The Stovebolt Site Forums The Shop Area Engine Shop 261 Updraft carburetor

I have a 871 Carter updraft carb on my 261 engine. I know the first series had the 2075 Carter, but those are like hens teeth. To get the most bang out of the engine, does anyone know if a larger jet could be found, would the increase be worth it? I appreciate any information, thanks.

A larger jet will not increase power. Do you mean a larger carburetor?

Yes, carb. Not jet.

You would need a bigger venturi, better airflow through the cylinder head and both manifolds, and a different grind on the camshaft. Putting one heavy duty link in a chain made of paperclips won't improve the strength of the chain. Updraft carbs in general don't lend themselves to high performance very well, and there's no room for any other style of fuel system on your truck, is there?
Jerry

A good machinest and a blank check could effectively transform an 871s into a 2075s (with the exception of the marking on the outside bowl cover).

Still probably less than the cost of a genuine 2075s, if you actually find one.

Jon.

What are the basic differences, Jon? I'm going to guess probably venturi, and maybe throttle plate diameter?
Jerry

I read the difference between the two is marginal. The engine pulls the truck up hills pretty well. I just thought there might be a way to get a little extra out if her.

Jerry - the venturii are the same; but the throttle body on the 2075s is larger than on the 871s; thus the transition into the intake manifold is smoother. Also, the metering calibrations are different, to allow for the better airflow of the larger throttle body. Again proving that, while venturi size is a major component in air flow, it is not the only component.

I didn't check all of the vents, restrictors, bleeds, etc.; but if I were still doing carbs, I think I could do the conversion in the machine shop in 14~16 hours. Machine throttle body, fabricate new throttle shaft, fabricate new throttle valve, resize main jet, power jet, and (I didn't check) maybe both idle tubes.

Just increasing the jet sizes without the throttle body change would probably do little, maybe nothing.

Jon.

That's been my experience as well- - - -to get any measurable increase in either power, torque, or RPM, it's necessary to flow more air. Back in my "claimer" racing days, the way engine cost was kept under control was to limit us to a Holley #7448 2-barrel carburetor- - - - flow rated at 350 CFM! It was pointless to get radical with cylinder heads, camshafts, intake and exhaust manifolds, etc. it the carb couldn't flow enough air to benefit from all that expensive go fast stuff. Of course, we got creative abut bending the rules. Flat washers between the carb and the intake manifold to suck air downstream of the venturi was one trick, but the tech inspectors learned to get suspicious of an engine that wouldn't idle. I had a lot more creative tricks up my sleeve that they had to work a lot harder to find. Like Smokey Yunick was fond of saying- - - - -"It ain't cheatin' if ya don't get caught!"

LOL!
Jerry