carter accelaration bog ????????

[CA_Kustoms]

I recently rebuilt the carb on my 54 Roadmaster, it is a carter 4-barrel. I went by the specs in the repair manual and the sheet that came with the rebuild kit. The car idles and runs great at speed but when accelarating it gets jumpy. It feels like when a flooded engine first fires up and it shudders the whole dang car. This occurs with modest pedal usage, however if I really ease on the gas it takes off very slow but smooth and if i give it a bit more pedal than i'd like(sorta like when you're trying to get into traffic) it stutters the same but comes out of it fairly quickly. As I remember, when I drove it home six months ago it ran pretty rough but didn't stutter with pedal pressure.(although it lacked the power that it has now)

O.K., O.K., so the question is...... Does this sound like too little or too much fuel? I set the accelarator pump to specs (9/32 from the top flange with the throttle closed.) Could this setting be pushing too much gas in? I know enough about carburators to get me into trouble and I've got a lot to learn, but my hunch is that I should adjust the pump back down(it was quite aways down before) and it should lean it out some and give better accelaration. Am I dreaming or does this sound like I might have an idea of what I'm talking about?

(sorry about the rattling on, I know nobody came here to read a book, but a better description gets better answers.)

[old-tank]

A check list for you:

1. with the engine off be sure the accelerator pump is actually working while looking down the carb

2. check the metering rod adjustment again and with the engine running and the cover over the metering rods off rev the engine to be sure they pull up out of the jets

3. be sure the gasket between the mid and lower sections is installed correctly...it will go on two ways and one is wrong

4. check the float level

5. check the timing and operation of the vacuum advance

Willie

[NTX5467]

Just a random thought . . . from an experience with a 1/2 QuadraJet 2bbl on an '80 Chevy pickup, plus from other experiences with a QuadraJet on my dad's '69 Chevy pickup.

If you can ease into the throttle and things work normally, but if you add extra loading to the engine, as in accelerating, and it does not want to respond, it can be either stuck/restricted/un-sprung power piston(s) in the primary side of the carb.

On our '69 Chevy pickup, my dad did not ever drive it hard enough to really get it to need the power mixture from the carb. Over a period of time, the power piston would stick in the "economy" or "idle" position. When it did that, it drove fine when you just eased around, but if you throttled into it, as soon as the accel pump shot was gone, so was the acceleration . . . until, if you waited long enough with enough road ahead, the rpm got high enough for the air valve secondaries to start openning and then it tried to make up for lost time (due to the additional fuel from the secondary side of things). Yet, when doing all of the diagnostic checks, everything looked normal. The fix was to put a can of Gulf TriAd fuel detergent in it and me go drive it, varying the vacuum levels a good bit, to get the valve free again. Then it'd be fine for a while longer.

On the '80 Chevy pickup, the owner did not like the way it ran, so he had a dealership overhaul the carb to get it to run better (somewhat hamstrung with 31" tires, 3.08 gears for economy, on a 305 with a "1/2 Q-Jet" 2bbl carb as factory equipment). What the dealership's operative did did not help anything, just made things worse due to a really poor acceleration performance.

A buddy of mine (and customer too, back then) was going to try to see what was wrong with it, after numerous rebuilds at the dealership to no avail. I was over there that evening when he brought the truck over. I got in it, started it, and tried the throttle response in Park. I put it in "D", nailed the foot brake, and then slowly throttled into it against the converter. It would go so far and then fall flat. I had read a trick in the Rochester carb book about using a screwdriver inserted through the bowl vent, to see if the power valve was working, so we did that.

After putting the wide blade long shank screwdriver through the vent tube, I restarted the engine and repeated the prior test. The book said that the screwdriver was supposed to be resting on top of the power piston, so when the power piston moved, so did the screwdriver . . . at least that's what it said it should do. In this case, the screwdriver did not move. So, my buddy pulled the top off of the carb and removed the power piston/primary metering rod assembly . . . NO power piston spring under the power piston . . . meaning that the metering rods were "fully engaged" with the metering jets in the "economy" position all of the time. Without the power piston spring to resist manifold vacuum, there was no movement of the metering rods to supply a richer mixture at lower vacuum levels.

So, my buddy went over and got a mid-range tension power piston spring (from an assortment that I had sold him previously, for playing with his own car), put it in the power piston's bore, and reassembled the power piston/metering rods in their designated place in the carb. When he got the air horn back on, we fired it back off to see if there were any leaks. It sounded better, so we reinserted the screwdriver, as before, and did the load test against the brakes. The screwdriver did indeed move up and down with varying loads (and intake manifold vacuum levels), so we deemed it "fixed". Then, the ultimate test . . . the owner backed it out into the street and then floored it. Even with the tall tires, highway gears, and 305, it sqalled the tires (as we cringed at what the neighbors might do, but we grinned too). When he got to the corner, he turned the corner and throttled into it again, same tire noise for an even longer period of itme. We said "Yep, sounds like it's fixed!" When the owner returned a few minutes later, he had this big grin on his face. He also openly wondered how the dealership guys had missed the fact that there should have been a spring under the power piston, or what happened to the original one. We figured that with each rebuild, they had no extra parts left over, so all was well, but did not (apparently) bother to think that something might be missing. Plus, possibly, the old deal about "He want's THAT thing to burn rubber, with those tires and a 305?" Be that as it may, he was happy and we were glad we fixed it very simply and easily.

As for my dad's pickup, it later got a fixed-jet Holley 4360 and the Q-Jet went into my archives.

So, this is why the item Willie mentioned about the metering rods (above) might be the key to the whole performance situation. If the rods stay in the "down" or "economy" position all of the time, there is no richer power mixture to help with additional engine loading from acceleration or going up an incline. And they'll stay there ("down") with no spring under them to resist manifold vacuum in pulling the power piston down. The jet/metering rod combination will determine the fuel curve calibration of the carburetor, but it takes the spring under the power piston to determine WHEN each segment of the metering rod is being used (timing of the enrichment events or a leaner mixture for lower rpms and cruise situations).

Just some thougths and experiences . . .

NTX5467

[JohnD1956]

I had the "Buick Stumble" in my 56 for a long time. Sort of got used to it although it always bothered me.

One day I had it idling in the driveway till it warmed up and I noticed water condensation seeping out from the base gasket. I got a new one and put it on and tightened the carb down as evenly and tightly as possible, without breaking the studs and the car ran right.

Not sure if this is your problem but I would think you need to check the gaskets like Willie said.

JD