Briggs Raptor III won’t idle with Mikuni vm22 26mm carb
- Thread starter RaptorIII
- Start date
The ones that came out of the box. I haven’t measured or taken it apart yet.
From the video, it appears some reversion from overlap of valves at low speeds causes reversal of intake flow.
Length and size of exhaust and intake manifold contribute to this as well.
Kinda normal for a flatty.
It doesn't sound like it is leaning out. It may require holding the throttle open wider, or higher idle rpm.
Have you ridden it, or at least loaded the engine with the brake?
If it stumbles on takeoff, you will need larger idle jet. With no accelerator pump, the idle jet must supply enough fuel to get on main circuit. The compromise is slightly higher idle rpm, and spitting some fuel at low rpm.
Get this part first, then look at high speed jetting.
Length and size of exhaust and intake manifold contribute to this as well.
Kinda normal for a flatty.
It doesn't sound like it is leaning out. It may require holding the throttle open wider, or higher idle rpm.
Have you ridden it, or at least loaded the engine with the brake?
If it stumbles on takeoff, you will need larger idle jet. With no accelerator pump, the idle jet must supply enough fuel to get on main circuit. The compromise is slightly higher idle rpm, and spitting some fuel at low rpm.
Get this part first, then look at high speed jetting.
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Thanks for the thorough write up. The exhaust is about 18” and intake is ~ 5”. There doesn’t seem to be an issue once I give it throttle, I’ve ridden it around and it was fine until I let go of the throttle, then it dies mid ride.
Interesting, I’ll have to give it a try. Was hoping to use an antique-style filter without much baffle, but function comes before aesthetics.
Sunset5523
Member
Adjust the float too low
Did you get it fixed? im very curious. I put a vm20 carb from EC carbs on my minibike and it was the best thing I had ever done. Idles perfect,runs perfect. As to your problem, in a somewhat order of likelihood, clogged or dirty low speed circuit in carb,Timing off or slipped keyway, low compression due to valves or rings, leaking head gasket, leaking intake gasket,plugged gas tank vent (gas cap) . or bad coil.I bet one of those will be the culprit.
There is a screw at the bell on carb its idle mixture screw turn it all way in and out 1.5-2 turns.if it doesnt run there ya need a smaller pilot jet.