I got this carb for my l69 and im wondering if its gonna dump too much fuel. I got a pretty radical cam edelbrock dual plane intake and am getting a 1inch spacer. Im scared of gas washing the motor and hurting the bearings. Thanks for any help.

 

wayyyyy to big... a 600 is more than enough for a 305.

on the othe rhand, it will prolly dirve fine, u'll be putting in smaller jets to make it right, but driveability may suffer a bit, and id be willing to bet u experiance a lot bogging issues.

 

i'm running a 750 holley on my 305. seems ok to me, it's all just tuning issues.

 

I had zero problems running my current 750 Speed Demon on my old 305. It ran better with that on instead of the Holley S/A 670.

 

Some old rumors never want to die.
The size of the carb has nothing to do with dumping more fuel into an engine.

 

Id say, i always figured it to be more of an issue of bogging out due to over-feeding.

 

Maybe overfeeding isn't too good a word choice for it.
Without the demand from the engine, opening too much carb kills the velocity or the movement of air/fuel.
With a vacuum operated secondary carb, you can go bigger since you can tune the opening of the secondary to limit the total amount. With a mechanical secondary, you got what you got good or bad.
Where they can get rich is when you need a really big accellerator pump shot to try and offset the momentary big gulp of air from popping the throttle open on a big carb.

 

Isn't the Road Demon Jr. only 525cfm? I've got the regular ol' Road Demon on my 305, and it's 625cfm. Runs pretty good. Alot better than the 650cfm double pumper on there before.

 

So, let me get this strait, if the size of the carb has nothing to do with dumping fuel into the engine, that means that I can take the 1000cfm dominator in the garage and bolt it to my 283? Should run fine, huh? Size has a little to do with it. I agree though, CHP just did an article where they took a 440hp crate engine and put something like 6 different carbs on it, everything from a 390cfm to 1000cfm. The 390 lost around 40 horses i think and the 1000 cfm made like 3hp under the rating. I think that it ran best with an 850 though.

 

A small engine will run with a large carb, just as a large engine will run with a small carb.

It's just not going to run the "BEST" depending on what you're looking for.

 

I agree entirely. Too many people think that bigger carb=more HP. Also, bigger carb can have some detrimental effects on an engine.

 

RD Jr's come in 525, 625, & 725 cfm models.

You should pick the carb so that it has the minimum flow necessary to support the displacement and max RPMs of the engine. Going larger does have negative consequences. A carb basically draws fuel into the air stream via a pressure drop produced by the air stream flow in the venturi. A larger carb than necessary will reduce the velocity of the flow, and therefore reduce the pressure drop in the venturi. Throttle response will be reduced, and larger jetting will be required to make up for the reduction in fuel draw. It also means the fuel will not be as well vaporized within the air stream, requiring even more jetting to get enough fuel mixed in the air for proper combustion. Taken to extreme, you can wash down cylinders, but mostly you'll carbon up the chamber & exhaust.

Bottom line: Use the smallest carb that properly feeds your maximum engine demand.

FWIW, I can't imagine a RD Jr being the proper carb to use with a radically cam'd anything. But then, I can't imagine a RD Jr being the proper carb to use with anything, period, but that's a different story.

 

Woah, that's bizzare. Why would you want to get a Jr model the same size as the regular Road Demon? Just because you like the little float bowls?

 

Littler price tag.

 

Littler price tag, but then again the carbs are setup to work around a certain range of mods. Getting the wrong carb because the price is good kinda cancels out some of the mod investment.

 

Got it on and running. Its running strong as hell, Gotta fix the timing a little and still do some tuning but the engine is sick. The tires wanna break free real bad, even easing the clutch out. I think with the spacer and the jetting it should be fine. Thanks for the help though guys.