Pavloszx Posted February 15, 2018 Report Share Posted February 15, 2018 I have bought a sherco st300 about a month ago. At first it was running okay but the last couple of weeks it is running lean like it's about to run out of fuel. Have checked the carb, the reeds, the fuel pump and the ventilation of the fuel tank. It all seems to be okay have also changed the spark and cleaned the air filter. The Jets size are the same as sherco manual refers. I have put the needle on position 1 instead of position 4 as the manual suggests still no major difference. The air screw is at 2 cycles out instead of 0.5. Have also tried the original settings with no results. The bike runs better when I have the choke on. Thanks for reading and for any ideas. Quote Link to comment Share on other sites More sharing options...
lineaway Posted February 16, 2018 Report Share Posted February 16, 2018 If the bike runs better on choke, then the problem should be the pilot circuit. There are two exists to this circuit. One under the slide and one in front of the slide. Spray contact cleaner into the pilot jet and you should get fluid out of both. The Keihin has got a known death barble. Find another carb to test with. Sometimes it may require a new carb. Quote Link to comment Share on other sites More sharing options...
copemech Posted February 16, 2018 Report Share Posted February 16, 2018 crank seals may lead to lean running as well Quote Link to comment Share on other sites More sharing options...
sirdabalot Posted February 16, 2018 Report Share Posted February 16, 2018 What make of carburettor does it have? Quote Link to comment Share on other sites More sharing options...
Pavloszx Posted February 16, 2018 Author Report Share Posted February 16, 2018 It has a kehin carb Quote Link to comment Share on other sites More sharing options...
Pavloszx Posted February 16, 2018 Author Report Share Posted February 16, 2018 It has a kehin carb Is there a way to test the crankcase seals? Before I dismadle the engine? Quote Link to comment Share on other sites More sharing options...
stpauls Posted February 16, 2018 Report Share Posted February 16, 2018 What year? Is it a rear fuel tank model? Quote Link to comment Share on other sites More sharing options...
Pavloszx Posted February 16, 2018 Author Report Share Posted February 16, 2018 2014 model Yes the tank is mounted on the rear Quote Link to comment Share on other sites More sharing options...
cascao Posted February 16, 2018 Report Share Posted February 16, 2018 4 hours ago, Pavloszx said: It has a kehin carb Is there a way to test the crankcase seals? Before I dismadle the engine? If there a fail in right side engine will burn oil from gearbox and smoke badly. If there leakage from generator side will should de able to see some leakage under electic coils. But this usually happen on much older bikes.... Seems like your carb have some blockage. Return the settings for what they are before problem started and give a good clean with compressed air. Install a gas filter since due the position of gas cap in this rear tank models, it is easy to get dirt inside gas tank. Quote Link to comment Share on other sites More sharing options...
stpauls Posted February 16, 2018 Report Share Posted February 16, 2018 Fuel cap cover to stop mud and dust: https://www.ebay.co.uk/itm/sherco-fuel-cap-cover/273005491984?hash=item3f90653710:g:~q8AAOSwyQtV3EuR Also fit one of these: www.ebay.co.uk/itm/Small-Petrol-In-Line-Universal-Clear-Fuel-Filters-Fits-Diameter-7MM-Pipe-Filter/253396996188?hash=item3affa3505c:g:~vQAAOSw9tJacCjq Before stripping the engine, your problem could be either of the reed block gaskets - especially the lower foam one. Use Instant Gasket for a temporary fix. Also check the fuel loop rubber piping that runs up to the top of the fuel tank, under the rear mudguard. This perishes and can cause all sorts of strange and curious issues. Best replace the lot with new tubing every couple of years 1 Quote Link to comment Share on other sites More sharing options...
copemech Posted February 17, 2018 Report Share Posted February 17, 2018 17 hours ago, cascao said: If there a fail in right side engine will burn oil from gearbox and smoke badly. If there leakage from generator side will should de able to see some leakage under electic coils. But this usually happen on much older bikes.... Seems like your carb have some blockage. Return the settings for what they are before problem started and give a good clean with compressed air. Install a gas filter since due the position of gas cap in this rear tank models, it is easy to get dirt inside gas tank. I have had these seals leak after only a couple years with the alcohol induced fuels used widely. one can also shoot a bit of carby cleaner around flywheel side to see if it picks up the added fuel. Quote Link to comment Share on other sites More sharing options...
bikerpet Posted February 21, 2019 Report Share Posted February 21, 2019 An old topic, but we never heard back from Pavloszx and I have just finished (I hope!) sorting out a very similar problem. 2013 Sherco 290. Over a week or so of almost daily riding it started to develop issues. Ran fine cold. Once hot it would start to run lean & not idle, better with choke to an extent. Sprayed WD40 over the crankcase joints etc. No result. Cleaned the carb and drilled the LH vent nipple while I was in there. Trimmed the slightly ragged end of the fuel pump pulse pipe at the manifold nipple and checked the nipple seal. Replaced the LH crank seal with viton (forgot I'd done this not so long ago when I had a similar issue. In that one when I went to replace the seal I found a couple of the crankcase bolts inside the flywheel area were slightly loose - easy fix). Waited a week or so for a new RH crank seal and replaced it. Tightened a slightly loose exhaust manifold bolt. Checked fuel breather. All to no avail. Thought for some time. Figured it seemed like fuel starvation more than air leak so started at the simple bits: Tank breather again. Check. Fuel tap flow. Check Fuel out of end of hose to carby. BINGO. No flow. Remove the Mann filter - blocked. Backflush it with syringe and compressed air. Lots of very fine grey bits. Reassemble and all is good. The correlation with Hot vs Cold must have been that when cold I never drive it hard. Once warm and giving it some throttle the carby starved. Hope that helps someone else 2 1 Quote Link to comment Share on other sites More sharing options...
BradleyCastrolMaxima Posted July 13, 2021 Report Share Posted July 13, 2021 On 2/15/2018 at 2:55 PM, Pavloszx said: I have bought a sherco st300 about a month ago. At first it was running okay but the last couple of weeks it is running lean like it's about to run out of fuel. Have checked the carb, the reeds, the fuel pump and the ventilation of the fuel tank. It all seems to be okay have also changed the spark and cleaned the air filter. The Jets size are the same as sherco manual refers. I have put the needle on position 1 instead of position 4 as the manual suggests still no major difference. The air screw is at 2 cycles out instead of 0.5. Have also tried the original settings with no results. The bike runs better when I have the choke on. Thanks for reading and for any ideas. Hey you said the air screw is out 2 turns which means you are getting too much air now. Mine is at about 1/3 a turn out to be a bit rich if you screw it back in to my setting or the factory half out then it should be a lot more rich. Just to make sure you are talking about the right screw if the air/fuel screw is near the air filter then it is the air screw which means the farther out it is the leaner it will be. If the screw is closer to the engine then it is the fuel screw which means the further out it is the richer it will be so just go from that mine ran lean and adjusting the air screw to 1/3 out and adjusting the idle to my climate then it is fine and my spark plug is really dark brown. I use 80% Maxima formula k2 with a 20% mix of Maxima castor927 just for the smell and my bike runs great, hardly any carbon, and I have yet to ever foul out a plug using that mix. I use Maxima for everything it is a great product. Except for my coolant I use Twin Air Ice Flow and that works amazing. I have a 2016 st300 and I love that thing to death. Good luck. Quote Link to comment Share on other sites More sharing options...
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