firecat Posted November 25, 2012 Report Share Posted November 25, 2012 Hi, I have just stripped and rebuilt my 2002 sherco 250 after getting it out of storage (12 months) and finding it was noises, vibrated like hell and would not idle. The guys at splatshop were extremely helpful with advice and quick deliveries of replacement parts. I have rebuilt the bottom end of the engine (new main bearings, new seals and gaskets throughout, and new float jet). It started second kick and ran so much quieter and smoothly than before. I was well pleased with myself until I could not get it to idle. I can manually hold low revs but cannot set it on the idle speed screw. I did not replace the idle jet when I replaced the float jet as I managed to clear it but on the basis most of everything else has Ben replaced I am wondering if it could be the culprit. Advice would be appreciated! Cheers Quote Link to comment Share on other sites More sharing options...
b40rt Posted November 25, 2012 Report Share Posted November 25, 2012 Sounds like throttle cable snagged / routed incorrectly. Quote Link to comment Share on other sites More sharing options...
dombush Posted November 25, 2012 Report Share Posted November 25, 2012 Questions:- When you hold it ticking over manualy, does it tick over freely and without labour? Does it pick up from low revs quickly or does it hesitate ? Dom Quote Link to comment Share on other sites More sharing options...
firecat Posted November 25, 2012 Author Report Share Posted November 25, 2012 Sounds like throttle cable snagged / routed incorrectly. Hi, I cannot see how it is the cable, slide clicks shut as it ough to, the cable is a straight run. Why would the idle speed adjment screw not work? Quote Link to comment Share on other sites More sharing options...
firecat Posted November 25, 2012 Author Report Share Posted November 25, 2012 Questions:- When you hold it ticking over manualy, does it tick over freely and without labour? Does it pick up from low revs quickly or does it hesitate ? Dom Hi Dom, Thanks for responding. The answers to your questions as follows. It ticks over very well when held on the throttle, you can hold it at a very low idle speed. It picks up quite cleanly and quickly. Any thoughts? Quote Link to comment Share on other sites More sharing options...
b40rt Posted November 25, 2012 Report Share Posted November 25, 2012 Hi, I cannot see how it is the cable, slide clicks shut as it ough to, the cable is a straight run. Why would the idle speed adjment screw not work? Just a suggestion, you'll work it out. Quote Link to comment Share on other sites More sharing options...
firecat Posted November 25, 2012 Author Report Share Posted November 25, 2012 Just a suggestion, you'll work it out. Sure hope so, apologies for being abrupt in my response, all the best Quote Link to comment Share on other sites More sharing options...
b40rt Posted November 25, 2012 Report Share Posted November 25, 2012 Sleep on it, surprising what occurs to you in middle of the night !! Quote Link to comment Share on other sites More sharing options...
dombush Posted November 26, 2012 Report Share Posted November 26, 2012 So, a few widespread ideas to mull over Idle fueling or transition ports blocked, these are the tiny drillings in the main throttle bore on the reed valve side of the throttle slide. (not the idle jet) Idle air bleed blocked (one of the ports on the bellmouth of the carb) Jets / idle mixture screw blocked. Remove everything from the carb and spray through with carb cleaner then blow through with an airline. idle Jet not screwed in properly or even missing (sorry) Leaking or poorly sealed choke plunger (choke operates only at small throttle openings) Broken reed valve petal (this can affect starting ability also) and result in spitting back through the carb. Ignition timing too advanced. Do the basic marks line up? Whiskered plug (unlikely, as this is normaly intermittent running / very hard to start) Float height wrong (fuel level too high / low). something wrong during re-assembly of the crankcases causing binding. (crank binding, crank pinion to clutch ring gear, clutch bearing etc.) My suggestion here is to take the plug out and rotate the crank with the flywheel.. does it feel free? Is it running very rich on idle, meaning it would normaly tick over but cant due to mixture? There's nothing blocking the exhaust / inlet from your rebuild (rag / exhaust bung etc.)? If you wind the tickover speed screw out, can you discern when the slide stops stopping on the screw and hits on the base of the carb? Point being... is it hitting the screw? Air leaks.... many causes although normally causing high or variable tickover. Can usualy be identified by weak running or by inability to hold steady revs at no load (not in gear) Dom Quote Link to comment Share on other sites More sharing options...
