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2011 St250 Air Mixture And Jets


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Dellorto PHBL 26

First off its a FUEL screw not an air screw on the Dellorto.

Pilot Jet : 33-36

Main Jet : 118-120

On a 33/34 pilot the fuel should be 3.5 turns out. If you are on the richer 35/36 the fuel screw its best to lean it out to around 2.5 to 3 turns out.

Wouldn't think the s3 exhaust would effect it really... not sure...

Check your spark plug colour, should be a nice chocolate brown colour.

Edited by lewis cosgrove
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Dellorto PHBL 26

First off its a FUEL screw not an air screw on the Dellorto.

Pilot Jet : 33-36

Main Jet : 118-120

On a 33/34 pilot the fuel should be 3.5 turns out. If you are on the richer 35/36 the fuel screw its best to lean it out to around 2.5 to 3 turns out.

Wouldn't think the s3 exhaust would effect it really... not sure...

Check your spark plug colour, should be a nice chocolate brown colour.

Agree with this general range of things, well put!

I suppose if your weather never changes, then set it and forget it! Last week here was near 0 C, in the summer 40 C so adjustability is needed. Thus I try to keep a jet in there that I can adjust to the day as needed for best running, and they can be sensitive as this IS a FUEL trim screw, so 1/8 turn makes a change.

Those running the leaner jets just run them wide open at 3.5 or so. It works for some, but cold enrichment is limited.

Edited by copemech
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The front pipe will not affect jetting (unless you flatten it on a rock). Is you bike running o.k at the moment?, If so count the number of turns by screwing it in all the way (only so it just touches, dont screw it in hard or you can damage the seat).

When you know the number of turns it runs right at you can experiment either way slightly and see if it runs better.

Also when stripping and cleaning the carb you have somewhere to start with setting the screw when you put it back in.

The delorto carb doesn't usualy go out of tune as long as it's clean, just set and forget.

Some people get all paranoid about mixture and jetting, If it works o.k and you have limited knowlege about carbs leave it alone, Ride it and have fun!

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