2/stroke is 4/stroking?

[AussieSteve]

Not sure where to start here. I'll do it bit-by-bit.

Hey gang,
Everything's running well (49cc Skyhawk), but after about 16-17mph, motor starts 4/stroking. I have big time gone over it for air leaks.

Air leaks do not cause 4-stroking - quite the opposite.

Ok, same gas ratio mix as of 2 weeks ago 25:1 ,and would run in the lower 30's mph? Needle is in the same place(2nd down from top)....Mmm,
Oh, I also put a new plug wire on (better in quality). A new plug cross over from NKG------ Autolite 4093 ....gap 0.20 , stock muffler with one drilled hole at base.Took air box off, only using foam filter. (Much more air flow)
So, I thought high speed jet, but it ran at speed a few weeks ago with everything same/mix 25/1.
PS- It had original (CHINA) everything when it ran faster?
Sense new, I've ran about 4 full tanks.
TY, Glen Ideas welcome.

Forget the fuel/oil ratio - that's fine.
More important than the 'speed' that it starts 4-stroking is the throttle opening. (0-3/4 throttle or wide-open-throttle?)

Are you sure that what you're experiencing is 4-stroking?

What colour is the plug? Why not stick with an NGK B6HS, I don't think that an Autolite 4093 is the same? Also, I'd open the gap a little more, to 0.024", if I were you.

Finally, read this for a bit more basic info:- NT Carb Tuning Basics

Let us know how you go.

 

[geebt48cc]

Hi there Steve....

Hope that 4th was good.

See it runs well with everything till It gets pasted 3/4 throttle. Then it will acts like the motor is starving for fuel. Brand new in-line filter also. (It wants to go faster, but will only hold about 19-20mph?) I even took the carb apart to make sure float was sitting at 21mm.....its right on it!.......(Everything looks clean and tight/ thumbs up there!~)

It might be running a bit rich. Would that cause the problem? (It's on second setting from lean or top of needle)...........but yes, I'm trying the find a NGK B6HS...........but I was told at Advance Auto that this Autolite 4093 was it's cross over? Still even with the other original plug, it does the same, but didn't with same plug a tank ago.

..............Steve, thanks for your time.

Glen

 

[AussieSteve]

I'm still confused. You say it's 4-stroking AND starving for fuel. They're diametrically opposed. 4-stroking is caused by TOO MUCH fuel. (Sorry to yell.)

Did you watch the video on 4-stroking? It's important that you know which is which.
Again, what colour is the plug? (That's the key - without that info, we'll get nowhere and, ideally, you need to do plug chops at 1/2 throttle and WOT as in NT Carb Tuning Basics. Can't help much until then.)

Sorry, Glen, I don't mean to sound rude. (Just realised it looks that way.)

 

[geebt48cc]

Stops powering RPM's after 20mph

Yes, it's running rich. Took plug out after 5/min run- (darker and a wet place) so I put e-clip on very top of needle, and still loses after 1/2 to 3/4 throttle no more gain?. Just stops taking anymore RPM's?

1,Carb clean
2.float on 21m
3.zero air leaks
4.new plug and wire/cap

 

[Al.Fisherman]

loses after 1/2 to 3/4 throttle no more gain?. Just stops taking anymore RPM's?

Is this something new or has been this way since build?
I would start by making sure that the throttle cable is the correct length and pulling the carburetor slide high enough and is not restricting the air flow. Try without the air filter also.

 

[geebt48cc]

Ok, I'll try that with throttle cable length. No, to answer your question, it started doing about a month ago. Total age is about 300 miles or 10/15/09 49cc Shyhawk 2/stroke.

Heck, was running at 30+ easy...............Now, maybe 22mph. But, I just go easy for a few miles a day.

Glen

 

[geebt48cc]

Nope, slide works fine................but thanks. See, I would think the jet size, but it was doing fine a couple of weeks ago?

Then 30+.......Now maybe 20.......?

 

[AussieSteve]

Maybe you had an air leak that's now cured. That would account for the sudden change in mixture.

 

[geebt48cc]

Yes Steve that could be true, but I'm still stumped to why it's running great, but only first half of throttle................? Then it stops taking anymore throttle or RPM's

Glen Note: It's as lean as E-clip can be placed on top of needle.

 

[AussieSteve]

If it's 4-stroking at WOT and everything else is OK, the main jet is too large.
The needle only has an effect until about 3/4 throttle. Since it's running great up until half throttle, you have the needle set about right.

If I were you, I'd try a smaller main jet to help it rev out properly.