2X4 carbs too hot???

[don whitehead]

Hi Folks,
Finally got my carbs to run, floats set, etc. Car runs great for 30 mins. Then carbs seem to get hot, fuel percolates. (90 degree day) When I take off the air cleaner, lot of fuel vapor steams up. Car running at 180 degrees verified with IR. Still runs ok on the road, but starts to stumble when I roll up to a stop lite afte 30-40 mins. Stalls. Re-starts, and runs still stumbling at idle. Especially after I stop the car for 10 mins(go into store etc. ) and then return. carbs absorb heat I guess. Its a brand new engine, block, carbs, etc. Aluminum manifold 283 270 hp. New fuel pump, water pump, alum rad. etc. Everything new except rods and oil pan.
I was told that I should eliminate the heat riser with the 2in spacer and install blocking plates to keep exhaust from flowing thru manifold cross over. Heat riser not stuck. Ideas, thoughts, suggestions would be appreciated. I never drive it in winter,,,,,sounds reasonable? Especially with todays fuel?
Don

[Clem Z.]

Re: 2X4 carbs too hot???

block the heat riser crossover passage in the intake manifold with .005 stainless steel shim stock. use stainless steel as any thing will burn thru. just drain down the water in the rad,loosen all the manifold bolts and slip the shim stock between the intake manifold and head. i have done this in my working days to dozens of cars with aluminum intakes not just corvettes.

[Clem Z.]

Re: 2X4 carbs too hot???

block the heat riser crossover passage in the intake manifold with .005 stainless steel shim stock. use stainless steel as any thing will burn thru. just drain down the water in the rad,loosen all the manifold bolts and slip the shim stock between the intake manifold and head. i have done this in my working days to dozens of cars with aluminum intakes not just corvettes.

[Duke W.]

Re: 2X4 carbs too hot???

Try wiring the heat riser open (counterweight pointed down) and see how it works. Blocking the heat riser open or replacing it with the FI spacer is probably a good idea, but I wouldn't advise blocking the passages. I tried this with my 327/340 and once the engine came off the choke it would stumble on starting from a dead stop until the engine had been running for at least a half hour.

Duke

[Duke W.]

Re: 2X4 carbs too hot???

Try wiring the heat riser open (counterweight pointed down) and see how it works. Blocking the heat riser open or replacing it with the FI spacer is probably a good idea, but I wouldn't advise blocking the passages. I tried this with my 327/340 and once the engine came off the choke it would stumble on starting from a dead stop until the engine had been running for at least a half hour.

Duke

[Clem Z.]

Re: 2X4 carbs too hot???

duke,i have done dozens of cars and only in cold weather,below 30 degrees was there any problen with hesitation till warm up. this can be cured by just riching up the pump stroke.

[Clem Z.]

Re: 2X4 carbs too hot???

duke,i have done dozens of cars and only in cold weather,below 30 degrees was there any problen with hesitation till warm up. this can be cured by just riching up the pump stroke.

[Jack layton #896]

Re: 2X4 carbs too hot???

Installing shims and opening the exhaust heat riser will help but only a small amount. The negative characteristics you describe are almost inherent to the 2x4 system. Todays gasoline probably compounds the problem. Todays fuel tends to vaporize at a lower temperature, but in reality those WCFB's sitting on the aluminum intake simply absorb heat and transfer it directly to the fuel. Also, WCFB's do not respond well to hard braking. They "flood"! In the 1950's a flooded carb was a common occurence. Now you just put 2 four barrel WCFB's on your motor. Call that
"double flood"! BTW they will also flood when going around a sharp corner ! Changing gasoline fouled plugs was normal Sat. morning maintenance - like washing and checking the oil. Now you know why you can't find spark plug shielding for 2x4 C1's. Nobody wanted to continually mess with those things considering how often plugs needed changing. Even the regular 1x4's would "lead foul" a set of plugs in several months.
Chevrolet's response to all this mayhem? 1. Fuel Injection was the long term goal beginning in 1957. 2. Short term intermediate solutions are called - AFB which was in fact a significant step toward reducing all this flooding business. Then the use of an insulating block between the intake
and the carb. 1965 saw the Holley carb and center pivot floats on the top performers. 3. Elimination of the manifold cross over heat passages. 4. TPI and on to todays present fuel injection systems.
So here you are rebuilding a 2x4 WCFB from the 1950's and experencing some driveability problems. The main difficulty is that your expectation level for driveability is set with todays standard as the measure for your 1950's Corvette. Therefore, understand that all these modification will make minor improvements but the whole thing will never approach 1960's standard let alone 2000's. Another suggestion might be to raise the float levels to help with the flooding problem. You might also experiment with jets and rods to lean this thing out. I would research this info through some carb rebuilders. Tuning these 2x4 WCFB's is going to be a real learning experience. Makes you appreciate those early Sebring drivers who could keep them running without flooding as they turned left, right and braked hard. Had to keep the R's up to keep the plugs clean while you down shifted into 1st in a non-synchro 3 spd, twisted the non-power steering LARGE steering wheel, stay off the brakes which were only good
for a couple of uses per lap. You have heard of jet aircraft which would "Flame out"? 2x4 WCFB's will do you the same harm - especially in a panic braking scenario.
Enjoy your learning!

