Hi, I'm Mike and the proud owner of a 1970 Chevy C10 short bed 4x4. It's got a 1991 L98 350, 700r4 and a NP 241c Transfer case. When I bought the truck it had been sitting for 4 years in a heated shop. I got the impression it was never driven. I drove it before I bought it and it ran well. About a week after I bought it, it started bogging down at steady speed 35, 45, 50 mph. It suddenly felt like it was starving for gas. It's got an Edelbrock 1406 performer carb on it so I got a rebuild kit and went through it. Problem gone! That lasted about 3 months of daily driving, then all of a sudden the bog is back. It takes off fine but at 30 or 40 mph it drops out and feels like its starved for gas. I tested the fuel pump and its fine, new gas filter, it's clear and unclogged. My fuel pressure is a steady 6-8 psi. I guess my question is, are there any known issues with the Edelbrock 1406? I'm getting ready to pull it and go through it again and wondering if I shouldn't just get a Holly. Thanks!
1991 L98 350 bogs down...
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What is the fuel pump?
Are you using a gauge?
The Carter/Edlebrock likes between 5 to 6 psi max, 8 psi will blow fuel past the inlet valve stopping it from closing and flooding the float bowls resulting in rich running.
This carb also likes to be cool, to that end there should be no intake exhaust heat and an insulating spacer placed between it and the intake of not less than a quarter inch thickness, but better at a half inch. This does not mean this carb needs an airgap intake but it really doesn't need an exhaust heated crossover that may be present with L98 heads as they retained that passage for the EGR system with the original TPI fuel injection of that engine, so if your intake has the exhaust hot spot under the plenum it is likely to be active, the intake gaskets with thin metal plugs do not resist burn through for very long. For a setup like yours I always close off the manifold passage with a fabricated quarter inch thick aluminum plug having an interference fit in the passage and flush with the machined intake mating surface so as to beef up the metal plug of the gasket set.
Having set for years assumes whatever fuel was in the tank and fuel system is either old or has evaporated, this leaves gums and varnishes behind that can get through flters and collect in carb passages. With the carb you have these can also collect in the vacuum piston passages and its bore affecting the piston's ability to move the metering rod which in turn affects mixture ratio. You also need to check the floats for leaking fuel into them, ethanol fuels attract water which corrodes little pin holes in these soldered brass floats so they don't sit well for long periods, as long as washed by fresh fuel this doesn't become a problem, but it is if you just shut the moror off and walk away for a few years.
The Carter now made by Edlebrock is touchier than a Holley but rewards the extra effort with better fuel consumption. It is more like a Q-Jet in function and complexity.
This not to rule out other causes like a distributor or coil going out, fouling spark plugs, or cam timing set loosing time, but ya' gotta start somewhere.
Bogie
Are you using a gauge?
The Carter/Edlebrock likes between 5 to 6 psi max, 8 psi will blow fuel past the inlet valve stopping it from closing and flooding the float bowls resulting in rich running.
This carb also likes to be cool, to that end there should be no intake exhaust heat and an insulating spacer placed between it and the intake of not less than a quarter inch thickness, but better at a half inch. This does not mean this carb needs an airgap intake but it really doesn't need an exhaust heated crossover that may be present with L98 heads as they retained that passage for the EGR system with the original TPI fuel injection of that engine, so if your intake has the exhaust hot spot under the plenum it is likely to be active, the intake gaskets with thin metal plugs do not resist burn through for very long. For a setup like yours I always close off the manifold passage with a fabricated quarter inch thick aluminum plug having an interference fit in the passage and flush with the machined intake mating surface so as to beef up the metal plug of the gasket set.
Having set for years assumes whatever fuel was in the tank and fuel system is either old or has evaporated, this leaves gums and varnishes behind that can get through flters and collect in carb passages. With the carb you have these can also collect in the vacuum piston passages and its bore affecting the piston's ability to move the metering rod which in turn affects mixture ratio. You also need to check the floats for leaking fuel into them, ethanol fuels attract water which corrodes little pin holes in these soldered brass floats so they don't sit well for long periods, as long as washed by fresh fuel this doesn't become a problem, but it is if you just shut the moror off and walk away for a few years.
The Carter now made by Edlebrock is touchier than a Holley but rewards the extra effort with better fuel consumption. It is more like a Q-Jet in function and complexity.
This not to rule out other causes like a distributor or coil going out, fouling spark plugs, or cam timing set loosing time, but ya' gotta start somewhere.
