Carburetor experts only, please

RE: 1955 R162 with BD 264 Holley 1901FF Carburetor
Engine runs smooth as silk until placed under a load. If you feather the accelerator and use the gearing, you can manage to develop speed but if you simply push the accelerator down hard it loads up. Carb has been rebuilt twice and the local carb expert is unable to sort out a solution.
What say you?

My first thought is that your main jet is clogged. When you 'feather' the gas peddle all it is doing is allowing the higher air flow to suck more gas out of the carb.

Have you verified your accel pump works? You know, take the air cleaner off, and open the throttle, you should see a stream of gas squirting into the carb.

One other idea, sounds less likely, but... have you verified that your distributor is advancing as it should? A distributor that will not advance will kill the power and might seem like a gas starving issue.

Truck running at idle, you should be able to push down on the accelerator at a reasonable speed (remember this is 50 yr old technology) and the motor should speed up. You should not have to feather it. 1) verify accel pump is working 2) check your timing 3) verify timing advances as motor speeds up 4) clean the carb yet again, verifying the main jet has a clear path

google Holley 1904 and you should be able to find lots of info. The web link below has a pretty good picture of whats going on.

http://www.tocmp.com/manuals/Carbs/Holl ... _53B6.html

good luck. Keep in mind, what appears to be a carb issue is not always the case. I had a bad coil that would cut out after it got hot. I kept thinking I had a carb issue as it was really hard to start after it died, seemed like it was not getting gas. The coil was ~ 5 yrs old with low hours on it (maybe 20 hrs run time). I kept focusing on the carb. I eventually checked the spark and was able to sort out the issue. Truck has run great ever since.

Although is seems you are pretty sure its a carb issue I would consider ruling out other issues. Spark? How do the plugs look? Good blue, at least decent blue spark at the plugs? Timing? Distributor advance? Fuel supply good? Filter clear, pump working good. Todays gas blends really wreck havoc on the old fuel pump diaphram.

Let us know what you figure out.

The Holley 1901FF is a two-barrel carburetor.

So the 1904 information won't apply.

Assuming the person who has been inside the carb is at least semi competent, I would say check the spark advance curves. Make sure the vacuum advance is working and is connected to the correct supply. There are three types of vacuum ports, Manifold (high at idle and drops under load) Ported ( which will be low/no at closed throttle and rises to manifold as the the throttle is opened) and Venturi Vacuum which is low to no at idle and increases with air flow thru the carb. Also check the mechanical advance curve. If the ign can't advance it will cause what you say
Define "Loads up" Back fire? runs rich? bogs down?
Is the carb the correct "list" for the application?
Does the heat riser function? is it stuck in hot or cold position
Diagnosing "drivability" problems is hard enough when you have the vehicle in front of you, almost impossible over the internet.

56-s-fan
what i know so far: main jet clear, accell pump works, distributer advance works, timing ok, point dwell ok, spark plugs 1 & 2 a little sooty but no sign of fouling 3 thru 6 as they should be, fuel supply: i use non-eth premium, with new filter

corn binder 89
correct carb, heat riser non-functioning

would either of you know what the main jet should be? currently a 97

thank you for your comments, greatly appreciated

Premium is a waste of money and can be counter productive on a low compression engine.
" Timing OK " doesn't cut it, check you advance curve with an advance timing light. I had one engine the dealer kept telling me it needed a new carb when it was the distributor shaft bushings, when it tried to advance you lost all dwell
Carb heat riser is there for a reason, get it working or you'll be back with more run ability issues.
You need to know that static, mechanical and vacuum advance are all working properly and that the dwell doesn't go crazy when one or the other advances start to move things.
Look for vacuum leaks between manifold and head.
Off idle bog (which is what your description sounds like) is most often not enough advance as the engine translons from the idle circuit to main metering and a corresponding leaner mixture.

I'm with Cornbinder89 here. As legendary Smokey Yunick is alleged to have said, 99% of carburetor problems are ignition related.

Centrifugal advance weights in the distributor can hang. Vacuum advance systems are notorious for vacuum leaks before the advance unit and for bad diaphragms in the advance unit.

It has been awhile since I was into one of the 1901FF carbs, however:

I would start with a compression test, because you do not have uniform plug conditions.

Assuming the compression test is good, then as others have said, my guess would be ignition. Although there are some vents in unusual places in that carburetor that need to be clean (assuming your local guy checked and cleaned all of the vents).

The factory main jet was 0.053 (stamped number 53)

NEVER believe a stamping number on a jet. Enthusiasts have been drilling them oversize at least since the 1930's (plus, sometimes they are difficult to read). Use an orifice drill set to measure the orifice.

And, I do not know if this is an issue on the I.H.C. 1901FF, but the Ford versions of the 1901FF REQUIRE the original air cleaner anchor stud and large metal washer to be in place for the carburetor to work properly. The I.H.C. anchor stud and metal washer look exactly like the Fords, I did not check part numbers. If these items are not in place, a pair of bleeds are not properly sealed.

It is a good carb, albeit one that needs occasional attention. Check your owners manual.

And I am in complete agreement with Cornbinder on the premium fuel. Not only does it cost more, it may actually run WORSE on older engines that have insufficient static timing and compression to burn all of the fuel.

Jon.

FYI
combiner 89: heat riser does function, static, mech, and vac advance working as they should and no vac leaks
buzzman 72: to my knowledge, Smokey did not race any IH vehicles
carbking: compression test within specs, jets to spec, orig air cleaner washer and stud in place, completed a timing by vacuum with little change

thank you again for positive feedback

one last question being, what modern carburetor would you suggest?

Edit, I was thinking it was the 3 bolt 2bbl but see it is the 4 bolt.

Just because things move doesn't mean that it is correct. It is why Buzz and I say check the curve. Spec's for the mechanical and vacuum advance are in the service manual for that truck.
There are several things that can cause an off idle bog, most common is ign related, but a low wet float level will delay the transition from idle to main metering system. There are other tuning things that can be done to effect when the transition takes place but these require someone who is very comfortable working on and dialing in carbs, which from your posts, doesn't sound like the carb guy you have.
Accelerator pump will also cause a off idle bog but that should be self evident when looking down the throat.

Your best bet is to stay with what it came with. Find someone local that is good with carbs to set it up, check the curves and check for vacuum leaks.