Whats wrong with my 49cc 2 stroke engine? PLEASE HELP!

[Bonefish]

While you got it apart.......

Doing this will isolate some variables and make any further trouble shooting easier if any other problems occur.

Backing off the throttle arm stop screw so that just the little nub on the screw or just a couple of threads show on the back side of the stop screw black support brace should be a good mark to measure.

Next, run your throttle cable like it would be installed on your bike,(with all the bends in the cable) but do not have it hooked up to the engine/carb. Twist the throttle grip and make sure the cable runs smooth in the cable housing and does not get hung up with any bends in the way you have it run to the engine. You might wanna add some 3&1 oil inside the cable housing, so that the cable is lubricated, but make sure you clean off any access at the ends so it does not attract any dirt/grime.

Then, rig it up like you are going to run it, start engine, and adjust idle screw.(the one that has the spring on it) so that your engine sounds like cat sitting on your lap with its motor running(purring) while your petting it. Not too much( or the cat sinks his claws into your leg) not too little(or the cat keeps looking at you to pet it some more).


I have the same/similar engine. It has lots of power, gearing this inexpensive engine properly will make it outshine expensive engines that have fixed gearing.

This should give you a decent foundation to build upon.

 

[rob0101]

Cheers Bone fish, i have adjusted the throttle arm stop screw so that the little nub on the screw shows and set up the throttle cable etc so its all set

just to make sure, is this the idle screw with the spring you are talking about?

ive never touched this screw before but the engine is second hand so the previous owner may well have. how would i go about adjusting it? turning it which way, how much, does what? and how can i tell if im doing damage lol

thanks!

 

[GearNut]

The screw with a black arrow pointing to is is a fuel mixture screw. It regulates the high speed fuel circuit.
If you turn it in too far you will damage the fine tip of the screw and the precision fuel port that the screw works in conjunction with.
Turn the screw out to enrichen the high speed fuel circuit, turn it in to lean the high speed fuel circuit.

The screw with a red arrow pointing to it is the idle speed adjusting screw.

 

[motorpsycho]

WAIT!!!That carburetor does not have a slide at all.
It uses a barrel shaped device with a large hole going through it to regulate the air flow.
The screw with an arrow pointing to is is a fuel mixture screw. It regulates the high speed fuel circuit.
If you turn it in too far you will damage the fine tip of the screw and the precision fuel port that the screw works in conjunction with.
Turn the screw out to enrichen the high speed fuel circuit, turn it in to lean out the high speed fuel circuit.

thanks for correcting me....i know NOTHING about this carb and i assumed it was a typical style carb.
I will delete my post so he does not get the wrong information.

 

[GearNut]

It's cool, motorpsycho.
I had that exact carburetor on my go-ped before I went to a high performance one.
It is alot different than a HT carburetor.

Thank you very much for your concern, alot of folks would have just left their post in place.
You are a good person!

 

[rob0101]

Right, im guessing if my engine is dieing when i accelerate that its not getting enough fuel, so i will unscrew the screw with a spring on it a little bit to allow more fuel in, and see how it goes!

P.S what is a good/correct ratio of fuel to oil to put in this engine, im guessing 25:1 but is this abit oily?

hoping to try the engine with these few tweaks i have made tomorrow evening

thanks!

 

[GearNut]

32:1 has never failed me.

 

[rob0101]

Ok...

So i got home today, made up some 30:1 fuel, put it in, AND...nothings changed

this is exactly how the engine is behaving - with the choke nearly on fully it idles good, but if i rev it, it dies, and if take the choke off it dies.

Im completely out of ideas? thanks for all your help so far

...but what next?

could it be the engine is getting a lack of fuel?

thanks!

 

[GearNut]

The choke plate restricts air flow resulting in a richer air/ fuel mixture.
So yes, the engine is suffering from a lack of fuel or a bad air leak between the carburetor and cylinder.
If the engine was sitting around for a while before you got it, with fuel in the carburetor, your problem could be caused by gum and varnish buildup inside the carburetor.
I would clean the inside of carburetor next. They can be tricky as there are little springs, a fuel valve and somewhat fragile reed valves inside them.

Edit: ONLY if it has been sitting for a long time.

 

[GearNut]

I checked on a web site that sells the RacerX scooter, which is what I have, and they recommend 32:1 oil ratio.
Ironically that is what I run in all my 2-strokes anyways.