Known porting degrees

[Jrok]

What's up guys . Just recently started tinkering on these cheap ass motors, and have learned a ton from these forums . Wondering if there were any agreed upon timing durations /positions for these 66c engines? (with cylinder reed in particular ). I'm mostly aimed towards the top end,without losing too much bottom end power. I realize these engines vary greatly,but figured I would ask if u guys have any "known good " degree values . Also, how about widths for intake,exhaust, and transfer, boost ports ?


Thanks in advanced ! I appreciate it a lot !

Jason

 

[Street Ryderz]

What's up guys . Just recently started tinkering on these cheap ass motors, and have learned a ton from these forums . Wondering if there were any agreed upon timing durations /positions for these 66c engines? (with cylinder reed in particular ). I'm mostly aimed towards the top end,without losing too much bottom end power. I realize these engines vary greatly,but figured I would ask if u guys have any "known good " degree values . Also, how about widths for intake,exhaust, and transfer, boost ports ?


Thanks in advanced ! I appreciate it a lot !

Jason

What type of reed? a cylinder port reed with windowed piston is different than case reed induction,and some will still limit duration some what.24mm across on everything works well,you can go to 26 safely on the exhaust with the right shape, Aim for 15-20 degrees of blow down duration,raising the exhaust past 168-170 degrees duration or 24mm to top of port from deck put's it below 100 degress from tdc and losses alot of torque also if your not using at least a 1" dia header right from the flange it will run hot.

 

[Jrok]

What type of reed? a cylinder port reed with windowed piston is different than case reed induction,and some will still limit duration some what.24mm across on everything works well,you can go to 26 safely on the exhaust with the right shape, Aim for 15-20 degrees of blow down duration,raising the exhaust past 168-170 degrees duration or 24mm to top of port from deck put's it below 100 degress from tdc and losses alot of torque also if your not using at least a 1" dia header right from the flange it will run hot.

gt80 style reed , through the cylinder, with windowed piston and boost port. thanks for helping out. when you say 24mm on everything do you mean the transfers aswell?

 

[Street Ryderz]

gt80 style reed , through the cylinder, with windowed piston and boost port. thanks for helping out. when you say 24mm on everything do you mean the transfers aswell?

yes and there are waysto correct the short wall aswell most of this can be found here.

 

[Jrok]

ok here's what i went with for starters. what do you think? any suggestions? i couldnt really safelly widen the transfers without a 90 degree rotary. I removed the huge ledge from it though. Right now i'm stuck with the stock 44 tooth, driven gear that comes with these kits. With it stock, 30 was the highest speed i could achieve on a flat road, even with an expansion chamber exhaust. After that little bit of porting and main jet adjustment I am able to get it to 38.

I drilled the main jet out 2 sizes bigger. The problem i am having now is it takes quite a bit of time to fire up no matter where i have the throttle or choke. It goes from not reving at all to taking off all the sudden after almost reaching the bottom of the decent size hill that i live on. The carb is the knockoff keihin that comes with the gt7 kit. Do you think i need to get the gt8 jetting kit sold on ebay? I was afraid to drill out the pilot jet considering the tiniest drill bit i have wouldnt fit (.343mm)

 

[Street Ryderz]

I would raise the needle two notches,and check to see where the air screw is set.if that doesn't change it look for air leaks.

 

[Jrok]

forgot to mention have it up to second leanest needle height. I cant seem to get this thing to idle either . U have to constantly rev it to keep it running. The air screw seems to like it better when most of the way in . Throttle height screw seems to have little effect until all the sudden its reving to the moon.

 

[Street Ryderz]

forgot to mention have it up to second leanest needle height. I cant seem to get this thing to idle either . U have to constantly rev it to keep it running. The air screw seems to like it better when most of the way in . Throttle height screw seems to have little effect until all the sudden its reving to the moon.

Sometimes when the needle is to low (lean) it blocks to much of the emulsion tube (jet body) and doesn't alow enough fuel through for low rpm or proper start up (idle) speed.Though this seems more like an air leak being bad enough to not allow start up.

 

[Jrok]

ill bring some brake clean home tomorrow and see if it reveals any leaks.