4 stroking, low power, carburetor adjusted..

[AlexClink]

Greetings,

I've had my 66/80 2 stroke for a while now. As of lately it seems to want to 4-stroke and even backfire at times, resulting in low power and jerky riding. I've set the slide needle's c-clip to almost all of the notches with little change in the engine's behavior. What else could be causing this? (I assume it's running way to rich).

I've replaced the spark plug, set the needle to various settings and changed the fuel in the tank.

I did notice that the old plug was black and wet.

Any ideas?

Thanks!

 

[AussieSteve]

Alex, first remove the carby and give it a good clean with fuel or carb cleaner then compressed air.
Next ensure that everything is tight and check the float level.

Is it 4-stroking and backfiring at 0-3/4 throttle or at WOT?

(The black/oily plug does indicate a rich mixture.)

Check out this thread, NT Carb Tuning Basics, for a little more info.

 

[AlexClink]

I cleaned out the carb with some carb cleaner and compressed air. I fiddled with the float... and after getting it together, it seemed to want to 6-stroke :O. So I messed with the float some more and now it won't start. I'm pretty confident that I can get it going again...

I have one question; Could the float setting cause my engine to run rich or lean?

I'm pretty sure I'm setting things right.
- C-clip is set to the second notch on my slide needle (from the top)
- I can't really adjust my main jet
- float was set at 21mm (before I messed with it)

Thanks! I appreciate the advice.

 

[AussieSteve]

Yes, the float-level setting can affect the mixture. Best thing to do is set it back to 21mm and work from there.
Next, since it's running so rich, try raising the clip to the top notch of the needle to lean it out more.

If it was running OK before, though, the mixture shouldn't have really altered. Otherwise I'd recommend a smaller main jet.

Double-check that there isn't any fuel in the float, indicating a puncture. That would cause it to suddenly go richer.

Also, it's not a bad idea to make sure that your electrical connections are all good and that the high-tension lead is well screwed into the CDI and attached to the plug cap well.

 

[AlexClink]

Thanks Steve!
I don't mean to dig up old topics, but I thought it'd be best to post my solution.

The high-tension lead was loose and producing infrequent spark. Tightening that solved the no start problem. Correctly setting the float helped the mixture. All seems well... I wish I had done that before ordering a new carb.

 

[AussieSteve]

I'm glad it's solved. Shame about the new carb, but it won't hurt to have a spare.