Holley Spreadbore 650 double pumper

[bear351c 10,270]

20 hours ago, gregaust said:

 

They usually only have 6 base plate screws , 2 spare holes . 

 

Thanks mate.!  That solves that issue. 

[gerg 10,871]

I was thinking the same thing Bear, the surfaces aren't machined so maybe they rely on thick gaskets to take up any wonkiness in the as-cast finish.

Holleys in particular have lots of circuits going through tiny passages in the gasket surfaces, so any small gaps between these circuits might have cross-feeding and affect the tune.

For a carby that's made in Japan, I can't say the casting quality is terribly good. Maybe Holley farmed it out to a Japanese factory very early on when Japanese quality wasn't quite what it had become by the 80s. These were a 70s replacement for a Quadrajet so I guess they may have cut corners to get it to market quickly.

I don't really know if making everything dead-flat has an effect on how well it works but I figured it wouldn't hurt do do it right while it's in bits

Those blank holes@gregaust mentioned are the ones that go under the power valve cavities? I drilled and tapped those too so I now have 8 x 6mm screws holding it all together.

Next is assembling the bowls and internals... And buy a wideband kit to tune it

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[bear351c 10,270]

Yup, reckon you're right.  I have watched a guy on Utoob who actually mills the faces to get them flat again, Serious carby guy.! 

[gerg 10,871]

Yup, reckon you're right.  I have watched a guy on Utoob who actually mills the faces to get them flat again, Serious carby guy.! 

I thought of that too, but gripping such an irregular shaped body in the vice isn't easy, it would be best to make up some kind of jig for it in that case. Knowing my luck, the body would jump out and Chernobyl itself in the cutter head or something dumb like that

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[bear351c 10,270]

Bah ha ha..........that's never happened to me. Not even once....

 

Small drill press mill with a fly cutter, and cross drive table would be nice.

[gerg 10,871]

This weirdo thing is a dual stage power valve. First stage opens at 10.5, second at 5.5. first gives around 0.030 of equivalent total PVCR while the second gives whatever your metering block PVCRs are drilled to, up to a maximum amount which I can't remember right now but I seem to recall 0.045 each side being the maximum that the valve can suport. I measured mine and they are sitting at around 0.035". Above that amount of enrichment, the valve can't flow enough so you'll have a lean-out at a certain power level. I would guess that this valve would flow enough on the primary side to support an engine making 300-350hp.

The reason why they made these is to try and get maximum economy and lowest emissions out of the factory-style Holleys of the 70s and 80s. One model that comes to mind is the first of the Fox body 5.0 HOs with the special Holley 4180C (600 cfm) square bore, which was considered a very good carby considering the tough emissions requirements of the time. They came with dual-stage power valves like the one pictured.

The premise behind them is that while jetting for cruise AFR, there needs to be some richness dialled in to cover the part-load conditions seen somewhere between cruise and the usual opening point of a standard power valve. With a dual-stage, you can jet leaner without the need to fudge it to cover any holes in the fuel curve. At light load the first stage covers this slightly richer requirement, then the second stage kicks in when the load comes on fully. So instead of the enrichment coming on and off like a switch, it's staged like a multi-step needle on a Carter/Edelbrock or even a bit like a bike carby.




Dummy assembled



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[bear351c 10,270]

On 12/24/2021 at 2:14 PM, gerg said:

This weirdo thing is a dual stage power valve.


 

 

 

Hmmm........ cool idea. If it actually does what its designed to do, why didn't we see more of these little fookers.??

[gerg 10,871]

 
 
Hmmm........ cool idea. If it actually does what its designed to do, why didn't we see more of these little fookers.??

Probably cost... They're about 5 times the price of your regular power valve but also people have just broadly accepted that you can't get economy out of a Holley, so don't bother chasing it. They aren't recommended on performance carbys, so I wouldn't use one on anything bigger than say a 600 square.

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[gerg 10,871]

So it's now on the car and running, haven't taken it out yet but had a few hurdles when reassembling.

Secondary pump housing had these weird channels cast into it that were bypassing the umbrella check valve and back to the bowl, could hear air hissing past it when testing. It would have had pissy flow once all together. So I epoxied up the channels to make the housing flat just like on the front bowl.


It's hard to see here with the clear epoxy, but it's there.



And I marked where the edge of the umbrella check valve would seal on the housing, you can see why it would bypass.



I can't find any pics or forums about this kind of accelerator pump, but it's irrelevant now...

Test run on bench with pump fixed:

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[gerg 10,871]

First drive impressions: pretty good for an old dunga. My dad brain made the mistake of buying 57s jets... The ones that came in it were 57s too. In any case, it surged on light throttle so that told me that 57s are lean. So, I swapped in some 59s I had.

The secondaries were also way lean at 67 (wrong on a non-power valve block) so went right up to an 89 drill on some jets I didn't want. Apparently 87 is the correct secondary jet for this carby, so not far off. If it had a power valve in the secondary, you would subtract 8-10 jet sizes to get the right mixture under load.

I don't see the point in running a power valve in the secondary, you're always under power whenever they're open, so the power valve will always be open under load or closed when the secondaries are shut. Blanking it off and jetting up to compensate is the go I reckon. Less failure points to worry about.

Just got back from a test n tune, it has woken her up a bit, feels more lively than the street demon, but has sacrificed a little bit of bottom end torque and smoothness (probably from having older design boosters).

You can still feel a little bit of leanness when accelerating moderately, in that once the pump shot is done, the power drops off a tad. Still might need more jet but I'm happy with the WOT performance.

Now to see if it guzzles the juice or is somehow actually better than the street demon.

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[bear351c 10,270]

Good stuff, mate.   Carbies are a dying art.

