Sandy Koocanusa
Serious Thumper
Offline
Don't blame me. I didn't vote for him.
Posts: 1878
Bigfork, MT
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I'm struggling with getting my jetting correct. I have read for hours about this, and I'm not going to ask the usual questions, I promise. I just need someone to tell me if I'm making up some of what I think I know, or if it is actually correct.
A brief history: When my bike was stock, it ran just fine. I read all of the articles and got rid of any backfiring issues by simply adjusting the idle air screw. Then I got creative (rarely a good thing with me). I took out most of the stuffing from my stock muffler. It sounded good, but it ran lousy. Way to lean and no more adjustment available. So I increased the size of the pilot jet from 47.5 to 50. With that change, the bike ran waaaay to rich. I turned the screw all the way in and backed it out about 1/8 turn, but it was no good. Loud booming backfires on decel, gold pipe, and about a 20% reduction in mileage.
So, I got to snooping some more and decided that maybe Oldfeller and Yoda were on to something. Last night I ripped up an air filter and put together a Nufoam and canola oil replacement. I left the door off the air box, too. It's too soon to tell for sure, but at least the backfiring seems to have stopped. I'll check the mileage in a couple of days.
Here's where I'm unsure... I THINK that when I twist the throttle, more air is allowed into the carburetor. I THINK that this increase in air draws more fuel through the jet (which allows, but does not cause, the fuel to pass). So I THINK that with proportionally larger jetting and air intake, I should be able to achieve the same power and mileage with less throttle as I had with the small jet and congested intake. I think that increasing all these things should allow more power if I choose it, but that I should still be able to drive economically by twisting the throttle less.
If 1/2 throttle allows 1 drop of gas and 14.7 drops of air into the engine with a small jet, then 3/8 throttle should allow the same 1 drop and 14.7 drops in with larger jet and air intake, right? Same amount of fuel/air, same power, same mileage?
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