Engine Trouble 66/80cc idle adjustment?

[Joe]

Searched and I haven't found any info on this.

First off, this a new build and my first build.

So the problem is, I can't get my engine to idle. It runs, but I have to keep it at part throttle to keep it running. I've messed with the little screw on the side but I get nothing. Is that idle speed or idle mixture adjustment? There's only the one screw. All parts are stock.

Thanks,
Joe

 

[wan37]

If there's one screw it's Idle screw.Do you now what carb it is?

 

[toojung2die]

Every new build I've seen needs an o-ring to seal the carb to the intake manifold. Tuning the carb or getting the engine to run right if there's an intake air leak will be difficult or impossible. You can buy o-rings at any hardware or home improvement store. Bring the intake manifold or carb with you to get one that fits snug. Lacking an o-ring you can use silicone gasket sealer but you have to wait for the silicone to set. Make sure the manifold to engine gasket isn't leaking too. A little silicone gasket sealer on this spot helps ensure a good seal.

That screw adjusts idle speed only. There is no mixture adjustment screw. Air/fuel ratio is set by the main jet size and position of the clip on the throttle slide needle. Changing the position of the throttle slide needle is only required for partial throttle mixture adjustment and it usually will idle without changing it's position in the beginning.

 

[motorpsycho]

I'm placing my bet on the carb slide being 180 degrees off.
if you take out the slide in the carb and look at it, you will see that it has 2 slots cut into the sides of it (a long slot, and a short slot).
the long slot goes to the right side of the carb and gets lined up with a small pin that's cast into the inside of the carb body.
the short slot goes to the left side of the carb and will line up with the idle screw.
if the long slot is on the left side (where the idle screw is), the idle screw will have nothing to contact on the slide, so it can't raise or lower the slide to increase/decrease the idle.
I don't know how many times i have heard this problem, and how many times i have seen the carb slide installed wrong. it can go into the carb 2 ways, but only one way is right.

 

[wan37]

I will place my bet on motor ,because I have done it and it would rev very high if a air leak....lol

 

[motorpsycho]

oh, one other thing...
are you sure that the choke isn't stuck closed?

 

[Al.Fisherman]

http://www.youtube.com/watch?v=lbtDMFUiD0k
At the 10 second mark the choke is open (running position)
At the 19 second mark the choke is closed, on some bikes the choke needs to be anywhere between open and closed to start. On my engines, normal start position will be open.

 

[Joe]

I'm placing my bet on the carb slide being 180 degrees off.
if you take out the slide in the carb and look at it, you will see that it has 2 slots cut into the sides of it (a long slot, and a short slot).
the long slot goes to the right side of the carb and gets lined up with a small pin that's cast into the inside of the carb body.
the short slot goes to the left side of the carb and will line up with the idle screw.
if the long slot is on the left side (where the idle screw is), the idle screw will have nothing to contact on the slide, so it can't raise or lower the slide to increase/decrease the idle.
I don't know how many times i have heard this problem, and how many times i have seen the carb slide installed wrong. it can go into the carb 2 ways, but only one way is right.

I noticed the two slots when I was putting the cable into the slide. I took it apart thinking that was the problem, but I had it right. It was then that I noticed the notched and angled portion at the very bottom and how it lined up with the idle speed screw. So the good news is that it does idle now! However, is an erratic idle normal? I had some cork gasket material and made a gasket to go between the intake tube and carb. So I doubt there's a leak there. IDK... I'm thinking a little bit longer intake manifold might help.

Like I said, this is my first build. I'm learning that these are not ready to go out of the box... after assembly of course. That chain tensioner is WORTHLESS!! The welder is going to get good use tomorrow!

Thanks for the help!

 

[HeadSmess]

define "erratic" please

 

[motorpsycho]

a cork gasket between the intake tube and the carb? the thing to cure an air leak at the carb /intake tube connection is to install an o-ring in the end of the carb and then slide the carb onto the intake tube so that the o-ring seals between the tube and the carb.
please explain how you did this with the cork gasket, because if you did what i think you did, part of the intake tube may be blocked by the gasket.
in "erratic" do you mean that the idle speeds up and slows down on it's own?
normally if you have an air leak, the engine will idle REAL high and you will have zero throttle response when you twist the throttle.