Jerky accleration and jerking in all rpm levels

[harveyjp11]

This is the first time I have posted on this forum but I am at a loss so I am asking for some guidance. I have a carbureted 1989 Festiva with only 63,000 miles. I bought it with 48,000 and at the time it jerked in 2nd and 3rd gears...I replaced the clutch and all ignition parts except the coil but no positive affect. I checked the timing and corrected it---few degrees out...but the jerking continued but only once in a while--usually about 30-40 mph in 2nd or 3rd gear. Today I was driving about 75 mph and the car lost power and started to jerk again...all the way to work. Later, as I was getting back home, it would not get going out of a stop without having to accelerate hard and then engaging the clutch; hesitating and bucking through the lower bands of power until it was accelerating hard but it would still buck and hesitate just not as forcefully. It was smooth when accelerating hard or when going up hill--because you have to accelerate to go up a hill. On a flat or downhill it would just buck and sputter even when I tried to regulate the speed at about 50 mph or 2200 rpm. Once I arrive home I checked the timing belt to ensure that it had not jumped a tooth in any of the cogs on the cam or crank....no problems there. I lifted the air cleaner cover, checked for fuel...no problems there--at idle. Finally, with the transmission in neutral I opened the carburetor up and found that the engine would almost die out when accelerating though about 3000 rpm and then continue strong. I am not well versed in the carburetor system and I am at my wits end with this problem. Any ideas? Accelerator pump?

Thank you,

James Harvey
New Orleans

[ricko1966]

Not the accelerator pump it just gives a shot of fuel as you depress the throttle it won't cause problems once you are moving. Try pinching the fuel line shut with vice grips with the engine running blip throttle a few times. do things get better? Do this until it dies from fuel starvation the quickly release the vice grips as it's dying. What I am trying to determine here is if the needle and seat are leaking causing flooding, when you stand on it it can use the extra fuel because you are giving it extra air.Releasing the vice grips quickly after it dies is if you have dirt in the needle and seat when you run the carb dry the needle is as far open as it will go when you release the vice grips the rush of fuel sometimes will wash the crap out of the needle and seat. I hope that works. When is the last time you replaced the fuel filter ?

[WmWatt]

When you step on the gas you increase engine vacuum (suction) which pulls more air/fuel mix into the cyclinder. If you have a vaccum guage you can see this at idle when you pull on the accelerator cable in the engine compartment. As ricko suggests the flow is probably be restricted. If the spark plugs weren't firing that would also show up on a vaccum guage as vibrating needle every timethe engine misses. I find a vacuum guage a cheap way of monitoring the engine once in a while. I plug it into the top hose on the distributor. Looks like you are on the way to soving the problem.

[FestYboy]

Ummm you have that quite backwards.... When the throttle is opened, vacuum DROPS. Fuel flows due to pressure differential within the venturi. As the volume of air past the venturi increases, the pressure differential increases as well (think of how a wing works). That area of low pressure is fed fuel through the Jets and the approximate 3psi of fuel pressure in the bowl.

In the OP, the coil has not been replaced, nor has the ignition system been tested for spark leak. Test for spark leak and do a compression test before condemning the carb.

[WmWatt]

^^ thanks for pointing that out. The needle on the vacuum guage does drop. As you say I remembered it backwards.

[Old70]

Put a yellow bottle of heat in it and a can of Sea Foam. Both in the gas tank. Less than $10 for the both of them. Usually cures this.

[bravekozak]

Get rid of the stock computer-controlled feedback carburetor and replace it with a rebuilt non-feedback Escort carb. You can then disconnect the ECA computer and remove it for long term bench testing.It also wouldn't hurt to change both of your fuel filters.