Idle issue

[ninjascoot]

OK so i today i used the info on setting my idle speed thinking that would solve the issue with my scooter not wanting to idle. While i was setting the idle i noticed that the rpm's are moving up and down. Its runs at what seems like a normal idle and then revs up and stays at the higher rpm for a minute or two then returns to the normal idle and then repeats that over and over. I was thinking that choke might be bad or something. Also while setting the idle i noticed that there is a noise coming from what seems to be near the rear wheel it sounds like a squeaking and is heard more when the rpm's are higher. Need help, please let me know what you think.

[Fox]

I think you should adjust the idle mixture screw on the carburetor. Turn it to the left slowly until the idle speed picks up and smooths out. Then readjust the idle speed if necessary.



If you don't have a mixture screw (Some have a plug in them now) maybe the then make sure the valves are adjusted properly.

[ninjascoot]

Thanks Fox...When I said that I was "setting the idle", I meant that I was adjusting the idle mixture screw on the carburetor (per adjustment settings on the tech support thread). During and after the process, I'm still having the same issues. I was kind of hoping that someone might have another idea...if there's anything else it could be.
Any ideas on the squeaking? I was thinking maybe it was the clutch, and I'm hoping that my clutch isn't starting to go out.
I appreciate it, and I'll look into adjusting the valves, as well.

[90GTVert]

For the surging idle, check for intake leaks. Make sure the diaphragm is in place properly in the top of the carb. Wouldn't hurt to check the operation of the enricher I suppose.


The squeaking could be the clutch or maybe the brake shoes out of round. If it's squeaking more at high RPM, I'd think it wouldn't be the clutch shoes and bell, more likely a problem with clearance or something. I've had the bell just barely touch the CVT cover before and make a noise. You'd see evidence of that if you popped the cover off. I've had a rear brake shoe out of round before just enough to make a noise at speed. I just used some emery cloth to go over the shoes and drum, then sprayed them off with brake cleaner, and it quit.

[ninjascoot]

Ok thanks i will do all of that and get back to you guys thank you again

[vvtr]

yeh as said, check for leaks around the intake.
also check the vacuum hose(s) for perishing as this could be another possible place for a vac leak!

imo on the cheapy chinese 4t's, once you start meddling with the carb you may as well throw it away and fit a new one.
saw a link on here from someone to some good replacements for less than $20

the engine will idle higher with a weak mixture.
at low rpm & with an incorrectly adjusted mixture screw, the engine is drawing a weak mix and consequently idling fast.... this draws more vacuum across the idle circuit and pilot jet, and more fuel, which richens the mixture a little so the rpm drops lower...... the lower rpm = lower vacuum = less venturi effect = weaker mix, so the rpm rises again etc etc...

thing is though, owners always seem to fiddle with the carb before looking for more obvious causes!
invariably this just causes more issues than you started with!

because you mentioned a squeak from the back end, im wondering if the rpm could be rising & falling due to frictional losses somewhere in the cvt... may be it's just dirty inside, worn belt, fibres of the belt wrapped round the shaft in the clutch...
you wont know until you open it up for a look.

[ninjascoot]

thanks vvtr i did do some work on it today, i am still checking for vac leaks and i got some of my parts i order today so i installed those (cdi and coil) then checked spark just to make sure it wasn't that. With the parts, i have great spark so moving on to vac leaks tonight. I have only had the scooter for almost a month and i didn't pay much for it so main goal is to get it running good. I looked at other posts and will be taking my time to get this problem fixed

thanks for all the help so far
Dan

[Fox]

I can't stress how important it is to have properly adjusted valves. If one is tight you'll lose compression and that causes idling and starting/stalling issues.

[ninjascoot]

i will be checking the valves next weekend i have no more time to work on my scooter this weekend and had to pay bills so i am short on cash and was told by the wife not to spend anymore money not even the seven bucks for a set of gauges....... I'm the king of this castle when she not around....lol

[Deleted]

I too agree with Fox on the valves. Your very next step should be checking the valves.

I dare say he and I probably do more work on the 4 stroke qmb motors than anyone here. We see time and time again many starting, running and idling problems cuaused by valves being tight or loose (usually too tight from what I have seen).

The stock carbs on the qmb motors are junk. I use Keihin carbs for replacements. They are jetted 85/33 and have made every bike i have put them on run great.

www.ebay.com/itm/270871310675?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_7322wt_922

Only chinese qmb scoot i have seen one of these on it stock was a Baja Sun City 50. I was able to clean it to make the bike run. All other stock 139qmb carbs i dont even waste my time with them anymore, they get replaced.

At a price of $36.90 its a no brainer in my book. I have saved myself so much time and hassle but just replacing a stock carb thats causing issues with the one above. I keep one on hand at all times.

[ninjascoot]

OK i will be sure too make sure to keep that in mind for the future, i don't know where i would be without you guys, you have helped more than you could know. I mean i am not dumb and i did work at a dealership for five years working on cars but i have been out of it for awhile now. It's nice to see people on a forum really care about whats happen on the forum and answer posts.

Thank you
Dan

[Fox]

Just so you are aware, you don't really need a gauge to check the valves. Open it up and see if one is tight. A strip cut off an aluminum soda can is a good substitute gauge. The main thing is that there is a gap/play in both valves when the engine is at TDC. If they tap loud after then close them a little.

49ccscoot.proboards.com/index.cgi?board=4ttech&action=display&thread=713

[rocketdog]

I vote for either an intake leak or too tight a valve setting. This type of valve train has a tendency to tighten up over time. The soda can trick is a good one Fox. Ought to be close. .004 of an inch or so. After you set the lash rotate the engine over a couple of revolutions and check it again Ninja.

Went and miced one. A Stroh's beer can is .0043 close enough. And you get a great reason to drink beer, not that I need one. "I had to Honey, I needed it to fix the scoot".

RD

[rocketdog]

Feb 18, 2012 4:22:51 GMT -5 stroker said:

I too agree with Fox on the valves. Your very next step should be checking the valves.

I dare say he and I probably do more work on the 4 stroke qmb motors than anyone here. We see time and time again many starting, running and idling problems cuaused by valves being tight or loose (usually too tight from what I have seen).

The stock carbs on the qmb motors are junk. I use Keihin carbs for replacements. They are jetted 85/33 and have made every bike i have put them on run great.

www.ebay.com/itm/270871310675?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_7322wt_922

Only chinese qmb scoot i have seen one of these on it stock was a Baja Sun City 50. I was able to clean it to make the bike run. All other stock 139qmb carbs i dont even waste my time with them anymore, they get replaced.

At a price of $36.90 its a no brainer in my book. I have saved myself so much time and hassle but just replacing a stock carb thats causing issues with the one above. I keep one on hand at all times.

Thanks for that link, BTW, Fast. I bought one and it's top notch at a very reasonable price.

RD

[ninjascoot]

thanks for the help but i thought that the valves needed to be at .002 to .003, everybody has said "to check the gap and makes sure its right" setting them to .004 isn't going to matter, i just want to know because the impression i have got from here is that these scooters don't like and thing but spec. settings

Dan