Correct, the accel pump is checked w/ignition off. Good idea to have a big fire extinguisher on hand that you know works for this sort of gasoline-related work.
On my carb, when the accel pump fails, the cause is a split in its rubber diaphragm, and that does produce a small external gasoline leak, right at the front surface of the carb in my case, so it is pretty obvious. Since you aren’t seeing any gasoline leaks in the carb area, your accel pump could still be ok, but the internal passages that provide a path from the fuel bowl to the accel pump ports could be clogged. I’m thinking at this point you may have more than one problem. I’m predicting you (or somebody) is going to be inspecting the fuel level in the fuel bowl soon … lol …
This part of owning an old car is supposed to be part of the fun btw. How are you finding it?
I purchased this type of car just so i could work on it. No computers but it has been frustrating. I like doing the work but i dont like not getting results.
I’m not a mechanic. I have no training but I’m learning. I new carb is $450. If i could just feel confident i have a carb problem i would replace it. Same with the fuel pump. Both are relatively straightforward and work i can do.
IMO you definitely have a carb problem. We classic car owners wouldn’t usually solve that sort of problem by purchasing another carb though. That’s not cricket. We’d take the current one apart and see if we can figure it out, probably rebuild it at the same time, which means buying a kit of replacement parts, soaking the disassembled parts in carb cleaner, putting it back together, then blowing the internal passages out w/compressed air. If it still didn’t work, then we might buy a replacement carb. But probably not … lol …
If OP decides to replace the carb, might want to consider installing a more simple 2 barrel design with no secondary throttle valves. Presuming OP isn’t planning on entering any drag races.
@quig_at_home_187298 I am concerned that you are NOT listening to us. I don’t see any feedback that you are even using the correct starting procedure yet. Press, release, start.
Have you taken off the air cleaner when it is cold and you have not tried to start it. You need to do this.
Remove the air cleaner.
Look on top of the carb and you see two flapper valves. One should be closed, it is over the secondaries and it controls air/fuel from the secondaries during full throttle acceleration. The other is over the primaries and if the engine was warm before shut off, it should be open.
Move the throttle linkage to open the throttle and the choke should snap shut. However, if you have an electric choke, then it may be closed if it is not connected to the throttle cam. The throttle cam is the notched part I told you about earlier, the throttle stop screw (idle speed screw) sets on it.
I don’t believe that your accelerator pump is bad because if it was, you would get a lot of stumbling when you are driving around. If you stepped down on the gas pedal too quickly, your engine would probably die. Just to be clear, if you are getting some stumbling every time you step on the gas, unless you step on it very slowly, then the car is not driving normally and you may have a bad accelerator pump.
Do the steps above and report the results. I can’t help you any further until I know those results.
Edit: Watch this video, it will visually explain what I have been trying to say.
The flapper over the secondaries are a mechanism to keep the engine from stumbling when the secondaries open quickly. The flapper is counter-weighted so that it is ALWAYS closed until vacuum pulls the throttle blades open. Even if the secondary throttle blades open wide the flapper won’t open until there’s enough airflow to overcome the balance weights on the flapper. And even then they don’t immediately snap wide open, they open gradually as airflow increases.
It was (I understand) fairly common in the old days to shave a little weight off the balance weights to make the secondaries open faster. It could work if you took weight off in very small increments, but once too much weight was removed the secondaries would open too quickly and the engine would fall on it’s face when the throttle was floored.
Not quite. The flapper over the secondaries is controlled by vacuum. As little as three inches of vacuum will open them completely. The secondary throttle plates at the bottom of the carburetor are mechanically linked to the primaries and begin opening somewhere between 50 to 75% of the primary openings and are fully opened when the primaries are fully open.
This drops the vacuum in the manifold to zero and in the case where the secondaries are larger than the primaries, it can make it difficult for the primaries to meter fuel properly. So when you are at idle and jab the pedal to the metal as in a drag race, both sets of throttle plates open wide and at low RPM, the manifold vacuum goes to zero, but the upper flapper plate over the secondaries stays closed so air only goes through the primaries.
As RPM rises, vacuum rises in the intake manifold and at 1 inch of vacuum, the plate over the secondaries starts to open allowing more air and fuel into the engine. By 2 to 3 inches of vacuum, the plate is fully open allowing as much fuel and air as the engine can take, up to its maximum CFM rating.
The secondary’s air valve uses spring tension that can be adjusted fairly easy… They mechanical secondary throttle plate linkage is also progressive as Keith mentioned…
It is basically the same as the Thermoquad (which is close to the Quadra jet) and my T-quad secondary’s open VERY fast as soon as I snap the throttle… with NO bog…
And BTW Keith, we still have no idea what is meant by MSD ignition, lot of questions have yet to be answered… Why I stopped helping… lol
What ever you do, do not follow George’s advice to switch carb and manifold to a two barrel.
If mine and budget allowed I would switch to fuel injection.
Keith:
I share that same concern, which is why I originally hesitated to blame the accelerator pump.
But after Quig_at_home said there was no fuel squirt when opening the throttle (15 minutes after turning off the engine), it sure made the accelerator pump suspect. (Unless the squirt was there and he didn’t see it.)
@quig_at_home_187298:
Question for you. Once the car starts, during your driving, do you get any hesitation whenever you press on the accelerator?
Yeah, MSD makes a lot of ignition systems. It could be an old one that uses the points or it could be a modern one that includes a whole new distributor and sets the timing with a computer.
But honestly, that is not really an issue with me except for not knowing if it is providing spark during the start cycle. And if it isn’t, it might not be the MSD ignition, it could be that it was wired wrong or the ignition switch has an internal fault.
I am at the point where I can’t help anymore without some feedback. I don’t need feedback for my ego, but I do need to know the results of my recommended tests before I can make any more suggestions. I’m sure that is true with everyone else here to.
Good point. OP might want to check the spark’s color using a spare spark plug. A couple of years ago my truck developed a problem where it would crank ok but wouldn’t start. When I checked the spark, it had a good visual spark, but the spark color was orange-red instead of the normal blue-white color. Turned out the ignition points had oxidized, preventing a full charge to the coil. I scraped the points’ surfaces, blue-white spark returned, engine cranked and started.
