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1987 F250 XLT automatic with a Holley carb.
Posted in 1987-1999 and was recommended this sub. I'm rebuilding my carburetor and inspecting/cleaning all the exterior parts having to do with choke and acceleration and all that good stuff. After researching about the dashpot for deceleration I'm curious if anyone has some info on here. Wondering specifically about clearance from accelerator linkage. And also, I'm assuming that this is vacuum controlled, but I'm not finding anything to verify that. Where would the vacuum hose come from?
I know it's not that big of a deal, but I am having an issue with hesitation/stalling on punching of the gas and letting off quickly. Figured hooking this up may help a bit. Couldn't hurt at least.
I can't help with the dashpot but I don't think it will help your issue. I didn't hook mine back up when I changed carbs and don't have that issue unless it's still "cold"
It could be a vacuum leak somewhere causing that or other issues with the tuning of the carb. not enough transfer slot exposed etc.
As far as I know, there is no vacuum line to that dashpot. If there is a line to it, it would hook to the aircleaner horn to keep dirt from getting in. It's just a diaphragm assembly with a tiny hole in it. It acts like a delay like you thought, letting the throttle slowly come back. Besides helping the stalling issue it also helps with emissions. If you are going down the highway and suddenly let off the gas pedal and the carb shuts, the engine goes extremely rich for a short period and this bad for emissions. If they hold the throttle open for a short period of time it lets more air enter the engine as it decelerates.
The older cars and trucks used this mainly for what you were describing, stabbing the throttle at low speeds, especially with a automatic trans, tends to setup some interaction between the engine and the torque convertor and it will have a tendency to stall. You may be able to tune it out, but it's easy to use the dashpot. I would just keep adjusting it till you find the spot you like best.
As far as I know, there is no vacuum line to that dashpot. If there is a line to it, it would hook to the aircleaner horn to keep dirt from getting in. It's just a diaphragm assembly with a tiny hole in it. It acts like a delay like you though, letting the throttle slowly come back. Besides helping the stalling issue it also helps with emissions. If you are going down the highway and suddenly let of the gas pedal and the carb shuts, the engine goes extremely rich for a short period and this bad for emissions. If they hold the throttle open for a short period of time it lets more air enter the engine as it decelerates.
The older cars and trucks used this mainly for what you were describing, stabbing the throttle at low speeds, especially with a automatic trans, tends to setup some interaction between the engine and the torque convertor and it will have a tendency to stall. You may be able to tune it out, but it's easy to use the dashpot. I would just keep adjusting it till you find the spot you like best.
Yeah, it's just weird because I don't see how it would do anything without a vacuum line hooked up to it. When I suck on the dashpot it extends and slowly closes back up, so that would lead me to believe that is supposed to have vacuum attached and it would extend when punching the gas and then the throttle linkage would "catch" on the diaphragm and slowly be let back down. It makes sense, but nobody seems to have it actually hooked up. I may just remove it since it's not really doing much.
Yeah, it's just weird because I don't see how it would do anything without a vacuum line hooked up to it. When I suck on the dashpot it extends and slowly closes back up, so that would lead me to believe that is supposed to have vacuum attached and it would extend when punching the gas and then the throttle linkage would "catch" on the diaphragm and slowly be let back down. It makes sense, but nobody seems to have it actually hooked up. I may just remove it since it's not really doing much.
While you are playing with it, lightly push on the plunger with your finger. It should slowly retract. That's how it works, there is just a chamber in there with atmospheric air inside, and when the throttle pushes on the plunger, the air inside the chamber is expelled through a small hole, giving it a "time delay". Try and it and see. It should not need a vacuum line, unless it's some other type.
Apparently they did have a vacuum version called a vacuum kicker.
That's what I have on my '84 351W 2bbl. There's a control solenoid on top of the driver's side valve cover and a small electronic control module on the aft side of the firewall, above the gas pedal.
On the vacuum diagram, it's labeled TK for Throttle Kicker.
I guess you could say the throttle kicker is a "smart" version of the basic "dumb" dashpot. The dumb version is always active, and slows the closing rate of the throttle every time you take your foot off the pedal. (Similar versions are found on many vehicles of the era.) The smart version is retracted by default, and only extends when commanded, as determined by the controller.
I'm with Dave and don't think a failed dashpot (either style) would affect performance. Their primary purpose was to keep the air/fuel ratio from getting too rich when closing the throttle and vacuum is highest. If stuck retracted, or offering no resistance to retracting, the worst you'd see is some light popping in the exhaust. If stuck extended, idle speed would be too high.
I suspect you've got a vacuum leak somewhere, and it is worsened during the high vacuum of deceleration.
FWIW, my throttle kicker diaphragm developed a leak. I plugged the control line (always retracted now) and have noticed no change in performance.
That's what I have on my '84 351W 2bbl. There's a control solenoid on top of the driver's side valve cover and a small electronic control module on the aft side of the firewall, above the gas pedal.
On the vacuum diagram, it's labeled TK for Throttle Kicker.
I guess you could say the throttle kicker is a "smart" version of the basic "dumb" dashpot. The dumb version is always active, and slows the closing rate of the throttle every time you take your foot off the pedal. (Similar versions are found on many vehicles of the era.) The smart version is retracted by default, and only extends when commanded, as determined by the controller.
I'm with Dave and don't think a failed dashpot (either style) would affect performance. Their primary purpose was to keep the air/fuel ratio from getting too rich when closing the throttle and vacuum is highest. If stuck retracted, or offering no resistance to retracting, the worst you'd see is some light popping in the exhaust. If stuck extended, idle speed would be too high.
I suspect you've got a vacuum leak somewhere, and it is worsened during the high vacuum of deceleration.
FWIW, my throttle kicker diaphragm developed a leak. I plugged the control line (always retracted now) and have noticed no change in performance.
Ok, yes. that's the ticket. Thanks. I realized it was the Throttle Kicker after looking at vacuum diagram and doing some research. Couldn't figure out the vacuum routing for it with all the other emissions crap hooked up so I'm just gonna leave it disconnected since I see no solenoid on the drivers side valve cover and don't care enough to track one down. It does always stay retracted and only when you suck on it (or vacuum builds) does it extend. Was messing around with it and hooked it up to manifold vacuum and of course it just extends and stays that way and there's no setting it so that it doesn't push the throttle (causing a high idle) and simultaneously work to retract and catch with the throttle deceleration. Anyway, I appreciate the advice and info. I'm scouring the emissions system now for a leak somewhere.
