school me on alky carbs for gx390 clone

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.


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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

interesting information . my combo started at 18hp stock and with 246 cam(stock rockers) on methanol and 36mm mikuni roundslide the computer says 31.3 hp so our numbers are close on your 32hp combo

out of curiousity, who makes this billet head and what cam are you running in the 50hp combo and what rpm range.

thanks.
 
Hi there. Would eny body know what jet sizes and pop off pressure to start with for a guide line. For sbn 38 motor is a gx 440 40mm in take 35 exhaust arc rod and flywheel 1.3 rocker and nr 307 camshaft.
 
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
Where would I purchase a 33 mm like your talking about Brian ? Thanks
 
Mikuni has not made the 33-34 pumper in quite a few years. The best bet for purchase might be on bobs or ebay Chuck.
 
I have a couple of recently purchased 33 mm Mikuni pumpers in stock.
 
Brian, are those 33 pumpers tilly's not that it matters just haven't seen new 34 mikunis in at least 10 years probably closer to 15yrs. Chuck.
 
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