Unstable idle speed By lencho (Read 8,893 times)

[lencho]

I have a 2008 150cc gy6 Bashan scooter. It had 35 miles on it when I bought it this spring and now almost 900. This scooter has never idled properly. It stalls when it is cold and when it is warmed up it will cycle between barely running(1500 rpm) and so fast the clutch is catching (3200 rpm). The enricher is operating properly, I followed the advice on this site and measured how much it extends. Also, when it is first started, the enricher works and it has a fast idle for only 20-30 seconds. Then the rpm decays and quits. I discovered that the idle mixture screw was completely closed, and thought I found the problem. Nope, I have run it with the idle mixture positioned anywhere between closed and 4.5 turns out with no success. Once it is warmed up the idle will slowly decay until it quits. If i bump the throttle when it decays to 2000 rpm I can keep it running. I have to do this about once every 5 seconds. If I give it a bit more throttle and run it up to 3000 rpm, the engine will stay there and then begin it's decay again. I disassembled the carb and cleaned it (it looked new) with no improvement. I looked for vacuume leaks with none found. If i adjust the idle speed screw to increase the rpm just so it won't die, the idle jumps to over 3000 and stays there.

A thought I had was if the ignition had an advancing function built in and has gone screwy, this could be my problem. Does the ignition advance the timing?

I'm at my wits end. Any help would be appreciated!

Lencho

[Alleyoop]

It is running LEAN, if you rev it up and the rpms stay up there for a few seconds then finally start to come down it is NOT GETTING ENOUGH FUEL. Your whole entire problem is FUEL DELIVERY. Now here is the thing You say you turned the IDLE MIXTURE SCREW do you mean the FUEL RATIO SCREW or IDLE SPEED SCREW. The IDLE SPEED SCREW is the one on the THROTTLE SIDE it has a SPRING ON IT. ALL THAT DOES is raise or lower your IDLE.

You need to adjust the FUEL RATIO MIXTURE SCREW which is on the side of the CARB.

So before you start the scoot Turn the FUEL RATIO SCREW CLOCKWISE until it stops and then turn it COUNTER CLOCKWISE 2 1/2 turns.
If the scoot starts try it at that setting. If it does not want to stay running then YOUR PILOT JET IS CLOGGED and OR the PILOT JET PASSAGE.
Get back on this and here is a picture of the carb so you know what is what on the carb:
Alleyoop

LEFT SIDE OF CARB WHERE FUEL RATIO SCREW IS AT:



RIGHT SIDE OF CARB WHERE IDLE SPEED SCREW IS AT:

[lencho]

It is the fuel ratio screw that I have tried between closed and 4.5 turns out.

I've set the mixture screw at 2.5 turns and will see how it runs on the way to work in the AM.

If it is running lean at 4.5 turns out there must be a vacuume leak wouldn't you think?

Thanks for you advice!

Lencho

[Alleyoop]

If it was running good before this, then yes you must have a vacuum leak. Check your intake manifold they usually crack also your Air Filter tubing they get hard and crack.
Alleyoop

[lencho]

So today I drove to work with mixture screw set at 2.5 turns, no change. Still idling too high followed by decay and stalling. Tonight I decided to look for vacuume leaks. I removed both vacuume lines from the intake and connected them with a hose so there was no vacuume being used for the accessories... No change. I removed the intake and inspected for cracks... No cracks. Then I removed the spacer and the attached pics are what I found. Is this normal or a potential source of a vacuume leak? The side with the grove is thi intake side that has an O ring and the side with a lip is the head side that has a paper gasket.

What say you?

[lencho]

I guess I'm not able to attach a pic. The chose file button is Greyed out

Anyway the plastic spacer has a grove on the top side where the O ring seats and a lip on the bottom side that looks to match the hole in the head. Is this normal?

Lencho.

[Alleyoop]

To find an AIR LEAK get a spray bottle of water and spray individual areas IF THE IDLE CHANGES you found a leak.
Alleyoop

[Bashan]

Aug 29, 2012 18:54:20 GMT -6 lencho said:

I guess I'm not able to attach a pic. The chose file button is Greyed out

Have you considered Photobucket? Attachments are from when Proboards first opened and they suck.

Aug 29, 2012 18:54:20 GMT -6 lencho said:

Anyway the plastic spacer has a grove on the top side where the O ring seats and a lip on the bottom side that looks to match the hole in the head. Is this normal?

I've never seen one like that but anything is possible. The spacers I've used are flat on both sides without any grooves. If you have scratches that are more than just superficial they can cause leaks. Also, gaskets go bad, I'd replace all that you can, I use one on both sides of the spacer. Check the O-ring on the manifold too. Where the carb hooks into the manifold is a common source of leaks also. Your problem at this point really sounds like a vacuum leak to me. Try the test Alley outlined. Some people even use carb cleaner but it's bad for the rubber.

[kz1000st]

How come nobody is saying adjust the valves? 900 miles, that's prime time. .004 inch on both, .005 on the exhaust if you're picky.

[lencho]

Here are the intake spacer pics. Does this look right?

I will check the valve clearances tonight.

Lencho

[Bashan]

Well that's bizarre, I've never seen a spacer like that. It looks to me like an O-ring goes around that lip. Could there have been one or did you take it apart for the first time? Congrats on getting the Photobucket account.

[Kaveman]

Must remember that with chinese scoots and their engines, you never know whats under the hood till you have to work on it !

[lencho]

I was unable to verify that the spacer is leaking by spraying water on it. Of course, the fan shroud makes it difficult to get access to the spacer, but no matter how hard I tried to get water around the spacer, there was no change in RPM.

Didn't check the adjustment on the valves yet and the engine is hot so it will have to wait for another day. Will valves that are out of adjustment cause the problem I'm having?

[lencho]

I am going to change the spacer and gasket. unfortunatly there are no scooter parts stores where I live. Before I order one on line, does anybody know if there are other scooters with the same spacers? What about the Honda Ruckus? There is a Honda dealer here that stocks all kinds of parts, but if you walk in and say "... chinese scooter" they show you the front door.

Lencho

[sprocket]

Just cover both sides of that spacer with red high temp silicone,about 1/8 thick...let it set for an hour and bolt it together and leave overnight...you will never have another vacuum leak...