Honda GX340 new guy!

[thefarmer355]

First I would like to introduce myself I am T.J. from South Carolina, small town farm kid 25 years of age. Been neck deep in making things go fast and hot rodding all my life...


I recently acquired a hemi head predator 60363 part number... tore it down removed all the governor assembly as specified by several you tube videos, we then threw it on a home made go kart frame and proceeded to break the engine in, with an old clutch and chain we were roughly at 32mph top speed but the engine wouldn't run "wide" open, it would plateau off which has me stumped... i was thinking it would over rev and float the valves, the speed also flattened off so it wasn't b/c of too high a gear.. it has me stumped, guessing i would say it was only turning 4500 rpm if that, But it has the stock muffler and air filter on it..

My next question is, I scored a elec start honda gx340 for free, it turns over fine, and looks very clean on the inside with a 1inch straight shaft, my question is do the parts for 390/420 clones or honda's fit these as well ? just aiming for something me and my buddies can fool around with in the yard. Thanks guy's love the wealth of information you guy's provide here!

 

[davidlamb78]

I'm sure you're floating the valves. There are many threads here that offer parts lists to make it go fast. You'll be directed to read the "sticky" thread about modifying your motor, so might as well throw that out there. Check out the OldMiniBikes warehouse for parts. These things can go fast, but you'll need a little cash to get there. Welcome! Affordable Go Karts has a great page as well. Read the performance mods page. AGK - Performance Basics - Affordable Go Karts

 

[65ShelbyClone]

My next question is, I scored a elec start honda gx340 for free, it turns over fine, and looks very clean on the inside with a 1inch straight shaft, my question is do the parts for 390/420 clones or honda's fit these as well?

The only difference between a GX340 and a 390 is the bore size and possibly carburetor. The really new (think I saw 2012+ mentioned) GX340s are just tamed-down 390s.

 

[thefarmer355]

Thanks guy's yes I have already read the sticky about engine safety and am fully aware of the danger, I have 2 dirt ovals less than 15min's from me and have seen a few disaster's. Billet flywheel and rod are the first things I'm ordering for the predator. I was thinking shave the head, port/polish and black mamba jr cam ? As for the honda 340 it may get bored out to a 390.. I really want it to scream being that I got it for free because it was supposedly locked up.

 

[thefarmer355]

So is the gx340 head the same as the gx390? and what are the stock valve sizes ? I was thinking of shaving it .100 and a light port and polish with ss valves and heavy duty springs,