backpressure: what are the facts?

[RMWdave]

OK project clean the ports and git her breathing better has progressed to the point where I have broken 2 motor mount bolts and can pop wheelies from a rolling start consistently (my laughter can be heard for blocks) I am at point where I have excellent low speed power and am maintaining 30mph at 3/4 throttle above that I am getting 4cycling or short cicuiting. The jet in the carb is removable does Anyone know where I can get bigger jets to cure my high rpm lean condition? The ports in the cylinder (intake and exhaust) are oval nd much larger than intake or exhaust manifold has anyone tried a larger exhaust or intake or would this drop backpressure too much? It seems wrong to have an oval exhaust port with the area (aprox ) of a quarter with a dime sized pipe bolted to it.

i thought that to be stupid as well. i bet if you made a nice matched pair (eshaust flange and intake) alone the engine would work 5x better than it does as far as 4 stroking goes.

 

[DJEEPER]

Get the tuned pipe from SBP. it has a much larger port than the SHOTTY stock pipe. I didnt use the gasket supplies (aluminum) and used some red RTV. (works well!) This way i know im getting the best flow possible.

I really need to get in there and port match/polish on my HT.... ugh

 

[nedwreck]

I was looking for decent exhaust system for my bikes and ran across Santa Cruz motors (santacruzgreenmotors.com) and found an amazingly good looking pipe. Its on the pre-assembled bikes and yes it is available as a part it includes the connector pipe, expansion chamber, and awesome stinger (resonator). SS mountinghardware. I ordered one for each bike and will post again after install abt. PerformANce gains. NO report needed on coolness factor! Talk to Rich at scgreenmotors about. Custom needs to. ned

 

[nedwreck]

Forgot to tell the best part about santa cruz greenmotors exhaust 89$ which includes shipping!!!

 

[nedwreck]

My experience this last riding season, with daily commute taught me these little motors are happiest loud. And with low back pressure. The expansion chamber pipe with resonator I installed worked great for a time until the fibrous packing in the stinger became soaked with gas and oil from the over-rich mixture (not lean as I thought )once the packing clog was removed it. Took. Off like a rocket. The resonator can fell off and with the chamber and. Straight pipe its loud, staccato, and brutish. Still having the rich condition I bought an 18mm mikuni carb from bikebandit on the web. WhAt a differeNce!! Sweet smooth idle, good. Power overall and I haven't even.
re-jetted for optimum tuning. IT fits the stock cable(!) but I had to build up the stock manifold with a piece of tubing for a spacer this Careb is the real deal with separate idle circuit with its own jet and an air adjust screw, a main jet and needle for upper throttle range and a genuine choke circuit with auto pop off. A concise 20 page tuning manual is available everywhere carb is mikuni vm18 mm (internal bore mount is 26mm needs spacer for stock manifold) round slide for 2cycle 67$ everywhere and. Worth every cent. Finally a dry sparkplug I can read instead of a wet mess. Happy cycling to all. Does anyone know of a 100cc version of the chinese single speed motor?