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Old 03-03-2003, 05:28 PM
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Post Double Pumper vs. Vac Secondaries

Last year I did several exieraments with secondary springs in my carb.I kept going lighter each time expierianceing better perfomance.They say to go down in size till you expieriance a bog then up one size.Well I got to the lightest and no bog,so I made the linkage mechanical for an expieramnet.I took it to the street and stomped it there was a split second bog,which I attribute to no secondarie squirters but after the bog the car took off like an animal.
So I'm thinkin I wanna find a rebuildable 600-650DP.Way more tuning capabilities too.Two sets o squirters and pumps and jets etc..
Thing is I here all this crap about how terrible gas mileage becomes.How can this be unless you got your foot in it hard enough to open the secondaries???Considering my car turns approx 2400-2500 at 55mph I don't think I'll be in it that hard...well unless...but thats another story.Anyone have gas milage stories when swapping over??

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Old 03-03-2003, 09:03 PM
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[quote]Originally posted by 78 monte:
<strong>How can this be unless you got your foot in it hard enough to open the secondaries???</strong><hr></blockquote>

Aren't you wanting mechanical secondaries?
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Old 03-03-2003, 09:30 PM
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Not sure what ya mean??
I don't have one in front of me to look at but I thought there was slack in the linkage on the side of the carb,so it didn't open till the butterly was cracked 1/4 or so??
I rebuilt one about 3yrs ago,but can't remeber.
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Old 03-03-2003, 09:47 PM
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Well, I'm not really sure to be honest, I never had one, but if that's true, then how would the secondaries reach WOT?
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Old 03-03-2003, 10:01 PM
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Ratio between the size of the linkage pieces the secondaries have a smaller piece.So they need less travel too be opened.
Not to mention can you imagine tryin to creep a car forward in traffic with say a cop in front of you when everytime you crack the throttle your open the 4bbl.

[ March 04, 2003: Message edited by: 78 monte ]</p>
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Old 03-03-2003, 10:13 PM
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Holley double pumpers have direct acting links, thus the need for the double pumps. The secondaries begin coming on as soon as you crack the throttle. Are you sure there isn't a leak in the secondary diaphragm circuit or a plugged pitot tube (little tube in the primary venturi that sends a signal to the diaphragm)? Sounds like your ssecondaries won't ever open automatically like they should due to problems with the system, not carb design.
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Old 03-03-2003, 10:26 PM
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When I went to the track I was disapointed to find it run 14.5,but don't think the secondaries were working right as it was struggling to pull in the topend.Tried to confirm it by the seat of my pants at home by locking out the secondaries and it felt the same.
So I replaced the diafram which was dried.
I'm sure theres vacuum at the diafram as each spring made a differance.But a weak signal I don't know,which would amount for it needing the lightest springs.I did spring changes after the diafram replacement.
On the lightest spring it pulled strong with the secondaries open pretty wide by 3000 or so.But it seemed to have more grunt with the secondarie linkage made mech.
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Old 03-04-2003, 06:10 AM
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How big is the carb and engine? You may have the rare exception of too small a carb on too big an engine. I would still try to make the vac secondary work. Try taking the carb apart and noting part #s for all the metering blocks, jets, squirters, etc. and calling or e-mailing the info to Holley for their advice on modifications. My guess is that your carb just needs tuning to come to life.
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Old 03-04-2003, 06:56 AM
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It was just a mild 350 so a 600 vac should be fine.Actually I've got a differant but similar motor goin in for spring so I still gotta see how it runs on the new motor befor I start changing anything.But I had been thinking double pumper for a while since I played with it.
As for the carb when I got it it had sat for years and dried out.I rebuilt it 3 yrs ago,everything but the diafram and shaft bushings.All new non stick gaskets,50cc excelerator pump,high flow needle and seats.And cleaned the **** out of it.I blew through all the passages in the metering block and everything was clear.And I rejetted it.
Allthough it may need cleaning again,maybe I'll pull it apart and blow it out again.I built it used it for a summer,then the car had to sit for a year so it could be full of crap.I don't remember how it ran the first year but I think I would notice no secondaries.
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Old 03-04-2003, 09:54 AM
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When you tear it down, note the sizes of power valve, metering body, etc. I think a few changes in tuning will do the trick. Speaking of power valve, have you sized it properly? Should be rated 1 number lower than idle vacuum reading.
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Old 03-04-2003, 01:32 PM
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Nah,I just stuck the power valve from the kit in.Its for lower vacuum but I have no clue what rating or if it matchs my setup.That'll be next to change,well if its not right allready.
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