|
|
Post by motomech on Feb 28, 2008 22:44:24 GMT -5
It's no secret that today's scooters have their carburetors calibrated lean, very lean. Until the day when these out-dated devices no longer come on new scooters, we live with it. But do we have to?
The vast majority of what described here as "backfiring" is more accurately described as a lean misfire. It's comes about when, on trailing throttle, the fuel/air ratio falls below what's needed to combust. The un-burned gases build up in the muffler to the point they become dense enough to "light-off".
These are "low-speed" circuit issues and that's where to start in the quest to a smoother and quieter running scooter. Specifically, the fuel mixture screw. There are photos here that pin point it's location, but since it's a fuel screw, it will be on the engine side of the carb. It may be blocked off with an anti-tamper feature, a "blind plug". These plugs can be removed by carefully drilling a sm. hole in the center of it(It's only a couple of millimeters thick, so don't go too far into the screw head)and then thread in a sm. wood screw. Then that can be pulled out with a pair of Vise Grips.
In a perfect world the low-speed adjustment would be aided by the use of an Exhaust Gas Analyzer(only Yamaha requires their dealerships to have a E.G.A.), the adjustment can be made fairly accurately via the "idle drop" method.
Gently seat the screw and turn it out three full revolutions. With the engine warm and the idle speed set low(below 1,000 r.p.m.), slowly turn it in till the idle starts to slow down. Then out a 1/2 turn. From the factory, the screw will often be out only 1/4 to 1/2 a turn, but for good results, the screw will usually end up 1 to 2 1/2 turns out. Reset the idle, button her up and it's done.
Postscript added;
I suppose in cases where the mixture screw is just not accessible, the carb would have to be removed(rotated?) and the "By guess and by gosh" method of adjustment would be the one to use.
The key is to determine the factory setting by gently counting the turns in. This would pretty much always will be > than 1.
The vast majority of Asian MC's and scooters will end up at 1 1/2 to 2 turns out and that is where I would set it.
Once past 1 turn out, it's not really a critical adjustment. In fact, due to the limited adjustment range and effect on the power band, one really can't get them too far out to create any kind of rich condition.
And going past 3 turns out can relieve too much tension from the securing spring, and they can fall out.
|
|
|
|
Post by mcmama on Apr 26, 2008 23:50:34 GMT -5
Great post, but I don't seem to see the pictures...
Thanks
MCMAMA
|
|
|
|
Post by ladydi on May 10, 2008 14:56:22 GMT -5
Ok Boyz.... I need some help here. ;D Back to the (sore) subject of my '07 Sunflower Chinese 150cc Scoot...  After the winter thaw (long winter up here), I changed the plug, the fuel filter, blew out the lines, added carb cleaner to the gas......Left it idle for oh, 40 minutes or so....then it started spitting and sputtering and shut itself down (almost like it choked itself).  Soooo I guess I have to pull the carb, clean it, the sediment bowl and whatever else comes my way. I only have one problem, I DID NOT get any type of paper/pictures with it and since Cypress went out of business, I am flying blind  here and I need some help. (Give me an old fashion Holley 4 Barrel from the 60's & I can do it - BUT something as small and probably stupid as this, I'm lost)  Duh, yeah I used to tinker with cars in my younger days before they started using all the computerized automated crap.. ha ha ;D So if anyone can help me out with suggestions to make this an easy transition, I sure would appreciate it!  Thanks in advance, Di |
|
|
|
Post by rusty on May 10, 2008 15:50:24 GMT -5
IMO, I would think that if you let it idle for 40+ minutes, you may have fould a spark plug, I would check that before tearing down the carb. Just a thought
Rusty
|
|
|
|
Post by ladydi on May 18, 2008 17:52:11 GMT -5
[glow=red,2,300][/glow]No soap! thanks for the advice. I took it to my buddies shop to have him rip the carb apart. Just a waiting game -  Hope to have it back tomorrow - but...the weather sucks out here, so I'm not missing any ride time |
|
|
|
Post by ladydi on May 21, 2008 20:12:28 GMT -5
WELL, UPDATE TIME - Just got the scoot back from the shop - 251 miles, fuel filter (as stated earlier) and the carb....both were filled with dirt..... not gum, varnish, or goo.... the setiment bowl on the bottom of the carb was solid 'dirt', like from the ground......... how? any input? |
|
|
|
Post by glasuan on May 22, 2008 9:37:59 GMT -5
The dirt could be from the cheap hoses breaking down, and filling the carb. Have you replaced your fuel lines on the scoot with better quality ones yet? I bet the winter really did a number on them.
