leaky BN38

[stephfamly]

Rebuilt 2001 GTS BN38 Mikuni carb (by me) and used authorized Mikuni parts. Performing the pop-off pressure test, air leaks between carb body and pump assembly body. Suggestions how to determine what is malfunctioning. Thank you for your responses. Don

 

[JeremyD615]

I’ve had some problems with the gasket and diaphragm not sealing on the pumps recently. You’ll have to pull the pump back apart and make sure there are no creases or tears in either the gasket or, more likely, the clear plastic diaphragm. If it appears to be okay, bolt it back down to just snug and then go around and tighten the bolts/screws down a bit at a time until you get everything tight... Then try the pressure test again...

 

[stephfamly]

Thank you. I'll try it. The gasket (not the clear plastic) is a manilla color. I normally see a black color for sealing gaskets. Can this be an incorrect sealing gasket?

 

[mikidymac]

Yes, the gasket should be black, you used the wrong one.

Check this out.....Carb Rebuild Thread.

 

[JeremyD615]

Yes, the gasket should be black. I’m not sure what the application is for those other gaskets, but they shouldn’t be used here even though they do come with the kits.

 

[mikidymac]

The Yamaha's use that gasket. Remember, seadoos aren't the only skis using the Mikuni carbs.

 

[JeremyD615]

Good to know. I was always curious what setup used those pieces...

 

[mikidymac]

There are also two different black rubber sheets for the fuel pump so make sure you use the correct one also.

I recently had a carb fail the final leakdown test only to find out that from a sealed Genuine Mikuni kit there were two of the black fuel pump gaskets stuck together and leaking between them. I never noticed it when putting it together. I removed them pulled the gaskets apart and the leak was gone.

 

[stephfamly]

Problem fixed and pop-off pressure now works. Used wrong gasket. Thanks everyone.