Not Running Crisply - Yr2002 250

[thedktor]

Hi all,

New owner here down in Hants. Got me a tidy 2002 250 Sherco and it runs very well apart from at low revs. It feels over-rich and not very "crisp", a bit like the choke is half on (it isn't). It always picks up cleanly, its just at steady, low, throttle it doesn't run as smoothly as some other bikes I've ridden and the exhaust note is a pronounced POP POP POP.

All jets etc are standard, #33 pilot, D36 needle 3rd notch down. Turning the pilot screw doesn't seem to affect the problem - it appears to be the next jetting circuit up, but before the needle clip can affect things.

Is this normal for this bike, anything I can do to crisp it up a bit?

Thanks for any advice

TD

Edited February 28, 2008 by thedktor

[jmck]

From what you are describing, it sounds a bit rich on the idle circuit.

Assuming that the engine is within spec, proper compression, tune up, fresh petrol, air filter is clean, etc., there are three main components in the carb that control idle and low-speed metering.

By saying that adjusting the 'pilot' screw seems to make no difference leads me to think either the float level is too high and/or you need to go one size smaller on the pilot jet. Set the air screw 1/2 ~ 2 turns out to start with and see if it runs any cleaner any better.

[neo]

Try this lot......

With a fresh tank of fuel. Make sure you have high(est) octane fuel with an 80:1 Synthetic oil mix. Then rev her up, really high, for a few seconds and she how she runs then.

If no change.

Remove the carb/inlet manifold and check the reeds are closed.....if not, buy new ones

If no change.

Buy a Flywheel puller and retard the ignition a few millimetres....read the Sherco notes on this:-

http://www.sherco.com/downloads/wayne/Sher...iming_Guide.pdf

http://www.sherco.com/wayne_corner.html

Best of balance.

Neo

[thedktor]

Thanks for the helpful suggestions.

Checked the reeds and all OK. Not tried the ignition timing yet as don't want to reduce power at all - the motor is just about spot-on really in terms of ease of use vs power.

Tried dropping the needle instead, which had no effect but made the bike pink a bit when hot. Also screwed in the pilot screw enough to make it feel very soft and lean off idle but again no improvement to the steady throttle "two-strokey-ness".

So.... jumped on a 2007 Sherco 250 ... and ...er. ....it was exactly the same!

So I will either live with it or get another make thats a bit smoother like my mate's GasGas 270.

TD