copemech Posted November 26, 2012 Report Share Posted November 26, 2012 You don't have to replace the idle jet, but you want to be darn sure it is clean. Find a fine wire to pass through it and blow out the passages. You did soo much jostling of things you gotta insure the basics are correct. Are the float arms setting level with the carb body now when inverted? Quote Link to comment Share on other sites More sharing options...
firecat Posted November 26, 2012 Author Report Share Posted November 26, 2012 The float arms are 18.5mm off the carb base. The plug is not showing black after five minutes or so of running. The idle jet was blocked after the bikes lay up. Not fuel varnish but a green,/white hard crystalline crud. It wrecked the float valve and that was replaced. The pilot I unblocked (so I thought) with some copper wire but the hole is fine and I am unsure if it is fully clear. Quote Link to comment Share on other sites More sharing options...
firecat Posted November 26, 2012 Author Report Share Posted November 26, 2012 So, a few widespread ideas to mull over Idle fueling or transition ports blocked, these are the tiny drillings in the main throttle bore on the reed valve side of the throttle slide. (not the idle jet) Idle air bleed blocked (one of the ports on the bellmouth of the carb) Jets / idle mixture screw blocked. Remove everything from the carb and spray through with carb cleaner then blow through with an airline. idle Jet not screwed in properly or even missing (sorry) Leaking or poorly sealed choke plunger (choke operates only at small throttle openings) Broken reed valve petal (this can affect starting ability also) and result in spitting back through the carb. Ignition timing too advanced. Do the basic marks line up? Whiskered plug (unlikely, as this is normaly intermittent running / very hard to start) Float height wrong (fuel level too high / low). something wrong during re-assembly of the crankcases causing binding. (crank binding, crank pinion to clutch ring gear, clutch bearing etc.) My suggestion here is to take the plug out and rotate the crank with the flywheel.. does it feel free? Is it running very rich on idle, meaning it would normaly tick over but cant due to mixture? There's nothing blocking the exhaust / inlet from your rebuild (rag / exhaust bung etc.)? If you wind the tickover speed screw out, can you discern when the slide stops stopping on the screw and hits on the base of the carb? Point being... is it hitting the screw? Air leaks.... many causes although normally causing high or variable tickover. Can usualy be identified by weak running or by inability to hold steady revs at no load (not in gear) Dom Hi Dom, Thanks for the comments Lots of stuff to go at here. [*]idle Jet not screwed in properly or even missing (sorry). It is definitely in there, will need to check it is fully home again. *]Broken reed valve petal (this can affect starting ability also) and result in spitting back through the carb. Checked these during the rebuild looked good to me. [*]something wrong during re-assembly of the crankcases causing binding. (crank binding, crank pinion to clutch ring gear, clutch bearing etc.) My suggestion here is to take the plug out and rotate the crank with the flywheel.. does it feel free? Sweet as sweet can be, no tight spots at all. *]There's nothing blocking the exhaust / inlet from your rebuild (rag / exhaust bung etc.)? No [*]Air leaks.... many causes although normally causing high or variable tickover. Can usualy be identified by weak running or by inability to hold steady revs at no load (not in gear) could as the cases were split but plug looks good after several mins of running. That leaves all the other items to check out. Patience is a virtue! Pity I was not blessed with much!! Quote Link to comment Share on other sites More sharing options...
tltel Posted November 26, 2012 Report Share Posted November 26, 2012 you only mention the idle screw, what about the mixture (air/fuel) screw, it might just want setting up, not sure what carb you have, if you search the forums on here, there are some good tips on setting up carbs. Also check that the end of the idle screw is not worn. Should be impossible but is slide in back to front? TLTEL Quote Link to comment Share on other sites More sharing options...
firecat Posted November 26, 2012 Author Report Share Posted November 26, 2012 you only mention the idle screw, what about the mixture (air/fuel) screw, it might just want setting up, not sure what carb you have, if you search the forums on here, there are some good tips on setting up carbs. Also check that the end of the idle screw is not worn. Should be impossible but is slide in back to front? TLTEL Thanks for the suggestions. Mixture screw is 3.5 turns out from fully in. (Dell onto) Will recheck end of idle screw. Slide is in the correct way (cut out locates on carb body) Thanks Quote Link to comment Share on other sites More sharing options...
dombush Posted November 27, 2012 Report Share Posted November 27, 2012 That leaves all the other items to check out. Patience is a virtue! Pity I was not blessed with much!! Keep going, the answer is in there somewhere Dom Quote Link to comment Share on other sites More sharing options...
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