Pulls harder when Cold.

[chris2470]

I've been trying to find the solution to this, but I'm all out of idea's.
Basically it definitively pulls a lot harder when it hits the power band soon after it has been started, then after 5 minutes or so it seems to lose that bang when it comes on song. It still runs perfectly well and has done for 2000 miles or so but there is a pronounced drop off after 5 mins of running. My only guess is that it night be the pipe causing this, as its a stainless Devtour. Don't get me wrong it's still no slouch, but there is a definite drop off when full warmed up. This may be perfectly normal but I'm unsure so any ideas would be gratefully received.

[bristolmod]

could be your jetting............

try increasing your main jet (and pilot) by a couple of sizes- this may produce a bit of "roughish" running whilst still cold, but should improve when the engine warms up.

Worth a try IMO

Chris

[CPH Lambretta]

Sounds like something electrical breaking down when the engine gets warmed up

[J1MS]

I doubt it's the Devtour that's loosing you power once the engines warmed up, most likely somthing else.

[DaveInPortland]

As the cylinder heats up it expands and your rings give a little. Basically, your compression is dropping a wee bit. It happens on all engines. New rings may help or may not. Nature of the beast.

If your carb air inlet is coming from under the panels (via open carb or snorkel with a pod filter) then the air taken in gets warmer as the engine warms up. Known fact that colder air in = faster engine, warmer air in = slower due to oxygen concentration.

Just a couple of suggestions.

[sean brady scooters]

do you run it open ,or have you an air filter fitted...

[sydduckett]

Whilst my scoot doesnt loose power when it gets warmed up it does run far crisper/faster on a cold day...Only decent thing about cold weather and scooters i can think of....

[joey]

...too rich? plug colour? what kit is it?

[chris2470]

Thanks for all the input.
Its a Ali 225 kit that has been cleaned up and ported by M Abbey with a 70mm Asso piston and rings fitted. AF head with 1.2mm squish. Open mouth PWK 28mm, jets are 128, 40, JJH middle clip, this does sit under a full panel so heat could be a factor but I find it still drops off even without it fitted. The plug seems fine, like I say it has given me around 2000 trouble free miles.
The drop off isn't massive it still pulls well in every gear, if you rode it you would probably ask whats the problem but a slight drop off there is.
I did wonder about the stainless pipe as I thought I read something somewhere about is not dispersing heat as effectively and then reflecting it back once hot.
Looking at it again however I think it could be the rings that need changing as the gaps may gone out of tolerance.
Thanks again for the help.