk was. I just brushed it with some same 400, just enough to get the junk off. The needle was aluminum so I knew it would be easy to get into it with some heavy sanding.



hondabuster

Thanks for the link, I will check it out!

Brent

 

Excellent link.

 

BTW, forgot to update, once put back together she fired right up!!

Brent