Tuning for speed :)

[theguy2024]

Been enjoying riding my 76cc china motor but I wanna try and get it faster. Just finished up another top speed test I maxed out at 48km/h (30mph). What are some thing I can do to go higher? I have a mz65 clone pipe on. Is the squish important for speed? I’ll need to buy solder and a digital calliper if so. I ported it a little bit without checking timing and all that which I don’t know how to do.

I have a #85 jet in there and the clip on the middle position out of the 5. I noticed I gained 3km/h when switching from a #80 to #85.

is bogging down when you’re too lean and four stroking is too rich? It’s definitely doing one of those at max speed.

Also will retarding or advancing the timing do anything? Sorry a lot of questions lol love this community

 

[Larry Trotter]

Put the original jet back in. Raise or lower the needle. If you run out of mixture control either richer or leaner then change jets. Likely you are running rich and 4 stroking. Gearing will probably do lots more for speed than doing jetting. Even this little guy makes 32mph any day.

 

[Greg58]

How many miles do you have on the engine? Every one I've built got a lot better power after a couple of hundred miles, I always suggest making one change at a time, if you do several upgrades at a time and something goes wrong you won't know which one helped or hurt. Squish is important, but a good seal between the head and cylinder will help it run as it should. I sand the head and cylinder deck on sandpaper taped to a 1/2" piece of glass, I sand till I getting a good flat surface on each, use a torque wrench and tighten in an x pattern to no more than 12 ft lbs. As for jetting you'll need to learn to read the spark plugs, dark brown porcelain is rich, light gray is lean.

 

[2stroker412]

Put the original jet back in. Raise or lower the needle. If you run out of mixture control either richer or leaner then change jets. Likely you are running rich and 4 stroking. Gearing will probably do lots more for speed than doing jetting. Even this little guy makes 32mph any day. View attachment 111772

What kind of bike is that?

 

[Larry Trotter]

What kind of bike is that?

It’s a combination of 3 different ones. Started as a 20 inch girls schwin then a seal post and top bar from a road bike and suspension forks from an unknown 20 inch kids bike.

 

[Larry Trotter]