GX390 Recoil Usage w/Aluminum Flywheel

Rod Knock

New member
Hi all. Long time reader, first time poster. Apology if this question has been answered, but I have not found so in my searching.

I'm building a GX390 for a kart, and want to focus on lightening the engine as much as possible, yet still retaining use of the recoil starter (only). Question then becomes, how light of flywheels have been used in built 390's, and the recoil still works? Meaning, there is enough rotating mass to start the engine, and have a reasonable low/stable idle?

I acquired a Raceseng finned S2 "Rev" wheel, but it is very light, and very small diameter. Looks like most of the Arc wheels are at least 4lbs, and larger diameter.

Thanks for the guidance on what has worked for you.
 
I put the S2 finned flywheel on my motor with a recoil starter, it was impossible to start and would bite hard when it kicked back. That was with a stock cam and 1.23 ratio rockers and milled head for 10:1 compression , 30deg timing. You might be able to make it work with different camshaft and timing but short version is recoil wont work in my experience. The same motor with a stock iron flywheel was a dream to start on recoil.
 
Thanks.

Anybody have cases of a recoil in use successfully? I would guess a conventional diameter Arc flywheel @ 4lbs or so would be the minimum required for pull start and idle stability with a stock tuned centrifugal drum clutch?
 
On mine I can get the idle down low no problem with the small flywheel, it's just the recoil start issue. With a larger cam you might have different results, easier to pull over but harder to get the idle down.
 
Thanks. What lb flywheel do you use, and are you able to recoil start it?

Any others with this info, please also chime in. Thanks.
 
i am using the ARC electric start flywheel and modified the cup to fit instead of a starter nut. 10.2:1 compression ratio 1.2 ratio rockers 275 cam WITH compression release. Pull to compression stroke and it works great.
 
I have used ARC adj. timing flywheels with a recoil starter, had to drill out the holes of the 6 bolts in center hub into the recoil hub then, remove the bolts from flywheel center hub and got longer ones then reassembly the whole thing useing the 6 bolts from the flywheel hub to whole the starter hub.......anything lower than 3lbs will be a beast to start...the 5lbs electric start one wasn't bad at all, but the 2.9lbs was small dia one was impossible.........advice put in the longest cord you can put the houseing.....helps with the snapback.
 
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