|
|
|
|
Post by motomech on May 22, 2008 18:27:32 GMT -5
WELL, UPDATE TIME - Just got the scoot back from the shop - 251 miles, fuel filter (as stated earlier) and the carb....both were filled with dirt..... not gum, varnish, or goo.... the setiment bowl on the bottom of the carb was solid 'dirt', like from the ground......... how? any input? I would think that dirt in the float bowl would have come though the induction tract. Was the carb throat dirty? Did the shop say anything about a loose clamp, air boot off, air filter not sealing, etc.? I would ck. all that stuff, to be sure that it doesn't happen again. Also, can you look inside the fuel tank with a flashlite? |
|
|
|
Post by griff10 on May 22, 2008 20:01:35 GMT -5
WELL, UPDATE TIME - Just got the scoot back from the shop - 251 miles, fuel filter (as stated earlier) and the carb....both were filled with dirt..... not gum, varnish, or goo.... the setiment bowl on the bottom of the carb was solid 'dirt', like from the ground......... how? any input? I would think that dirt in the float bowl would have come though the induction tract. Was the carb throat dirty? Did the shop say anything about a loose clamp, air boot off, air filter not sealing, etc.? I would ck. all that stuff, to be sure that it doesn't happen again. Also, can you look inside the fuel tank with a flashlite? Dirt in the float bowl can't come from the air intake, two completely different parts of the carb. Likely left over from assembly, someone dropped a part and didn't clean it up. All sorts of bad things happen with mass production in this country as well as out of it. Bill H. |
|
|
|
Post by ladydi on Jun 1, 2008 21:05:55 GMT -5
Well, I don't know if they changed the hoses while working on it, I'll have to check it out to see -but that I can understand, being cheap chinese stuff .... OR, with the way my luck runs, they probably used tsunami damaged parts when they built mine without cleaning out the dirt from the floods. ;D that's how my life is because........ NOW, since I had drained the tank to change the fuel filter (stll very clean btw & 100 more miles on it since changing)... The gas gauge is stuck on full! When I first turn the key, it hesitates going up (kind of marking the spot where it actually is, gas wise) then it continues up to the full mark and stays there....... Always something - I would love to go for just one ride without something going wrong - Tonight it fell on me when I was leaving work, like it's possessed! Got 'road rash' on my ankle and calf and it got scratched up pretty good.. I felt like walking away from it. If I knew then what I know now about Chinese scooters, I would never have gotten it! What a piece of sh*t........ sorry, I am a little peeved right now, can you tell?? Thanks for all your input though, I truly appreciate it. |
|
|
|
Post by kikuta688 on Jul 5, 2008 17:24:18 GMT -5
Correct me if I'm wrong here...
But after reading motoman's post, it almost sounds like we should go ahead and adjust this mixture, regardless of whether or not we are having a known issue. He states that you can't really make it too rich.
I don't really know if I lean out or not on my Lance Milan, but if adjusting it can't hurt, I'd rather go ahead and do it as a form of preventative maintenance.
Make sense, or am I wrong here.
|
|
|
|
Post by motomech on Jul 6, 2008 12:20:07 GMT -5
Yes, that's what I'm saying.
They are probably all adjusted lean from the factory.
|
|
|
|
Post by kikuta688 on Jul 6, 2008 15:18:44 GMT -5
Thanks Motomech!  |
|
|
|
Post by finnie9 on Jul 17, 2008 12:05:58 GMT -5
Can someone post a photo showing (or describe) the location of the fuel mixture screw on the CF Moto 244cc engine? I can't find the thing.
|
|
|
|
Post by scosgt on Oct 28, 2008 22:42:29 GMT -5
Isn't the idle adjusment screw different from the mixture adjustment?
|
|
|
|
Post by greg on Nov 9, 2008 20:52:11 GMT -5
Isn't the idle adjusment screw different from the mixture adjustment? yes! throttle your bike and look near the carb see the thingy moving thats your throttle. the screw with a spring is the idle adjustment. adjust it till your back wheel just starts to barely move,but doesnt. the airfuel is on the other side of the engine. just a screw flush with the carb. i had problems keeping my scoot running more than a few minutes i turned that screw out one turn and its fine ever since. |
|
|
|
Post by Blayne Mathieu on Jun 15, 2009 11:19:58 GMT -5
Well Written, bone for you, sir.
|
|
jumpin
New Puppy Dawg
Posts: 3
|
Post by jumpin on Jul 13, 2009 8:12:21 GMT -5
So just to confirm: Turning it out (CCW) is adding more fuel to the mix and turning it in (CW) is adding less fuel to the mix?
