IL 6 250 running rich. I haven’t been able to run it enough to adjust much but I did get the timing at 5 BTDC & seemed to be chugging over well. Exhaust not on yet but it seems to be blowing dark exhaust out. When I get the expansion plugs replaced I can dealing with the carburetor. Any advice on where to begin setting the 2 needles? They R both at 2 1/2 turns now. What is the function of each needle please?
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
That's WAY too much carburetor for a 250. Any chance of going back to the proper intake and carb setup? Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
if he wants to stay with that style Motorcraft carb .He should should be looking for one with the .98 venturi. Not common. Most common are 1.28. way to big. Joe
just retired and finally making headway on my project truck. 1940 GMC AC152.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I’m sorry, I thought I had answered. I know very little about carburetors. What makes a carburetor too big for a particular motor? What size carburetor should the 250 run? I’ve run this carb or one just like it for 17 years & never adjusted the needles but mostly because I couldn’t reach them with the hot motor running. They faced the valve cover.
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
The size of the venturis (the restrictions about halfway down the body of the carburetor) must match the size of the engine to allow the fuel and air to mix properly. A too large opening will let too much air in, and won't mix the right amount of fuel with it. That's known as running "lean". The driver opens the throttle further, which makes the problem worse because the engine gets even more air. Eventually, the "power" system of the carb opens up due to low intake vacuum, and the mixture gets VERY rich. If a carb with the proper size venturi is used, it requires less throttle opening to get the right mixture, and the power system only works while passing, hill climbing, trailer towing, etc.
Virtually all 250 engines were equipped with 1 barrel Rochester carburetors at the factory. A few Mercruiser marine 250s ran a small 2 barrel Rochester carb. Someone has installed an aftermarket 4 barrel intake and adapted a clone of a Ford carburetor to the manifold that's totally inappropriate for anything other than racing. All the adjusting screws do is allow the idle mixture to be adjusted for the smoothest operation. Once the engine gets up to 1500 RPM or so, the idle screws have no effect at all.
The Ebay link I posted is for a Ford 260 cubic inch V8, which has only slightly more cubic inches than a 250 Chevy. One with that calibration will probably be closer to the right performance without having to swap the intake manifold back to an original 1 barrel intake. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thanks Jerry, the previous intake was a 2 barrel Clifford intake with this carburetor & Headers. I thought it best to use a manifold to get rid of the headers. The only intake I could find was this 4 barrel & a reducer for a 2 barrel. So in your opinion I should look for a small Rochester and I can keep my intake?
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
Aftermarket manifolds in general on street engines don't impress me much. Anytime an adapter has to be used, it diminishes the efficiency of the manifold. Going from a smaller carburetor to a bigger manifold has less of a detrimental effect than the other way around, but neither approach is as good as an original equipment manifold and carburetor. The small bore Rochester 2 barrel is probably the best of a bunch of bad choices, if you insist on using the aftermarket intake. I'd start looking for a good condition rebuildable Rochester 2 BBL for a 1955-57 265 V8 as the best option for a 2 barrel on a 250 inline six, or one for a Mercruiser inline 250 equipped with the Rochester. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
BC59, Those carbs would be a very poor choice. They're the big venturi Rochester 2 BBL, with an outrageously high float level to compensate for the low air velocity through the big diameter venturi. That's the same basic carb that was used on 389 Pontiac 2 BBL engines. The small venturi carb would be a much better one to use. Jerry
Last edited by Peggy M; 02/09/20249:39 PM.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
