I have a 100 horsepower flathead with 2 one barrel carburetors that has been on the truck for 10 years. It smells rich at idle and lean at high end and runs perfect at a quarter throttle. It started to have issues, so I had both carburetors rebuilt three times, messed with the jets, adjusted the timing, and put a new coil on it. Do you think this an ignition problem or a fuel problem? Please help.
V8 Flathead Problem
- Thread starter wolfords
- Start date
rotorwrench
Well-known member
What distributor are you running? The stock 8BA distributor was a Holley Load-O-Matic and has to be connected to a carburetor that was designed to work the spark control. Most 8BA engines run a single Holley/8BA model 94 carb but it's a 2 venturi unit.
Ken/Alabama
Well-known member
Started to have issues. What are the symptoms ? What year flathead?
It's an 8BA flathead. The distributor is factory and is connected to the front carburetor (which are Holley AA94 two barrel - two of them) which have all been on it for the last ten years until it started having this issue. I've had the carburetors rebuilt, messed with the jets and the advance on the distributor, and put on a new blue streak coil.
The issue is that at three quarter throttle it acts like it's starving for fuel, and as I begin letting off the throttle to about quarter throttle it takes off like a bat out of hell and runs okay.
Thanks all.
The issue is that at three quarter throttle it acts like it's starving for fuel, and as I begin letting off the throttle to about quarter throttle it takes off like a bat out of hell and runs okay.
Thanks all.
Last edited:
rotorwrench
Well-known member
The stock distributor doesn't work well with multiple carbs so you might think about changing to an all centrifugal advance type or a modified later model GM distributor with centrifugal and vacuum spark control set up with proper advance curve for better mileage. This would improve the way the engine operates but it may not be your major problem. With Holley 94 carbs you can have either an over rich acceleration schedule due to power valve problems (leaks) or an overly lean schedule due to accelerator pump or other power valve issues (not functioning properly). The accelerator pump is easy to check for function but the power valves, not so much. They can blow out and cause a constant leak or they may be malfunctioning and not working at all. You'll need to know if you had valves in both carbs or just one and what size of valve or valves.
Progressive throttle linkage doesn't seem to work as well on dual carbs. It does work well on triple carbs though. We still don't know what type throttle linkage you have there so its a guessing game.
Progressive throttle linkage doesn't seem to work as well on dual carbs. It does work well on triple carbs though. We still don't know what type throttle linkage you have there so its a guessing game.
These carburetors were professionally rebuilt by Daytona Engineering in New Smyrna, FL. They sent it back with 51 jets with 7.5 power valves. This is an old school build but this set up has been on this truck for 10 years and worked perfectly until recently. My local mechanic is wanting to put smaller power valves in. The carburetor guy says that is not going to be the problem. I messed with it all summer and I really think it's in the distributor.
ford38v8
Well-known member
First thing, please do not create multiple threads on the same subject.
To your problem:
I'm not a multi-carb expert, but it does sound like your problem is related to your use of multiple carbs. Several things are different than with a single carb, and your having the carbs rebuilt may not have properly addressed these issues, as the rebuilder must consider how the carb is going to be used:
1 - Power valves are different, as the vacuum is less with dual carbs.
2 - Idle needles adjustments will differ also, some guys close off one carb's idle needles.
3 - Linkage is important, and there are different types for different needs.
4 - Main jets are different, smaller than with a single carb.
5 - With all the expected different parts installed, then comes the tuning. The tuning of one carb to its engine needs an experienced Mechanic, and tuning dual carbs needs that Mechanic, a Magician, an assortment of the different parts mentioned above, a refrigerator full of beer, and a full weekend.
EDIT: Whoa! it's an 8Ba! Stock distributor needs a single carb.
To your problem:
I'm not a multi-carb expert, but it does sound like your problem is related to your use of multiple carbs. Several things are different than with a single carb, and your having the carbs rebuilt may not have properly addressed these issues, as the rebuilder must consider how the carb is going to be used:
1 - Power valves are different, as the vacuum is less with dual carbs.
2 - Idle needles adjustments will differ also, some guys close off one carb's idle needles.
3 - Linkage is important, and there are different types for different needs.
4 - Main jets are different, smaller than with a single carb.
5 - With all the expected different parts installed, then comes the tuning. The tuning of one carb to its engine needs an experienced Mechanic, and tuning dual carbs needs that Mechanic, a Magician, an assortment of the different parts mentioned above, a refrigerator full of beer, and a full weekend.
EDIT: Whoa! it's an 8Ba! Stock distributor needs a single carb.
Dave Castle
Senior Member
The Op said it ran fine for 10 years, it is not a wrong part issue, it is something that has gone wrong recently !
deuce_roadster
Well-known member
What about the fuel pump and or fuel pressure regulator?
jhljr44@yahoo.com
Member
Condenser caused that same problem on my 36.
scicala
Well-known member
" My local mechanic is wanting to put smaller power valves in."
One other thing to note is that power valves in this type carb are not larger and smaller as far a fuel flow. They are just an on/off thing that come in different vacuum ranges as far as when they open. There are two orifices in the fuel channel under the valve that control how rich or lean it will be after the valve opens.
Since it ran good before, and the calibration Daytona used is right in the ball park, I would look for other issues, like fuel quality, or possibly ruptured power valve from a backfire as mentioned earlier.
Sal
One other thing to note is that power valves in this type carb are not larger and smaller as far a fuel flow. They are just an on/off thing that come in different vacuum ranges as far as when they open. There are two orifices in the fuel channel under the valve that control how rich or lean it will be after the valve opens.
Since it ran good before, and the calibration Daytona used is right in the ball park, I would look for other issues, like fuel quality, or possibly ruptured power valve from a backfire as mentioned earlier.
Sal