Mikuni pop-off pressure

[Petron]

Hopefully someone can explain this one.

I'm rebuilding my Mikuni BN-401 (SB) carbs (1996 SeaDoo GSX). The manual calls for pop-off pressure ranging between 23-43 PSI.

Good news is my pressure is reading at 30 PSI.

Bad news is once I install my new regulator diaphragm & regulator chamber cover I decided to check pop-off pressure again (before completing rebuild) and pressure reads at 18 PSI +/-.

I have new needle & seat (1.5 size), dull silver spring, along with rebuild kit that I've used.

Any explanations? Thanks

 

[nswillin]

The Mikuni carb manual says the 1.5 mm needle valve size and the dull silver spring should have pop off at 45psi.

They also say to do the test with the regulator diaphragm off to observe the needle valve.

The seadoo manual says use the 80g spring (black one) and needle valve 1.5mm which will give you 30 +- 10.


You said you checked this "before completing rebuild." What was it after rebuild?

Remember the needle neeed to be wet to get a good reading. Spray it with WD-40 and then check it 3 times.

 

[Petron]

After rebuild it was around 30 PSI. Like I said, once I installed diaphragm & regulator chamber cover I check it again, and again, only to find it read around 18 PSI.

I think I found the issue. I purchased a new needle & seat package (1.5mm) from SBT.

The bottom section of the new seat is actually different to the original Mikuni one (I'll try post some pics). Once I reinstalled the old one with a new o'ring (sprayed with WD40) I was reading a strong 32 PSI, even with diaphragm & regulator chamber cover on.

This is what I found, interesting.

So should I settle for a strong 32 psi (as per seadoo manual) or 45 psi (as per mikuni manual)

 

[PWCdoc]

I think I found the issue. I purchased a new needle & seat package (1.5mm) from SBT.QUOTE]

HHmmmmmmmm.

 

[timmyboy76]

I think I found the issue. I purchased a new needle & seat package (1.5mm) from SBT.QUOTE]

HHmmmmmmmm.

lol....ur outta control, doc...:cheers:

 

[Petron]

You guys are too funny.

Basically the needle & seat package I purchased from SBT (1.5mm) has a slightly different SEAT base to the original mikuni. Once I went back to original needle & seat (changed o'ring) my pop-off pressure was on the money.

I'm happy, she sounds good & RPM is perfect.

:cheers:

 

[nswillin]

Thanks for the update. Hope everything's good now.