Refurb Go Cart Build

[ScottH]

I am a rookie at go cart builds but a friend gave me a Bristers Fire To Go go cart so I decided to give it a try.
It had a Honda GX390 GCAK QA2* UT1 engine that sat for who knows how long. So, I decided to rebuild engine and chassis rom the ground up. Looking to ride semi off road, Also, my teenage son will be riding most of time.
Looking for your suggestions:

Stock carb modified with #117 main and #40 pilot ??? is it dependable. ???
Debating - Oil level sensor on or off ??
1.3 rocker arms - economical - NR is out of the Billet steel 1.3, (I looked for these) ??
Billet Piston Rod long or short ?
Piston Head Flat or concave ?
Need to have head bored, it appears out of round from my analysis. Bored to what dia. ???
Coil with digital Ignition w/o rev limiter ???
Thinking about aftermarket electric start kit ???
Thinking about torque converter ?

So far I have:
Gutted the engine
Replaced orig. crankshaft with new one. No mods. Had to cut old one in half as clutch was rusted on.
Replaced bearings all new in crankcase.
Removed governor
Replaced Head with new small port milled head 0.050, single HD springs 35lb, 31mm and 36 mm cyls. <--from NR racing
Chromoly pushrods
Billet Crank cover plate

Thanks for your help.
I will elaborate on frame and chassis upgrades later. Have some upgrades already but finish engine first.

 

[JTSpeedDemon]

Sounds like you have a pretty good grasp of this stuff for a rookie!

 

[madprofessor]

Rod and piston: My experience is mostly with Predator 212's fresh out of the box at 6.5 hp., but the current one's hotrodded up to 15+ hp., so not a total luddite about it. My current hemi version comes with a flattop piston already, and lots of hotrodders prefer the flattop for high performance applications. Your absolute first mod though should be a billet rod, preferably one with a scoop milled into and bearing oil passage drilled through the "splash" arm, with rod bearings included. I use an ARC 3.328" billet rod that's .020" longer than stock, in conjunction with a thinner .012" stainless steel head gasket, to get a massive compression increase for no effort (would always replace rod, stock or not).
Oil level sensor: Removed on mine because my performance parts guy says it can cause motor to start cutting out at high rpm's, and if unused for that reason, might as well make room for some extra oil by taking it out. However, I never advise people to do it because if they start blowing oil from a sudden leak somewhere and don't know it, the lunched motor needs to be their problem and not mine. Note that the high rpm's problem would only come into play if governor is deleted.
Ratio rockers: Don't use them myself since my heads stay stock, the milling and oversized valves being too little reward for the cost. Stock 1:1 rockers are fine with stock valves, retainers, and pushrods. Roller rockers don't add anything in this configuration, and ratio rockers are just a change my performance guy says to stay away from without head work and a complete stainless valves and retainers and 22# springs set.
Electric start: If you can afford it, do it. Just remember that you have to have a charging system, and a battery mounted somewhere.
Ignition: Not familiar with small engine digital stuff. I do use a high performance ignition coil with 8mm silicone plug wire, but not for hotter spark. That's handled by the rare earth magnets in my billet flywheel (28 degrees timing advance, plus 7.2 degrees advance key). The high-perf coil has the resistors disabled to prevent timing retard at high rpm's.
Chromoly pushrods: Be absolutely certain they're exactly the same length as your stock rods. Remember that if you do the ratio rockers change that a different length will be needed for them.
Carb jetting: No idea what's good for that engine of yours.
Billet cover plate: Nice. Did you shim the crank play if needed? Now get yourself a complete high-perf stud kit for it and the head and etc., OEM bolts like to strip and/or vibrate loose.

 

[ScottH]

After reading other posts, I decided to post pics as I do my build. Here’s what it looked like when I got it.

 

[ScottH]

Haven't been on here in awhile but wanted to up date my build. It's up and running.
Seeking suggestions for better easier steering instead of linkage rods.

 

[madprofessor]

better easier steering instead of linkage rods.

Don't personally have the experience myself, but I've heard a few folks say that rack and pinion steering is tighter than pitman arm setup you have. Either type though, can be improved by using the stiffest type tierod connectors, like heim joints (tierod ends) instead of ball joints, and tierods of the largest diameter available. Links to aircraft heims and 3/8" tierods below.
How to improve by not having tierods at all? I have no idea. With your pitman setup, easier steering would be automatic if the tierods were connected to the pitman arm closer to the steering shaft. Unfortunately, that would also increase the minimum steering radius, couldn't turn as tightly.
Easier steering principle was applied to my current build by using different size sprockets in a chain drive for the steering. It helped a little with the main chain drive at front of kart, but I got something like power steering by also doing the same on a chain drive from the left-drive position to the center-drive position of the steering shaft. Pics below of setup before final cleanup and paint..............
AZ8276-13 - Solid Tie Rod 3/8-24 x 13" long | Go Kart & Mini Bike Parts | MFG Supply
3/8"-24 Rod End Assembly Female | Go Kart & Mini Bike Parts | MFG Supply

 

[ScottH]

Wow. That's a nice setup. Looks more advanced than my capabilities.
I will have to research into some of the options you have given me. I have looked at rack n pinion but you have given me more ideas to look into.
Thank you for the input.

 

[madprofessor]

FYI, Scott..........The whole chain-drive steering on a pitman setup thing wasn't the original plan, it was supposed to be a homemade rack and pinion setup. A couple of hilarious mistakes made me decide to cut most of the front off the kart, start all over. What did not change was wanting to use the huge Monroe MA775 airshocks (15" ground clearance, down to 2" if desired), so the big tower was there to stay.
Made it impossible to angle down to tierod level, so chain-drive had to be invented. The left-drive chain-drive was because the angle of the moveable shaft (center/left) was too extreme for the u-joints, hence a chain-drive there too. Just opportunistic to make it power steering with a big gear ratio.
Note: Functioning quick-release hubs on steering wheel, center dash, left dash. The red one you see in front of dash is only to allow the shaft to freely slide back and forth a little as the threaded 3/4" shaft screws in/out of a 2.25" long coupling.
Pic below of previous rack and pinion with skimpy tierods after upside down reversal (all now cut off), and pics of current dash (with 12vdc Cuervo Gold and O.J. dispensers). Note the dual gas/brake pedals so your feet are always evenly set.