I know all combos are different, but I'm just looking to see what jets, power valves, and squirters others are using. It has the 50 cc pump in the rear (I had to clearance the carb mounting pad to get the carb to sit flat). Engine has about 10.5 to 1 compression with TA aluminum stage 1 heads. Cranks up and idles but wants to stumble a little when you give it the gas. I've never been good at tuning so any help is appreciated!
Front squirter of the Carb could be to small or timing could be off alittle, you have to see what the vacuum is at idle that will give you an idea what power valve to run, lets say if it reads at 8 inches at idle then you can run a 4.5 power valve. just to give you an idea good luck!! :TU::TU: I think Ronbz455 here on the board runs that combo on his car he can tell you what he use's.
carb number ? new ? correct rear metering block ( should be 4 corner idle ) ? initial "bog" then go ? bigger shooter probably . go - "bog" - go ? correct nozzle size but too small pump - but you already have the 50cc pumps front and rear you said . might be worthwhile blowing out the feed line from pump to shooter ? some "light acceleration hesitation" tips from my holley book - distributor/intake vac leaks including vac hoses etc . air bleeds clogged accelerator pump failure clogged idle transfer slots there were a few others but did not seem to pertain to your vehicle setup - hot air choke etc , basic tune stuff .
It's a 4781-5, used but looks like new, been sitting for a long time. It does have 4 corner idle screws. The squirters are #31. The front acc pump is small, the rear one is larger. Pulled the front bowl off, but couldn't get the metering block off. The front jets are #76. I did squirt cleaner through the front squirter passage, seemed to be OK. Someone had written "76" on the front metering block, and it looks like "80" on the rear, but I won't really know until I pull it off and look. The carb gasket seemed to be dry, so I changed that out, it may have been leaking air. That's about all I did today, but I did putt it around a little. I didn't hook up a vacuum gauge yet, but it's on the list of things to do.
ok - 4781-5 , regular dbl pump , manual choke carb . here's oem specs for it from holley info catalog : needle n seat - 6-504 primary jets - 80 secondary jets - 78 front power valve - 65 rear power valve - 65 primary shooter - 31 secondary shooter - 31 at least that'll give ya some basic info and maybe a "start point" . just thinkin - the jet markings on blocks sound off ? metal or black floats ? jet extensions ? float level should be "level" approx with bowl upside down . supper time !
I'm not sure of the history of this carb, but it and the intake may have been on a 455 that came apart (cam in 3 pieces!) a long time ago, and the carbs been sitting ever since. The underside of the intake has pushrod dimples on it. The jets may have been changed, or the metering blocks swapped by mistake. The float is white plastic and the float was set like you posted, level with the bowl upside down. Haven't looked in the rear yet to see the jet size or if there are jet extensions. I think I'll go do that now and post what I find.
Just realized the factory jets were 78 and 80, not 76 and 80, so they've been changed in the past. Pulled the rear bowl off and the rear jets are 80. Pried the rear metering block off to look at the power valve, and the gasket was glued on (most of it still is!) so that's going to be a mess. Didn't see any numbers on the power valve so I may figure out a way to test it and see what it opens at. That's it for now.
remove gaskets CAREFULLY . disrupt the metal surface as little as possible . if ya start getting anxious just walk away for a sec .
I think the plastic floats use a dif setting when assembling carb . but either way I would say it should be the same when ya do an external adjustment with the sight plugs off . i'll check info shortly . edit : yeah - primary side , 7/64" reg floats , 5/16" plastic . secondary side , 13/64" reg floats , 3/8" plastic . the plastic floats ride higher on the fuel so need to be set higher . if set the same as regular floats = less gas in bowls = could run lean .
I finally found what looks to be a "5" on the power valve. I made a doo-hicky so I can pull vacuum on it, and the valve starts to pull in at 5 inches and is fully seated at 11. I was thinking a number 5 would be fully seated at 5 inches and start to open at less vacuum, but what do I know? o No: Thanks for the float info, I'll check it when I get back out there.
they sure could mark those valves ALOT better . some have numbers on the wrench flats . on a 6.5 valve for instance there will be a 6 and a 5 on large inner surface . of course the stamping is crap usually and there are other numbers on there sometimes for whatever reason .