[gerg 10,871]

I'm a bit of a meat-axe at this but I'll gladly share what I know, it's rare to find anyone who knows them and the ones that do don't like to share. With any luck the interballz will be better for having some knowledge on it preserved.

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[bear351c 10,270]

Yeah, I've learnt heaps from the Interknob.  Uncle Tonys, Luke (Thunderhead289), Muscle car solutions, all have interesting videos, once you trawl through the garbage while they try to entertain you. Good vids on the Rockys Roadshow channel, full rebuild of TQ and Rochester carbs, but MAN.!  he drags it out..

[gerg 10,871]

Yeah, I've learnt heaps from the Interknob.  Uncle Tonys, Luke (Thunderhead289), Muscle car solutions, all have interesting videos, once you trawl through the garbage while they try to entertain you. Good vids on the Rockys Roadshow channel, full rebuild of TQ and Rochester carbs, but MAN.!  he drags it out..

Yeah that's the challenge... Finding a good presenter that both gets to the point and shows stuff that is useful, not take 40 min to tell you 90% of what you already know. Uncle Tony is pretty good, he gets to it pretty quickly. I saw a vid of his just this morning about resurrecting a stuffed car battery using a stick welder (looked sketchy but that's how he rolls).

Above that level of skills, people start getting very cagey about their craft, as they likely are specialists in the field and only give away snippets of info that keep it mysterious and therefore doesn't kill any business for them.

Vizard is good but I feel that his tech videos are an annoyingly slow drip feed of info.

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[bear351c 10,270]

2 minutes ago, gerg said:

Vizard is good but I feel that his tech videos are an annoyingly slow drip feed of info.

 

Yep, he's the worst...... So knowledgeable , but so hard to listen to. 

[gerg 10,871]

 

Yep, he's the worst...... So knowledgeable , but so hard to listen to. 

To be fair, he did mention in one video that he had surgery a few years back, sounds like they removed a brain tumour or something and he lost a lot of his ability to recall memory, which explains why they stop and start his videos all the time. Maybe he needs to go over notes constantly?

 

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[bear351c 10,270]

Yeah, fair enough. Not knocking the guy's intelligence or knowledge, he is a Guru.....  I just have a short attention sp..  Look, a squirrel. 

[Kiwi-E 731]

I'm a bit late to the party here, but I ran the same carb on my mild 351c (302 2v heads) with a eldelbrock performer manifold & spread bore adapter.

 

After messing around with the wideband gauge and some street tuning it ran really good.

 

After a number of different squirter trials, I ended up increased the primary squirters from 25's up to 31's and the secondary squiters from 37's up to 42's. This kept the AFR readings pretty smooth when matting it from any rpm. (manual trans) The factory acc. pump cams seemed to work best for me. 30cc primary pump and 50cc secondary pump.

 

Looking at my jet box, i lowered the primary's from 68's to 66's, and the secondaries from 76's to 75's. Although I probably may have gone back to 76's to be safe. WOT AFR was about 13:1 from memory with the 75's.

 

I never played with the primary PV, and can't remember what vacuum it was. Secondary PV was blocked off.

 

Different motors and all,.... but there's a reference for what seemed to work pretty good for my motor for what its worth.

 

Edit:

Just looked again at the jetting you've tried already .... Quite different,....... Take the above with a grain of salt

 

[bear351c 10,270]

Good info, cheers for that.

[gerg 10,871]

I'm a bit late to the party here, but I ran the same carb on my mild 351c (302 2v heads) with a eldelbrock performer manifold & spread bore adapter.
 
After messing around with the wideband gauge and some street tuning it ran really good.
 
After a number of different squirter trials, I ended up increased the primary squirters from 25's up to 31's and the secondary squiters from 37's up to 42's. This kept the AFR readings pretty smooth when matting it from any rpm. (manual trans) The factory acc. pump cams seemed to work best for me. 30cc primary pump and 50cc secondary pump.
 
Looking at my jet box, i lowered the primary's from 68's to 66's, and the secondaries from 76's to 75's. Although I probably may have gone back to 76's to be safe. WOT AFR was about 13:1 from memory with the 75's.
 
I never played with the primary PV, and can't remember what vacuum it was. Secondary PV was blocked off.
 
Different motors and all,.... but there's a reference for what seemed to work pretty good for my motor for what its worth.
 
Edit:
Just looked again at the jetting you've tried already .... Quite different,....... Take the above with a grain of salt
 

Funny, I was just going to update on the carby and suddenly there's a new post!

Thanks for that mate, that's not far off what I have, looks like you went a bit richer in the primaries and much leaner in the secondaries, I went 63/89 but I did open the primary main bleeds a tad (one drill size over stock, probably 37 up from 35), which has the effect of lowering the effective jet number but altering the fuel curve too. Your squirters are likely right for a bigger motor (351 vs 302), I have 25/37 in mine and it feels spot on.

The biggest gain on this carby, economy-wise, has been idle circuit tuning. I have opened up the idle air bleeds a ton (it's at about 70 now) and it has made a massive difference to cruise economy. I haven't touched the IFRs as I prefer to play with the bleeds before drilling the metering blocks, and if it comes to the worst, (ie going too big) I can just drill and tap them for replaceable bleeds.

So... This is the 4th carby I've had, and in the past, the absolute best that any of the others could do was 420 to a 65 litre tank, with the average sitting around 380-400. This last tank, albeit with lots of motorway cruising, just got 460 and only used 60L. So sitting around the 13L/100km mark. I'm pretty stoked, and I'm sure that on a long trip with pure highway running and a careful right foot, I could crack 500 k's. That's 6-cylinder territory!

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