139qmb dies past idle By deepcrk06 (Read 4,528 times)

[deepcrk06]

HI All, need some assistance for a dummy here. I have a 139qmb 50cc engine, ran fine till I went over rail road tracks. Motor died. Got the bike home and found no spark condition. Replaced CDI and now have good spark. Engine will start and idle fine. Go to give it gas and it dies. Took carb apart and soaked, cleaned and dried it out. put it back together and still have same problem.

Compression: 90 lbs
Great Spark:
New pit cock vacuum pump
new vacuum lines and fuel filter
set and rechecked valves at .004 mm

bike idles great, just can give it any gas.

cleaned carb, nothing to adjust as it all preset.

Open to any and all ideas.

[millsc]

check the airbox to see if you cracked it

[Alleyoop]

Welcome deepcrk06,
First your not a dummy, you just need to learn about scoots and motors that is all WE ALL DID.
Usually going over big bumps or holes and stuff and something happens it is usually because something came loose.
Is the Air Filter on good and in one piece. First check for AIR LEAKS maybe when you went over the tracks the manifold cracked and it is sucking air or the AIR TUBE connected to the carb cracked etc..
From what you said the carb is re-set means that the FUEL RATIO MIXTURE screw is PLUGGED. A lot folks will drill the plug off to get at the Fuel Ratio screw some just order an aftermarket carb that has the Fuel Ratio Screw available for adjustments.

But if it was running good before the BUMP over the tracks I would guess something came loose and or something cracked and letting a lot of air in which will not suck in enough fuel.

If you could take pictures of the carb area and hoses that would maybe we can spot something from the pictures.
Alleyoop

[deepcrk06]

Continue trouble shooting, friend had a scooter that he modified so i replaced the goose neck (carb to head) intake. Replaced the air filter assembly, and all the vacuum hoses have been replaced new. Guess it time to buy new carb. (wish he still had his old one but he gave it to someone else) anything else I should check?

Bike use to run great, never had any issues with it starting or running and could maintain 35 mph with it on flat ground, did bog down little on hills but I expected that) bike has 3000 miles on it and this is first sign of problems I have had with it.

I changed lines one line at a time so I know they are correct.

If I want to replace carb, do you have a good recommendation?

[mself52]

shoot a pm to tvnacman i bought a carb from him at the best price i was able to find he is good guy and fast shipper i believe alleyoop has even bought a carb from him

[deepcrk06]

further trouble shooting - nothing past idle -

for the fun of it - removed cover over the diaphragm - and as i increased throttle i lifted the diaphragm out - speed went up and was able to get full throttle while holding the diaphragm out of the carb - so i suspect something in carb is blocked or bad - so i am going to order new carb as that seems to be where the problem is - or am i missing something?

[Cruiser]

What you proved with this test is that something is wrong with the needle jet diaphragm. If the main jet was plugged, moving the needle jet would have little effect. The diaphragm may have a small hole or tear in it and that would give you the problem you described. Lifting it manually showed that the rest of the carb is probably OK. The diaphragm can be replaced. Scroll down about 60% of the page. $7.95.

www.scrappydogscooters.com/Replacement_Parts.html

[Alleyoop]

Cruiser is right on, if you pulled up the diaphgrm which raises the needle out of the main jet then what the problem is the needle is not rising out of the main jet when you open the throttle to allow more air in which in turn RAISES the needle out of the main jet to get more fuel sucked in.

So yes your diaphgram rubber part most likely has a rip or holes and will not rise.
Now if the Diapghram you get comes with the needle look at both needles and make sure they look the same thickness IF NOT use the new diaphgram BUT Take the needle from the OLD Diaphgram and put it in the NEW Diapghram. If the needle thickness are not the same that will effect the amount of fuel it gets mostly up to 3/4 throttle which we call the low and mid-range.

If thicker than what you had you MAY need to go up a Size on the Main Jet to make up for the extra thickness of the needle.
If thinner than what you had you MAY need to go down a Size on the Main Jet to make up for the extra thinnies of the needle.

BUT if your carb has the FUEL RATIO MIXTURE PLUGGED I would just buy a new carb with the Fuel Ratio Screw available for the $7.95 plus $3.00 in shipping your paying half of what you can get a new carb for.
Alleyoop

[deepcrk06]

First and foremost, Thanks for the assistance and suggestions.

Friend of mine had another 4 stroke carb that had the float bowel broke and housing cracked so I took the diaphragm and main jet from it and put it all in my carb. I still have the same problem. Is their something I am overlooking to get the vacuum \ air lines in the carb to get this to raise correctly?

I did order a new carb today also, just playing with things now to learn more about these carbs and the motor on this bike.

Again thanks to all who have responded.

[Alleyoop]

Take a picture of the Carb area and the hoses, if you swapped out what you say you did then something is wrong. The carbs are very simply so you either put it together wrong or left out something or something is blocked or hanging up.

Now on the AIR INTAKE side of the Carb you have AIR PORTS and one of the air ports feeds air UNDER the Diahgram to make the Diaphgram Rise and raise the needle. So make sure none of the air ports are blocked on the Carb.
Alleyoop

[deepcrk06]

Alleyoop, only connections on this carb is throttle cable, carb bowl drain port, fuel inlet and the electrical connection for the enricher. so I must have done something wrong putting carb back together again. Will wait till Sunday now when I have free time again to take it all apart and start over. Found a great breakdown pic to look at this time while I put it back together again to see what I might have done wrong.

As I said in the beginning, dummy here and have lots to learn.

Thanks for being patient with me and for your assistance.

[Alleyoop]

So your saying you DO NOT HAVE A VACUUM hose coming from the INTAKE MANIFOLD?
Do you have a FUEL PETCOCK or DO you have SHUTOFF VALVE that you have to TURN the LEVER so FUEL FLOWS TO THE CARB?

If you have a SHUTOFF VALVE you and the INTAKE MANIFOLD has a VACUUM port that must be BLOCKED OFF.
Here is what I am talking about this is my Carb on my Trike:
Alleyoop

[deepcrk06]

From the intake - vacuum goes to pit cock to operate gas pump

on the carb their is no vacuum going to the acv diaphragm vacuum port as shown in your pic -- so on the carb their is just the bowl drain line, gas inlet and the en-richer to plug in. On my acv diaphragm their is no where to plug a vacuum line.

did not have chance yesterday or today to play with it. Just giving up and waiting on new carb.

[Alleyoop]

Ok so you do have a PETCOCK or a FUEL PUMP-- A PETCOCK is a Vacuum Operated Valve IF YOUR TANK IS HIGHER THAN YOUR CARB. A FUEL PUMP is a Vacuum Operated Valve IF YOUR TANK IS LOWER THAN YOUR CARB.

So yours does not have an ACV VALVE what your saying as ACV it is a PUMP that when you twist the throttle enough it pushs the rod down and squirts some gas into the carb to get sucked in. Your Carb is one like this
Alleyoop

RIGHT SIDE OF CARB:


LEFT SIDE OF CARB:

[deepcrk06]

vacuum line from intake to fuel tank - sits higer then the motor - so I guess it a petcock, and yes the last pic of carb is the one I have.