And you need to add more fuel to the mix to get rid of the "Lean Misfire", right?
|
|
|
|
Post by Chi Makwa on Sept 6, 2009 0:42:20 GMT -5
So just to confirm: Turning it out (CCW) is adding more fuel to the mix and turning it in (CW) is adding less fuel to the mix? And you need to add more fuel to the mix to get rid of the "Lean Misfire", right? Yup, that's it. From what little I know about engines, it's not always a great idea to run rich either. Doesn't that increase the risk of carbon buildup, valve damage, & plug fouling? That's what they taught us at flight school -- about aircraft engines anyway. (Airplanes have a mixture control lever right in the cockpit because they fly through different air densities at different altitudes.) |
|
|
|
Post by als01seville on Sept 13, 2009 22:24:56 GMT -5
To adjust your air/fuel mixture you want the highest rpm when adjusting. If the bike has a tach its much easier but if not it is up to your hearing capabilites. Turn the air/fuel mixture screw 1/8 at a time counter clock wise (richer) if the RPMs go up keep turning it 1/8 until the RPM Drops then turn it Clock Wise 1/8 and that should be your highest setting.
If turning it 1/8 Counter Clockwise Drops the RPMs right away then Turn it Clock wise back 1/8 to the starting point and Turn it 1/8 Clock wise if the RPM increase Keep Turning it 1/8 at a time until the RPMs Drop and then Turn it Counter Clock Wise 1/8 and that should do it.
You then may have to adjust your Idle down by turning the idle screw Counter Clock Wise a little to lower your idle.
|
|
|
|
Post by justbeclaus1 on Apr 21, 2010 9:42:23 GMT -5
Hello all new to this post I have a Linhai 300 amd have to always have to adjust the air/fuel mixture.Is there a spring that stops this from turning out of adjustment? Thanks for the help anyone (just a old timer enjoying life)
|
|
|
|
Post by als01seville on Apr 21, 2010 15:39:27 GMT -5
Hi Justbeclaus1, Yes, there should be a spring that stops the screw from turning itself due to vibration. But if the screw is turned out to far the spring is useless it does not have enough tension anymore to hold the screw in place. But if your screw is out 3 or more turns out to get the scoot to run right that means that you need to go up 1 or 2 sizes on your Pilot Jet. But if you do not want to do that adjust your Air/Fuel mixture and then take some Clear Silicone and put a dab on the screw and outside of the carb to hold it there WORKS LIKE A CHARM  Alleyoop |
|
|
|
Post by hudson169 on Aug 29, 2010 12:02:58 GMT -5
WOW great discussion very good info. thanks guys
|
|
|
|
Post by danillobh84 on Jul 26, 2011 23:13:23 GMT -5
can you make a short video of it ?
|
|
|
|
Post by skuttadawg on Aug 1, 2011 23:56:52 GMT -5
My scooter is lean misfiring at first I thought it was a bad coil till reading up and road tests with n without helmet . It idles great , takes off good and tops out good . When I go slow like 30 mph and I twist the throttle it is hesitant and sputters for a good second slowing speed down then it picks up speed . I know these scooters run very lean and have fuel air screw sealed up . I have a TaoTao Atm50A with AirSal 80cc BBK , 5 gram rollers and bigger jets were installed by my dealer I dont know what size but Im guessing I need bigger ones . I plan on getting a Mikuni carb I think 22 or 24mm will be good size and adding Kehin jets and performance air filter along with performance exhaust . I can cruise 50 easy on level road without any wind pushing me ( lol ) and Im 200 lbs . I dont want to go over 55mph as 10inch wheels are speed rated up to 62 mph . I just want a lil power for hills and make a lil thunder
|
|
|
|
Post by skuttadawg on Aug 2, 2011 0:05:02 GMT -5
OOOps I forgot to mention maybe running too lean contributed to my 2nd piston cracking .The first one was from simply putting 87 gas instead of premium I didnt even get to run the gas out and poof . After reading in here I want to thank who posted only get gas where each grade has its own hose instead of one hose and 3 buttons .If previous person got 87 its still in the line and I notice a diff too. Im lucky some places here dont ad ethanol which is bad on small engines and you lose mpg . I love filling up for $2.50 @3.43 a gallon price
|
|
here and I need some help.
Duh, yeah I used to tinker with cars in my younger days before they started using all the computerized automated crap.. ha ha ;D
Hope to have it back tomorrow - but...the weather sucks out here, so I'm not missing any ride time 
