Heres the combo: 355 with world s/r(1.94/1.5 valves) and a 205/216@.050 cam with Holley 650DP...prolly puts out 300-330hp. I have a slight hesitation after hitting the throttle from cruise. I just got a 3-wire heated O2 sensor hooked up and it shows me that I go really bad lean for a second or two when I hit the acc.(lightly or heavily-doesnt matter), you can feel the car stumble and hesitate then it takes off and sensor goes back to rich.

So far I changed PV to a 10.5(stock was 6.5 but I pull 17-18"), upped squiter size to .031 on primarys(was .028), put an acc. pump cam in(went from stock pink to white) that gave a bigger shot when I just hit the throttle(figured this would help the lean bog). I did each of these mods one by one and the bog has not gotten better or worse, I don't know where to go from here!

This is the odd thing- from a stop if I gun it WOT the engine performs wonderfully throughout the gears(no bog) and it stays rich except it goes lean when I get off throttle real quick to shift which is expected. This bog occurs only when I get on the throttle while I am cruising. The Jets are 65/73 (the sensor showed I was running rich at cruise so I jetted down to 65s in primarys too...still running rich at cruise tho)

What do I do now?! .031 squiters seem pretty big for my mild motor...and according to the sensor I have to go even leaner on the primary jets to at least get near stoich....I want EFI! Please help me out! Thanks

On our chassis dyno we quite often find that the squirters are too large for the situation, which shows up on the graph as an 'S' shaped section when you stab the throttle. The engine goes too rich right away, but leans right out when the pump is dry. Changing to a smaller squirter will provide a better mixture and cover the dead spot. We recently tested a 383" motor with a 770 Holley that came stock with an .025" squirter. The f/a ratio went down to 10 on the squirt, so we changed to an .021" sqirter with an orange cam to get the best response.

Yes, go down on primary squirter size and back to the orange cam. I'd try a #28 squirter to start and stick with the orange cam.

If the problem persists you might have to play with the secondary pump. I think this might actually be the case since you said it goes fine from a stop but hesitates from a roll. Bigger cam and smaller squirter on the secondary would be my best guess.

As for your cruise mixture, you really don't want to tune for a stoich mixture at cruise anyway. IMO you want to tune for an optimum WOT mixture and let cruise mix fall where it may. If you get WOT mix where you want it (shoot for about 12.9:1) and part throttle is still too rich you might want to go back to the 6.5 PV and see what happens with your mix at cruise (if anything).

Just my opinion.

You also may have a slight amount of slack in the acc pump linkage. I had the same symptom as you ( with a 700 DP). I carefully adjusted the acc pump so the linkage would move as soon as the throttle did. My hesitation went away. I'm using the stock sized pump/cam that came with it.

Also make sure the primary throttle plate to idle transfer slot positioning is correct. Aim for 0.040" of the slot showing under the throttle plates. Readjust idle RPM by opening the secondaries a tad if necessary.

I was getting fed up with the DP (put on a white acc. pump cam[much bigger shot right when you hit throttle compared to my stock pink one] and again absolutly no change in its behavior) and so I put on a rebuilt 750 Vaccum Secondary Holley..it has .025 squiters and 10.5 PV and I jetted primarys down to 68. I put it on the car and there was absolutly no change..didn't run any better or any worse then the DP..still great WOT from a stop but bogs then goes when acc. from a cruise.

I'm beginning to think that maybe something else is the culprit here? I don't know what to do now!

First of all, the white one is not a "bigger" cam than the Orange, it is smaller and will shoot LESS fuel. Did you ever go back to the orange like I suggested?

BTW Pink is bigger than orange and brown is bigger yet.

You also might want to make sure that your ignition timing and advance curve are set correctly.

Heres the update...put in an orange cam(thank you Eric smile.gif .... and .031 squiters in the Vaccum Secondary...problem gone! no more stumble ...Ooo and I put the orange cam and the pink one side by side and the pink one is considerably smaller by a lot...sure you aren't thinking of the red? Or maybe the one I have just faded and looks pink now!

I brought the car to the track yesterday and got a 14.7@96mph with a 2.29 60ft time(racing a manual with a line lock and street tires blows!...first pass was a 15.7 with a 2.99 60ft and man was i pissed)..best reaction time was a .524 tho! I wanted better but I don't think the ET is that bad considering this is a 3800lb 81Z with a mild 355(world s/r small valved heads and a 205/216@.050 cam), 4-speed, and 3.42s. I think I'll go back with the double pumper(w/ orange cam and .031) and see if I pick up a couple tenths, the car didn't feel as powerful in the first 1/8th with the vaccum. If it doesn't run much faster then I will just keep the VS...the extra 2-3mpg is nice! Thanks guys!

always good to hear of a successful outcome! Happy motoring!

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