Air /Fuel Jetting(Hot Air)

what happen's to a carburator's air/fuel mixture as the ambient air temperature rises say 20-30 degree's? Will you need to fatten the sizeor make smaller the jets in the Carb? In the primaries or secondaries? Thanks In Advance

with the air temp rising , the air density drops causing a drop in performance.The first thing I would do is to add a Phenolic spacer,1 or 2 " high ,that would keep your fuel much cooler passing trough a much cooler carburator.20 -30 degrees is not a lot to effect performance. I run my boat in hotter wheather occasionally without much loss in performance.The Dodge boys introduced the phenolic bodied Thermoquad carb back in the seventies with great sucsess [my 72 Challenger had it] and my 96 Mustang GT, Corvettes,Mercedeses and other makes turned to composite intakes for smoother runners and cooler fuel delivery to gain a few horses.The ambient temp is always lower in a boat than a car anyways, providing you have good ventilation under your enginebox [if you have one].

with the air temp rising , the air density drops causing a drop in performance.The first thing I would do is to add a Phenolic spacer,1 or 2 " high ,that would keep your fuel much cooler passing trough a much cooler carburator.20 -30 degrees is not a lot to effect performance. I run my boat in hotter wheather occasionally without much loss in performance.The Dodge boys introduced the phenolic bodied Thermoquad carb back in the seventies with great sucsess [my 72 Challenger had it] and my 96 Mustang GT, Corvettes,Mercedeses and other makes turned to composite intakes for smoother runners and cooler fuel delivery to gain a few horses.The ambient temp is always lower in a boat than a car anyways, providing you have good ventilation under your enginebox [if you have one].

Thanks Spectra, as far as the spacer goes that is no an option, my motor cover will not allow for it. So , do you think i will have to adjust the carb jetting at all to maintan same flow as present now?

You can try to go down in jet size,but you going to loose power regardless.Turbocharged engines have the same problem with high ambient temp loosing horsepower ,hence the introduction of intercoolers.Jaguar had a system they used the freon from the airconditioning to cool fuel,but it's out of question for boats.Maybe you could rig up a heat exhchanger system that filled with alcohol to keep your fuel cool.You probably heard of the coolcans for dragsters ,but it's a short term solution.Maybe somebody on this forum will have a good advice for you.

You can try to go down in jet size,but you going to loose power regardless.Turbocharged engines have the same problem with high ambient temp loosing horsepower ,hence the introduction of intercoolers.Jaguar had a system they used the freon from the airconditioning to cool fuel,but it's out of question for boats.Maybe you could rig up a heat exhchanger system that filled with alcohol to keep your fuel cool.You probably heard of the coolcans for dragsters ,but it's a short term solution.Maybe somebody on this forum will have a good advice for you.

Gerrit,
Per the "Holley Carburetors & Manifolds" book (HP 6-76) page 114, I quote: "The density change reduces volumetric efficiency and power, even though main jet corrections of approximately one main jet size smaller for every 40 (degrees) F ambient temperature increase can be made to keep mixture ratio correct."

So , essentialy the hotter it gets the richer my motor will run? Guess its better than too lean. Thanks Guys