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Sherco Kehin Carb


stmarysloch
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I have bought a 300 ST 2013 model . I really like the bike but am struggling setting the carb up , it runs on a bit when blipping the throttle ( over revs like air leak ) . I have noticed on stripping carb that the float chamber overflow is blanked off with a screw ( could not see it before for overflow pipe ) has anyone seen this before ? I have had these carbs previously on Gas Gas bikes and do remember periodically them pouring fuel sometimes from the float chamber overflow Pipe , is this a mod then . Also what is the correct float height please

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Sorry I should have explained better , with the bike out of gear and you Rev it the revs don't die down as they should . There is no problem with the cable ( I have checked this ) , however I have seen an earlier blog on here regarding someone cutting down the length of throttle return spring , therefore weakening it . Am now going to measure this .

Thanks

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Sherco's with Keihin carbs do run on the lean side. 1st thing to do is check the float height is correct, You can find the info on Splatshop's website.

The fuel pipe can pinch between the top of the carb and the airbox, Check this and also check the tank breather is working as it should.

They do leak fuel from the overflow even when the floats are set correct, If you adjust the floats to stop it leaking so often it will run even leaner, It's the angle of the carb that causes this. Make sure the overflow pipe is routed so the fuel leaks to the ground and not near the rear linkage or painted parts.

The 1st and cheapest mod to do is change to a 48 pilot and a 128 main, The air screw will be at around 2 to 2.5 turns to dial the pilot in, Needle 2nd groove from bottom.

Changing to a number 3 slide will help but they are £60 so do the jets 1st and see how it is.

Boyesen carbon tech reeds will help also and give a better control over the throttle response.

It took me hours of experimenting to get mine running how I like it, Most riders don't even notice they are too lean.

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What he said, plus. You can run the carbs with the overflow blocked off. You still need to insure it is clean and set properly. There are setup details on Splat website. I also drill out my left side bowl vent.

Erratic and floaty idle could be a sign of crank seals leaking air. I give them 2-3 years on average, and yours is approaching that mark. Viton seals a must.

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What he said, plus. You can run the carbs with the overflow blocked off. You still need to insure it is clean and set properly. There are setup details on Splat website. I also drill out my left side bowl vent.

Erratic and floaty idle could be a sign of crank seals leaking air. I give them 2-3 years on average, and yours is approaching that mark. Viton seals a must.

I remember I drilled out the other vent on mine that also helped with the fueling.

Good point Cope, Crank seals are probably due by now on that age of bike.

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Hi thanks for all the replies . After reading these and other earlier posts made some further investigations today . Found the slide return spring was cut down ( managed to borrow another to try ) , incorrect float height

( set up as advised splat shop). Ran bike in garage seems much much better , going to try out at weekend properly . The blocked off overflow is a mod done apparently by some to stop problem with fuel pouring from said pipe .

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I too have a 2013 ST300. I am new to Trials so I have a bunch to learn. I did some winter maintenance on the bike that entailed removing the carb. The bike ran fine prior to my work. I put everything back together and when I got to re-attaching the fuel lines I became confused. I eventually got the job done and the bike started and ran fine. I am trying to learn the basics of controlling a wheelie. The technique I am using is to lift the front wheel while keeping both feet on the ground to learn clutch modulation and throttle control. Now (after my reassembly), with the front tire in the air, the bike wants (and does) stall out and fuel was leaking from somewhere. Today I went to work on the bike to troubleshoot this problem and found the gas leaking from the "T" in the fuel lines. This explanation would be simpler if I would include some pictures but unfortunately I do not know how to do that- I am humbly sorry! The "T" is located on the line that comes out the top of the Dellorto pumper. This would be my first question: 1. Is the Dellorto part the pumper? My carb is a PWK Keihin. 2. Is this combination of Dellorto and Keihin the stock setup? Assuming, for now, that the Dellorto part is a pumper, I just do not understand the workings of the pumper carb. The pumper has three ports. Looking at the assembly as it is mounted to the fuel tank while on the bike, the bottom left is marked with an arrow and the word "In". The hose to this port comes from the petcock. The top port goes to the "T" and is marked with an arrow and the word "Out". At the "T" one hose runs to the top of the fuel tank and the other hose is connected to an in-line filter that goes to the carb. The last port is also located on the left side just higher than the "In" port but this third port has no markings. The line from here is connected to the left side of the carb bowl. I had the carb apart but at this point I do not remember if this bowl connection was open or shut. So, 3. I am asking for help in an explanation of the function of each of the three ports and how the pumper system works. I am heading back out to the barn to see if there is an obvious reason why the fuel was leaking from the "T". I hope the write-up makes sense! All help will be appreciated,Thanks, Chuck

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The Keihin carb is correct for your bike on that year.

The Dellorto unit is a fuel pump, Very simple it runs on Vacuum from the inlet to make it pulse a diaphragm that pumps fuel.

The Diagram should give you a better explanation.

Pic from Splatshop that I have labled.

New-Fueling-System_zpsgwgzazad.jpg

Edited by steve_earle
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Because part of the fuel tank is below the level of the carby, the pump is required. The pump is simple, it sucks fuel from the tank and blows it toward the carby. On later models there is the "T" to return excess back to the tank so as not to overpower the float needle in the carb.

The vacume line to manifold uses engine pulses to work the diaphragm in the pump, and there are both inlet and outlet ck valves in there so fuel flows one direction, with fuel on one side of the diaphragm and the pulsed vacume on the other.

If your bike still runs poorly with front wheel elevated you likely have a float level issue.

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I did not have the line connected to the manifold properly. Thanks Steve for that diagram. Then, at the "T" connection, the fuel line had a small nick which was the source of a leak. Copemech, the bike now is running and idling okay after the proper hose installation. The next time I have the carb accessible I will check the float level. I was able to ride the bike for three evenings in a row after making the proper corrections. I did not notice any fuel leaking on the ground for those three evenings. Then on the forth ride I did notice that fuel was again dripping on the asphalt. I have not been able to check the bike out since that last practice session. Is it expected for gas to leak from the breather pipe hose when the front wheel is elevated for extended periods? This may be common sense, but still I need to ask. I am trying to learn to ride a wheelie and am only at the point of being able to balance the bike with both feet dragging. Thanks again for the help, Chuck

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