Mikuni Super BN question

[smitty]

Rebuilding the carbs on my 96 GTI. The sea doo manual lists several different springs for the needle valve arm ( 51 gram, 65 gram, 80 gram and 115 gram to be exact. The mikuni carb amnual lists springs at 65 grams, 80 grams, 95 grams and 115 grams.

I have new needle valves which are 1.2's. This size isnt listed in the mikuni manual as a choice.

Seems like the info in these two places ALMOST is the same...

SOOOOO the question is for a stock ski with 1.2 needle valves, which spring should I use and what should the pop off pressure be set at ?


Thanks

Smitty

[1fastski.com]

Re: Mikuni Super BN question

the 95 with 20 to 25 popoff will work fine

[Bill O'Neal1]

Re: Mikuni Super BN question

Without looking at the Mikuni chart, 1.2 with a 95 should be way up in the high 30's psi.......
If you can wait till morning, I'll look up the correct specs for you. Never heard of a 51 gram spring..........

[Bill O'Neal2]

Re: Mikuni Super BN question

The manual lists the 1.2 needle valves in the 1996 GTI dual carb motor. This is the smallest of all the Mikuni needle valve specs in any of their engines. I was wrong about the Pop off pressure guess that I made last night. A 95 gram spring with a 1.2 N&S would be well over 45-50 PSI pop off. The oem manual doesn't list the gram size of the springs. So, you need to look at what is in there to detirmine the size of the spring. BTW, springs only need to be replaced when they have rusted, so if they look new, you can reuse them.

115 gram = gold spring
95 gram = longer dull silver spring
80 gram = black spring
65 gram = shorter shiney silver spring.

A 65 gr spring is shorter (15mm) and the coils are right hand wound.
A 95 gr spring is a longer length (16mm) and has left hand wound coils.
Looking closely at a 65 gram spring, you will notice it is shiney silver colored and has a double wrapped top and bottom coil. A 95 gram spring is a dull silver color and has a single wrapped first coil on the top and bottom.

OEM Jettting specs for a 1996GTI dual carb motor are 67.5 low speed jets with 130 high speed jets, 1.2 needles and seats ( I'm guessing a 80 or 95 gram spring) with the high speed adjuster needles closed and the low speed adjuster needles set at 1.25 turns out, plus or minus 1/4 turn. The OEM manual calls for 40-56 psi pop off pressure with a minimum stablized pressure of 24 psi.

[1fastski.com]

Re: Mikuni Super BN question

i have always run lower popoffs and have great results , the skis always start easy and run better then stock setup skis .

BUT if you feel safe run by the book :-)

[Bill O'Neal2]

Re: Mikuni Super BN question

Chris,
I have run into some starting problems with the "I" series carbs when lowering the pop off pressure, especially on the twin carb models. If the ski is out of the water it will start just fine, but after warming up and while in the water, they can be difficult to start, sometimes needing to be lifted in the rear to get the exhaust outlet above the surface of the water.

[smitty]

Re: Mikuni Super BN question

Just installed new black springs. Both pop offs are right at 49 PSI. Is this olay for a stock ski ???

Thanks for all the help!!!

Smitty

[Bill O'Neal1]

Re: Mikuni Super BN question

Yeah, that should work.