Intake and exhaust lengths

[Winkie77]

I recently tried to upgrade my exhaust to expansion poo poo pipe. I am experiencing extreme sluggishness with new pipe. I'm wondering why effects are opposite what I desired and expected. New pipe is 24" to expansion then muffler. Intake has a 7" manifold with a couple bends. Motor runs good, 30mph flats, with short stock pipe. Have jets for my nt carb but moving up to larger jets only makes it run worse, running 65 now. Also if I take off the air filter it runs like crap, seems rich, can more air flow through carb make engine run richer? Have replace intake and exhaust gaskets, port matched, checked float height, cleaned carb, plug chop, new plug, removed fuel filter, hmm. Any ideas? Is my intake too long? Should I get a better carb? Looking at some keihins, but seems like overkill on a little China girl.

 

[Frankenstein]

Dead mice in the muffler? Some people had bug nests too..

Check it out see why the muffler effed it up?

 

[Deleted member 12676]

when I tested exhaust lengths I found the length I liked best and that too long or too short gave worse results.
You should also do tests.
Change the carb? Nah, it doesn't even have a dedicated idle circuit but who cares about those nit-picking details? Anything that makes it look like a real 2 stroke is good enough. The Chinese would never stiff you to make more money, nah, not the chinese.

 

[Deleted member 12676]

oh also the new pipe make have more or less resistance to flow which affects back pressure which affects engine running. these engines like back pressure but too much will make them run hotter.

 

[Winkie77]

Thanks Frankenstein, I did check pipe, cut off muffler and left expansion and did a visual plus some probing, nothing in there. Pipe is flexible so I straightened and could also see daylight through it. Thanks Jaguar- Maybe it doesn't have enough backpressure with new pipe? Ran better with stock restrictive one. Haven't tested lengths as new pipe is woven flexible steel and I don't thing I should weld on it. Also not sure why it runs so poorly with the air filter removed. Spark issue? I'm using B5hs spark plug gapped .031 and slightly upgraded cdi and magneto, still want to upgrade to Jaguar cdi and coil, but hard to justify if I can't keep the bike running right after other upgrades. Also it has lost a little hill climbing power recently, new/better rings? Gt5 Engine with high comp head has about 300 miles and was broke in properly. Also when I got the engine the lower head gasket was a little funky, could a crankcase leak cause any of this? I have new upper and lower head gaskets and debating removing jug and replacing them. Also I live in Hawaii at sea level if that matters much

 

[Frankenstein]

Yeah that header is like a foot too long lol...

 

[butre]

that pipe isn't any less restrictive than the stock pipe, and that "expansion chamber" isn't going to do anything.

 

[Winkie77]

Ok, I guess it was a poor choice. Should of done sbp for twice as much! Then I wouldn't be left with a piece of scrap metal. Anyway it's my first build so you live and learn.