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It probably lacked power at top end. He stated he was 30 miles in his commute. He could have been running wide open for a long time. I am sure this is how the bike was ridden for quite a while. When you look up the cause for a melted piston you will see lean fuel mixture is a likely cause. If it was my bike I would up the main jet to a 110 and the pilot to a 25. A little rich is much better than a little lean. It cools the valves. |
What size pilot jet comes stock in a Mikuni VM26 carb? I haven't changed mine out but have the main jet at #120. Is the 25 pilot jet a "sweet spot" when running a #120 main jet?
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I am not sure what comes in the mikuni. I think 20. but again not sure. The main jet would the one to worry about here because at wide open throttle that is the one delivering the gas. If your 120 works and up to 1/4 throttle is good. you should be all set. I am running a 27.5 and a 115 in a mikuni. I have the exhaust and modified the air box. I am at 400 feet. Different places need different jets. Elevation and air temp all play in to the mixture.
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Vermont ain't flat... :-) |
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I'll be avoiding those Wingsmoto main jets in the future and will stick to Mikuni brand - the Wingsmoto jets don't thread in so well. |
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http://4.bp.blogspot.com/-k8EnLdp-Ef...jet_usage1.jpg |
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Yes. The needle meters the flow from the main through the carb. A thinner needle or raising the needle equals more fuel from the main sooner. It is the transition from the pilot jet to the main. Yes, they both need to be sized correctly.
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The main jet does not play a direct role in fueling until right around the 3/4 throtte mark. You would be surprised at how big of a difference in main jet you can run and not be aware of the difference below that point. The main jet is the total fuel level that passes through the needle jet (emulsion tube), but the needle restricts flow through the needle jet as low as 1/8th throttle through 5/8 throttle, thus rendering the main jet size itself more or less inert until the passage restriction of the needle has opened up an area at least equal to the area of the main jet at the emulsion holes.
You could put a 110 and a 120 main jet in the same carb, on the same bike, and never know the diffrence until you go beyond 5/8 throttle, and definitely once you reach 3/4. |
I noticed a big difference when going down a notch on the needle inside the Mikuni carb. Definitely made the Hawk run a lot richer, so rich at all throttle positions (combined with a #120 main jet).
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Although you don't feel the difference, fuel is drawn through the main jet as the needle valve is raised. That is what I was getting at. |
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A week has passed since my bike melted down and 4 days since sending pics to APSUSA.com and no parts or engine have have been sent out yet. I have spoken to both Don and Greg and both have told me they waiting to hear back from their supplier and are trying to figure out what caused it before shipping me anything. With the thought that if they simply send me replacement parts, I could end up with the same problem down the road. I have requested a new engine because this one is full of metal flake and chunks of melted piston and an exhaust because I don't know how much metal chunk flew into it and is lodged in it. It's the general consensus here and with Don that it was running lean, but why? Hopefully this can get resolved by tomorrow and a replacement engine will be on the way. |
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Received a call from Mr. Don with instructions to pack the engine up in a box and he will issue a pick up to ship it back to the supplier. They will either rebuild or replace the engine with a turn around time including shipping of about a week. This is pretty good news I think. Don has some good southern charm and words of experience that makes me feel like he is taking care of me. |
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OP it is nice that they are actually working with you to fix the problem. Hopefully the process goes smoothly. |
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