I think I may need a rebuild, but.

My Dart with 3.55 rear, Clifford headers & intake, Holley 4160 vacuum secondaries, and mild cam in June returned 21 mpg. on that great $4.45/ gallon gas. Now it's using the top third of a tank to go 45 to 50 miles on the cheep $2.15 gas. Dollars per mile remained constant, but fuel consumption seems to have become a bit glutinous. I suspect the secondaries are cracking open too soon, but what do I know.

Changes performed since June: installed missing long spring on 11-R mechanical advance (7-R vacuum can); set valve lash .002" over standard .010" & .020"; and reset timing to 12 deg advance at idle. These changes increased manifold vacuum, smoothed out the loping idle, and perhaps increased performance marginally as judged by standard SOP test method (seat of pants).

There is no bog on take off, looks to be a good strong accelerator pump squirt, but there is a nice flat spot when wide open throttle is applied at road speed say 45-70 mph. The engine has always had this flat spot, but it seems to be more pronounced now.

There is no smell of gas when parked, no gas leaks in and around the carburetor, no back fire up through the carb, the choke pulls fully off when warmed up, no spark knock, and no black smoke out the back.

Do I need to change out the secondary's vacuum spring, or perform a total rebuild? Any ideas.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Secondary spring may be part of it, but a good question is how old is this Holley... those made before 1993 do not have any backfire protection and any little 'pop' will ruin the power valve...there are kits that can fix this flaw for about $10 and 5 minutes with a drill and punch...

more seriously...

Have you driven around with a vacc. gauge yet to see where your 'cruise' vacc. reading is, and how the reading dips when you hit the 'go' pedal... if the reading 'dips' into the range the rating the power valve has on a regular basis you'll lose plenty of mileage that way...

The reading can also help you determine your timing and where your vacc. advance is at... if you are using a EI distributor, you can get away with more vacc. advance 7r is a good start, but tit may want more at cruise.


-D.Idiot

I agree with DI, after checking the power valve and installing the blow protection (if yours doesn't have it), I believe you would be much happier with a 11R vacuum pod for more advance at cruise resulting in better mileage. You may have to unscrew the pod a little so it won't come on at idle. Example: on my 74 I have it unscrewed 3 turns.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I do have the orange box, so I'll be shopping for an 11 R can. Someone want to share a part number for a 11 R? Would that be a VC 208?

I have not driven with the vacuum gage in the cockpit, just used it under the hood. I'll have to get an extra length of hose, and run it through the window.

I think the carb is post 1993 vintage, but how dose one identify the anti backfire upgrade, or lack of upgrade?

From a Sep. 24, 2008 post under "Engine" titled: Compression & Vacuum questions by me:

September vacuum test results after valve lash adjustment & vacuum leak eradication program completion:

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I would procure a VC-239 instead of the VC-208...and see where that leads. I would get the hose and get some drive numbers first, before making the mods....

-D.idiot

Maybe later on today, just too cold this morning to play with junk @ 18 degrees F.

Perhaps I give the old girl a cold start test. When I first got the Dart, she would not easily start below 50 deg. because of a poorly adjusted choke , and non operating electric pull-off.

Off to NAPA for hose & VC 239 can.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Road test vacuum readings:

Secondaries open around 10" to 12" of vacuum.

Constant speed of 45 to 60 mph vacuum runs a 16" to 17", closed throttle vacuum goes to 24".

Slightest throttle opening, or hill drops vacuum to 9" to 10" which is where the secondaries open.

Vacuum never drops below 5" at wide open throttle.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

WOT I think needs to be 1.5" The vac at cruise on flat ground? Sounds low.

The vac climbing a hill sounds OK. I am going off numbers in my 6000lb van and a 360.

Not a Hooolee expert but sounds like a PV change maybe in order. I would think the secondaries opeing at 10 is too soon. Maybe a different spring in the vac diaphram.

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

Where is the vacuum gauge connected? Does the gauge read Zero when the engine is off or the gauge is disconnected? How are you verifying the secondary opening? The are called vacuum secondaries, but they do not work off manifold vacuum like the power valve. Air flow through the carb creates the vacuum that opens the secondaries.

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Joshua

Josh,

Gage is new, reads zero at atmaspheric pressure, & vacuum hose is new.

Connected gage to the vacuum port at base of carb under center of front fuel bowl. Or, in other words, center of primary side of carb below venturi & butter fly.

