When I try to accelerate agressively there is an engine "droop" (momentary lose of power) then the engine accelerates normally. This occurs throughout the gear range at all speeds ie in 4th gear at 100 km/hr if I accelerate (floor it) there is a droop followed by normal acceleration. I've had the carb cleaned and was told that the secondary was sticking. After the cleaning the problem was less noticeable but still there none the less. Under light to moderate acceleration, the problem is less noticeable. The engine is well maintained and has 145K kilometers. Could this be an accelerator pump problem?

 

I think you're right. The symptoms sound like a classic accelerator pump problem, assuming that modern carbs are similar in design to what I'm used to. It's easy to check. Just open the throttle quickly while looking into the carb and see if gas is squirted into the throat.

I'm surprised that an '88 came from the factory with a carb. I thought just about everything had fuel injection by then with the exception of maybe a few Honda models.

 

I was surprised as well, about the carburated 2.0L I mean, when I bought the truck 6 years ago. I had owned an '85 2.3L fuel injected model and assumed that anything newer would be the same. Obviously not the case.
I've done a little checking under the hood since my original post. If I move the accelerator from under the hood (at the front of the carb) I can watch the mechanism depress the plunger of the accelerator pump at the (looking from front to back) left side of the carb, and there is fuel injected into the carb. The accelerator pump does work, however, if I manually depress the plunger of the pump, there is a noticeable difference in the sound and therefore, I am assuming, the amount of fuel injected. The sound is more like a spray bottle sound if you know what I mean. I was told that the accelerator pump is used primarily for the first start after the truck has been sitting for a while; overnight for example. It is more difficult to start (numerous pumps and several turn overs) after it's been sitting. But the name of the pump would imply that it is used for other than that reason. Are these cleanable items or am I better off replacing it. Or is the linkage adjustable between the throttle and the pump? I have a Haynes manual but it doesn't get too deep in the verification of this part. Thanks by the way for the reply.

kc

 

My '87 2.0 came withe a 2 barrel carb. I think that was the last year of the carbs.

 

The accelerator pump is there because when you step on the throttle to accelerate, the air flow will increase at a faster rate than the fuel flow, resulting in a lean condition temporarily. That's the droop that you feel.

The last car that I worked on with a carb was my '71 Ford, which I got rid of a couple of years ago. If the carb on your truck is anything like it, you should have a way of adjusting the accelerator pump stroke to shoot more fuel in. Or, maybe it's just time for a rebuild and cleaning. To get to the accelerator pump, you probably have to take the carb apart and while you're in there you may as well rebuild it. You could just try cleaning the hole where the fuel comes out with some carb cleaner and see if it helps.