JpMotorsports

I just got my 72 running again after detailing the engine and bay. I put on my rebuilt original q-jet and notice a little hesitation when I would put my foot into it. My uncle told me about this trick he saw about using a little oil (I use 3 n 1) to lube the shaft and bushing. I must say after a few drops and and few test drives it dose seem to work. Has anyone else heard od any tricks or fixes like this? From what I read it is a common issue on the q-jets for this pump to wear out.


Here's a link to a youtube video about it

61reoldsman

Yeah I've heard of that old trick and it'll get ya out of a jam but if the pump is sticking then something is amiss in there , I'd change out the old pump and clean inside the bore with some very fine crocus cloth and reassemble with a brand new pump with an ethanol resistant pump cup.JMO

toymobile

That would work fine on a LEATHER pump but not many of those left.

davebw31

grind about 1/8 inch (and no more) off the end of the metal plunger shaft (the end where the linkage arm moves the plunger shaft down). This trick "raises" the cup in the "well". This will increase the amount of fuel in the pump well as well as increasing the "stroke" thus providing more fuel through the accelerator discharge circuit.

BILL DEMMER

and this can cause problems. just get the right pump and there is no need(or benefit) from doing this.


bill

davebw31

Bill:


Not true! I have done this modification to the plunger shaft end on many, many Q-jets on my own cars and for customers who drive on the street or have all out race cars. I never had a problem or complaint! Now if you take to much material from the end, you will have a problem, as the cup will not be seated in the well wall! This will cause binding or sucking air.


There is differently a performance gain. Think about it, you get a "longer timed fuel shot" and a larger amount of fuel in the well, thus providing more fuel to the accelerator pump circuit, thus more fuel to the engine off the line...............

Koda

Removing material from the shaft would raise the initial position of the pump shaft as it's spring held up there. However, it would also raise the bottom position too, unless the pump already bottoms out and is stopping the linkage there and by doing the mod you give it a little more room to travel. Which is it?

davebw31

read the post again! More room to travel............ The whole purpose is a longer fuel shot and more fuel through the accelerator (squirters) circuit..........thus more fuel to the engine off the line...........= more torque and HP at the initial hit of the torque converter on auto cars, however another trick on auto equipped is to "lean out the primary circuit", which will also give you more torque. Stick, it also helps these cars. If you do not understand how a carb works you won't understand what I am saying!!!!!!!!!!!!!!

Koda

I don't think you understood what I was saying.

BILL DEMMER

VERY true!! you can over-do it on the fuel shot. just throwing fuel at things is not always an answer. and yes, as mentioned above, if you take too much off the shaft, you can get above the taper of the pump well/uncover the pump fill slot/roll the pump cup over.
btw, i've done way more carbs. than you've ever seen.


bill
www.sparkyscarbs.com

RAStacy

Hi I'm an Old Olds mechanic 1968 -1979 as davebw31 said but instead of grinding it off take some pliers and bend the tab down alittle. worked for me years ago, it gets you over that point and you don't mess up the lever.

BILL DEMMER

the factory prescribed method was to bend the accelerator pump lever(using the correct pump assembly).

bill

young olds

i understand what your saying and have thought the same thing. cutting the shaft will raise the accelerator pump up in thee bore but the linkage that pushes the pump down only pushes it a certain amount. unless your bottoming out theres no way your increasing the pump shot as the pump is still moving the same distance. you would have to push the pump a further distance to increase the pump shot which is where arms, that make contact with the pump, with a different pivot position come into play.

BILL DEMMER

there is generally an abundant amount of travel in the primary accelerator pump mechanism. the pump will bottom in it's bore well before you open the throttle fully. when the pump plunger hits the bottom of the bore, any further travel of the pump stem just loads the spring, and the pump stem slides into the body of the pump.


bill

BlackGold

Thanks, Bill. You're the only person to explain how the pump shot could possibly be increased without modifying the pivot or length of the lever arm. Without your explanation, it was like someone claiming they increased their engine's displacement by using shorter connecting rods. Umm, no.