250cc Idling Poorly. By carefulrider (Read 592 times)

[carefulrider]

Hello again all:

Regarding my 2006 model year, JMStar/Jonway VIVA YY250T-2, Flagship-Style body, 244 cc (copy of Honda CN250, upright or vertically oriented) engine; 10" rear wheel:

The motor does not idle smoothly; the air filter &/or air filter box is not connected to the carburetor. The air-fuel mixture screw is turned out 2-3/4 turns.

Immediately upon starting a cold engine & including after it has warmed up, I turn the idle adjustment screw in 1/4 turn, & there is no change in RPM, then suddenly the RPM goes up to beyond idle speed. Same thing when I turn the adjustment screw out 1/4 turn. Then it's too slow & it will die. So what if I turn it 1/8th turn, you say? No change in RPM. So what have I done to remedy this?

1. Cleaned the carburetor three times. All orifices permit daylight to be seen through them. I have not cleaned the anti-backfire section of the carburetor.
2.Checked the fuel petcock in the following manner:
Sucked in on & blew out into the outlet to the intake manifold. No leak in either direction.
Sucked in on & blew out in to the inlet from the fuel tank. No leak in either direction.
Sucked in on the outlet to the carburetor. No leak. Blew out into the outlet to the carburetor. Air moved freely out of the mouth. I believe the petcock is functioning as it should.

The following are additional symptoms:
1.When I spray starting fluid around the intake manifold, the engine RPM reduces.
2. When I remove the vacuum line at the intake mainfold, it is wet around the internal diameter.
3. When I remove the carburetor from the intake manifold, the intake manifold is wet.
I conduct all these tests without the air filter & air fillter box connected to the carburetor.

I don't know what else to do, so your advice & admonishements shall be well received.

[alleyoop]

The motor does not idle smoothly; the air filter &/or air filter box is not connected to the carburetor.

You MUST have the Air Filter and Air Box connected to the Carb OTHERWISE it is impossible to adjust the fuel ratio mixture on the carb.

So The first thing is connect the Air Tubing and Air box up to the carb Then it will act much different when you adjust the fuel mixture screw.
Alleyoop

[carefulrider]

Thanks for that. Shall connect the air box & proceed from there.

Now, a day later, I re-connected the air filter box to the carburetor & started the motor. It amazes me how it starts with just half a turn of the starter motor. After the usual fast start, the motor idled high, & then unprovoked, idled low, & rough at both speeds. Then it would idle high, where the clutch would engage, & then cycle down again. This continued for approximately four minutes, when I thought I should check if there was an air leak from the air filter box up to the carburetor, making it as if no air filter box was connected in the first place.

I placed a piece of paper over the air intake holes of the air filter box, & the engine died at once. This made me conclude that there was no air leaking in to the carburetor air intake, from the air filter box side. It should be noted that the engine had reached operating temperature, & the enricher & thermostat had both moved into the position they should have, & the coolant fan motor operated normally.

I left it there with the thought that I shall start it again tonight & see if there is a change in idling.

One observation is that with the connector tube that connects the air filter box to the carburetor is in place, I see no way to access the air-fuel mixture screw to adjust that mixture. So, for the present, the air-fuel adjustment screw remains turned out 2-3/4 turns.

Shall report after I start the motor again later today.

[alleyoop]

It the idle bounces up and down drastically it is to LEAN it needs more fuel so you have to turn the Fuel Ratio Mixture Screw Counter Clockwise to feed it more fuel.
Alleyoop

[carefulrider]

Okay, thanks for that. Does the counter clockwise adjustment hold true for carburetors with the downward pointing screw head at the back of the carburetor?

The screw is currently out 2-3/4 turns. I shall turn it till it is out 3 turns.

[alleyoop]

You have a carb like this and yes Counter Clockwise like unscrewing a screw.
Alleyoop

[ellpee]

You may or may not find -- your scooter is a few years old -- that the mixture adjust screw is plugged. That's to keep the looneytoons California emissions people happy, I'm told. If so, you'll have to remove that plug before you can get at the REAL mixture screw and make any adjustments.