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Mikuni bs32 (CV carbs) main air jets

  • Thread starter Thread starter boris.h
  • Start date Start date
B

boris.h

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Hi all
One question: on my gs 650 /550 with bs32 carbs, velocity stacks, open header and muffler... m'y main air jets are #200.
I think this size is for gs 850 ones. But what size should I put? I do not understand when they are important? Idle? 1/8 throttle, wot...?
Thanks a lot!
 
Just for clarification, what you're referring to as your "main air jet" is in fact the pilot air jet. The stock 650 pilot air jet is a 160. For a stock 850 they range from 180 to 200 depending on the year. In most cases you don't have to change the pilot air jet at all. Most mods center around the main/needle jets since that's where carb and exhaust mods really kick in. With stacks and, assuming exhaust, I would look for a Dynojet kit. They're already calibrated for mods of that type. The pilot circuit would be in the lower throttle opening range. Just off idle to 1/8 and a little beyond.

Might help if you gave more detail on what bike and mods your talking about. A GS550 would be a bit different then a GS650.
 
JTGS850GL said:
Might help if you gave more detail on what bike and mods your talking about. A GS550 would be a bit different then a GS650.
Click to expand...
Yes, but in his case, ... it's BOTH!! :-k

Evidently you are not 'in-tune' with one of the popular performance upgrades for the smallest four-cylinder GS. You can install pistons, cylinders and head from a 650 onto the lower half of a 550 and get 650 performance with a six-speed gearbox. :encouragement:

Boris, since you effectively have a 650, I would go with 650 jetting, with appropriate adjustments for your modifications. I am at work right now, so I don't have my jetting charts handy, or I would give you some suggestions.

.
 
Steve said:
Yes, but in his case, ... it's BOTH!! :-k

Evidently you are not 'in-tune' with one of the popular performance upgrades for the smallest four-cylinder GS. You can install pistons, cylinders and head from a 650 onto the lower half of a 550 and get 650 performance with a six-speed gearbox. :encouragement:

Boris, since you effectively have a 650, I would go with 650 jetting, with appropriate adjustments for your modifications. I am at work right now, so I don't have my jetting charts handy, or I would give you some suggestions.

.
Click to expand...

I'm pretty up to date on the mod. Just didn't assume that this was the case since it wasn't stated literally. I wouldn't assume any lack of knowledge simply because I requested clarification.:-\\\
 
From post #1:

"One question: on my gs 650 /550 with bs32 carbs, velocity stacks, open header and muffler... "

So either he put a 550 top end on a 650 engine, or put a 650 top end on a 550. Either way the pilot air jet size will be close enough not to matter. The 850 needs bigger air jets, to lean the mix out a tad, since it has a bigger displacement which will pull more fuel through the same sized BS32 carbs as on the 550 and 650. I would try to get all four pilot air jets the same or close to it and I'd go with what the 650 carbs came with if you can find them. I think it was 160 but it's been a few months since I looked it up.
I have four 150s in my 550/675, because that's what I had laying around here. There's no problem adjusting the idle, throttle response is great.
 
Yes, stock pilot air jet is 160 for a GS650. Agreed that you shouldn't need to mess with the pilot air jet at all from stock but since he has 200 in there I would change them to 160s. All of the pilot air jets should be the same. A bigger issues is with the main air jet. If he has GS850 carbs then he has 1.7mm air jets in the mains. The stock 650 came with 2.0mm jets. Might find mixtures a little richer then expected. The Dyno-jet kits come with a new press fit main air corrector that's smaller then stock and would compensate for any differences.
 
I ordered 160 air jets. My 200 ones are too big that's for sure...
 
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