See Fig. 4, it is labeled Full manifold vacuum source:

http://www.holley.com/data/Products/Tec ... 8108-2.pdf

When opening throttle & vacuum drops to the 10" range, a flat spot manifests it self, than she starts to pull harder. I had guessed that is when the secondaries were starting to open. That flat spot is always there, more noticeable at lower rpm, less so at higher rpm. If one quickly lets off during hard accelleration, than floors the go peddle, the flat spot almost disappears. Vacuum goes from 5" to 24" back to 5" during this process.


It is very easy to dip this engine to 10" or less with not much throttle movement.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Sounds like what you are feeling is the Power Valve coming in. Standard valves come up to 10.5" HG. That's a good one for use here. There are economy type dual stage power valves that come in at 12.5" and another value, like 5 or 6" as an example.
If you pull it and it's a dual range, install a 10.5. You will not be able to get your slant six to run right with the dual stage power valve.

You aren't getting full throttle if your seeing 5" HG at WOT. Even with the little 390, at WOT before the secondary opens, you will still see close to or zero. Nuthin' on the gauge. At low RPM, which is the definition of these engines, you can't pump enough air to keep a noticeable differential across a 4bbl carb.

You really need to know what secondary spring you have in there. Anything above plain, and you likely aren't opening the secondary at all. If you aren't getting WOT, the secondary won't open up anyway.

Do you have the Chrysler throttle lever adapter installed? Without it, it's not possible to operate the throttle all the way with a cable type accelerator linkage.

CJ

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Part of Tyrde-Browne Racing

I do not have the Chrysler linkage.

Today I received a little book titled "Holley carburetor Handbook 4150 & 4160 Selection, Tuning & Repair" by Mike Urich. HPBooks, 1980. I read it this afternoon, and now have a better understanding of how a Holley works.

Back to the gas hog.

When the secondaries open will I hear a deep wail like a V8 makes, or different sound?

Ceej I think you may have something there. I do not hear any different song from the carburetor at WOT. That flat spot must be due to a lean condition just before the power valve opens. So if the power valve opens at a little higher Hg than that flat spot would lessen.

As for the spring operating the secondaries I have no idea which one it is.

Tomorrow I will make another vacuum test run. This time I will have a clipboard and take notes, rather than trust the dome to remember all the fine points of the data. I did notice when at low idle in gear, car not moving, the needle oscillates rapidly from 0Hg to 14 Hg. a few more rpm smoothes it out.

So do you have any ideas why fuel consumption is way up?

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Yep, you are dipping into your power valve and with that open you are guzzling gas (pretty bad when they call it the "economizer" valve...)...
the lowest PV is 10.5... stock for that carb was like a 7.5-ish...

what technically needs to happen here is two-fold...the flat spot is probably a lean spot between your idle/transition circuit and the main metering coming in... when it dips in the vacc. area the PV is rated at... you get a big 'gush' of gas and it takes off... to cure this per the book you have... you will be working toward changing the accelerator pump shot to cover that 'spot' (or a combination of a 'shooter' and a pump cam)... the other thing is to tune the primary jetting so it's adequate and not 'rich'... and a possible 3rd scenario can also be having to put a wire of a certain size into the air bleed so the idle circuit jumps to the main circuits a bit sooner...

If you change your timing, you will have to retune your carb too...
I concur that the vacc. is a bit low, and the vacc. drop when you are on the pedal is a bit much... if you richen the mix and the vacc. reading goes up, you're a bit lean...don't over do it though.

good luck,

-D.Idiot

Im by far no expert.But when I had my srt-4 and the vac/boost guage started to jump around on me I traced it down to a vac leak. I had almost the same symptoms,flat spot at speed,HORRIBLE fuel economy...and this leak was small... were talking I did a pressure check on the intake side and it took close to 2 hours before it dropped significant psi.ended up being the inlet side of the intercooler had a mini baby leak where the inlet tube met the intercooler frame.Replaced the hose and clamp,problem went away.

Again I dont know if this will help,but it sounded strangely familiar. Check for vacuum leaks if all else fails

ALL of the above - and compare your setup to the one in the slantsix racing manual did mine letter for letter the same and I have NO complaints

I know it is not the list 8007 but it works

Package: 4 Barrel Set-Up General Multi-Purpose
Carburetor: Holley List 6299
Manifold: Offenhauser Aluminum 4 Barrel PN P3690801
Manifold Modifications: None
Carb Specifications: 390 cfm Holley, vacuum secondaries
Primary Jet: #49
Secondary Jet: #52
Power Valve: 25R-591A-65
PV Channel Restriction: .052
Idle Air Bleed: .078
High Speed Bleed: .043
Diaphragm Spring: Yellow

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Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars