50/50 on the pumps. Right now I am using the smallest air bleeds I have for the idle circuit. Motor still reacts with a slight stumble when i crack it. A month ago it was fine but the weather has become cooler. I also tried a massive squirter on it but all it doe's is cover up the problem because driving at part throttle was extremely too rich. I am also using the most aggressive pump cam, brownish.
The brown cam is not the most aggressive. It has the largest pump shot, but it sounds like you need a cam that has an aggressive ramp to start with (at tip-in), then levels off at mid-throttle. I believe it's either the Blue or White cam that has that quality, but the only pump cam that will utilize the 50cc shot is the brown cam. In most cases though I don't think the 50CC shot is necessary. You can get an idea of how each pump works by simply eyeballing the curvature to see if it will squirt a lot at tip-in, or more at mid throttle, etc. Also the pump shot profile will depend on which screw holes you use... usually hole#1 gives more overall pump shot and more agressive at tip-in while hole#2/#3 are more mild. I scanned the pump profiles with my scanner, traced them in autocad, and plotted the 'shot curves' (vs. throttle position) in an excel spreadsheet. I can post a picture of that, might be a little helpful, but also is a little difficult to read and compare directly.
The reason for my short response earlier is because you gave no information as to what pump config you are currently using, or a good description of the problem. If I were to say "I have a 289 with a 750 carb and it doesn't run good, what jets should I run?" would you be able to help me at all?
I'm figuring that the white and blue cams won't really help but I could be wrong. They don't offer even half of the travel that the brown doe's. The thing is the blue and the white may offer that little extra responce but my motor likes that heavy shot. I'm probably going to have to get the vac gauge on it and play with the idle mixtures screws again I guess. The least i can do is try both of them at the track, it won't hurt anything. Thanks.
Is it fighting you by laying over when you hit it? or is it stumbling at a slow roll on?
If its the latter, I think its the modern HP series emulsion curcuit in the main wells as well as the IFR thats above the fuel level (early carbs the IFR was below the fuel level).
As geeky as it sounds, there was a NASA study on fuel/gas seperation at different fuel and air quantities, what it loosely showed was that at different a/f mixtures, the air and fuel can seperate (wasnt my brain that figured this out)
I am soon going to try an early metering block on my 1000 to see if it will help the IFR issue as well as giving me a different emulsion setup to play with. I've gone as small as I wish on the IABs it helped, but same deal (assuming its a tip in buck and not WOT) it aint right yet
Here's the graph I made a year or two back for the Holley accel pumps. Looks like my memory was wrong, the blue and white have a high initial shot, but not as high as the brown. The only cam that has more initial shot than the brown is the green. Also, most of the cams, when installed with the screw in the second hole, retard the cam about 5 degrees, which basically moves the curve to the right in this graph, which gives you a BIGGER initial and overall shot (I had that backwards also in my previous post). So the green cam on the second hole will give you an initial shot that is a little stronger than the brown, but you'll be down in the 30cc total shot instead of 50cc of the brown pump cam. However, if you think you need the maximum volume of pump for drag racing, you can always keep the brown on the secondaries, and put the green in the primaries, and you wouldn't be giving up MUCH volume of pump shot when you floor it (roughly 80ccs instead of 100ccs total).
'86 Bronco, 300hp 460, E4OD
'85 Ranger, 350hp 289, T5, [email protected] (1.96 60') on street tires
<font size=-1>[ This Message was edited by: Motorhead on 10/21/06 3:14pm ]</font>
What size is the carb, trans type, launch rpms and when is it laying down on you? What squiter nozzle number do you have? One trick is to adjust the pumps lever so it touches the cam once you're at launch RPMs. This way you don't waste part of your CC shot by opening the throttle at the lights. When you mash the pedal then you get your full CC pumps shot.
Right now its a tip in stumble. Sitting at idle if i crack it, it will stumble. I'll try a green on the front and see what happens. Heading to the track in an hour or so. I gotta check the idle circuits too. I have a 45 squirter on the front and back. 1000hp C/4 with a 5000 8". I leave at 2,500 but really it will stumble if you crack it off idle. Thanks for all the info.
My 1000 fights me more with a slight hesitation when rolling on at light load, on the street its like if you slow down for a red light and it turns green, when you lightly get back in it bucks a little
If you mash it a little more, even slightly more, no issues at all, the pump does its thing. I think mine is more of a transition fuel issue where yours may be accel pump
I tried the green pump cam but it slowed me down. Stayed with the brown pump cam. Got rid of the stumble by evening the primary and secondary idle circuits until they were about even. Picked up a tenth. Thanks for your help. -Joe Sulligan.