Should the accelerator pump shoot gas out the entire length of its movement? Mine shooots out starting from the least little movement but it stops shooting out about 3/4 the way down. Is this normal? If not what is causing it?
Far as I know, there are dozens of different pumps, and at least that many different springs used on and under those pumps. The factory set up each Quadrajet according to application. Usually by the time we get to these carburetors the factory pump is long gone. Most aftermarket kits will NOT contain the correct OEM length pump, so it's difficult to assess accellerator pump operation. Combine that with the wrong spring(s), and different size discharge holes in the airhorn, etc, etc. For ethanol enhanced fuels, a Viton pump seal (fluoroelostomer) is required. We also recomend using the later style pump with a garter spring under the seal, and new springs on and under the pump. Just a side note here. There are at least 5 grades of fluoroestomer pump seals in circulation. We've upgraded ours several times to the latest version. The "soft" light blue seals are giving troubles with ethanol fuels, even though they are labeled as "ethanol resistant", and can be found in some aftermarket kits. The best seal will be a hard dark blue seal. Never install a black bunna rubber or neoprene seal, it will fail in contact with ethanol. Accellerator pump shot is determinded by the height of the pump, and how much fuel is trapped under it, and how long the stroke. Keep in mind that the fuel under the pump is not compressable, so any movement of the pump must push fuel out of the carburetor thru the discharge holes, or the spring on the pump must compress, or both. For these reasons, there is no direct answer to your question, as the amount of throttle angle required to bottom the pump out in the well depends on many factors. This includes how long or how far the pump must travel to deliver all the fuel under it, which varies considerably with various pump length(s), strength of the pump duration spring, and even which hole the link to the pump arm is in. What I recomend here, is to upgrade the pump to the late style pump shown. They are superior everyplace to the stock pump, and come with matching springs and retainer. These later style pumps have the seal expanded against the bore, so no throttle movement is required to move the seal lip out and start compressing the fuel under it.....Cliff http://www.v8buick.com/attachment.php?attachmentid=157433&stc=1&d=1263036697
Cliff just checked out your site, i had no idea you wrote that book on Qjets! I had no idea who i was talking to. Im going to take the air horn off tomorrow and see what the issue is, if its not obvious ill be ordering one of your pumps they seem reasonably priced, ill get some screws too if you offer them as a set of 4. This is great. Thanks
Gary, talk to Cliff first. If you plan to take the air horn off the top of the carb, you'll need a new gasket for reassembly. Devon
I just rebuilt it, the gasket is stil fresh, ive had it off a couple times to adjust the float since i rebuilt if a few weeks ago.
Couple of other items we consider manditory for a complete/correct rebuilding. Replace the secondary plastic cam and spring. Install the correct .135" high flow needle/seat assembly, make sure it has a Viton tip on the needle. There isn't an over the counter kit out there these days that comes with these parts. New power piston spring. New float. Pull the idle tubes and clean in and under them. Replace the entire early style accl pump assembly and both springs, as mentioned. Pressure test the bottom plugs, and install screw in plugs if they are leaking. Dabbing epoxy over leaking plugs is about effective as cutting your arm off and putting a bandaide on it! Already covered in another thread, install bronze shaft bushings for the primary shaft. Most main castings and airhorns are warped some. This isn't a problem for most builds, unless the airhorn is "humped" up some, which can cause fuel and air leaks between the parts. We have thick gaskets for this problem, and also recomend to genty sand the airhorn across the front bolt holes slighlty so it can re-conform to the main casting. I would also recomend reading our book, there is a chapter dedicated to complete/correct rebuilding which covers the items mentioned in greater detail......Cliff
now that i think of it, i first noticed the problem after I took the distributor out and put it in the wrong way and had a few backfires out the top of the carb. I took it out and got it in the right way now and the car runs perfect. Well not perfect, do they ever run perfect? Question: Can a backfire mess up the acclerator pump?
Make sure you reseat the check ball as outlined in Cliff's book. I had a carb that had a problem with the accelerator pump only after the car warmed up. It got lots of pump shot while cold, but not after it reached operating temperature. I polished the pump well and struggled with many different pumps, seals springs etc. etc. etc. I was just about to toss out the main casting. Finally, reseating the check ball solved the problem. This is critical to proper pump operation.
Good advice Jim, a very simple step that if left out can cause MAJOR issues once the carb is placed in service. We quit using the accl pumps that don't have a "garter spring" for the same reason, inconsistant pump shot/fuel delivery shows up with all sorts of problems on the street and track. Just make sure to GENTLY tap a good check ball into the seat. I use a brass punch for this purpose. Last year we had two folks break the entire bottom out of the accellerator pump check ball well of the main casting, there is no repair when this happens.ou: I've been doing this for at least 30 years, and to date haven't hit one hard enough to cause this problem. I use a very tiny machinists hammer, maybe they were using a 6 pound sledgehammer, not sure?......Cliff
