TNG 50cc Won't Start On its Own, or Stay Running By ajacks504 (Read 3,799 times)

[ajacks504]

Hi Scooterdoc! First post!

I'm working on a 2005 TNG Venice right now and having some issues.

Symptoms:
The scooter will not start, turns over, but will never catch.
If I spray carb cleaner in it, and open the throttle almost all of the way, it can get it to start, then it will run somewhat rough, until it runs out of carb cleaner, then it dies.

What we have done:
Replace the old gas, flush the fuel lines.
Verified that gas makes it to the carb. If I pull the fuel line, and turn the engine over, fuel flows free. So, I've got vacuum, I think.
Pulled the plug, cap, stuck a nail in it, and watched it arc over to the plug's cap (didn't have the right socket to remove it). The spark looked very weak, but it was jumping 2 gaps, possibly a problem.
Removed carb, cleaned and inspected. It wasn't really dirty, and everything looked ok, but admittedly didn't give it great a good look over.
Adjusted the jet, all the way in, out almost all of the way, trying at various rotations... nothing.

I think this is where we are:
- Exhaust system isn't clogged, shouldn't be the issue.
- Fuel delivery to carb is good, pulls vacuum.
- At least getting some spark, enough to start carb cleaner.
- Air isn't the problem, won't run with the air box off.

I'm worried that possibly the float might have a pinhole in it, and never letting any gas in there.

What should we try next?

Thanks for your suggestions!

[rob63]

If it starts on cleaner then it`s a fuel problem, did you take the jets out of the carb and make sure they are clear ?

[ajacks504]

Thanks for the reply Rob,

Our carb clean inspect was a little lacking, its possible that I didn't do it correctly. My understanding is that the jets are the small brass screws... this carb had only one that I could tell. The carb is the 1E40QMB / Minarelli type I believe.

Know if a good reference of a carb teardown that include the jet(s), are there more than one on my carb?

[rob63]

Once you`ve got the float bowl off there should be two jets visible. The main jet is the one which the needle sits in, and close to it should be the primary jet. Unscrew both and make sure they`re clear, also squirt some carb cleaner or similar through them and into any orifices you can see in the carb. Make sure the float bowl is clean, and hold the carb upright and move the float up and down with the tip of your finger. You should be able to check if the float valve is working ok.

[Alleyoop]

If it starts when starter fluid or gas is fed by hand into the carb or intake the carbs jets and or passages are clogged.


Take the Carb bowl off and take the jets out and clean then make sure you can see daylight through them. Then that is still not good you must clear out the PASSAGES as well. So get your Carb Cleaner with a long thin straw and stick it in the holes and spray. The Spray into the Holes have an EXIT inside the VENTURI or by the butterfly or some outlet.
Alleyoop

What kind of carb is on there a CVK type carb or a SLIDER type THROTTLE CABLE going into the center top of the carb?

[ajacks504]

Thanks Alleyoop and Rob,

Its SLIDER type, the THROTTLE CABLE goes into the center top of the carb.

[Alleyoop]

Ok then the Carb has an AIR RATIO SCREW not a FUEL RATIO SCREW.
The AIR RATIO SCREW is on the RIGHT SIDE NEAR THE AIR INTAKE. They are very finicky, you turn them 1/16 at a time. CLOCKWISE takes away AIR and makes it richer, COUNTER CLOCKWISE ALLOWS more AIR and makes it LEANER. The Center screw is for raising or lowering the IDLE(CLOCKWISE Raises the IDLE and COUNTER CLOCKWISE Lowers the IDLE).

So on those carbs the FUEL IS CONSTANT according to the jet sizes and you either add air or take aways air.
Alleyoop

[ajacks504]

Ok some updates from last night.

Dismantled the carb again:
- When I pulled it out, the carb was flooded (full of gas).
- Removed the jets, cleaned with a thin, solid core wire, can "see the light" thru every tiny orifice there is on the thing.
- Inspected the float, no pinholes I could notice.
- Reassembled.

Same symptoms! Will start and run off of carb cleaner, or gas manually put in, but won't run off of the carb to save its life... with or without the air cleaner.

I closed the idle screw almost all the way, then experimented with trying to start it with the twist throttle in various positions (should do same thing as fooling with the idle screw).

The only thing left is the air mixture screw? I tried starting the throttle barely open, and the screw in various places. Lean, then getting richer, 1/8th turn at a time.

What now!?!?! ;D

[Alleyoop]

OK do this, crank the sucker a few times and take out the plug since it did not FIRE the plug should be wet if it was sucking in gas. If dry it is not sucking in gas. Did you clear out the passages? Like I said it means nothing if the JETS are clean the passage outlets are TINY and I mean tiny like a speck. DID you spray into the holes without the jets and see spray coming out in the VENTURI?

Did you SPRAY in the AIR INLET HOLE where the AIR RATIO SCREW is? The only other possible problem is YOU HAVE NO COMPRESSION or it is very LOW which will not create enough suction to draw fuel in.
So also check your compression,
When checking compression you have to HOLD THE THROTTLE WIDE OPEN when cranking to get a good reading otherwise you will get a low reading.
Alleyoop

[jct842]

what are the valve clearances set at?