Jetting starting point high velocity motor.

[michaelbrenner]

I have a 61x cylinder / 62t case / dual 38 mikuni setup. I'll be running flame arrestors, removed chokes, filled crossover, and reed stuffers on my engine that has some porting on the cylinder and case. I'll be running a b pipe with a limited chamber. I will be running at sea level. I filled the crossover and use reed stuffers to increase throttle response and brap in general.

I know Factory pipe recommends a 70 pilot, 135main stock needle seat and 95gram spring.

I'm wondering what I should run ballpark to begin my tuning.

Since my crossover is filled, I have researched on this site and figured most people use a 115 gram spring to increase their popoff since the signal to the carb is stronger.

I also thought that a ported engine would favor slightly leaner jetting aswell? Is this correct?

I'm thinking that a 132.5 main, with the stock pilot, stock needle/seat and a 115 gram spring would make my motor run about right or be closer than FPP recommendations. What's your take? and what's the rational behind it?

Thanks guys.

 

[robertg]

It seems like everyone with dual 38mm carbs is within 5 of the 70/135 jetting. Every motor can be slightly different. I was running a 115 gram spring when I had 38's.

 

[michaelbrenner]

UPDATE: I'm still tuning and riding here in San Diego! I'm wondering if my crossover being filled is increasing my low speed throttle response too much for the 70 pilot jetting. I'm finding the motor has good response at 5/8 or 3/4 of a turn on the low speed adjuster. I'm wondering if I should go to a 67.5 pilot to get the adjustment back into the 1 to 2 turn range. Anyone have any input on that? Also, I'm running 132.5 mains with 1 turn out and a 115 gram spring in each carb.

 

[Mike W]

115 gm spring is a little high. I ran 95gm/72.5 pilot/ 135 main without the crossover being filled. I deffinatelly would not go lower on the main and pilot especially running 115gm spring.

 

[John_Ciocca]

UPDATE: I'm still tuning and riding here in San Diego! I'm wondering if my crossover being filled is increasing my low speed throttle response too much for the 70 pilot jetting. I'm finding the motor has good response at 5/8 or 3/4 of a turn on the low speed adjuster. I'm wondering if I should go to a 67.5 pilot to get the adjustment back into the 1 to 2 turn range. Anyone have any input on that? Also, I'm running 132.5 mains with 1 turn out and a 115 gram spring in each carb.

If it bothers you that you are ~3/4 turns out on the bottom and desire to be say, 1.5 turns out go for it. Performance wise you gain nothing but if it makes you feel like you dialed it in perfectly by being 1.5 turns out it won't hurt anything. 1 turn out on top is fine.

There are many setups in different skis where the the high speed adjusters are almost closed.

JC

 

[michaelbrenner]

It's running freaking crazy now. I'm getting excited. Handling isn't there yet. I shimmed the grate 2 washers worth. I'm still dialing the rideplate because 2 washers on that was too much, it was nose steering again. I guess I'll go back to just 1 washer on the rideplate and see how that is. It's getting faster!

 

[Mark44]

Try pulling out those stuffers you may find some more power.

Mark44

 

[michaelbrenner]

The stuffers aren't in there. I'm happy with the power right now. It cavitates right off idle. Still don't have the handling I want, once it's hooked up and on plane, it is fast..... Running the 132.5's and I'm under 1 turn and still trying to get more by leaning ever so slightly. Still tuning the pipe as well, it isn't sizzling yet. Once I get the pipe sizzling and the porpoising under control I'll be a lot better than I am now. Midrange response is pretty crazy. makes throttle control an issue when riding the hood!

 

[Big Kahuna]

It seems like everyone with dual 38mm carbs is within 5 of the 70/135 jetting. Every motor can be slightly different. I was running a 115 gram spring when I had 38's.

when I had TLR do my cylinders while running the 38's the only jetting that worked was 105 lows and 135/140 high I ran both 1.5's and 2.0's at different times (changing the springs). A friend had the same porting and had to run the same jetting also while using a dry pipe instead of the B Pipes......

Every setup is different.