I have two Holleys, setup exactly the same,, a 750 dp downleg & an 830 hp annular. Both perform flawlessly. Both were ran on dual plane & SP3 intakes. Also used to run an 850 Speed Demon dp downleg that also performed very well. I should have tried my buddy's 1050 Dominator before it was sold.
If you changed carbs and still have this bog when you step on the gas I would look at a vac leak or an ignition system that is not up to the task when the throttle is stepped on. An ignition system that is not up to the task will stumble when throttle is stabbed. afr at 10 at wot is too much. I have year old gas in my car and if anybody should have trouble it should be me and I had that car out last weekend and I experience non of the problems you are having. I stab the gas and it responds. I would double check that ignition system and see if can shoot lightning bolts from 1 inch away I know mine does. I have the MSD set up dist and ignition. you should not have this kind of trouble with the SP3 mine starts up faster than with the DP intake
I suppose ignition could be gone through but it's all new and quality parts. Ive ran it at night with hood open and seen no arching. The intake could need resealed and even suggested it 6 months ago BUT every single one of you guys told me that my combination was going to bog hardcore off the line if I didn't have a double pumper. you guys all told me that the sp3 needs a double pumper. I solved my bog off the line with my 50cc accelerator pump. Which I believe most of you had to do as well. The carburetor that I ran yesterday is a vacuum secondary and has stock pump cam, stock squirter, stock accelerator pump. Keep in mind I have no stall and a 256 rear end. The downleg carbs jetting is extremely close to my annular carb but had a way better afr without changing anything. Check image. My annular carb has to be jetted down 7 sizes to get a similar afr as the stock downleg carb. I believe that This much of a jetting change is causing the low speed stumble. The 65 jets aren't supplying enough fuel to the metering circuits.
I tried this carb. Read post on page 47. Downleg carb almost with almost exact same jetting ran a pretty good AFR right out of the box. But my annular is pig rich
Keep in mind I'm not having an issue when the throttle is being stabbed I'm having an issue at very "light tip in" very small acceleration from a stop sign or stoplight etc. I'm certain that is because of the amount of decrease in the main jet size causing the lean stumble. With factory jetting the stumble is gone. But is just so incredibly rich once I get up to cruising speeds. The downleg carb was really close out of the box
Maybe not just a downleg booster carb, but a completely different carb all together. Like Larry said, Holleys are pretty close right out of the box....as you just found out.
Yeah I'd be switching to a 4150 double pumper with downleg boosters....with a street tune. Yes, completely different carb. I'm not considering just changing my boosters.
I have the standard 750 dbl pump with 4 corner idle. I was just out yesterday and I have to say my light tip in from stop is on it now, no slight bog. I know what you are saying about this problem since at a stop you want that carb to get up the moment you touch the gas. I do use the shooters with the tubes on them. I have a really large rpm meter I bought 30 years ago and I use it with the vac gauge to set those 4 corner idle screws and keep the rpm at 700 in drive. I get the screws to start to stall down the rpm 25-50 rpm then I go back to that spot before the rpm lowering down. I spend a good 20 minutes playing with them till all 4 screws will take the engine down a few then go back up a scotch or is that scoch If you can't get this worked out I would look at resealing the intake. I sprayed the intake gasket with copper spray so they would stick to the heads then just dropped that intake on those pins and bolted in. It can be easy to get those composite gaskets to move when dropping on the intake. you can probably only go down about 2 sizes on the primaries with jetting as the carb is very close out of box usually it is the other way around to make the power. It will start to run lean on primaries with over 2 sizes down at that point I would think. Mine is 70-78 from factory I have it at 72-80 is it right heck I don't know afr could be thru the roof or in the basement. I just know the car starts up in seconds and has no problem on tip in and I even use a non projected NGK plug that is burning great. Leave it sit for an hour and no gas needed to start back up. and rocks jammed to the floor with no smoke and the nitrous kicks it in the a...
I know you have the 256 gear with the cam and yes the jam to the floor could give you trouble with the pump shot tailoring.I had the same basic cam with the comp 268 and 256 gears I was trying to use a Holley 650 dbl pump spreadbore. Yes, hard to tune in the pump shot for the off line when the convertor is stock and those gears. The off idle touch of the gas should be no different than what I have it should go instantly. 256 gear or not My only difference is I have a 3000 stall and the rpm probably goes up faster before the convertor pulls I know I am at 2 grand the moment I step on the gas but I start at that 700 rpm at idle from light or stop. I would get the standard Holley carb get the better one with the idle air bleeds to change if you want that feature. Try to see if you can get that carb tuned in you have on there now and see if you can get there with it it won't matter that it is a vac secondary carb that just means the power wont be as strong on top end but you should be able to get the carb dialed in on the take off from tip in and on the floor. you will like the intake the moment you get that bigger gear in there and go to a 3000+++ stall rock and roll then 4 speed auto with lock up convertor best thing I ever did.
