[chillywilly638]

Hi
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.
Thanks

 

[HitCat44]

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 If it has been rebuilt by you or another, the screw with the tab has been replaced by a straight end with blade type slot and non-tabbed one usually.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.

 

[Buickguy]

Idle drop air mix procedure.

 

[twitch]

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 If it has been rebuilt by you or another, the screw with the tab has been replaced by a straight end with blade type slot and non-tabbed one usually.

Okay, hang on, I'm confused. I tried to perform this idle drop procedure today; the instructions in my manual are nearly identical to the ones BuickGuy posted, except the number of turns for the initial opening is different for newer Rebels.

But...I'm supposed to remove this tab on the pilot screw? My manual doesn't say anything about that. Seems like that tab would be there for a reason, but I certainly can't turn it 2 3/4 turns while it's there. So I need to go out and get a normal screw that will fit? How can I unscrew it out of there with that tab in place? File down the tab?

 

[88nightrider]

The tab is there to limit adjustability.
If you dont want it, just file it down.

 

[Guba]

twitch the pic you posted is of the throttle stop screw. The pilot screw has a plastic tab on it that prevents it from turning a full 360*.

I wouldn't remove the tab from the pilot screw, if you have to adust it, your not too far away from the factory setting to begin with.

 

[Buickguy]

The tab is to not allow the pilot screw to go too rich. That could violate EPA standards.
The tab stop on the float bowl is what it would hit against.

 

[Guba]

Ooops, thanks for pointing that out BG. My pilot screw has a black tab on it, so twitchs pic didn't stand out to me.

 

[88nightrider]

The tab is to not allow the pilot screw to go too rich

Isn't it usaly a bit too lean as stock?

 

[Buickguy]

Yes it is. Maybe I should have specified too rich for the EPA standards.

 

[twitch]

Okay, so is it worth going to all that effort if I'm not having any performance problems? I was only going to do it because my service manual says it's a good idea if you don't know whether it has ever been done.

As of right now, I'm thinking of just leaving it alone unless someone convinces me otherwise. I found it set open as far as the tab stop will allow. My idle is about 200 RPM too high, but I can fix that with the idle adjuster.

If I understand what you all have posted, the stock is setting is government-mandated "too lean." What are the long-term effects of running lean? Engine damage? Poor mileage? Poor performance?

 

[brach77]

running lean can destroy your engine do to running way to hot. Your milage and proformance will aslo suffer.

 

[gnbgnb]

Back in the carb. days for cars, the emissions folks at the EPA forced the auto mfgs to put those plastic caps on so adjustments would be limited. Usually if you had to break the cap off, your carb. needed a minor or major overhaul kit put in. Most adjustments could be made with the cap on, again if your carb. wasn't very far out of adjustment. As B-Rock mentioned, running to lean can cause serious problems to your engine, and on cars to converters.

 

[88nightrider]

One way of knowing if you are funning too lean or too rich is too look at your spark plugs.

 

[HitCat44]

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.

 

[Guba]

If I recall twitch, you bought your bike brand new. I wouldn't think mother Honda would turn it over to a dealership with something like that seriously out of adjustment. Extremely lean conditions will make the engine overheat and give less power. A hot engine can result in pre-ignition of the fuel/air mixture. I don't really think you have to worry about it until you have to take the carb apart. That is, unless you want piece of mind and just want to play.

 

[88nightrider]

If I recall twitch, you bought your bike brand new. I wouldn't think mother Honda would turn it over to a dealership with something like that seriously out of adjustment

I think I have heard that stock rebels got bluing on the exhaust pipes.
Would not that indicate a lean condition?

 

[Guba]

I think I have heard that stock rebels got bluing on the exhaust pipes.
Would not that indicate a lean condition?

Mine didn't start to blue until I started making some long distance highway riding. I don't think it was from being too lean, probably from adding more throttle to climb hills at highway speed.

 

[twitch]

If I recall twitch, you bought your bike brand new. I wouldn't think mother Honda would turn it over to a dealership with something like that seriously out of adjustment. Extremely lean conditions will make the engine overheat and give less power. A hot engine can result in pre-ignition of the fuel/air mixture. I don't really think you have to worry about it until you have to take the carb apart. That is, unless you want piece of mind and just want to play.

WIN. I would do it just to do it, IF it didn't involve modifying a part that's there for a reason (even if the reason is just to make Uncle Sam happy). I'll wait until the carb needs service and I'll do it then.

Thanks to everyone for your advice.

 

[chillywilly638]

Thanks for your help guys. But I caved and took it in to a shop to get it adjusted properly since I would have never gotten it. They told me that they had to screw the adjuster all the way in and in theory it should not but running because of that but it is so they said there's most likely something wrong with the carb.