fuel air mixture screw

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ucandoit
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fuel air mixture screw

Post by ucandoit »

What is the factory fuel-air mixture setting on the Buddy 125. How many turns out? I've read it so many times on this site yet cannot find it using the search.
My gas mileage is not very good---approx. in the high 70's mpg. But what concerns me is that the scooter has had a history of faulty petcocks and gas getting into the engine, coming out the airbox, etc.
I cleaned the carb. a few years ago when I had these issues and did set the air-mixture screw as a mechanic instructed me, but I cannot recall the setting.

Things I've done in the past: 1. Replaced the petcock--the new one still sticks at times because when I put the scooter in winter storage, the petcock did not hold back gas. That is why-- 2. I installed a fuel shut off valve (plastic lawn mower type) in the fuel line. I cannot, however, reach it without removing the pet carrier.
3. lowered the carb. float. I just estimated. That really helped and gas no longer came out the airbox and the engine didn't "bog" down as much.

4. Replaced the spark plug, which looked as though the engine was running rich. I judged this by studying various photos of spark plugs running lean and rich, etc.

My biggest concern is that I suspect gas is leaking into the engine because I notice my oil level has gone up a bit, about 1/4 inch over the full line, just like in the past, and my mpg is not so good. It is not the original carb. The seller's friend had put in a new one.

Should I remove the carb again and lower the float again or replace the float pin, which looked good to me before? Should I install a new petcock? When I removed the fuel hose today from the carb. the petcock was holding back fuel, unless there is a small trickle that I don't notice.
The scooter starts right up and runs well, though it misses a bit at around 28-30 mph. It has always done that.
I'd like better gas mileage but esp. want the engine to last a long time. I just feel the engine is running too rich. Too much gas. What would be the order of steps to take. I'd like to recheck the air-fuel mixture setting first.
dasscooter
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Post by dasscooter »

Throw that junk out and order an OEM carburetor from Scooterworks. It's expensive but you won't have another problem.

Your nice Taiwanese carburetor was likely replaced with a $20 carburetor made out of pot metal.

EDIT: A good carburetor will prevent fuel from entering your engine even if your fuel tap is stuck on.
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babblefish
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Post by babblefish »

The idle mixture screw factory setting is 1.5 turns out from closed.
Does your replacement carb have a metal top cap (covering the rubber diaphragm) or is it black plastic (like the factory original)?
Some people can break a crowbar in a sandbox.
ucandoit
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Post by ucandoit »

Babblefish: The top appears to be black plastic. I do not think it is a cheap "knock off", but I do not know this for sure.
When I got it, 4 yrs. ago, it ran poorly, stuttering upon acceleration, gas pouring out the airbox (with engine off). I ended up siphoning the tank in my panic. Am sure gas was getting in the engine, so did a lot of oil changes. I cleaned the carb, removed a leaf, replaced the petcock, etc. but it still stuttered. Finally I took the carb. to a mechanic and he lowered the float which helped a bit. Eventually, I lowered it again and that helped too.
But the petcock fails every Nov. when I try draining the carb. for winter storage and my mpg is not very good. At that early time, I "messed" with the mixture screw thinking that may help, following P.O.C. Phil's post about it. He cautioned against messing with the mixture screw if you do not know what you're doing, and I didn't, so of course he was right.
But, a few days ago I again followed his guide to adjusting the screw, beginning with 1.5 turns out. I had the idle very low; maybe too low; the engine was not running smoothly.. I don't know what 1000 rpms sounds like. Turning the screw in made it worse, so turned it out and ended up at 1.75, which is richer, but do not really feel confident about it. Am pretty sure it is rich, as the spark plug also indicated. I think I should have had the idle up a bit doing all this. It throttles up smoothly and falls back okay, in my opinion. But, I don't know how the mixture screw works, why it is critical, it's relationship with the idle speed, etc. If I can find a safe route to a dealer, I think I will ride it there and get their opinion and maybe they will make the correct adjustments.
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JettaKnight
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Post by JettaKnight »

ucandoit wrote: But, a few days ago I again followed his guide to adjusting the screw, beginning with 1.5 turns out. I had the idle very low; maybe too low; the engine was not running smoothly.. I don't know what 1000 rpms sounds like. Turning the screw in made it worse, so turned it out and ended up at 1.75, which is richer, but do not really feel confident about it. Am pretty sure it is rich, as the spark plug also indicated. I think I should have had the idle up a bit doing all this. It throttles up smoothly and falls back okay, in my opinion. But, I don't know how the mixture screw works, why it is critical, it's relationship with the idle speed, etc. If I can find a safe route to a dealer, I think I will ride it there and get their opinion and maybe they will make the correct adjustments.
Don't use the the mixture screw to adjust idle speed - use the idle adjustment screw.