I'm not a hundred percent ready to give up on the annular carb. It was $800. I just dont understand How the jetting can be so far off when being compared to another 750 with the same jetting. But am learning still. I have an afr and with the primaries jetted down 7 sizes I'm in the 13.5 to 14 range. With stock jets it is incredibly rich but the tip in stumbles are gone. The stock 750 with downleg boosters and similar jetting had a nice cruise afr right out of the box. I read two great articles by David vizard. he really really likes the annular booster carb and in both his articles he recommends going to a much larger high-speed air bleed. Because annular tend to go rich. The Air bleed that comes on my annular carb is very close to the same size as the downleg carb. I plan to jet down just two or three sizes and see if I develop a lean stumble and then do the rest of my jetting with the high-speed air bleeds and see what I can accomplish
I didn't have to do anything with it. it had a nice off idle throttle response right out of the box. So did my edelbrock. Because the other two carbs work good off idle I do not think it's an intake seal. But one thing that has always bothered me is I used the .040 intake gasket which held my intake up quite a bit off the end seals. The Gap at the end seals is massive in my opinion. So if I do reseal the intake I think I'm going to use twenty or thirty thousands gaskets. TA recommended the thicker ones because I decked the heads .020
keep on tuning but don't let the afr meter be your complete guide listen to what the engine tells you also. you need a track to get 60 ft times 1/8th times and 1/4 mile along with mph this will dial in the carb and the timing A G-Tech might help with a good lonely back rd it reads 60 ft with 1/4 mile times they may give mph too haven't seen them in a while
I literally just got done messing with it and took it on a test drive. I jetted it to size 69 jets (my last combo of jetting was using a 65) stock is 72. I installed size 37 high speed bleeds up from 33 to delay the mains from starting up during transition. This has appeared to work perfectly. Sitting in park and slowly revving to 3000 rpm I could see where the afr changes from transition to the mains. There was a real rich spot in there before I made this change. I'm cruising now in the 13 range and has noticeably more power. Before I was trying to get to a good AFR only by changing the main jets and when I was down seven jet sizes I was actually Starving the other circuits for fuel. Causing metering issues. This combo is using more main jet and a bigger air bleed to reach a a similar cruise AFR as before. Not quite as good but close. Either way it's exactly what vizard recommended. As of right now the lean stumble appears to be gone and performance is up. Really performing good. BUT idle is still pig rich. 11.5 in park. 12.5 in gear. I've read numerous stories on the net with guys struggling to get there mild cam/double pumper combos to idle right. My cams advertised duraration is 288 and is 220 @.050 and has some overlap. Could be a stinky cam...tonight i produced a couple nice burnouts and was able to pull away from a stop without the dreaded stumbling. If the 11.5 idle is acceptable by you guys I'll run it...maybe I should run the stock slightly hotter ur4 plugs to help with fouling....?
my overlap is 230-245 @ 0.50 The 11.5 is rich isn't that supposed to be at 13? Don't crutch it with hotter plugs
Everything I've read says to shoot for 13. If i set it to that it does fine but develops way more lope. then when I drop it in gear the engine labors a little and the idle goes way lean like into the 15- 16 range. Which creates a horrible lean stumble on acceleration
Trust your gut instead of the AFR meter. Plus they get fouled up and need to be replaced often especially when you run the vehicle rich it ruins the sensors.
Stinky and eye burning rich though...I'm not going off just the afr. But I'll run it the way it is. 11.5 is what it likes.
I installed a 600 cfm double pumper and the car is happy. My 750 quickfuel still had off idle low speed stumbles despite multiple tuning efforts. I recently bought a 600cfm summit double pumper. Out of the box settings are pretty close. Minor jet changes is all it needed to have nice Afr readings. Nice crisp throttle response at low speeds. I did have to install the 50cc pump to get the pump shot right for mashing the throttle...still tuning the accelerator pump circuit...but it's close. I've put a couple of hours of drive time on this new carb. I plan on a 100 mile round trip this weekend. So far theres no feathering the throttle from a stop sign and it pulls hard to 5000rpm with ease. Was able to get a decent burnout as well. Vacuum is a solid 13-14. Unfortunately the afr still dips into the 11s when coasting. I'm going to mess with the air bleeds a little. My quick fuel constantly dipped into the 11s but it was also rich in all of its circuits. Check the pic to see what the plugs looked like after maybe 1000 miles with the 750 quickfuel. Also, I did something interesting...I tried the quickfuel metering block on the new carb and it ran like total crap. So kind of wondering if my metering blocks were the problem...
life's going to slow down a little bit for me now that it's close to winter and my gutter business has slowed down. I'm Going to play around with the car a little bit this winter. Haven't done much with the 2004r that I bought. But maybe it'll get rebuilt and swapped in before spring along with a stall converter. Also looking at finally doing the disc brake conversion.... my wife has planned a couple vacations over the winter because this is when we have the most time to do it. So not sure where my budget is going to be. But one of the more affordable things I can do is play around with my old quick fuel 750. I ended up taking it off and running a cheap summit double pumper that I had good results with. But I'd rather be using my $800 carb lol. I think the metering blocks were an issue ...that carb was always rich. I even tried the metering blocks on my cheap Summit carburetor and it made it run like dog crap. So I think I'm going to get some new billet metering blocks with more emulsion jets. Stay tuned!
