How much performance is hidden in jetting?


I've a Suzuki Z400 QuadSport with a Pulse Charger full exhaust, no airbox lid and no snorkel, Pro Design Pro-Flow foam filter, and a FCR39-MX pre-tuned by Sparks Racing.

I'm using a 165 main jet, needle on 3rd clip and 55 pilot (the factory settings).

It's a bit rich, and I think it'd be necessary to drop to a 155 main jet.

My question is, how much does a rich mixture affects to performance? A friend of mine, who is a mechanic, has told me that a slighty-rich mixture (as mine) can drop around 2 hp in the Z400.

I think it's too much, and the difference between a perfect-jetted and a slighty-rich (for example a main 5% bigger than the perfect one) engine could be 0.5 hp at the most.

What do you think? A before-after dyno graph would be very a perfect explanation.

just depends on how can 2hp easily.

just depends on how can 2hp easily.

2hp by dropping the main from 165 to 155 (assuming 155 the perfect one)?

yes,thats correct.

oh my God! that's a lot! Jetting is more important than I thought in relation to performance.

Quite a bit.

Also, the Z does not like to run in the "ON" petcock position. You may notice stalling in WOT long straight runs or it shutting off occasionally after a hard run.

For "hard" riding run in the "prime" position, just REMEMBER to put it back in the "ON" position when the engine is stopped or it could flood.

CORRECTED, sorry........jackass moment !

Thanks Burned !!

you got that backward on the petcock.

you got that backward on the petcock.

I fixed the thread.

Does NOT like "ON" position on fuel petcock.

Run in "PRIME" for best results.

When stopped put back in "ON" fuel petcock position.

Thanks again Burned..U da man!

its pretty common with vacuum operated petcocks.

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