[Jack layton #896]

Re: 2X4 carbs too hot???

Installing shims and opening the exhaust heat riser will help but only a small amount. The negative characteristics you describe are almost inherent to the 2x4 system. Todays gasoline probably compounds the problem. Todays fuel tends to vaporize at a lower temperature, but in reality those WCFB's sitting on the aluminum intake simply absorb heat and transfer it directly to the fuel. Also, WCFB's do not respond well to hard braking. They "flood"! In the 1950's a flooded carb was a common occurence. Now you just put 2 four barrel WCFB's on your motor. Call that
"double flood"! BTW they will also flood when going around a sharp corner ! Changing gasoline fouled plugs was normal Sat. morning maintenance - like washing and checking the oil. Now you know why you can't find spark plug shielding for 2x4 C1's. Nobody wanted to continually mess with those things considering how often plugs needed changing. Even the regular 1x4's would "lead foul" a set of plugs in several months.
Chevrolet's response to all this mayhem? 1. Fuel Injection was the long term goal beginning in 1957. 2. Short term intermediate solutions are called - AFB which was in fact a significant step toward reducing all this flooding business. Then the use of an insulating block between the intake
and the carb. 1965 saw the Holley carb and center pivot floats on the top performers. 3. Elimination of the manifold cross over heat passages. 4. TPI and on to todays present fuel injection systems.
So here you are rebuilding a 2x4 WCFB from the 1950's and experencing some driveability problems. The main difficulty is that your expectation level for driveability is set with todays standard as the measure for your 1950's Corvette. Therefore, understand that all these modification will make minor improvements but the whole thing will never approach 1960's standard let alone 2000's. Another suggestion might be to raise the float levels to help with the flooding problem. You might also experiment with jets and rods to lean this thing out. I would research this info through some carb rebuilders. Tuning these 2x4 WCFB's is going to be a real learning experience. Makes you appreciate those early Sebring drivers who could keep them running without flooding as they turned left, right and braked hard. Had to keep the R's up to keep the plugs clean while you down shifted into 1st in a non-synchro 3 spd, twisted the non-power steering LARGE steering wheel, stay off the brakes which were only good
for a couple of uses per lap. You have heard of jet aircraft which would "Flame out"? 2x4 WCFB's will do you the same harm - especially in a panic braking scenario.
Enjoy your learning!

[Tom Wander]

Re: 2X4 carbs too hot???

I had a near new '59 2x4 in 1960. I never had any trouble with the carbs, or leaks or any of the other "urban myths" that are now so common. I drove it for two years in Minnesota summers and winters. Ignore the myths and find you a good carb man.

Tom Wander

[Tom Wander]

Re: 2X4 carbs too hot???

I had a near new '59 2x4 in 1960. I never had any trouble with the carbs, or leaks or any of the other "urban myths" that are now so common. I drove it for two years in Minnesota summers and winters. Ignore the myths and find you a good carb man.

Tom Wander

[Clem Z.]

Re: 2X4 carbs too hot???

one of the flooding problems in left turns was caused by raw fuel being sucked down the vacuum passage that run from the choke pull piston off thru the main body and the fix is a piece of brass tubing between the main body and the top cover of the carb to prevent the leak thru the gasket seal.

[Clem Z.]

Re: 2X4 carbs too hot???

one of the flooding problems in left turns was caused by raw fuel being sucked down the vacuum passage that run from the choke pull piston off thru the main body and the fix is a piece of brass tubing between the main body and the top cover of the carb to prevent the leak thru the gasket seal.

[Duke W.]

Disagree on the vapor pressure issue.

Today's gasolines have LOWER vapor pressure. Maximum vapor pressures are set by Federal and CA standards, and low vapor pressures help reduce evaporative emissions. Also, today's fuel injected cars will start on higher vapor pressure fuels because of the fine atomization produced by the injectors.

Duke

[Duke W.]

Disagree on the vapor pressure issue.

Today's gasolines have LOWER vapor pressure. Maximum vapor pressures are set by Federal and CA standards, and low vapor pressures help reduce evaporative emissions. Also, today's fuel injected cars will start on higher vapor pressure fuels because of the fine atomization produced by the injectors.

Duke