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Looking to replace a 750 Holley double pumper on my 400 small block in a 73
I'm looking for the best tbi for the money. Lots of reasons.....non ethanol gas is only sold at 1 gas station within 30 minutes. They close at 5 and are closed on weekends ! No credit cards....
Anyone with opinions please let me know. Btw this car is not original.
No problems just the occasional bogging at low speed. Cutting off after a full throttle run. Easy to flood out taking off. I just figured it was the gas.
Have you checked the float levels?
Have you checked with the engine off if the primary and secondary accelerator pumps are shooting gas out the squirters?
Is this car an automatic or manual?
What is the initial timing set for?
What is the total advance set for?
Seem to be a lot of things to check before investing in FI
I'll check all that. This carb baffles me . It will run great. Then the next day it won't run . Sometimes it cuts off and won't take gas then it runs great. ? I'm ready give up.
I'll check all that. This carb baffles me . It will run great. Then the next day it won't run . Sometimes it cuts off and won't take gas then it runs great. ? I'm ready give up.
First of all the so-called "double pumper" (mechanical secondary) carburetors are track racing carburetors and were never intended for street use. Street engines operate between from 550 rpm to 5500 rpm and have ever-changing needs for throttle openings. Track racing carburetors on the other hand operate around 4000 rpm and up under almost constant wide open throttle. A mechanical secondary carburetor can be used on a street engine but it provides way too much throttle opening in many instances whereas a vacuum or AVS will prevent too much throttle being applied. That's why none of the high performance engines ever came from the factory with a mechanical secondary carburetor.
When you give a mechanical secondary carburetor a full throttle at low rpm the air velocity thru the primary and secondaries drops to almost zero and you get a huge bog or flat spot until the rpm gets high enough to accept that big of a throttle opening. If you would simply put a correct Holley on it like a 600 cfm vacuum secondary your problems will likely end.
Have you checked the float levels?
Have you checked with the engine off if the primary and secondary accelerator pumps are shooting gas out the squirters?
Is this car an automatic or manual?
What is the initial timing set for?
What is the total advance set for?
Seem to be a lot of things to check before investing in FI
since you asked for opinions, ditch the dp carb, get a proper street carb, and someone who knows how to dial it in for your particular engine. all your symptoms point to wrong carb setup...
I disconnected the mechanical secondary and it runs good. It's too easy to flood with the double pumper setup. I'll get a 600 Holley with vacuum secondary and electric choke. $300 vs 2000$ for fuel injection sounds good to me.
Many 'carb' problems are actually ignition problems. Check your points and condensor or your HEI/electronic ignition box, if you've converted.
Don't forget to check/clean the electrical connections...especially the grounds to the electronic ignition systems.
P.S. If you have points and you've cleaned up your engine compartment, including painting the distributor hold-down bracket, that may be your problem. The "distributor housing/hold-down bolt/hold-down bracket to the engine block" is the ground path for the distributor's electrical system. Didn't know that? Well, it is. Make sure there is a 'clean metal' path through those touching parts so the ground circuit can be made WELL.
I'll check all that. This carb baffles me . It will run great. Then the next day it won't run . Sometimes it cuts off and won't take gas then it runs great. ? I'm ready give up.
In the late 70's early 80's? my dad rip a retired Navy aircraft tech and machinist tossed the carb on his 400 sb Avanti for the then new and high dollar Holley pro jection for all the same reasons lots of people do not like carbs, However, too many Holleys and yes DP'ers run really well on street cars, the problems you have are tuning and or physical issues with the carb and possibly other things like 7T1vette is talking.
Originally Posted by toobroketoretire
First of all the so-called "double pumper" (mechanical secondary) carburetors are track racing carburetors and were never intended for street use. Street engines operate between from 550 rpm to 5500 rpm and have ever-changing needs for throttle openings. Track racing carburetors on the other hand operate around 4000 rpm and up under almost constant wide open throttle. A mechanical secondary carburetor can be used on a street engine but it provides way too much throttle opening in many instances whereas a vacuum or AVS will prevent too much throttle being applied. That's why none of the high performance engines ever came from the factory with a mechanical secondary carburetor.
When you give a mechanical secondary carburetor a full throttle at low rpm the air velocity thru the primary and secondaries drops to almost zero and you get a huge bog or flat spot until the rpm gets high enough to accept that big of a throttle opening. If you would simply put a correct Holley on it like a 600 cfm vacuum secondary your problems will likely end.
And we are off..again..
The simple fact even if some people insist on ignoring it...remember people once thought the earth was flat is DP'ers / MS carbs do very well on more street cars than I can count, the cats tune them and it happens, saying they are never any good on a street car is nonsense and misinformation.
I will not get into pointless debates what any carb was made for and try to force some cat to believe as I do and run what I tell HIM to run.
My dads Avanti happened to have been runing a DP holley, my dad wasn't scared to dial it in and his 400 Avanti was a sleeper terror when I pushed him why the swap to FI he said, I like the faster starting and better mileage....
I absolutely will be going to FI. Not today, but the plan is in the works. I wanted to get my car on the road. Accomplished. Mine is a work in progress. 4 yrs to restore and get it on the road. The rest of my life to upgrade.
Yup, ran a D.P. Holley 750 back in the day in a Camaro, along with a very early nitrous system. Car ran like a bat out of hell. Darn things aint worth a hoot on the street. Riiiight.
Last edited by Sunstroked; 08-07-2015 at 01:12 AM.
In the late 70's early 80's? my dad rip a retired Navy aircraft tech and machinist tossed the carb on his 400 sb Avanti for the then new and high dollar Holley pro jection for all the same reasons lots of people do not like carbs, However, too many Holleys and yes DP'ers run really well on street cars, the problems you have are tuning and or physical issues with the carb and possibly other things like 7T1vette is talking.
And we are off..again..
The simple fact even if some people insist on ignoring it...remember people once thought the earth was flat is DP'ers / MS carbs do very well on more street cars than I can count, the cats tune them and it happens, saying they are never any good on a street car is nonsense and misinformation.
I will not get into pointless debates what any carb was made for and try to force some cat to believe as I do and run what I tell HIM to run.
My dads Avanti happened to have been runing a DP holley, my dad wasn't scared to dial it in and his 400 Avanti was a sleeper terror when I pushed him why the swap to FI he said, I like the faster starting and better mileage....
Toobroke is the worst "broken record syndrome" case I've ever seen. He has an opinion and he's apparently very proud of it. I suppose we should all be happy for him. Thankfully there are plenty of folks here at the forum who know better than to buy into his misguided little campaign. I look at the bright side- it's providing the rest of us with some great entertainment. I wonder if he thinks he's serving some higher purpose. Anyway, we may as well just continue to enjoy it for what it's worth.
08-04-2015, 09:15 AM
Bolt on fuel injection anyone?
..
I wonder if he thinks he's serving some higher purpose. 
Anyway, we may as well just continue to enjoy it for what it's worth. 