It just seems like you're adjusting and playing with too much stuff. My petcock's been fine for 11 years, but I don't go messing with it. A bit of Sta-bil in the tank and leave it alone for the winter. I've never felt the need to drain the tank.

And fuel economy depends on a lot of issues - most importantly riding style, which is why mine economy sucks.
ucandoit
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Post by ucandoit »

Jetta. I drain just the carburetor for winter, not the gas tank. In fact, I fill the gas tank up with non-oxy gas when I put the scoot in storage. This has worked out well. A scooter mechanic told me that petcocks sometimes stick in cold weather and we have very cold weather here. The little valve I put on the fuel line will make draining the carb. easy from now.
I'm not trying to adjust the idle on the scooter, but rather the fuel air mixture because the spark plug, when I changed it, indicated the engine was running too rich. My attempt to tune it didn't pan out, but I don't think any harm has been done. I can put it back to the factory setting of 1.5 turns out.
Am glad your petcock has worked well. Most owners agree with you and say they have no problems with theirs. Carbs. can be a pain, though, sometimes. I think the scooter I bought had set a long time. I use the Seafoam occasionally.
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JettaKnight
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Post by JettaKnight »

ucandoit wrote: I'm not trying to adjust the idle on the scooter, but rather the fuel air mixture because the spark plug, when I changed it, indicated the engine was running too rich. My attempt to tune it didn't pan out, but I don't think any harm has been done. I can put it back to the factory setting of 1.5 turns out.
Am glad your petcock has worked well. Most owners agree with you and say they have no problems with theirs. Carbs. can be a pain, though, sometimes. I think the scooter I bought had set a long time. I use the Seafoam occasionally.
I'm not sure if adjusting the screw is effective as changing out the main jet.
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babblefish
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Post by babblefish »

The air/fuel mixture screw only affects idle to about 1/4 throttle so adjusting it and looking at the sparkplug does no good. The overall lean/rich adjustment is done with the main jet. Check the main jet size to make sure it is correct for your engine displacement: 92 for a 125cc and 102 for a 150cc.

If your float bowl has a tendency to overfill then I would check the float valve (the little thing attached to the float with a black rubber pointed tip) to make sure it isn't damaged or has a bit of dirt embedded in it. Also check the valve seat for dirt.
Some people can break a crowbar in a sandbox.
ucandoit
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Post by ucandoit »

Thank you Jetta and Babblefish. I didn't know to what extent the fuel mixture screw and the jets affected things. I checked the mixture setting again to make sure I felt confident about it and the engine runs smoothly at low idling. It accelerates nicely and drops back down well, too. It is set at about 1 3/4 turns out. I'm done with that, hopefully.
When I cleaned the carb. a few years ago, I did closely check (used a magnifying glass) the little needle valve point and the valve seat and both looked good. What I really know nothing about are the jets in a carb. I read about owners changing jet sizes, but I'm clueless about why, and since this is not the original carb. they may have changed the jet size.
I took the scoot for a ride and it performed very well, no stuttering at all. So I will just follow things for now, and, as my husband sometimes tells me, "calm the hell down". I think I have a little PTSD (I'm using the term lightly) from the incidents when both float and petcock failed and gas flooded the garage floor and I had to learn why that was happening and how to correct it.
lovemysan
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Post by lovemysan »

If the petcock sticks pull the vacuum line off the intake and gently blow then apply vacuum(aka suck) a few times. It will loosen up. Ive installed brand new ones that leak. The local shop mechainic taught me this trick, doesn't work so well on the chinese bikes. Also would recommend replacing the needle and seat or the whole carburetor. Or have a known good shop repair it. You could be missing something simple, I know i have. But as you know this could damage your engine and its not just an oil dilution issue. The fuel will strip the oil film off the cylinder wall and cause it to wear out the rings.
161cc big bore kit, NCY big valve head Hand ported, NCY transmission kit, jetted and tuned. I can port your cylinder head.
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