In gear idle rpm is 650+/- with osculating needle zero to 5 “ Hg. of vacuum with a pronounced lope, and park idle is 1100 rpm with 8-9â€￾ Hg vacuum. Cruse vacuum at 2500 to 3000 rpm is 15 to 17â€￾ Hg on flat ground.225 ci, oversized valves, 9.1 calculated static compression.

I have a mystery cam that came with the car, and have recurved the distributor not to advance until 1500 rpm’s to settle down the idle.

Presently have 2.5 power valve installed, and 51 jets. I believe at idle, PV is activated & dumping excess fuel, while in stop & go traffic. In town fuel mileage is not good, and highway mileage is 17.5 to 18 mpg.

I called Holley tech line, the guy recommended blocking off the power valve, and jetting up six sizes of jet to 57, rather than installing a 1.0 in. Hg valve which I have on hand.

Presently I have very good plug color with the 51jets. Wouldn’t 67 jet’s make a rather rich mixture for general driving, and increase fuel usage?

Bill

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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

Once you plug the power valve, there is no fuel coming through that part of the circuit at hard throttle, so you need to jet up. I recall that it was about 4-6 jet sizes up when I ran this on my 500 Holley 2bbl way back when.

I am actually going to do this on my 500 again due to an issue with power valve fluctuation when I stage my racecar at the dragstrip. I do not need the "step up" function that you usually need on a street car, so I can plug it.

Your big cam may require this plug and could still work very well. Worth a shot! I would say go with 56 jets and see how it goes.

Do you have an O2 sensor? I am pretty good at tuning carbs "by ear," but man the O2 sensor takes you to the next level and saves a ton of time, especially a wideband sensor ($200 from Summit - AEM or Innovate).

Lou

_________________
Home of Slant6-powered fun machines since 1988

Dart 270,
I understand that, and I’ll be on the rich side 100% of the time. Most likely that condition will produce a bit more power the full rpm range.
No O2 sensor. I have thought about popping one in just to tune the carburetor, but haven’t gotten to it. I have seen a welded in anti-foul spark plug socket, and a cheap single lead O2 sensor set-up, and using a VOM instead of those LED equipped kits to read the voltage, or resistance, whatever, one can get out of it for 50 bucks or so.

I have been using my vacuum gage & tachometer to tune the idle circuit.

I know the power valve is still dumping some fuel at idle, because when I kill the engine running below 1100 rpm, it will run on or diesel. Higher rpm and it will shut off with just a little protesting half hearted semi back spin of one partial revolution, which bugs me practically when someone is around to listen to it… Not cool.

Bill

_________________
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

Bill,

You might be surprised, try it. A jump to two #57 jets is not that big a jump if the power valve is currently leaking or letting some fuel in when driving around town. My son had to do this on one of his cars and it cleaned up the idle very nicely for having a wild cam......the cam (vacuum pulse) just sends to many odd signals to the carb. Plug the power valve and bingo....

You may need to jet a little higher, maybe 60's.......

The plug will kill the back spin.

_________________
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

Just a thought, as if you haven't thought of it already:

Try advancing the cam some, or degreeing it to 100 deg centerline. That would likely get you more idle vacuum.

Good luck w/carb tuning!

Lou

_________________
Home of Slant6-powered fun machines since 1988

AG Ted,
[quote]the cam (vacuum pulse) just sends to many odd signals to the carb. Plug the power valve and bingo....[/quote]

All right I’ll order up a pair of 57’s, a pluger-upper, and see what happens.

Dart 270:

[quote]Try advancing the cam some, or degreeing it to 100 deg centerline. That would likely get you more idle vacuum.[/quote]

I haven’t yet degreed anything, accept my kids when they were up to no good years ago.

To be honest, I’m a bit reluctant to mess with the cam’s timing, as I don’t have a wheel, or someone at hand to hold my greasy hand while performing the unknown, or any information as to what the grind is. So I’m going to let it be.

I may back off the lash from, 0.013â€￾ & 0.021â€￾ a few thousands to pick up a little more vacuum.

Bill

_________________
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

Understood.

