Ive just installed a Gilera Runner ST 200 engine into my VX 125 frame. I had trouble starting the bike but I managed to fire it up by bleeding the air out of the fuel pump. Bike now starts and will idle but will die after a few minutes if left alone and will also die if I gently apply throttle. The ST 200 engine came with a Walbro WVF carb and has a 108 Main jet and a 36 Pilot jet. According to the Haynes manual Runner VXR 200 engines with a Walbro CV carb should have a 118 Main jet and a 34 Pilot jet. Should this be the same for both ST and VXR 200 engines? Im wondering if this is my problem and should install a 118 Main jet? Ive checked the resistance of the electric choke and its around 48 ohms. Haynes manual states Walbro carbs should be 30 ohms approx. Could this be a factor to why its cutting out? Also do you think the fuel pump needs bleeding more?
Did you check the valve clearances, they have a tendency to go out on the LEADER motors, I had very similar on my old VXR, ended up changing the carb and then went back to the basics and found a very tight inlet (problem solved)
No i haven’t as the engine has only done 4000 miles so didn’t think to. Does anyone know where I can order some main jets for this Walbro carb? Are kiehin/dellorto interchangeable?
Thanks, will check all tomorrow. Also are the leader 200 engines on the VXR and ST runners exactly the same? I ask as I'm referring to the old Haynes manual for Gilera runners 1997-2004 and it states main jet for a 200 VXR is 118. Thinking my problem lies here as the carb that was on my newly installed ST engine is fitted with a 108 main jet.
That sounds very much like a carb from a vx125. They had the Walbro carb and a 108 main jet. They are also prone to wear out internally for unknown reasons.
I must agree with you there, I think it is from a 125 as that’s exactly what jet is inside. Anyway she fired up today after some adjustment to the intake valves and a change of spark plug. Float height parallel to carb body. Still 108 main jet installed. Seemed to be idling quite nicely without stalling. I’m still not satisfied as I believe there’s clearly a jetting issue and I want to try a 118 main jet in it. Haven’t taken it for a spin yet but 1/4 throttled with the bike on the stand and had a couple pops from the exhaust (it’s standard btw). Is this jetting related?
Could be jetting. I found the specs for the carb setup if that helps. Carb: Walbro WVF-7H Starter jet: 50 Pilot Jet: 34 Main jet: 118 Jet needle (clip position): 465 (2nd notch from top) Idle speed: 1600 - 1700rpm
