Runtong jets and upgrade

[PsychDoc]

Ok- tried the #65- first ride seemed to be Worse?!? Went out again today and it ran about the same as the #66, maybe. 25-27mph is a struggle and the low end seems to have less torque. I did manage to squeeze out 29mph, must have had a tailwind.
Temp was right around 300f when I stopped. But it’s a touch cooler today, maybe low 80s. But what I did find- the head is around 300- the muffler is almost 600f! What the heck? Is this normal?

 

[PsychDoc]

Today was time to try the #64. Runs well. Still has some sputtering here and there but smoother overall. From 26mph and up is a bit hit or miss, at times it heads up to 28 without a problem and other times barely gets to 27- I am thinking aerodynamics is becoming a larger factor. It gets up the hills well- so that’s nice. Steady up a decent grade at 20mph.
And a new top speed of 30.3mph (ok it was a slight down hill- full tuck)
I may stick with the #64 and try some other modifications- clean up the ports- shave the head a bit-maybe try the extra hole in the emulation tube.
What is a typical top speed for a “stock” China girl with a 44tooth rear? And what might I see if I go with a 41t?

 

[PsychDoc]

Dropped to the #63 today. No discernible difference. However...
A post in a different forum explained an experience I had. When going over rough pavement, the engine moves from 4stroke mode to 2stroke. I read that rough road can shake the float bowl causing the fuel to ‘foam’ (or something like that) which creates a lean condition. All that to say I believe I need to keep getting smaller.
How do I know if I’m too lean?

 

[PsychDoc]

Greetings friends. The quest to find the proper jet size may be complete. Today I went with the #62. It is definitely weak on the low end until it warms up- then it wants to be going 5-7mph via peddling before it smooths out. Most 4stroking is gone. Occasional coughing and sputtering but I suppose that’s to be expected.
It was about 70f outside during my brief ride- 5.7 miles. New top speed- 32.3mph! But at that rate it feels like it’s on the verge of vibrating to pieces.
I suppose it’s time to move to different mods- cleaning up the ports and matching those as much as I can. And I probably need to actually true the wheels and repack the bearings. Then overinflate the tires and head to bonneville!
Thanks for the help.

 

[PsychDoc]

Oh- the head temp looked to be about 350*f post ride.

 

[GreasyChris]

Oh- the head temp looked to be about 350*f post ride.

When it's in the high 90s here my bike hasn't gone above 400° and I ride it like I stole it, so you're safe at 350. The leaner you run the bike the hotter it will run. You're right around the sweet spot. With the right mods you should be able to hit 40mph no problem

 

[PsychDoc]

When it's in the high 90s here my bike hasn't gone above 400° and I ride it like I stole it, so you're safe at 350. The leaner you run the bike the hotter it will run. You're right around the sweet spot. With the right mods you should be able to hit 40mph no problem

Thanks man- 40 would be fantastic. I’m following your build with some crazy mods, well beyond my skills at this point.
I’m going to stick with the #62 for now. It comforts me to know I have one more notch to go if needed.

 

[dchevygod]

Thanks man- 40 would be fantastic. I’m following your build with some crazy mods, well beyond my skills at this point.
I’m going to stick with the #62 for now. It comforts me to know I have one more notch to go if needed.

With bearing upgrades and a suitable port job it will spin up too 9-10k. Put a good pipe on and hold on!

 

[dchevygod]

With bearing upgrades and a suitable port job it will spin up too 9-10k. Put a good pipe on and hold on!

The engine i use is rated 4.2hp stock and is rated at 14000+. After minor upgrades Ive gone almost 70 mph "68.2" on that shifter build.

 

[CrazyDan]

The fastest I've went on my 53cc 4 stroke build is 53mph, was on a slight downhill, and regeared my bike to max out at a higher ratio so I can run faster out of turns for racing. Right now it does 49.6 mph tops, but I'm thinking about gearing it for 47mph for the races. I have a bit more power than my 53 mph run downhill. I might be able to do 55 mph if geared for it right now on the left side on the flats. If I did that, it would have to be single speed, and goodbye $50 for a single race stage to replace my clutch.