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sherco250cc

290cc Sherco Keihn Carb Set Up

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19mm with the carb held at a 45 degree angle :)

When i took my carb off to clean it out i put it back so as it was sitting up right with no angle and when i started the bike it red lined and reved its max the throttle was not stuck it was because there was no angle on it im sure. and when i managed to free the revs it sure took its time to come down the revs.

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As a bit of of a follow up, here is a quote from PeterB re the usage of the K carb on the gasser and his input!

" You need a 28mm flat slide Keihin, 122 main, 35 pilot, GJH (Best) or JJH needle. Also need a longer throttle cable (inner) that was used on the older 370 GG model and you must use an in line fuel filter.

Bye, PeterB. "

I think Peter is a pretty good ratchethead, and offers good suggestions. Point being, when you take in variations in bikes even, the resultant opinions can be very similar. Well, the motors are very similar really, specially when you are focused to the volumetric requirements of a given displacement at a given useful rev range the results are near identicle.

Then comes the rider, and personal prefs, and will the setup be right for them! Is it too aggressive?

In other words, if Peter or Clav threw in a 45 pilot with a JJH needle set in the mid, will the bikes then become overly sensitive for the riders? Who in fact are not Caby or others running this setting. Those guys like it RIGHT NOW! What happens then, in reverse?

In fact, I have noticed the more aggressive the rider, the fewer throttle settings they use, the application is all in the clutch side of things, which totally negates all ! They simply do not seem to care after a point!

Tell me if I am off the nut here!

You

Edited by clav3

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Hi copemech,

Thanks for the friendly comments!

Never been called a ratchet head before - I'm sure my next phone call from a trials friendly rider will start with hey ratchet head!

Anyway, I've been riding for a few years now so am a bit old fashioned and like to be precise with my (bike) carb set up, I do tend to run with the pilot a little richer than most but then still use a 35 on the Keihin (on a Raga 300). The GJH needle is definately the best for riders wanting a progressive feel in the way their motor picks up from low revs. The JJH works ok, probably has a quicker response but not as good (for me) as the GJH. The GG Ragas up to 2008 arrive with 122 mains and a JJH, they all ping at mid revs, too lean. I bore out the main to approx 126 which fixes the problem and the motor runs way out at the top end without any spluttering. Std reed v/v's. (I have a graduated long taper reamer used for boring LPG jets in the regulator business - courtesy of Fisher Controls Iowa that I have used for a few years to experiment with main jet sizing).

I find that younger lads aren't so fussy with carb set up or even have a well oiled throttle tube and use skills in other areas for sections, lots of stop start clutch stuff.

Ta ta, PeterB.

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Hi copemech,

Thanks for the friendly comments!

Never been called a ratchet head before - I'm sure my next phone call from a trials friendly rider will start with hey ratchet head!

Anyway, I've been riding for a few years now so am a bit old fashioned and like to be precise with my (bike) carb set up, I do tend to run with the pilot a little richer than most but then still use a 35 on the Keihin (on a Raga 300). The GJH needle is definately the best for riders wanting a progressive feel in the way their motor picks up from low revs. The JJH works ok, probably has a quicker response but not as good (for me) as the GJH. The GG Ragas up to 2008 arrive with 122 mains and a JJH, they all ping at mid revs, too lean. I bore out the main to approx 126 which fixes the problem and the motor runs way out at the top end without any spluttering. Std reed v/v's. (I have a graduated long taper reamer used for boring LPG jets in the regulator business - courtesy of Fisher Controls Iowa that I have used for a few years to experiment with main jet sizing).

I find that younger lads aren't so fussy with carb set up or even have a well oiled throttle tube and use skills in other areas for sections, lots of stop start clutch stuff.

Ta ta, PeterB.

Top job Peter! You are always helpful to others and share your experiences! Not everyone does that.

Of course there are a few such as JSE, if you ask the time, he will tell you haw to build a watch! :D

Sounds like a neat thing that little jet reamer! I have never done it, but when you get to a few of the old hands, I have even heard of them soldering them back up to start over if too large!

To tell you the truth, in my years of messing with these things, I have never directly corrolated jet size with a real unit of measure such as thousandths of an inch in bore or hundredths of a mm. Maybe a relationship to flow rate, which is really what it is about? To me, they are just relative numbers for a specific application. Would you know what the numbers actually mean? :hyper: I am not sure if it is not just simply flow related such as ml/min/hg but i donot know! Call me stupid! Next question, is the unit of measure standardized accross the industry?

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Call me mad, but I've drilled jets with guitar strings. i.e 48 gauge E string (0.048 inch) converts to 1.22mm (122 main jet) or 16 gauge string (0.016 inch) converts to 0.406 mm (40.6 pilot).

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Call me mad, but I've drilled jets with guitar strings. i.e 48 gauge E string (0.048 inch) converts to 1.22mm (122 main jet) or 16 gauge string (0.016 inch) converts to 0.406 mm (40.6 pilot).

So you have verified the jet numbers directly corelate to a metric diameter in hundredths of a mm?

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Hi copemech,

Thanks for the kind words. Most carbs run jet sizes as mm bore sizes, eg: 122 main jet is 1.22mm diameter, 95 is a 0.95mm dia. Pilot jets are the same (most carbs) so a 35 pilot is 0.35mm diameter. On the taper reamer that I use, it is calibrated in scfh propane gas, but has another almost linear scale that I use as a guide for boring main jets. I use two sizes, say a 118 and 122 and determine the difference on the scale then use this difference to relate to how much to bore out to. Anyway, it works.

Ta ta, PeterB.

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sooooo - all great info - sherco250, how did you make out with your carb issue, what have you tried?

cheers

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Hi copemech,

Thanks for the kind words. Most carbs run jet sizes as mm bore sizes, eg: 122 main jet is 1.22mm diameter, 95 is a 0.95mm dia. Pilot jets are the same (most carbs) so a 35 pilot is 0.35mm diameter. On the taper reamer that I use, it is calibrated in scfh propane gas, but has another almost linear scale that I use as a guide for boring main jets. I use two sizes, say a 118 and 122 and determine the difference on the scale then use this difference to relate to how much to bore out to. Anyway, it works.

Ta ta, PeterB.

I can see your relationship there! And yes, it will work fine!

Sort of reminds me of my Russian co worker who used to race go-carts over there! If they needed a needle change, just put it in the lathe(or drill)! And measure! :D

Edited by copemech

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Has anyone tried using the 5mm intake spacer off the '05 at a bevel, in an effort to keep the carby off the motor? Yet the tank and cable are still limiting? :hl:

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Of course there are a few such as JSE, if you ask the time, he will tell you haw to build a watch! :hl:

Alright, Mark!

I just saw this and the next time we're at a Trial and you whine at me, yet again,

"Joooooooon...which one is the brake and which one is the clutch?", I'm going to

let you figure it out for yourself!

^_^

Jon

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Alright, Mark!

I just saw this and the next time we're at a Trial and you whine at me, yet again,

"Joooooooon...which one is the brake and which one is the clutch?", I'm going to

let you figure it out for yourself!

^_^

Jon

He He! Funny you say that! I almost killed myself on a cheap Chineese moped a couple weeks ago! :hl:

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