Gx390 build suggestions

D

Daniel gx390

New member
I have a Honda Gx390 I put in a golf cart and I want reliable power. I have already bought some parts and will list them below. I am wondering if anyone with more experience with theses engine had any suggestions? I would like to stay stock carb, run 91 octane pump gas, avoid machine work, and if possible keep the balance shaft. Any suggestions?

Parts list
6272 ARC Billet Rod (stock length)
6623-E ARC Billet Flywheel
Dyno Cams 275 Grind cam
55 lb value springs
Aftermarket UT1 ignition coil
Lightly ported stock 12200-ZF6-406 head
1 1/4 header
Performance air filter adapter with filter
(Not sure of jet size but lager than stock)
 
Last edited:
How many rpm are you looking to turn it? If 3500 - 5000 then a stock Honda is more than adequate for RELIABLE power. The torque these engines produce are at lower rpm. Above 6000 rpm then billet rod and flywheel is recommended. The 275 cam is mild, the 55lb springs seem unnecessarily heavy at lower rpm and will most likely rob power and wear out the cam lobes prematurely. The performance air filter is a good idea. Porting and the UT-1 coil are +/-. More performance modifications often equate to less reliability.

Brian Carlson, ARC and NR racing are good resources for the GX390.
 
I really appreciate the information. I have already messed up a stock rod and crank from turning it to 5500 rpm. That's why I bought a billet rod.
 
You've got a fairly good list of parts for your application. I think you'll be just fine with a few exceptions. With no machinework, that means no more compression - which will obviously make less power, but it will last considerably longer. While these engines like compression and rpm, the connecting rods do not. The biggest thing to make power will be the carburetor. Leaving it stock will limit the power you can make. You've already included a bigger cam and porting in your build, but the stock cam and port volume were plenty for the already asthmatic carburetor. All you managed to do was move the power band up and necessitate turning more rpm to make power. You may want to rethink the carb and look at a nice aftermarket slide carb (Mikuni would be my 1st choice for performance and simplicity.)


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
34 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Daniel gx390 said:
Thank you for the information. I will look into getting one. What size would you recommend a 32mm or 34mm?
Click to expand...
Personally, I like the 33TM (with acellerator pump) for tunability and especially in your application where the engine may be idling. You certainly don't need that big of carb, but it's something you can "grow into" if you wish.
 
Daniel gx390 said:
Okay. I will look into pricing but I will go that route. I appreciate the information thank you for all your suggestions.
Click to expand...
Keep us in mind as you're shopping. :)
We stock parts for the 390s and still build them for customers.


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
34 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
You must log in or register to reply here.
Back
Top