Bignothing Posted May 2, 2022 Report Share Posted May 2, 2022 (edited) Hi everyone, new to the forum. I picked up a 2005 Sherco 250 2T and I’m having an issue with it. It starts and idles fine, but it falls flat at half or greater throttle. No power and it won’t rev out. Strangely, on rare occasion it revs out normally for a few seconds but then goes back to poor running. What’s been checked: Fresh gas at 100:1, new plug, no water in carb bowl, float height right on, reed valve good. Stock 118 main jet at 700 ft elevation. Air filter is clean. I think I’ve about eliminated fuel so I’m thinking it’s an ignition issue. Anyone have anything like this happen on these bikes? Thanks! Edited May 2, 2022 by Bignothing Quote Link to comment Share on other sites More sharing options...
stpauls Posted May 2, 2022 Report Share Posted May 2, 2022 Could be the main jet blocked, or the choke on/partially on. Dirty/blocked air filter? Quote Link to comment Share on other sites More sharing options...
Bignothing Posted May 2, 2022 Author Report Share Posted May 2, 2022 Thanks for the reply, stpauls. Negative. Main jet was removed and checked. Choke not on. Air filter not blocked and not that dirty. As noted, the bike runs great intermittently, so it points to something that happens occasionally, which makes it all the harder to diagnose. Quote Link to comment Share on other sites More sharing options...
stpauls Posted May 4, 2022 Report Share Posted May 4, 2022 Just re-read your post. Gas or petrol mix should be about 70:1 not 100:1. Might be trying to seize up! Quote Link to comment Share on other sites More sharing options...
turbofurball Posted May 4, 2022 Report Share Posted May 4, 2022 I run my '99 Sherco at 50:1 (with premium, dude!), as per the user manual ... I don't think the engines changed much between then and 2005. Quote Link to comment Share on other sites More sharing options...
Bignothing Posted May 4, 2022 Author Report Share Posted May 4, 2022 (edited) Thanks for the replies. Yeah, 100:1 seems too light on oil. However, a trials school with a fleet of mid 2000s Gas Gas 2Ts has run them for years like that without issue and they have a lot of hours on them. They also use 100 octane avgas. The more I think about it, I’m still leaning toward a fuel delivery issue. Electrical wiring issues tend to cause complete and abrupt shutdown and this problem is not like that. I had a bad ignition coil once that worked fine at idle speed but fell apart at higher revs. But it always malfunctioned the same way, not occasionally as is the current problem. Edited May 4, 2022 by Bignothing Quote Link to comment Share on other sites More sharing options...
Bignothing Posted May 7, 2022 Author Report Share Posted May 7, 2022 Fixed! The float needle was sticking closed. This explains why it felt starved of gas sometimes but ran well momentarily. Took it all apart and cleaned it. Float needle now drops under gravity to touch the float lever tang as it should. Runs perfect! Quote Link to comment Share on other sites More sharing options...
pedrocubby Posted October 3, 2022 Report Share Posted October 3, 2022 Sounds like your crankcase seals are goosed !! Quote Link to comment Share on other sites More sharing options...
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