1969 with 700R4 and HOLLEY DOUBLE CRAPPER - Page 2 - Chevelle Tech
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post #16 of 37 (permalink) Old May 30th, 19, 4:35 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

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Originally Posted by NickeyChevelle View Post
Here is holley's answer. QUESTION How do I know if a vacuum or mechanical carburetor is best for me?

ANSWER For street cars the vacuum secondary carburetor works best on midweight or heavyweight cars with an automatic transmission. They are more forgiving than a Double Pumper is because they work by sensing engine load. The mechanical secondary carburetor is best on a lighter car with radical camshaft and a lower gear and manual transmission or on a car that is going to be used for racing purposes.

Enjoy your vac sec
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post #17 of 37 (permalink) Old May 30th, 19, 5:52 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

This is a ZZ4 engine? If so, stock large ZZ4 HEI? has it been modified to work right? Vacuum advance degrees stop plate installed? Mechanical curve sped up?

If not, they don't run that well.
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post #18 of 37 (permalink) Old May 30th, 19, 10:39 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

True, it could be a pooch carb, which is why I asked if it had been gone thru recently and what had been done to it. With tuning , it can be made to work. Aint rocket science, but its not "forgiving" as Holley said. To Dave Rays' point, the engine may need some tuning to optimize it for the DP. Vac secs can be way more forgiving. BUT, back to the OPs request...

BTW, here's some rocket science, from true carb gurus... for the OP's "edumacation" on air bleeds, PVs , which holes the cams are affixed thru and even the size of the channel the PV opens to makes a difference.....

Harry in LA :
"Nice looking setup !
I did this same swap of my DP body for an HP body to get air bleeds and choke horn delete. I have a wideband in my '70 SS396. The larger IFR (.033) in the Quick Fuel red DP upgrade metering blocks was perfect. It solved my tip-in stumble. For air bleeds, I started going big, then, ended loving the small -- HSAB - 25 to 31; LSAB - 68 to 72. This improves gas mileage. (Right now, I am debating between 27 and 31 for the LSAB, and settled on 68 for the LSAB). 68 LSAB will not lean out the IFR and give me plenty of transition gas for overdrive on the fwy - idle is at a perfect 14.2 for my cam, with approx 1 turn of the idle mixture screws. I also ended up with a larger PVR (larger than the stock .059 - I drilled the next size up), high flow power valve, and 9.5 rating even though I have a 292H Cam (high duration). This large PVR and quick opening PV allowed me to go to 72 on the front jets. Rear jets are around 83, 84. The smaller HSABs (25 to 31) will make everything richer on the top end and leaner in the mid-range, so, you need a good, quick opening PVR to avoid going lean in the mid-range. I also ended up with the blue cam on hole 2 for the front and the black cam (hole 1) for the rear. 31 nozzle with extensions in the front and 35 nozzle in the rear with extensions."

But you wont need to be that involved to get it to work! Great carb tuning thread to learn from though.. Read on, and TUNE. Or punt and get a 3310.

Says the guy who is switching to a Qjet as my primary street carb.
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post #19 of 37 (permalink) Old May 30th, 19, 10:47 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

how about just unhooking the mechanical linkage to the secondaries and see if you can get the primaries dialed I'm? jim

Jim

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post #20 of 37 (permalink) Old May 30th, 19, 11:09 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

I had a big block for a while with a Holley double pumper and TH400. I have only general knowledge of components: Engine had an "RV" cam, TH400 "higher than stock" stall, and rear gears "Probably 3:55's". I drove it cross country averaging about 55 mph due to not enough radiator and got about 10 mpg. It had a manual choke and started without problems. There was no kick down connected for the trans, but with the double-pumper it didn't really need one. It would burn tires at will, cruise smoothly, and had no bog anywhere. It never smelled particularly rich. The combo worked extremely well. I wish I had more info to offer about the specifics but it can be done.
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post #21 of 37 (permalink) Old May 31st, 19, 10:18 AM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

! I've even taken the carb to a very well respected old timer who builds race engines and knows Holleys inside and out. He played with it, but it still has a HORRIBLE stumble just off idle.

Saying he played with it is pretty vague.
Could be he just messed with idle mix screws and float levels.


I have known many old timers that claimed they knew their stuff and maybe they did and they just got lazy or forgetful.
But I know none of them that really know their stuff..the one that I did know is long dead.


Had one of them messing with a new cam install in my buddies engine.
He had his own shop also.
Well they could not get the SBC to start. Said timing dots on the gears are lined up (pointing at each other ) and it is on number 1 cylinder ready to fire but pops back through the carb.


They messed with it for many hours.
I told him timing dots need to both be at 12:00 and then number 1.
The old timer got mad when i said that and started going off in a rant calling me stupid.
I told him $100 bucks says i am right.
He shut up and would not bet me.
I had it fired up in less than 10 minutes.. but get this it ran like crap!!!


Seems this old timer that knew his stuff had a neat way he always adjusted valves.


Turn the rocker nut all the way down until it bottoms out the plunger in the lifter than back it out 3/4 of a turn.
Yea that did not work out so well.


Not saying your guy is a dimwit like the above .. just saying there may be other things he could do possibly to make it right.
Wondering what he actually did.
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post #22 of 37 (permalink) Old May 31st, 19, 3:08 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

Quote:
Originally Posted by jeff swisher View Post
! I've even taken the carb to a very well respected old timer who builds race engines and knows Holleys inside and out. He played with it, but it still has a HORRIBLE stumble just off idle.

Saying he played with it is pretty vague.
Could be he just messed with idle mix screws and float levels.


I have known many old timers that claimed they knew their stuff and maybe they did and they just got lazy or forgetful.
But I know none of them that really know their stuff..the one that I did know is long dead.


