jet size 460cc build

D

dbdracing

New member
Building a 460cc engine zero deck height, 100 thousandths milled head , 310 lift cam going to be turning 6000-6500 RPM with gx390 bored carb. What would be a good starting point for jet size low and high side.

Thanks
 
About the best your gonna get out of a 390 carb is maybe a 24mm bore, give or take. On a 460 your going to be way under carbed IMO. But if that's what you have to run, I would start with a .042 main and a .024 low. In Honda speak, about a 105. That's gas of course. I only ever use an adjustable needle type jet the times I run alky so I don't know the size. I prefer the adjustable jet on gas too if the rules allow. If any carb is legal, strongly consider a 34, 36, 38mm Mikuni or Clements or Lectron. That will really wake that 460 up. Good luck
 
Thanks for the info, if I go with the Mikuni do you like round or flat slide. Are they easy to adjust on all I have ever worked with is clone carbs.
 
dbdracing said:
Thanks for the info, if I go with the Mikuni do you like round or flat slide. Are they easy to adjust on all I have ever worked with is clone carbs.
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I have no strong preference either way. I have seen about every type run extremely strong and about all types have issues. I have 3 SBNs and never ran one yet. Two 38s and a 40. I have a few rounds and flats. Some are cheap and others are $300 plus. Some just never run right. My suggestion is to buy from a reputable carb guy. Specify clearly what fuel you plan to run and get extremely clear adjustment advice. Find out if jets are readily available and/or if adjustable jets are available. In the long run it will be well worth the price unless you yourself are a carb guy
 
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