Here's a good one....
Has anyone changed the stock accelerator pump plunger that comes with a #1901 Edelbrock Quadrajet with the "Hi Perf Plunger" #1982?
It looks a whole lot shorter than the standard one, and I'm not sure if I have to start bending rods, etc, to get this thing to work.
Any takers?????? [img]graemlins/clonk.gif[/img]
Ok, I once saw a Rochester sitting on a shelf in a friend of a friends garage a long time ago - so I'll bite ...
The Q-jet pump has a maximum travel length of @21/32".
First make sure you've moved the push lever from the throttle shaft to the 'inner' hole on the pivot arm. This gives the maximum lever on the arm.
Next, mark the shaft at rest and then again at full throttle travel. This is the pump travel length.
An old racers trick was to shorten the stock pump @1~3/32" to get the maximum travel out of each pump shot, without raising the pump cup above the edge of the fill slot in the bore ...
You are going to have to check the stroke of the new pump to be sure it does not sit to high in the rest position or it will not cure your issues and will cause new ones.
Usually, just shortening the stock pump assembly by grinding @1~2/32" off the end is enough to increase the volume.
If, after you've optimized the pump travel, you're not getting the shot amount you need. You may need to check and enlarge the two accelerator shooter nozzles by drilling them out some.
Check the original size with a drill and enlarge by slight amounts (0.002 or so increments) until you feel good throttle response off idle under no load - test drive - if necessary, go up one more 0.002 size to get it - do not go to big! Going to big will be past the ablity of the pump duration spring to maintain pressure throught the whole pump shot.
Use of a slightly stronger pump duration spring (the spring between the cup and the shaft clip) is preferable to over-drilling the shooter holes.
The final thing to do is to increase the dia. of the pump bore. This will require some machine work.
The normal stock dia. is 0.645". The performance models and trucks use a 0.735" bore.
That should keep you busy until he replies ...