Eliminated Emissions Canister Problem By ndog1 (Read 1,872 times)

[ndog1]

I got rid of the whole mess of emissions plumbing on a Jonway GY6 with the QMB139 carb. Im running directly from gas tank to carb, manifold vacuum to tank vacuum, check valve gone, plugged all the holes with nipples on the airbox and soforth and am running the crankcase vent upward with a little filter catcher on it. Fuel tank vent is fine.

Seems like the jetting has been affected more than anticipated. 1. There are no fumes from all the sources coming in just pure air.
2. There might have been an increase in vacuum with simpler direct routing, causing the carb to suck more thru its jetting and circuits.

I am in South Florida which is obviously warm, humid and at sea level. What mainjet and pilot jet do you guys recommend for this climate? The stock was a 34 pilot and 74 main with the clip in the center.

It totally cut out anything over mid throttle so I got a hold of an 85 main and put a 35 keihn pilot and it runs good but seems rich up top. I have dropped the needle to the second leanest position and it helped but I am going to have to hunt down another mainjet. One other strange thing is that it will not idle with any pilot (even the stock) unless the air idle screw is turned all the way in clockwise.

Half the diagrams show a rubber washer, half dont....my only other guess is that it is missing (this is a friends scooter)

Thank you all

[Alleyoop]

What do you mean MANIFOLD VACUUM TO TANK VACUUM? If your Tank has a VENT hose which it probably had and was also connected to a CANISTER. THAT TANK vent hose SHOULD NOT BE CONNECTED to Vacuum, do the same as you did for the Crankcase Vent Put a Fuel Filter on the end and tie it up high anywhere(IT HAS TO VENT TO THE AIR). That may be why you need to turn in the AIR RATO SCREW all the way in to draw more fuel. Turning in the AIR SCREW cuts off more AIR so from what you are saying it needs more fuel.

If the Orginial was a 74 get an 80 main an 85 is usually to big for a NONE BBK MOTOR.

You say you are turning the AIR RATIO SCREW, Is this a 2 stroke?

Normally the 139QMB are 4 strokes and have a CVK CARB which do NOT HAVE a AIR RATIO Screw they have a FUEL RATIO SCREW to the LEFT of the CARB where it connects to the INTAKE MANIFOLD.

So which is it Because it makes a big difference what the problem is if you have to turn the SCREW CLOCKWISE. Turning it CLOCKWISE on a AIR RATIO Screw CUTS off AIR. TURNING the Screw CLOCKWISE ON A CVK carb your LEANING IT OUT which in that case means TO MUCH FUEL and your cutting down the fuel to have it IDLE.

SO WHAT CARB DO YOU HAVE, So I can tell you what the problem is and what to do?

Looking at the CARB is the screw your talking about on the LEFT SIDE or the RIGHT SIDE by the AIR FILTER SIDE?

Alleyoop

[ndog1]

INTAKE MANIFOLD vacuum nipple connected to the FUEL TANK PETCOCK VACUUM. Apologies should have added petcock. The vent hose is fine.


As I said, it is a QMB139 50cc 4 stroke engine and the screw to the left on the manifold side is via the manufacturer the "Air Idle Adjustment Screw"

[ndog1]

Just to clarify....I have been building race scooters for a long time...just never 4 stroke chinese.

I am aware that the internet has many names for the mixture screw the acts with the pilot circuit. So fuel screw then. (But the air from the venturi drives it LOL)

[Alleyoop]

Well so much for the Manufacturer user manuals they are written in CHINA and are usually worthless.

Ok so you have a FUEL RATIO MIXTURE screw NOT and AIR RATIO SCREW.

Since you have to turn it CLOCKWISE all the way or very close for it to idle means your cutting off fuel from being sucked out of the PILOT JET which means your PILOT JET is to big. On the 50s they usually come with 18mm carbs and a pilot jet anywhere from a #32-34.

Have you checked the ENRICHER to make sure it IS cutting off the Extra fuel after 3-5 minutes?
To check if the ENRICHERs Plunger is extending, take it off and lay it on its side and then cover the hole with your thumb and start the scoot. Then watch the PLUNGER on the ENRICHER it should start to extend out in a couple of minutes and fully out about 1/4 of an inch from the retracted position. If it extends out then it is working if it DOES NOT extend out then that is ONE problem causeing to much fuel and is why you have to CLOSE the Fuel Ratio Screw all the way or almost closed.

If the ENRICHER is working then you need to put in a smaller PILOT JET as well a smaller Main jet, try a #80 main. The #85 is to big and that is why you had to drop the needle to cut off some fuel in the mid-range. So with the #80 move the needle back to the center slot.

On a carb if you have the correct Pilot jet the Fuel Ratio Screw should only be out anywhere from Between 2-3 turns from the closed position. If its a little past 3 turns out that is ok as well if it is only out 1 1/2 turns. Reason it also depends on the amount of air the Air Filter getting if it is a little dirty and restricting air then it will run a little rich and you will close the Fuel Ratio to cut some fuel off and visa-versa. A little to much air is being sucked in then you may go past 3 turns a little bit.
Alleyoop

[ndog1]

Found the problem, the o-ring was shot on the fuel screw...had to fish hook the old one out. Went ahead and got the whole rebuild kit and an 80 main.

Idle circuit is great now, returned clip to middle and but in many of the components including 80 main jet. Was very surprised that it was cutting out above mid throttle.

Being a 4 stroke and having tried 85 and 80 now....started to get really frustrated. I pulled the carb back off and looked around at the new rebuild components.....very inconsistent. put back most of the old stuff.

Im thinking the problem is the float height....the new float needle and float were much higher meaning less gas.

What exactly is the float height for the stock carbs? Around 16mm??

The rebuild kit was like 18+.

[Alleyoop]

They are normally 17-18mm,
Here is what the carb parts are so you know what they are and where.
Alleyoop
This is a 50cc carb with a excelerator pump yours may not have a PUMP, it may OR MAY NOT have a ACV valve on the Right Side:

LEFT SIDE OF CARB:


RIGHT SIDE OF CARB PUMP:



NONE PUMP VERSION RIGHT SIDE WITH ACV VALVE:

[richardthescooter2]

Hey Alleyoop, do they make a carb for 250cc that has the fuel ratio screw on the side?

[Alleyoop]

You mean one like this 250 carb: ;D
Alleyoop

[richardthescooter2]

That would be great to have on my scoot.