largest carb for a chinese 80cc bike kit

[dondupuis]

Well compression is now 136psi. now retuning the carb, had alot more smoke now that i did not before. infact as rich as i ran before i never seen some come from both tips of my exhaust.. i opened up the intake gasket somemore to better match the head it's no longer blocking the intake.. i am still getting alittle air in through intake tube and carb working on a way to seal it up. I think my exspansion chamber is still a restriction as it's from a 49cc pocket bike and is on the small size maby 2" at its largest point. and looks like about 3/4" tubing..

 

[dondupuis]

current leak locations.
between intake tube and carb.
no exhaust gasket so leaking at head and exhaust..

i think i'm going to need to make a new intake tube for this carb. i will probably extend it some to clear the down pipe from the seat i don't have room for the air filter to fit otherwise..

 

[dondupuis]

Well finally got a video to upload.. can skip to about 3:33 where i get out on the road.
@ 4:42 i reliezed my fuel was off. and sorry i couldn't cut the video it kinda ends about 12:30

Would you guys say it sounds to rich or lean? in this video i believe the needle clip is 4th from bottom..
it's been moved up 2nd from top.



On the way home i change the needle setting a little bit leaner..

 

[Deleted member 12676]

the needle has no effect at wide open throttle settings, only the main jet does.

 

[KCvale]

Your expansion chamber could very well be doing more harm than good.
They need to be timed so the shock wave pulse hits the clean new fuel mix coming into the exhaust and shove it back in the cylinder just before the port closes.

 

[dondupuis]

cool. thanks for the info. i was starting to think that after seeing what some others have installed. however it has improved the lower RPM range i just can't seem to get WOT

 

[gary55]

if i take a mm of the head would that be to much. is there a rough average as to how much compression 1mm would add. ? I seen another post with the fella that has a very large expansion chamber installed. love that.. looking at some of my sleds to see what one is going to donat a pipe.. lol im just working on uploading a video. i will post soon. maby you can recommend some things..

A mm is to much for the slant plug head. In my experimenting I found by adding a second head gasket of .027 compression dropped 30 lbs.. So that's about 1.1 lb. per .001. I remove the material from the cylinder, and with a slant plug head I make the cylinders 2.730 top to bottom.

 

[Deleted member 12676]

there's too much variance between different engines so you first need to get a pressure gauge to see what it has now.
I think slant plug heads already cause enough compression on most engines.
If your setup has under 130psi then just remove a little metal at a time and keep rechecking the pressure.

 

[gary55]

I really gota start looking at the dates on these posts or invest in a time machine.