Post by oldchopperguy on Jun 14, 2013 22:45:23 GMT -5
I recently posted my exhaust mod (on my Xingyue 150) using a full one-inch inside-diameter header, and a 2-stroke-style 50cc "chamber" type muffler (which I'm almost certain was made for a 50cc GY6 4-cycle engine).
Please see picture below...
Please excuse the dirt, rust and ragged tarp... LOL! I'll post new pix in the show-my-ride section, when I get "Lil' Bubba" cleaned up
Now that I've ridden a week, and put a couple hundred miles on, I've found the system to run FABULOUS! So just minutes ago, concerned about a possible too-lean condition, I checked the plug for carb-jetting.
My carb is a Mikuni, but factory-style, added only because the original carb was bad. That was 4 seasons ago. It has whatever idle jet it came with, and a 110 main jet. With the STOCK muffler, and 3/4" header, the plug was the perfect tan/brown.
I expected the free-flowing exhaust to lean it out some... BUT... Now the plug is just a tad sooty-black. HMMMMM...
The engine has NEVER before run quite so strong and smooth, with INSTANT throttle-response, and I can live with a tad rich in this 100+ Texas heat, so for now I'm leaving it alone... BUT... What's up with the richer mix?
I believe this 2-stroke-style expansion/contraction chamber exhaust is doing something very good:
Even the stock cams in these GY6's are pretty aggressive, and I'm betting the intake and exhaust valve timing minutely "overlap" leaving BOTH valves open for a micro-second. And, during this overlap, the expansion chamber pulls a tiny bit of extra fuel charge into the combustion-chamber. Just like it would on a 2-stroke, but without ramming it back into the chamber to "supercharge" like on a 2-stroke.
If I'm right, it would explain why a MUCH more free-flowing exhaust would actually create a slightly RICHER condition than the same engine with a stock, restrictive exhaust exhibited. And it would at least partially explain the better throttle-response and overall performance I'm experiencing.
From time to time, I see these exhausts on 150 4-strokes, like the Vento, and also on 50cc 4-strokes (as well as on many 2-strokes).
My theory here certainly may be wrong. I'm no expert, but I can't argue with results. Common sense tells me a freed-up exhaust SHOULD lean out the mix, but this setup has richened it.
And it runs like a bear!
It idles SMOOTH, responds to a twist of the throttle like an EFI system, and will absolutely SCREAM past any sensible rpm. That was NOT the case with the factory exhaust. The 1-inch header MUST be a big part of this, but the richer condition I believe, is unique to the chamber-style, no-baffle exhaust. Who'd guess that these little GY6 4-strokes have just a hint of 2-cycle DNA in their blood?
At any rate, no matter WHY it works, it DOES work, and works well. And it's quiet...
Hope this may help others who are messing with exhaust mods... Go raid that old 2-stroke go-kart yard, and check out the junk 2-stroke and 50cc scoots in the local alley... LOL!
Leo (a happy-camper) in Texas
Please see picture below...
Please excuse the dirt, rust and ragged tarp... LOL! I'll post new pix in the show-my-ride section, when I get "Lil' Bubba" cleaned up
Now that I've ridden a week, and put a couple hundred miles on, I've found the system to run FABULOUS! So just minutes ago, concerned about a possible too-lean condition, I checked the plug for carb-jetting.
My carb is a Mikuni, but factory-style, added only because the original carb was bad. That was 4 seasons ago. It has whatever idle jet it came with, and a 110 main jet. With the STOCK muffler, and 3/4" header, the plug was the perfect tan/brown.
I expected the free-flowing exhaust to lean it out some... BUT... Now the plug is just a tad sooty-black. HMMMMM...
The engine has NEVER before run quite so strong and smooth, with INSTANT throttle-response, and I can live with a tad rich in this 100+ Texas heat, so for now I'm leaving it alone... BUT... What's up with the richer mix?
I believe this 2-stroke-style expansion/contraction chamber exhaust is doing something very good:
Even the stock cams in these GY6's are pretty aggressive, and I'm betting the intake and exhaust valve timing minutely "overlap" leaving BOTH valves open for a micro-second. And, during this overlap, the expansion chamber pulls a tiny bit of extra fuel charge into the combustion-chamber. Just like it would on a 2-stroke, but without ramming it back into the chamber to "supercharge" like on a 2-stroke.If I'm right, it would explain why a MUCH more free-flowing exhaust would actually create a slightly RICHER condition than the same engine with a stock, restrictive exhaust exhibited. And it would at least partially explain the better throttle-response and overall performance I'm experiencing.
From time to time, I see these exhausts on 150 4-strokes, like the Vento, and also on 50cc 4-strokes (as well as on many 2-strokes).
My theory here certainly may be wrong. I'm no expert, but I can't argue with results. Common sense tells me a freed-up exhaust SHOULD lean out the mix, but this setup has richened it.
And it runs like a bear!
It idles SMOOTH, responds to a twist of the throttle like an EFI system, and will absolutely SCREAM past any sensible rpm. That was NOT the case with the factory exhaust. The 1-inch header MUST be a big part of this, but the richer condition I believe, is unique to the chamber-style, no-baffle exhaust. Who'd guess that these little GY6 4-strokes have just a hint of 2-cycle DNA in their blood?
At any rate, no matter WHY it works, it DOES work, and works well. And it's quiet...
Hope this may help others who are messing with exhaust mods... Go raid that old 2-stroke go-kart yard, and check out the junk 2-stroke and 50cc scoots in the local alley... LOL!
Leo (a happy-camper) in Texas
