The Lightbulb in the Attic

[boyat68]

One of the things that I have discovered while working on my 80G carburetors: I put new seats and needles in. The seats were from mikes and had O-Rings and push in, held by a lock down clamp. The O-Rings seem to need soaking in fuel before they seat properly as they tend to leak for a long time after insertion, messing up your float height adjustments. For example, if you adjust your float height right after you insert the seats, then one cannot tell if the float height is correct as the level using Ken Talbot’s sight gauge method will seem to settle down and then suddenly start creeping up until the carburetors overflow. Since one does not know the cause right away, there is a tendency to readjust the floats until the level stops leaking from the air side of the carburetors. What this does is lead one to think that the level is correct, but when you put them back on the bike, odds are that they are too low. This causes confusion and many trips from the bike to the bench. In the mean time the carbs are left drained and setting over night and the O-Ring shrinks starting the grrr factor all over again. I recommend that when one takes the 80 type carbs off for repair, do the repair and leave them full of fuel over night before setting the float height. Also if the bike is left over the winter without fuel in the carbs, then there is a possibility that they will leak until the O-Rings swell enough to staunch the leak past the O-Rings. The light bulb finally came on.

[XSPastor]

boyat68,

You may want to check the bore that the seats are inserted into. That bore can get gunked up and cause even brand new o-rings to leak. I had that problem. The bores should be smooth and mirror-like. Use a tooth pick and some carb cleaner if you need to scrape them. This solved my carb leak.

Tim

[boyat68]

XSPastor:

Thanks for the reply, They have been scrupulously cleaned, the bore polished and carefully fitted; O-Rings to seat and lubricated to slide in. Either the O-Rings are a bit on the small side by design or selection, or they are a secondary source from the same manufacturer that works. The gist is,that left out of fuel for a brief period, they leak. Yesterday I left them soaking and went back to set the float height. I had to drain the fuel, remove the float chamber body, set the height, do 1-4 in sequence, replace the float chamber body and re-test. During that short time the O-Rings were out of the fuel, they had shrunk enough that it took several tries of refilling the bowls before the O-Rings seated and the level of the fuel could be read accurately. I had gotten #1 set a little high and have to go back and re-adjust.

I am toying with the idea that the O-Rings that Mikes uses are really not suited, and I may order the seats and O-Rings from a different supplier.

I am reluctant to put the carbs back on the bike, knowing that they may leak.

[mro]

I've used MikesXS 80's carb parts several times without any problems, but I have only set the floats with a caliper.

In the Yamaha manual (for the 81SH) it says to use the tube method for deturming fuel height in the bowl, but specificaly states that you need to run engine for a minute after you have them hooked up to be able to get propper fuel height. Think I'll just use my old caliper.


mro

[mro]

held by a lock down clamp

Check that it's NOT "bent" as to not apply pressure on the seat to hold it down.


mro

[81xsproject]

You can get o-ring sets from harbor freight. They have both nitrile and viton. You could put in your own larger o-ring.