Had one of them messing with a new cam install in my buddies engine.
He had his own shop also.
Well they could not get the SBC to start. Said timing dots on the gears are lined up (pointing at each other ) and it is on number 1 cylinder ready to fire but pops back through the carb.


They messed with it for many hours.
I told him timing dots need to both be at 12:00 and then number 1.
The old timer got mad when i said that and started going off in a rant calling me stupid.
I told him $100 bucks says i am right.
He shut up and would not bet me.
I had it fired up in less than 10 minutes.. but get this it ran like crap!!!


Seems this old timer that knew his stuff had a neat way he always adjusted valves.


Turn the rocker nut all the way down until it bottoms out the plunger in the lifter than back it out 3/4 of a turn.
Yea that did not work out so well.


Not saying your guy is a dimwit like the above .. just saying there may be other things he could do possibly to make it right.
Wondering what he actually did.
I agree, don't assume the old timer knew what he was doing. That's like the craigslist ad that says the used engine or trans has been "gone through". who and what does that actually mean?
Do some research yourself and you might be surprised how much you can learn in a short time of getting dirty.
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post #23 of 37 (permalink) Old May 31st, 19, 11:50 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

I think Mark Whitener may be on this board, seems to be a well known carb guru
Have a similar issue seems the accel pump cam needs to be alittle more aggressive.

How is your dist curve set up?
I wouldnt buy a new carb just because you have a stumble they are all fixable.
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post #24 of 37 (permalink) Old Jun 1st, 19, 1:27 AM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

TV cable should be checked on the 700R4.

So should the accelerator pump and it's fuel cct. I've seen the check valves stuck from sitting, gaskets blocking fuel pathways.....And the pump arm to cam set loose instead of .015 free play when throttle wide open. Need a set of fresh eyes at the scene.

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post #25 of 37 (permalink) Old Jun 1st, 19, 2:30 AM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

Sounds like a couple people lack the ability to tune a dp and get it to work taking a different way to get to a solution.

Also, using the term "old timer" does not mean the guy knows what he is doing. He may have built hundreds, but still make mistakes or just doesn't do a good job.

If people can do it, and it seems like they can based on comments, then someone else can too.


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post #26 of 37 (permalink) Old Jun 1st, 19, 10:46 AM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

A double pumper can work just fine on the street with an automatic, assuming the carburetor is in good shape, not overly huge for the engine in question, and is adjusted competently. People do it all the time, me included. I took my 850 dp off my 468 and replaced it with a 750 street demon in a search for better mileage. The 850's street manners were GREAT, I only hope I can get the street demon to run as well when I have time to tune it. Don't get me wrong, the street demon runs pretty well, I just haven't had the time to tune it like I had with the 850.

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post #27 of 37 (permalink) Old Jun 1st, 19, 5:13 PM
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You can spend hours on reading posts and be stubborn or whatever, or you can spend $350, get a Street Demon or whatever VS carb and start enjoying the car👍
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post #28 of 37 (permalink) Old Jun 1st, 19, 7:03 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

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Originally Posted by yanniziomas View Post
You can spend hours on reading posts and be stubborn or whatever, or you can spend $350, get a Street Demon or whatever VS carb and start enjoying the car👍
That the OP's car runs great with a friend's vacuum secondary carb should point him in that direction, IMHO.

Sometimes, there is a fine time between learning and p*ssing in the wind.

If cash is not tight, I'd recommend sticking a new carb on and enjoying the rest of the summer. A DP will sell on eBay or Craigslist.

Granted, it's a Free Country..........

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post #29 of 37 (permalink) Old Jun 2nd, 19, 3:16 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

I am one of those guys that hates a vacuum secondary on anything other than a close to stock or mild engine. I played with them enough to say that from personal experience. My crate engine ZZ502 ( in a 70 SS TH400 and 3:55 ) came with a 870 VS and although it ran pretty good, I always felt it was lean on hard acceleration and could never get that pause out of it when the secondaries came in. I tried every spring they make, some made it worse some better but never went away. I tried every trick I could find, jets, PVs , moved timing all over the map, etc etc. I went to an 850 DP with 79 primary jet , 82 secondary, 6.5 PV and never looked back, the difference was truly astonishing . From the first time I started it you could hear the change, and it takes throttle anywhere in the rpm range and just flat hauls the mail. Of course the mileage dropped considerably but I don't really care. I think it is possible GM put that VS 870 on there to be a "safer" option for a more universal fit into all the different combinations that motor ends up going into, and not max HP. Like say a 4x4 truck with huge tires and so on. Just my 2 cents.
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post #30 of 37 (permalink) Old Jun 3rd, 19, 3:42 PM
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Re: 1969 with 700R4 and HOLLEY DOUBLE CRAPPER

Yup!

BTW, when I said "pooched" above, I meant someone had altered some orifices or one of the carbs plates are warped = pooched = not repairable or tunable. Otherwise, its only a matter of patience, time and good testing procedure ( change one thing at a time AND understand the interplay of cam/squirter/ jet).

Before you folks have the OP spend money ( and I do like hte new Street Demon 750 cfm), lets take a look at our "timing chart" for the pump cams... I'd guess the shot is coming in too early, as a more restrictive 25 squirter mitigated the stumble.

What color is in there now ? With the chart below and here you can graphically see the "timings" of the various shapes of cams AND whether its affixed with hole 1 ( summer) or whole 2 (winter). See what color you have now, and move to a color that a bit more delayed BUT try it with the original 35 squirter back in as a baseline, NOT the 25. ALSO, I would use the STOCK JET SIZES - again, as a baseline. AND, I would try a pink cam first. They are the least volume and most delayed as you can see from the chart.

69, If you report back, we'll guide you through the tuning process. If you choose to punt, buy a 3310, or one of these:
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