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Gas coming out exhaust - Mikuni Carbs

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17K views 4 replies 4 participants last post by  kccats  
#1 ·
I have a 1987 Yamaha Exciter, that has set for a few years. I went through the carbs and cleaned them the very best I could. The snowmobile started and I ran it through the yard. Everything seemed like it was good and it idle great. Put it on the trailer to get it out for a long ride in a week. The wekend came and I was going to start it and it wasn't starting. I noticed some serious gas coming out of the exhaust pipe. I pulled the plugs and their wet.

I tried to do my research on this issue, I'm a bit new to carburators. All the forums on this said it was the floats or the needle seat. I pulled the carbs again and the floats seemed fine. I removed the float arm and pin and then the fuel inlet needle and seat. Cleaned and air blow. The needle seems to move up and down freely. I did this the same on both carbs. They both seemed the same. I put the carbs back in and gave it a pull, the sled fired over and quickly shut off. I then pulled a few more times and I could see gas dripping from the exhaust. I didn't even use the choke.

I'm stumped. The sled idle great a week ago and now I'm having the same issue after the second cleaning. I realy don't know where to go from here. Any ideas would be much appreciated.
 
#2 ·
The crankcase is filling with gas. Take out the plugs, and if lots of gas comes shooting out, your crankcase is full. A bad needle or seat will cause this. You may have to replace them.
 
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#3 ·
When you say needle, your talking about the the fuel inlet needle? If I turn over the carb so the floats are down and try to blow in the fuel intake, I cannot blow any air in there, I figured that would be a good test, but really have no idea. As I turn it over and the floats drop and I can blow air. When you say seat, your talking the brass thing that holds the needled with the metal clip. What could be a problem with this? Thanks for the info.
 
#4 ·
The seat is the brass part that the needle tip presses against to close it off.
To clean these, use a pencil eraser.
If you replace the needle and seats, use the viton (rubber) tipped as they seal better and last much longer.
 
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