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Craig taylor

St300 2010 carb tuning

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Hi guys I’ve swapped my 2005 290 to a 2010 st300 canastany rep and the 290 was so smooth and smooth bottom end , the 300 is horrible at idle / very low end , I’ve lowered the compression , retarded the ign and slow action throttle which has helped a lot but I feel it could be much better . Has anyone swapped the 28mm flat side dellorto carb for earlier type 26mm ? , strangely it will idle with idle mixture fully in or fully out with very little difference ?? , anyone had any success with this model , ???

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 The carb is plugged up, Keihin? The jet tower needs to be cleaned out. (But first make sure the pilot circuit is clear and working) The jet tower is the one with the security torx screws.

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Personally, I have found the Keihin carb particularly insensitive when trying to adjust by the "fastest idle" method.  In fact, one day I was riding with a rider on a new 250 Evo and when he went to adjust the idle mixture screw found that it had fallen out.  The bike still ran OK.  I try and use the "adjust and try" method.  Not that I would recommend it but a 26 mm OKO would be a simple swap as it is the same size and uses the same cable.  

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 Why would anybody buy a copy of the real thing that is new? It is called jetting 101. By the way, move your boot to the outside of your peg. Problem solved.

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Keihins are extremely sensitive to the air screw! A quarter turn is sometimes enough to turn a bike from burbling at idle to running on. If your keihin isn't responding to idle mixture adjustments, it needs a good clean

Putting a 26 PHBL dellorto is basically turning it into the standard non cabestany model, so it will run fine, and ultimately less fussy. Will a smaller dellorto sort your problems at the low end, possibly....

Edited by faussy

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1 hour ago, Craig taylor said:

Hi guys it’s a flat slide 28mm dellorto carb not Keihin, 2010 model 

oops, my bad. No experience with this carb im afraid, but the 26 mm dellorto round slide was the standard model carb back then as far as i know

Edited by faussy

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No matter the carb, you have a pilot circuit problem. That first needs to be cleaned. I would try a couple larger pilot jets to make sure before changing to a new carb. The carbs were notoriously lean on the pilot jets from the factory.

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1 minute ago, copemech said:

put a 26 dellorto on it and dump the flat slide!

If jetting does not help I will try swapping the carb to 26mm round slide , my older 290 was soo smooth 🙄

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The Cabestany is a very different weapon to your old bike.They are much more fiery with a lot of bottom end power,it won't ever be as smooth as your old one.A dellorto would help calm it down if you can't get it how you want with the flat slide carb

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The 28mm carb that Craig has is most likely the Dellorto VHST 28. It was the carb Sherco was using as its performance option during those years...Some years of those rear fuel tank models had intake manifold leakage/warp problems. The carbs were on quite an angle too, so the float levels need to be set accordingly to minimize flooding and rich fueling conditions...especially on down hills. Hope you get it sorted soon☺️ 

Edited by pauls320

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14 hours ago, pauls320 said:

The 28mm carb that Craig has is most likely the Dellorto VHST 28. It was the carb Sherco was using as its performance option during those years...Some years of those rear fuel tank models had intake manifold leakage/warp problems. The carbs were on quite an angle too, so the float levels need to be set accordingly to minimize flooding and rich fueling conditions...especially on down hills. Hope you get it sorted soon☺️ 

It is that carb , I’m going to play with jetting etc and try a 26mm normal carb just doing crank seals, reefs etc as well to make sure it’s as good as can be 

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Not trying to add more non-problems to your ''check out ''list, but make sure your fuel delivery hoses/ routing/pump is not causing your issues. Sherco did do some updates on later models because of fueling issues on that generation sherco..Splatshop had some relevant info on wsite. good luck 

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