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How to tune air/fuel mixture?

55962 Views 45 Replies 15 Participants Last post by  flitecontrol
Well like the title states, how do you tune the air/fuel mixture. I heard I could tune it with an rpm gauge. If so how exactly? I've called a couple of places but they each charge like 60 bucks. I figure I could waste 30 on the tools and never have to pay anyone to do it again.
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There is a write-up (by Chef if I remeber correctly) on how. There is a tab that has to be removed if it hasn't been already that allows the A/F screw to be adjusted. If it has been rebuilt by you or another, the screw with the tab has been replaced by a straight end with blade type slot and non-tabbed one usually. The screw is on the lower front side of the 250 carb and it takes a small stubby blade type screw driver. The write-up said to get it idling and warmed up. Be sure the choke is completely disengaged. Set the slow idle adjuster where you want it. Then turn the A/F screw either way until the sputtering/stammering barely begins. Then turn it the opposite way counting the full turns. When it begins to stammer again, stop. Then turn the opposite way One-Half the total turns you counted between "spasms". That'll get you close enough to ideal and no special tools or gauges required.
Use a dremel and "grind" the tab/flange on the screw down where you can turn it at will. Then, clean or replace your plugs and re-gap. Then follow the instructions posted by BG. As I said, if you or someone before you has rebuilt the carb, that screw has usually been replaced with a non-tabbed one. The kit I bought and used did. Whether doing so (tab removal) is necessary or not is subjective. Personally, it has been my experience and desire to take any adjustment or setting back to zero and re-do it all from scratch. Only way to be sure it is right. Not to mention that "right" on any used vehilce is different for every unit. Especially with the fuel system which encompasses many pieces and processes from the gas pumped into the tank to the exhaust coming out the end of the baffles. To apply the "cookie-cutter" to this or any of the myriad of settings in the fuel system chain normally misses the mark and may correct one issue but screw up another causing a larger problem in the chain. If I am going to invest the time and $, I like to do my best to insure I'm not engaging in an exercise in futility. But, that's just me and to each his own.
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Gas in the Oil? Sounds like a bigger issue than a dirty carb. Hope I'm wrong for your sake.
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