Quote:
Originally Posted by sweatmachine
I have a 904 bonnie with some headwork (bigger valves) and the Mikunis from Bill. The carbs made more of a difference in hp than did the engine work! This may be that they allowed the bigger engine to finally breathe whereas the stock carbs were a definite restriction.
I've been playing with the jetting a lot since I got them, and you're right getting to the needles is kind of a pain. Really not the carbs fault, more like the gas tank's fault!
I recently went to 142.5 mains (from 145's and larger) and I'm running the 96 needles in the middle position, and about 3/4 turns out on the idle mix. This combo really made a difference in the power from the previous jetting. It even sounds better.
Bill sent them to me with the 97 needles in the mid position and 147.5 mains, which felt really good, except at full throttle it seemed weak. I thought I needed a richer needle and leaner main, which is why I went with the above jetting combo, and it really runs good now.
I also get a lot of popping on decel, so I've been trying to gradually richen the idle mix, but I think part of the deal with these carbs is that they do pop quite a bit. If I tune the pop out completely then the bike is running way too rich.
I can almost assure you that you won't need the accelerator pumps. Once you get your needles tuned correctly it really eliminates the bog. You still have to be progressive in your throttle action, but above 3,000 rpms it's not an issue.
These carbs work really well! They are danm expensive, but for me they were totally worth the $$$.
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Thanks Sweat,
according to tuning manual the needle difference (95, 96, 97, 98) will affect only 1/8 to 1/4 throttle openings because the only change is the diameter of the cylindrical (not tapered) section. One should not feel any change with different needles above 1/4 throttle opening. So you strengthened full throttle response only with the reduction of the main jet (because you changed needle but didn't move e-clip from center position), or at least that's what theory says.
About the main jet tuning:
The "roll-off" method is mainly used to find out if the mains are too small (lean) because the mixture is richened for an instant when throttle is suddenly closed 1/8 of a turns from WOT. If the bike tends to accelerate then the mains are too small. But what if the mains are too big?
The manual says that a too big main can produce a bogging (overly rich condition) when throttle is suddenly closed from WOT to 1/2. So that's can be a way to check if the mains are too big.
Apart from this, there's always the good ol' butt-dyno