Bogie
Thanks Bogie for the quick reply! I'm running a stock AC Delco mech fuel pump and a fuel pressure gauge. My initial thought was the fuel pump.... that's the reason for the gauge but it runs a steady 6-8 psi. I rebuilt the carb, boiled it out , blew the passages clean, and it fired right up and ran great for the next 3 months. When it started bogging again as if a switch had been thrown. I thought it might be an ignition problem so not knowing the condition of the MSD ignition I replaced the entire distributor with a new Billet HEI unit and all new wires, new plugs and an Edelbrock Performer RPM manifold. It starts right up, idles great and with no load I can rev the engine to redline without a miss. But get on the road under load and the bog is still there. It doesn't always happen at the same RPM/speed and it will drop out/bog for a bit then ...it goes away and revs back up. Kind of "on/"off". When it's bogging I can still accelerate if I floor it and though it seems to have to power it will eventually get to 50-60MPH. In my teens and 20s (40+ years ago and I'm way outta practice) was an avid hot rodder and built my share of small block Chevy's and Fords albiet they were all 50's, 60's and some early 70's engines. I never ran into this weird bog problem running Holly, Rochester, Carter..etc carbs that's why I was asking if there are any known issues the the Edelbrock that might cause my problem. Thanks!
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A constant problem these days for carbs and mechanical fuel pumps is the fuels are formulatd for high pressure fuel injection.
This results in problems with vapor lock in long runs of fuel line from the tank to pump where the fuel by avtion of the pump st the terminums of the supply line reduces the fuel below its vapor pressure. It also results on fuel boiling within the carb. Plus, modern fuels have at least 10 percent alcohol in them which attacks older zinc coatings in fuel tanks and lines where new stuff is mostly alminum for hard lines. It also attacks older neoprene type rubber compounded gasket materials. Aclohol is hydroscopic which means it attracts water which then results in corrosion where ever anti-rust coatings are lost.
Now in particular the Edlbrock carb does not like fuel delivered at over 6 psi, not 8 it will have problems at that pressure that result in flooding the float bowls. With a mechanical pump a simple dead head pressure regulator set to 5.5 psi is sufficient to eliminate the overpressure float bowl problem.
A greater issue with modern fuel is the need to keep it pressurized so it is sbove its vapor point in the fuel lines. To that end the mechanical pump is elininated with a suitably sized electric pump at or in the fuel tank. Now the problem here is the electric pump delivers the same amount of fuel all the time whether the engine is at idle or WOT, so more pressure regulation is needed by either a pump with an internal bypass or the use of an external bypass off a bypassing regulator. This solves the vapor lock tendency of EFI fuel volatility.
The Edelbrock also likes to be cooler that it sees on most aluminum intakes, to that end a phenolic or wood spacer of about 1/2 inch helps elininate heat soak.
That's the modern world; we're over 30 years past carburetors, modern fuel is blended for sequential port or direct injection where all the mixing is done in the cylinder in the microscopic distance and time allocated there-in. No longer is it mixed at a carb, stored in a plenum, fed to the valve through a tube where there is turbulance, heat and time to effect mixing. New all that happens at the place and in the time of injection so the fuel needs to flash to vapor without all that old time mechanical mixing before it gets into the cylinder.
Bogie
This results in problems with vapor lock in long runs of fuel line from the tank to pump where the fuel by avtion of the pump st the terminums of the supply line reduces the fuel below its vapor pressure. It also results on fuel boiling within the carb. Plus, modern fuels have at least 10 percent alcohol in them which attacks older zinc coatings in fuel tanks and lines where new stuff is mostly alminum for hard lines. It also attacks older neoprene type rubber compounded gasket materials. Aclohol is hydroscopic which means it attracts water which then results in corrosion where ever anti-rust coatings are lost.
Now in particular the Edlbrock carb does not like fuel delivered at over 6 psi, not 8 it will have problems at that pressure that result in flooding the float bowls. With a mechanical pump a simple dead head pressure regulator set to 5.5 psi is sufficient to eliminate the overpressure float bowl problem.
A greater issue with modern fuel is the need to keep it pressurized so it is sbove its vapor point in the fuel lines. To that end the mechanical pump is elininated with a suitably sized electric pump at or in the fuel tank. Now the problem here is the electric pump delivers the same amount of fuel all the time whether the engine is at idle or WOT, so more pressure regulation is needed by either a pump with an internal bypass or the use of an external bypass off a bypassing regulator. This solves the vapor lock tendency of EFI fuel volatility.
The Edelbrock also likes to be cooler that it sees on most aluminum intakes, to that end a phenolic or wood spacer of about 1/2 inch helps elininate heat soak.
That's the modern world; we're over 30 years past carburetors, modern fuel is blended for sequential port or direct injection where all the mixing is done in the cylinder in the microscopic distance and time allocated there-in. No longer is it mixed at a carb, stored in a plenum, fed to the valve through a tube where there is turbulance, heat and time to effect mixing. New all that happens at the place and in the time of injection so the fuel needs to flash to vapor without all that old time mechanical mixing before it gets into the cylinder.
Bogie
I had a 71 Chevy truck that I had the same problem. I changed filter,fuel pump rebuild the carburetor same issue. It ended up being the pickup float sending unit. The sock on the sending had degraded that caused to get bogged down. Changed the sending unit. Problem solved.
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