Bike Revs Then Dies

[kingkay7]

Hi Guys,

I have a lexmoto XTRs 125cc and I have had various issues. Which I have gone through and fixed, but one issue persists and I am not sure how to fix it.

Firstly I was getting a bit of white smoke and when I took out the spark and covered it with my finger I was getting oil pushed out. So I changed the piston and rings and that seems better now. While I was doing the piston I changed all the gaskets, oil and the crank case seals. I also did the valve clearance, the only figures I could find online were 0.08 for intake and 0.15 for exhaust.

Secondly, when I was doing this, there was a lot of excess fuel in the rocker head. I got a new carb ( Mikuni VM26 ) as the crappy Sheng Wey had a acc pump which I heard caused quite a Few issues. However it also has smaller jets ( I believe the stock sheng wey had 125 Main Jet and 40 Pilot, Mikuni has 100 Main and 20 Pilot ) I think it may be too much of a step down. I also had to get a different air filter as the stock wouldn't fit on the Mikuni

Now it still does the Revs to about 4-5k on start up ( requires a bit of throttle to get started so may be pilot needs increased? ), after this 5 second burst it stalls. I have a brand new tank as I had rust in the old one and it has new fuel ( disgarded the old fuel ).

Any help would be greatly appreciated. I am not sure if its the carb or what, just dont know.

GK

[Tango]

Hard to say mate as the jetting will depend on the dynamics of the particular carb and air filter......but I would be trying to up the jetting just to see what it does......

[Grumpy Old Git]

It certainly sounds like fuel starvation.

If you want to stick with your new carb - I think you will need to increase the jetting (how much - no idea?).

Have you tried with the air filter removed? This may give a few more clues to the problem.

I assume spark is OK and constant?

[kingkay7]

Hi Guys,

Spark seems good when I put it to the frame. So when it revs high like that is that it running to Lean? Just changed the piston and rings so don't want to damage them! I tried increasing the mixture but couldn't see any noticeable difference.

I will try putting the old carb in and see what that's like. I was just worried this accelerator pump could be causing issues, what is the benefit of this especially when you have a choke?

GK

[kingkay7]

Hi Guys,

Got some more time on the bike yesterday. I flicked the choke off and tried to start which didnt work then when I flicked it on it started and didnt die. But it was revving high ( not adjusted idle screw yet ) but after a minute it started revving very high to the point I had to cut it off incase any damage was caused. Does it sound like I have an air leak or is this just the engine has warmed and is running more efficiently now? Daft question I know but I don't want to assume I know something, rather have it from you guys as you all know a hell of a lot more than I do.

Cheers,

GK

[Tango]

When it started revving higher did you try reducing the choke? If it continued to rev high with the choke off firstly check your throttle cable free play.........and if that's ok check around the carb for air leaks.....