I have a Yamaha Wolverine 350cc, year 2000. I have had it bored out with new rings and new valves and a timing chain. After a couple of weeks, it started running bad again and we discovered that the plastic cover for the air cut-off diaphragm for the Micuna [Mikuni] Carburetor is cracked. Glue did not fix the problem.

This part is unavailable to buy. I can not afford to buy a whole new carburetor. [Are] there any remedies to fix this problem? {Ray, IL, USA 2000 Yamaha 350 Wolverine ATV, YFM350FX}

Unfortunately, neither Yamaha nor Mikuni sell this carburetor top separately. You can either try again to repair this piece or find a replacement.

We will start with attempting to repair it. I do not know what type of glue you used previously, but most glues break down in the presence of gasoline and may hold pieces together but do not form a airtight seal, so finding one to work on part of a carburetor can be troublesome.

This carburetor needs to build up vacuum in order to work properly. The best way to achieve a temporary repair is to use black RTV silicone.

I say this is a temporary repair because this will seal it, but it will not last forever. RTV brand silicone is available in different colors that indicate the maximum heat range it will withstand. For your application the black RTV will be best.

Do not use household or bathroom type silicone. It will react with gasoline and oil & breakdown quickly when exposed to engine heat and the elements.

First, wash and thoroughly dry your hands, so you do not contaminate the surface.

Next, put the cap (or top) on the carb & take care not to over tighten the screws.

Using your clean finger, wipe a thin coat of silicone over the entire top of the cap including around the sides where it meets the carburetor body. Let this cure for one to two hours.

After two hours, repeat the same procedure. This time, putting just a little more silicone over the crack. You want to use thin coats, do not just glob it on there.

The silicone should create an airtight seal, allowing a build up of sufficient vacuum to operate. It will not be perfect and will not last forever, but it will be functional.

You should remain on the look out for a used carburetor or carb parts to affect a permanent repair. Some good places to look are , Craigslist.com and local swap meets or ATV clubs.

When you do find one, it will be easy to peel off the silicone and install the new cap.

This Mikuni was not exclusive to the 2000 Wolverine model. It was used on the following models:

The Yamaha OEM part numbers you are looking for are 4KB-14901-10-00, 4KB-14901-20-00, 4KB-14901-11-00 or 4KB-14901-11-00 Carburetor Assembly 1.