school me on alky carbs for gx390 clone

71 chevy

New member
im building a 460cc gx390 clone for methanol (alky , alcohol) and i dont know where to start on carbs.

what does one look for in an open carb? what size would work good?

ive heard about the hl380 but ive also heard of guys taking carbs off a motorcycle.

im just trying to get educated on carbs and dont see a lot of information out there.
 
im building a 460cc gx390 clone for methanol (alky , alcohol) and i dont know where to start on carbs.

what does one look for in an open carb? what size would work good?

ive heard about the hl380 but ive also heard of guys taking carbs off a motorcycle.

im just trying to get educated on carbs and dont see a lot of information out there.
If you are building an all out open,call Mike at V.K.E. for a 38 mm Mikuni super BN and get an intake from Parsons Racing Or build your own intake.Another good option is a Mikuni 33 pumper carb. with a Parsons intake or a home made one. If you are building a mild motor a bored 390 carb or a tillotson will work.
 
thanks guys.

bigblock honda, is there any advantage to a homemade intake other than, im assuming, cost?

thanks
 
thanks guys.

bigblock honda, is there any advantage to a homemade intake other than, im assuming, cost?
Nothing to do with cost, the ones that Parsons sell are straight off the port which makes for a bad angle and sticks the carb and filter out the side of the kart. I make mine curved to tuck the carb in behind the body. At $67.00 the Parsons intake is cheaper than the time it takes to build one even if you have the capability.
 
Thanks guys. If you have any pics of your fabricated intakes I would be interested. I've always also wondered of the typical location above the tire isn't getting some amount of heat from the tire and costing some power.
 
If you are building an all out open,call Mike at V.K.E. for a 38 mm Mikuni super BN and get an intake from Parsons Racing Or build your own intake.Another good option is a Mikuni 33 pumper carb. with a Parsons intake or a home made one. If you are building a mild motor a bored 390 carb or a tillotson will work.


hi. i have a question. do you have any experience with the tilly hl-380. will it support as much power as a mikuni super bn?
 
hi. i have a question. do you have any experience with the tilly hl-380. will it support as much power as a mikuni super bn?

I have never used a 380 and don't know how big the bore is but I doubt it is as big as a 38 sbn.Like I said before if you are going big bore, big stroke, big valve and big cam then you need a big carb.If you are staying closer to stock then a bored 390 carb, 28 mm mikuni, or a tillotson 355 or larger will work fine. There is also a 34 mm version of the sbn.The super BN is about the same type carb as a tillotson, but with removable jets and has its own fuel pump built in.
 
my goal is 40 hp because that will technically give me a little better power to weight ratio than the rotax karts.
 
hi guys i have a question- i decided to run the stock cam for now and keep it mild. i have two carbs- which would you recommend?

carb one - stock clone carb
carb two-mikuni 38mm on alky

i guess what i want to know is will the mikuni be too big for a 460 running the stock cam? i heard it fizzles out around 5700rpms
 
hi guys i have a question- i decided to run the stock cam for now and keep it mild. i have two carbs- which would you recommend?

carb one - stock clone carb
carb two-mikuni 38mm on alky

i guess what i want to know is will the mikuni be too big for a 460 running the stock cam? i heard it fizzles out around 5700rpms
 
hi guys i have a question- i decided to run the stock cam for now and keep it mild. i have two carbs- which would you recommend?

carb one - stock clone carb
carb two-mikuni 38mm on alky

i guess what i want to know is will the mikuni be too big for a 460 running the stock cam? i heard it fizzles out around 5700rpms[/QUO

Keep your carb size around the same size as the intake valve for kart racing, a larger can be used on drag race motors.
 
I really like the 33mm Pumper carbs from Mikuni -- Bore is slightly smaller than your current carb, but it'll throttle so much nicer with the accelerator pump.
I use it even with much bigger valves and cam and it'll still flow enough air to keep up. The same carb is offered in 42 and 45mm I think. The 45 is a monster and requires a billet head in my opinion. Realistically, your goal of 40 CHP isn't going to be attained until you go much bigger on valves and cam. Of course, everyone's dyno varies. On mine, a big valve ported stock head, .310 lift cam with 1.3:1 rockers and a 33mm carb is right at 32 CHP. Go slightly bigger on the cam and carb and you can realistically make 40 CHP. The billet head version with 45mm Mik. is right at 50 CHP.


-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cuts
www.CarlsonMotorsports.com

Celebrating 25 years of service to the karting industry

765-339-4407
bcarlson@CarlsonMotorsports.com
 
Back
Top