I have just purchased a 70 454-390 hp coupe. The car has the 435hp heads, and 3-2 carb setup. The problem is the engine runs rough, and seems to load up, even at idle. The compression checks out okay, and I have installed new #44 plugs, but still have the problem. The rear carb leaks gas. What should the main jet sizes be? Could there be a problem with the metering plates in the front and rear carbs? Even idling with the throttle closed, the engine almost chokes off and dies. Any ideas would be greatly appreciated. Mark
-
-
Re: 3-2 carb trouble
Mark------
My advice: SELL the 435 HP heads and the 3X2 set-up. Obtain a set of original heads, GM casting #3964290, or equivalent heads of other casting numbers. Obtain an original 3955287 intake manifold (these are not all that rare) or, if you wish, use one of the 68-69 L-36 manifolds. Obtain a new Edelbrock Q-Jet clone carburetor and install it on this manifold.
When you're all done after selling the existing parts and purchasing the new, you'll likley have money left over. Most important, you'll have a FAR better running, more reliable, more trouble-free, more driveable, more enjoyable engine that will produce more power and torque OF THE KIND YOU CAN ACTUALLY USE.
As a "side benefit" you'll have a stock configuration or, if you go all the way, an exactly correct engine configuration which will make your car more valuable. What more could you ask for?In Appreciation of John Hinckley -
Re: 3-2 carb trouble
Mark------
My advice: SELL the 435 HP heads and the 3X2 set-up. Obtain a set of original heads, GM casting #3964290, or equivalent heads of other casting numbers. Obtain an original 3955287 intake manifold (these are not all that rare) or, if you wish, use one of the 68-69 L-36 manifolds. Obtain a new Edelbrock Q-Jet clone carburetor and install it on this manifold.
When you're all done after selling the existing parts and purchasing the new, you'll likley have money left over. Most important, you'll have a FAR better running, more reliable, more trouble-free, more driveable, more enjoyable engine that will produce more power and torque OF THE KIND YOU CAN ACTUALLY USE.
As a "side benefit" you'll have a stock configuration or, if you go all the way, an exactly correct engine configuration which will make your car more valuable. What more could you ask for?In Appreciation of John HinckleyComment
-
Re: 3-2 carb trouble
Good advice on going to the four barrel. If you stay with the 3X2, you need to get the leaks fixed before anything else. These old Holleys are bad for the main housing to warp at the screw holes where the metering plates attach. I would disassemble and check them for flatness. Correct as needed, rebuild, install, adjust linkage. I think you'll like it when it works correctly.Comment
-
Re: 3-2 carb trouble
Good advice on going to the four barrel. If you stay with the 3X2, you need to get the leaks fixed before anything else. These old Holleys are bad for the main housing to warp at the screw holes where the metering plates attach. I would disassemble and check them for flatness. Correct as needed, rebuild, install, adjust linkage. I think you'll like it when it works correctly.Comment
-
Re: 3-2 carb trouble
Mark,
Never fear, the 3X2 will run great "when" you fix it properly. Chunk the carbs and go for a new set of Holleys in the box. They are being reproduced by Holley and should give you years of use if cared for properly. Cared for properly is driving them often and keeping fuel in the bowls. If they dry out you are in for a rebuild.
I just changed the carbs on my 67 400HP and still had the receipt for the ones I took off. Dated 1980.
Don't destroy the originality of your Corvette. The 3X2 setup will be a joy when replaced and maintained.
Regards,
JRComment
-
Re: 3-2 carb trouble
Mark,
Never fear, the 3X2 will run great "when" you fix it properly. Chunk the carbs and go for a new set of Holleys in the box. They are being reproduced by Holley and should give you years of use if cared for properly. Cared for properly is driving them often and keeping fuel in the bowls. If they dry out you are in for a rebuild.
I just changed the carbs on my 67 400HP and still had the receipt for the ones I took off. Dated 1980.
Don't destroy the originality of your Corvette. The 3X2 setup will be a joy when replaced and maintained.
Regards,
JRComment
-
100% Agree With Joe Lucia!!! *NM*
Comment
-
100% Agree With Joe Lucia!!! *NM*
Comment
-
Re: 100% Agree With Joe Lucia!!!
Jack,
Thanks for the e-mail updating me on the 70 with no tripower. Guess I'm either stupid or can't read. You be the judge.
Regards,
JRComment
-
Re: 100% Agree With Joe Lucia!!!
Jack,
Thanks for the e-mail updating me on the 70 with no tripower. Guess I'm either stupid or can't read. You be the judge.
Regards,
JRComment
-
Re: 3-2 carb trouble
JR-----
The originality of the car in question is "destroyed" WITH the 3 X 2 set-up. This is a 1970 Corvette. No 1970 Corvette was ever produced with a 3 X 2 induction system. In order for the car to be original, the heads and induction system need to be removed and replaced with the proper 1970 LS-5 components or, at least, components configured like 1970 LS-5 components.In Appreciation of John HinckleyComment
-
Re: 3-2 carb trouble
JR-----
The originality of the car in question is "destroyed" WITH the 3 X 2 set-up. This is a 1970 Corvette. No 1970 Corvette was ever produced with a 3 X 2 induction system. In order for the car to be original, the heads and induction system need to be removed and replaced with the proper 1970 LS-5 components or, at least, components configured like 1970 LS-5 components.In Appreciation of John HinckleyComment
-
Re: 3-2 carb trouble
Joe,
Thank you for pointing out again that I did not read the post carefully enough before I jumped in and tried to answer the question. You and Jack make two that have been humble enough to point that out to me.
Regards,
JRComment
-
Re: 3-2 carb trouble
Joe,
Thank you for pointing out again that I did not read the post carefully enough before I jumped in and tried to answer the question. You and Jack make two that have been humble enough to point that out to me.
Regards,
JRComment
Comment