GS 125 idle speed

[Mr Hammers]

So, we've put a new barrel, piston, rings, and cylinder head on my lad's GS 125. The new barrel and piston are big bore at 150cc.

Once it was all put back together it fires up, but having a problem with the idling, and also it doesn't feel particularly any more powerful than the tired performance as before. Not expecting a huge increase obviously, and it's still being run in, but it does feel like it runs out of steam after the initial pull away.

We increased the main jet size from 102.5 to 117.5 and then again to 120. We wanted to increase the pilot jet size too, but the screw head is knackered and as it sits in a well, it's impossible to get it out without destroying it (and we don't actually have another bigger pilot jet anyway).

The idling though is the bigger, more definite problem. You can rev it ok (it does falter slightly if you open up too fast or too slow), but it seems to take way too long for the revs to come back down, and when they do it will either be still too high, or it just dies completely. Whenever the idle screw is set - so you can get it running at 1500 and it will idle fine - but rev it again and it'll just conk out again. Turn the idle up, and it's fine, until you rev it and then it sits at 5k revs for a while, until it eventually goes back down again.

Not sure if relevant, but the starter seems to struggle a lot more than before, like there's a *lot* of compression. I'm assuming this is a good thing though, as everything is still new.

We're pretty sure the cam chain timing is fine, as moving a link either way would put it way out of line.

My feeling is that either the carb just needs a good service, the needle needs to come down a notch or two, or there's something else we're missing. Or of course, it just wants a bigger pilot jet.

Any thoughts as to what might be going on with it?

Cheers!
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A Guide To Powerbands

[Suntan Sid]

Revs dropping slowly, usually indicates running lean!
The pilot jet will need sorting as that effects 0 to 1/4 throttle and ultimately affects idle speed!

When I rebuilt my XL125 it felt under powered until it had a few miles under its belt!
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