Oil/fuel mixture wrong? RS125

Dimerz · Nitrous Nuisance Joined: 22 Jul 2016 Karma :

Hello again unfortunately, recently done a piston change on my 2008 RS125 as it got bent in by the power valve blade that snapped/got pushed in too far and hit the top of the piston, therefore made me lose compression to around 80-90ish it hink they said. Engine is working fine however i think my oil to fuel is wrong, ive tested it with my oil pump and the spark plug is blackish/oilly, when i went over to pre-mix the spark plug was much clearer but still didnt hold the revs, it just bogged down. The problem with the oil pump was always there, i would starts up the bike it would run and then bog down even if i start riding; because im assuming the spark plug gets too oily and cant spark. So ive gone onto premix now and will clean the spark plug once again and try it again but even bump starting it didnt work, so its not a battery issue. Any suggestions on what to do? Ive had this problem for a while, been fixing my bike for 2 weeks now, and i want to get out there no matter the weather, this 2 hour train journey to work is doing my head and bank in.

So far I have put in a new starter motor as it must've been wet from when i was cleaning it and so it smoked and didnt start again, a new starter relay, which wasnt needed, new piston kit, power valve blade and a bunch of spark plugs.

Pictures of the snapped blade, bent in piston and new piston.
https://imgur.com/a/5izZB

P. · Red Rocket Joined: 14 Feb 2008 Karma :

Well for one, premix will require you to change the jetting.

What plug are you using and what's the current state of the bike, you mention power valve so is it in a fully derestricted state or...?

Dimerz · Nitrous Nuisance Joined: 22 Jul 2016 Karma :

Its got a 34mm delleroto carb and an k&n air filter, not sure of jetting in it as i bought it like that. But this is full power as it has a solenoid, power valve and the other thing, i forgot now. Using the BR10EG plug in there.

P. · Red Rocket Joined: 14 Feb 2008 Karma :

38 seems big, I'd expect a 34mm. K&N rather than the OG airbox or just the filter element.

I'd be surprised if you can get it running nicely like that.

Having a quick read and look at my old stuff, I had a 34mm, which was up from the 28 stock. 38 just seems...wrong.

I'm far from a 2 stroke pro, so best wait for one of them, but I'd say that's a bit big and you are not doing yourself any favours with it on premix.

redeem ouzzer · World Chat Champion Joined: 06 Oct 2015 Karma :

38mm is far too big for a 125 single. Even a TZ250 with 90ps only needs 36mm carbs. Your chances of getting to run properly and actually be rideable on the road are about equal to the chances of bodytard winning a contest for best dental health.
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Dimerz · Nitrous Nuisance Joined: 22 Jul 2016 Karma :

My mistake its a 34mm carb, I always confuse myself over that.

P. · Red Rocket Joined: 14 Feb 2008 Karma :

But, the rest of my post, filter etc.

I'd have it set to stock before working anything out. Obviously that means checking carb. The auto lube is definitely working yes? It would only be black if its been set up by a retard and the pumps not been adjusted.

Dimerz · Nitrous Nuisance Joined: 22 Jul 2016 Karma :

Dimerz · Nitrous Nuisance Joined: 22 Jul 2016 Karma :

I have the stock carb and air filter but the carburettor is missing the top piece where the throttle inserts, im going to get it down to the mechanics tomorrow, i dont think i mentioned but i had a thick gasket on there amd after reading paddys engine, i chdcked my compression and it was at 90, i put a thinner top end gasket and it shot up to 110 so pressure is all good now. But still not starting, ill try put another new spark plug just for the sake of trying.