High compression on stroker

[Peteyparado]

160psi on 120cc stroker new hone bore rings an piston. squish is at .87 motor is currently being broken in so nothing pass 1/2 throttle..is that to high compression? If so how can I lower it my squish is already at .87..or should I use premium fuel??

[Wheelman-111]

Greetings:

If you don't address that compression ratio, you would need to use not Premium but 100 octane Low-Lead Aviation fuel or 120-Octane race gasoline. Assuming good port timing, that squish is too close to perfect to change the deck or cylinder height. You might consider carving a little more volume into the head.

[Peteyparado]

Man I was hoping for another answer.. Lol because I was thinking the same thing...what would be the max comp using 92octane??? 150psi

[Wheelman-111]

Greetings:

On one of my early AF05 Malossi 65cc builds, for some reason I decided to delete the base gasket and just trued the mating surfaces and assembled with Copper goo. Aside from jacking up the port timing, compression was in the mid-170s. It wasn't long before the first soft seize.

I saw the same compression with my MHR, and immediately set forth for the county airstrip and 4 gallons of Avgas 100LL. That one ran pretty well, unscathed on disassembly hundreds of miles later. I would think 150 would be risky on 92 octane. I'd venture closer to 140, with fat jetting and ample oil would be OK.

[Hppowdercoatings]

On my Spree I'm getting 142/145 psi. Comp reading.
I'm running 93/94 Octane with 32:1 Mix...
Keeping Tune a little on the Fat side...

[Peteyparado]

After break in I'll check again an check for detonation.. I'm running it super rich for now 140main I should be at 136-135 after break in.. I heard a lot of things people say 170 max 150 max so hard to judge.. I'll just keep checking

[veedubh20]

it is your moped to tune the carb.. all do look at the spark plug color and rejetting carbs.. need to go bigger main jet.. sound like you seize first piston, rehone cylinder and new piston in..


my jog get action ..

[Peteyparado]

I rehone because I had jus over 6k on the motor a bunch of 1/4 mile runs an daily driven.. I just felt it was time...but when I first build the motor the comp was at 145psi.. Did all that new stuff an psi went up to 160?? But yeah I got the main at 140 from 138