Another question:

Does the vacuum and idle quality get worse as the car heats up? If so, your lash is too tight and you can back off in 0.002" increments until the vacuum is similar at normal op temp (or hottest it gets) compared with after running for only a few minutes.

My apologies if you have done this already and posted it earlier.

Lou

_________________
Home of Slant6-powered fun machines since 1988

[quote]Does the vacuum and idle quality get worse as the car heats up? If so, your lash is too tight and you can back off in 0.002" increments until the vacuum is similar at normal op temp (or hottest it gets) compared with after running for only a few minutes.[/quote]

Lou, it is quite all right. That lash has been in & out in 0.002â€￾ increments up to 0.012â€￾ over stock several times. You just happen to jump in during a tight moment in its sinusoidal adjustment sequence during this magical mystery tour I have been on for the last few years…

Another question for you or Ted:

When I first started to unravel the secrets of this engine and carburetor’s workings, I followed the advice of Mike Urich, author of “Holley Carburetor Handbook 4150 & 4150 Selection, Tuning & Repairâ€￾, and progressively drilled the throttle plates until idle mixture screws would respond. Currently there are two 3/23â€￾ holes drilled, one for each primary plate.

Mike recommended that when an aggressive cam is installed it is sometimes necessary to let in more air to achieve normal idle speeds, and have idle mixture screws work.

Should I solder these holes up when plugging off the power valve & jetting up, or let them be for the present?

I’m tempted to keep the drill holes for now, making only one change at a time for simplicity.

_________________
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 keep holes for now.

If the engine vac has been higher before with looser lash, then you're on the right track with looser lash. At a certain point of loosening lash, you will see no further improvement in vacuum, and it will not run worse when hot than when cold or coolish. I'm just reiterating, since it seems like maybe you had better luck with looser lash earlier?

If the cam is really that big, then I can't believe you'll get it to run right with less than about 0.020" intake lash and more on exhaust. For reference, my '64 Dart cam set up at 0.025" int and 0.029" exhaust and has been in there running like hell for 40k+ miles. It is a bit noisy, but it is a big cam - 250 @ 0.050" and 0.510" lift.

Just feeding the fire here and spouting random thoughts this morning...

Lou

_________________
Home of Slant6-powered fun machines since 1988

Lou,

Is this the setup your getting the good mileage with, 27+ mpg?

_________________
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

Yes, that's the car. I would call it 25-27 MPG now. Car runs mid 14s in the 1/4 mile and uses pump premium. Obviously the big cam is not hurting it too much, although I'm sure I can do better.

Lou

_________________
Home of Slant6-powered fun machines since 1988

As of 5-2010 the intake was set at 0.016â€￾ and exhaust at 0.026â€￾ if I remember correctly. Notes are missing for this adjustment. I don’t recall a big difference in vacuum readings between: I = 0.012, and E = 0.021â€￾, and previous setting, however the valve train has been a lot quieter.

Tonight I’m going to loosen them up in 0.002â€￾ steps and see what happens on the vacuum gage during in gear idle & park idle. Other vacuum readings at higher rpm are not concerning me as much as the low rpm zone at the moment.

Also going to conduct a compression test after a looser setting has been made. The compression is down about 5 psi with the tighter settings.

Lou,
What rear gear & tire size are you running in the 64?

_________________
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 good on the adjustments.

3.91 rear and 24.7" diam tires, 0.63 overdrive on the 5spd.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Lou,

Would you mind putting together a comprehensive build sheet on the engine and weight, ratio, header, muffler, etc. on your car? I would like to get down in that range at the track and still have a daily driver. I know my car will never be that light but some next steps would be fun to work on! I always like a goal to work to.


My car weighs 3380 lbs with a full tank, 3600 lbs with me in it. Book specs show up to 3180 lbs. in 1974. I am not sure what would be a good choice for the next cam. I am running a E254 profile .435 lift now. It's fairly spunky at low rpm but poops out at high rpm. It would be nice to have a little more of both......

_________________
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

Lou:
Ah-ha. So that is the secret ingredient, over drive! Is the transmission a T5?

_________________
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