What size Venturi? It's stamped on the side of the fuel bowl driver side in a "clock", it will be something like 1.08 or 1.12. Post what it is.

You can make any of the Motorcraft carbs work OK, some better than others. Download the Ford carburetor manual and make sure that the setup is right every step of the way. The thing everybody seems to miss, is the fuel height in the bowl. The float height may need adjustment up or down after installation on the engine itself. If it's too high it will flood, if it's too low it will be starved for fuel.

What size jets are in it now? What # power valve? Trust me, you can make it work fine, just need to get it dialed in.

I believe a 1.21" Motorcraft is plenty of carburetor, but any carb needs to be setup right. For engine tuning a mechanic's vacuum gauge is real slick. Everything has to be just right before a carburetor will respond well to adjustment. By that I mean good, hot spark, correct ignition timing, smooth mechanical distributor advance + vacuum advance. Vacuum leaks will cause lots of problems.

The carburetor far too often gets blamed when something else is the problem. For a tune-up to remain satisfactory everything has to be checked and adjusted. Compression test. On these old trucks, the crankshaft damper weights tend to slip and bugger the timing marks. Is your 10° really 10°? That's why I like vacuum gauges. There's a million things that we can't see from here that only you can judge.

If a stock or stockish engine pulls 18" to 20" of idle vacuum at sea level everything mechanical is setup about right and in good condition. I doubt the carb Jets that are installed right now are too small, but it wouldn't hurt to check. They aren't included in rebuild kits, btw. Vacuum gauge is like a poor man's Sun machine, they show a lot of information if the user knows what to look for, and they will also measure fuel pump output pressure, something else that should be checked before carb tuning.

Setting the float height on the bench during a carb rebuild or whatever just gets the fuel height close, it's important to check the "wet float" or fuel height after installation on the engine and make sure this is within spec because the carburetor itself is calibrated for a fuel height accuracy within 1/32" at all times under all conditions, from idle to wide open throttle and everything in between. If it is not the correct specification, then dle mixture settings, jetting, and everything else will get skewed in order to try and compensate.

First thing though, verify that the fuel pump pressure output is not excessive, as this in turn will interfere with achieving the correct fuel height, this is a big problem with aftermarket fuel pumps sold today. It is also a fire hazard as eventually the needle and seat will be unable to prevent flooding. 5 psi is plenty. Your vacuum gauge also measures fuel pump pressure output. No need to start the engine, just crank the engine over for several seconds.

To check the fuel bowl height let the truck idle for a few minutes on level ground. Shut the motor off, and pull the air horn and measure the fuel height from the machined surface at the top of the bowl down to the surface of the fuel itself. Adjust the float height up or down as required to achieve a fuel height in the bowl that is equal to the dimension measured with a US quarter. This is 29/32" or near enough. The specific "wet float" height varies slightly by application but this should work very fine as the baseline for now. I like to remove the float entirely when bending the float tab. Don't have to do it this way, but the idea anyway is to avoid excessive downward pressure of the viton needle tip against the seat. For some reason some people got it in their head that the float must only be adjusted while the engine is idling. This is not the case!

If you're careful and keep a fire extinguisher nearby the engine can be idled slowly with carburetor air horn removed and check the fuel height in operation. Don't do this inside the garage, don't rev the engine. What you're looking for is that the fuel height maintains the correct level in the bowl. Be safe.




Wheeling with a Carb