After exhaust mod...cutting out at top-end.

i have that beercan airbox...it flows really freely, i can put my fingers about an inch away and feel it.
 
so I guess it's not a restriction by airfilter issue then... Did you try the leanest setting? I've tried all but that one, and found the leaner I go, the more the issue disappears. I'm just a bit weary of running lean, though by the engine sound, it definitely isn't running lean right now.
 
funny you should ask, because i just got back from trying all 4 settings...slot #1 is the most reliable throughout throttle range with a bit of "pop", #2 gives me more "scoot" but i get more "pop" at top-end.

i'm stumped...and tired of getting nowhere.

low-octane, 36:1 real oil, new NGK plug, #2 slot, no leaks, great starting, excellent performance...but still i can feel that top-end isn't everything it could be.

ignition?

anyone at all have any ideas?
 
on the way home just now it was doing it in full force. I did notice if I gave it full throttle going down hill (no I didn't let it over rev, just let it get up to what I am used to it being it's max rpm on flat ground), i could get it to go up to the normal top end rpms...and it didn't cut out at all.

It was pulling really hard on flat ground, but once you hit that point, the engine bogs, almost like it just instantly stops firing. You can let off the throttle, or keep on it, or go back and forth between full and no throttle, and you just get nothing...this happens for about 3-5 seconds...after that it smoothly kicks back in, sounding like it is running REALLY rich, and then gets back to normal...strangest thing...
 
mrsaxman99

take the airfilter box off and just screw back the filter and hard platic to hold it there and see if that improve it also cheap mod cost you nothing there was picture of some doing that here on this forum

I see if i can dig it up or someone might have it handy

Chieflets
 
i never get the feeling it quit firing, i just feel like it's firing too late...like all the combustion is pouring out of the exhaust instead of staying in the chamber.

i'm gonna sit back and hope someone hops in with a solution.

(i re-labeled the subject to catch more attention)
 
thanks for the relabel...tomorrow I'll try to take out the air filter element. I don't need pictures to do that. I've had this engine completely apart save for the crank. I know how everything works...my confusion lies in WHY things work the way they do. I'm about to just buy a stock exhaust (like mine was before I cut out the small tube) and be done with it. The 1/2 hp increase isn't worth this frustration...
 
I think you guys are having problems because you changed the back-pressure of your exhaust. 2-strokes don't always get more power just by opening up the exhaust, like a 4-stroke would. 2-strokes actually NEED some back pressure to run their best.

Ever notice how high performance 2-strokes have tuned pipes with large expansion chambers, but they don't usually have wide-open exhausts? The tuned pipes work by timing the exhaust compression wave to force a little pressure back into the cylinder through the exhaust port just before the cylinder goes back up to compress and fire, thus increasing your effective cylinder compression. The exact timing of the pressure wave is either engineered into the shape and length of the pipe (which is why many tunes pipes are only sold specifically for the engine they were designed for), or by adjusting the length of the pipe between the exhaust port and the expansion chamber.

We don't exactly have high-tech tuned pipes on our motors, but my guess is that you are experiencing a demonstration of the need for back-pressure to make a 2-stroke run properly. It's possible that removing the end of your muffler may have had a negative effect on the timing of the exhaust compression wave, which has ultimately lowered your cylinder compression.

$.02
 
that was what i think i didn't want to admit to myself...thanks a lot, blaze :)

putting the muffler end-cap (with small outlet) back on tonite, tomorrow i'll mess with the mixture one last time 8)
 
well it did in fact add a good bit of power to my engine, but yeah I completely agree with what you are saying, and it appears that the backpressure gets too low at the higher rpm's.

Problem is, the long narrow tube that is attached to that end cap somehow mysteriously got cut off :eek: I replaced the end cap, so I didn't think it would drop the back pressure all THAT much, but I guess it did.

So now the question is, should I buy a replacement stock exhaust, or look for a tuned pipe that might work.
 
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