Flooding Crankcase With Mikuni Carb

Its hard for me to remember to turn my manual petcock off everytime I stop the bike, and when I leave it on the crankcase floods ruining my oil. If I leave it on for 30 seconds with my Mikuni carb am I in danger of flooding the crankcase? I could get into the routine, but am likely to leave it on by accident for 30 seconds. Is the FCR the only other option I have?

your wored about 30 seconds

most of of the wornings about leaving the pitcock open is for those 30 minets to over nighters

the S and SM come with a petcock that turns it self off whin the motor is not runing ---- maybe you need to buy one of those petcocks ???

maybe your of the guys that really needs fuel injecton !!!!

Switching the tap off? .......... is it so hard to remember?!!!! but 30 secs should not be a problem, the problem is with the carb -I'd have thought a new needle valve is all that is required.


it really sound like East Coast bot a really worn out bike and now he is finding out it would have been cheeper to buy a new one

Maybe but the needle valve is just a few dollars!

Don't ever depend on the needle valve. Shut the fuel off every time. It may or may not have a problem with the float, needle, or seat, but if you shut the fuel off it won't fill the crankcase with gas.

it really sound like East Coast bot a really worn out bike and now he is finding out it would have been cheeper to buy a new one

$2000 for a 2001 s with 2800 miles on it and acribis 4 gal tank. neglected, not abused.

Carb style does not matter, they all weep fuel if the tap is left on or the float needle (or gasket) are aged.

Some bikes, the carb is below the valves and the intake is angled in such a way that fuel weepage comes out the bellmouth. Not the case anymore.

Tap off, key out is a habit to develop. My DRZ has the vacuum petcock, my other bikes do not. I have had to develop different habits for different bikes.

FWIW, my SM is 3.5 years old with a non-vacum tap and I NEVER switch my tap off unless transporting the bike to/from the track in the van. I've never had any problems whatsoever.... although others such as yourself have... odd :thumbsup:

And some day it will bite you in the butt. I have never had my crankcase polluted with fuel and I have never woken up to the garage flooded with fuel with my tank shut off. And I must say that I am always suspicious of my vacuum petcock.

+2 on GOF1's comments. Though I am suspicious by nature..... :thumbsup:

I think the bottom line here is that if your flooding the crankcase with fuel you need to replace the needle and seat. I switched mine over to a manual fueltap just because I switched my old DR over years ago and it drove me nuts that I had the habit of turning it off and couldn't. I still forget sometimes though.


$2000 for a 2001 s with 2800 miles on it and acribis 4 gal tank. neglected, not abused.

Sounds like a pretty good deal ya got!! Looks like it might not be a bad idea to replace the needle. or at least inspect it. I use the same type of petcock, but dont have any problems. BTW Dont worry about iowaBClivewire. He just likes to hear his head rattle. :thumbsup::moon:

so you can hear that too ?? wow

When you go in to replace the needle & seat be sure and check your float level as it can also contribute to fuel over flow.

yep,replace the float valve/needle and seat.easy fix

#18 Valve assembly needle.

Gets you the valve needle, seat and a new o ring.

It aint cheap, make sure it's not just a piece o crud causng the valve to leak.

18: VALVE ASSY,NEEDLE 481758-001


thanks. Ill check it out fist the bike has 3000 miles on it so I can imagine it has been exposed to that much crap. then again the last owner neglected it, the petcock screens were a mess so I presume the carb is as gunked up too. I got away with running it in the warm now that it is below freezing my bike wont start.

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