Mikuni problem

[Mike Hufnagel]

Anybody having problems with their Mikuni carb. leaking gas past the inlet needle & seat and going out the overflow tube?

I have replaced the needle & seat twice now and both times gas has leaked past the assembly no matter where I set the float level at.

 I had drilled & tapped the bowl drain for a fitting & clear tubing to see where the level was at. (With a gravity fed gas tank). With thye carb off the bike and hooked up to a gravity fed gas tank (no slide in carb) and the carb sitting at approximatly 30 degrees (like it was mounted on the bike) again, no matter where Iset the float level at, it still leaked past the assembly (one was brand new)& out the overflow.

I inspected the seat & needle itself (the seat & needle are metal to metal) and did not find any wear or dirt.  What gives !?!?!

74 Yamaha TY 250
75 Jackpiner w/ 250 eng.
80 Ktm Mc 400
82 KTM GS250II (import)
82 KTM 495
2) 84 Yam RZ350
98 KTM 300mxc
00 KTM Duke 2
06 KTM 950 Adv.
08 Suzuki DR70Z

[454MRW]

Does the float hinge pin have any burrs or wear on it? It doesn't take much to cause it to hang up, or if worn, cock slightly and jam. I had one that after polished up with emery paper worked a lot better. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR250 & OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R & CR150R

[Mike Hufnagel]

I don't bleieve it does , but may as well check.

I think what I might also do is physically(?) press down on the assembly with the bowl removed and see whats up.

I always thought that the needles were rubber tipped. I I may be thinking of Kehiens.

74 Yamaha TY 250
75 Jackpiner w/ 250 eng.
80 Ktm Mc 400
82 KTM GS250II (import)
82 KTM 495
2) 84 Yam RZ350
98 KTM 300mxc
00 KTM Duke 2
06 KTM 950 Adv.
08 Suzuki DR70Z

[Dwight Rudder]

Gasohol will affect the needle if it has a rubber tip.  If not use a bit of toothpaste as a lapping compound and twist the needle in the seat then wash out with contact cleaner.

[Mike Hufnagel]

That was going to be my next step, but I found the problem. The floats were not coming up high enough. I took 2 spare sets of floats/bowls (and the original one) , turned them upside down, and meaured from the flange of the bowl to the top of the float and found that there was a little more than 1/32 difference between the original one and the 2 spare sets. After resetting the floats to compensate for the 30' angle of the carb. everyting seems to be in order.     Now3 I got to lay down from all the damn gas fumes.

Thanks!!!

74 Yamaha TY 250
75 Jackpiner w/ 250 eng.
80 Ktm Mc 400
82 KTM GS250II (import)
82 KTM 495
2) 84 Yam RZ350
98 KTM 300mxc
00 KTM Duke 2
06 KTM 950 Adv.
08 Suzuki DR70Z

[242]

Note: On some of the older Mikuni carbs with a over flow-tube, the tube will split and drip, acts like a bad seat.