It's like an old game show game..."Name that cam!"

I can name that cam in 5 data points...Contestant #2...I Can name that cam with 3 data points....

I think once we get this figured out and get the cam dialed in on a good centerline...you'll have more power than you know what to do with...better idle...have to use an 8.5PV...and jet back to a 52...
and you'll save money from not having to buy any more carb tune up items.

It just feels like the cam is retarded so badly it's just not being effective...
(I think it's off about 1 tooth if it's a roller chain assembly...)


-D.idiot

I think I would do a leak down test on all the cylinders, even if you have to pay a shop to do it for you. THis does sound like there is something wrong, maybe cam not degreed right, valve leaking, unknown vacume leak, or even possible the carb just not even close to being tuned right on the idle and cruise. It could even be a dizzy/ignition problem.


Either way, go over the basics very good before tearing down. The over spin when shutting down could be a combonation of to fast a idle, incorrect timing ( to high on the base ) , or even too hot a plug ( staying hot enough to fire the fuel after shut down). Ofcourse degree the cam is a good idea and should be done even if you do fix your problem before then ( always worth power, drivability, MPG & smoothness) .


IMHO I would close the holes in your carbs plates. It takes a very radical setup to need that most of the time. Of course it comes down to the possition of the plates in relation to the idle slots in the carb to determin if they are needed or not even then. Most of the time even if it might show needing such a thing the problem can be cured other ways that make much more sense & tunability. It is a last resort think.

The one thing that keeps sticking out to me with your info of the problem is the heavy flucuation of the vacume & the spin back. Neither should be going on. If the cam was so big to help bring on these problems I feel like your power curve would be way higher than it is, plus your bottom end power would be very weak with the compression you have and things like burning tires would be very difficult. Some vacume movment with a big cam is normal, but it should not be nothing like your are descibing.


One other thing to look at if no one has meantioned it, check the PCV valve to make sure its not jumping open & shut when idling.


Jess

LUCKY13,

The head was rebuilt with oversized valves 6,000 miles ago. Vacuum readings did not change much after valve job. Cylinder walls were not scored, nor was there a worn lip at the top of stroke. Compression is down a little in #4 after valve job, but the rest are 150# and above. For now I’m ruling out the head.

Ignition system is new, distributor is tight, no slop in X or Y axis.

No vacuum leaks.

When power valve plug is in place, there is very little to no back spin. With #1.0 & #2.5 power valve, all kinds of back spin, particularly with hot engine. I may have to make a heat deflector, as Ted has suggested that per haps I’m getting some peculation in fuel bowl. The carburetor is generally hot to touch after engine reaches operation temperature.

I do know that the power valve is pulsating to the beat of the vacuum gage needle, and every time it swings down to zero those valves pop open providing a shot of fuel. And, swing it dose at 600 rpm when in gear; zero to 6â€￾ Hg.

I will plug the holes in the throttle plates, but previous experience had shown that idle quality, and adjustment suffer greatly. Presently when the vacuum tap cap at the base of the carburetor is removed to attach the vacuum gage, idle speed increases noticeably. This injects additional air over and above what throttle plate holes provide. I’m still pondering this event.

I have less than 0.026â€￾ of transition slot showing when throttle plates are closed, and no flat spots at any throttle opening.

Engine smoothes out at 1100 rpm, vacuum gage needle steadies around 950 rpm at 10 to 11â€￾Hg. This cam likes the rpm’s.

What I’m going to do first is take some readings to identify what that cam is, and if it needs to be advanced or retarded a few degrees to correct this vacuum problem. At present it is the only unknown part to the puzzle.

I’m still scrounging the gear need to degree a cam, once I have it, I shall get to it. Just because I have been procrastinating measuring my mystery cam, doesn’t mean I’m not curious as to what is in there. There are a few others here, that if they lived closer to me, would have shown up, put me in a head lock, and forced a reading, because the mystery has been driving them nuts… LOL

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

Ted,

I couldn’t take it any longer with 1.0 “ Hg power valve puking fuel at low rpm along with the kick back death sputter, it's all just too irritating. Re-installed the power valve ‘plugger-upper’, while keeping the 57 jets in place. Also changed out the purple secondary vacuum diaphragm spring to the lightest spring...

Death sputter is gone, idle quality is smoother, and vacuum gage is pushing 13 inches Hg at 1000 rpm. The change was noticeable immediately when the engine fired up, it was more settled.

I know, I reported that 57 jets produced lackluster performance on the road, but I’ll give this combination a second chance. Perhaps with the secondaries opening a little sooner performance will be a bit better…

Tomorrow we head down the road to a car show, so I shall have a chance to see how this combination works during a 40 mile trip on two lane back roads, with top speed limit of 45 mph. Short test runs sometimes don’t tell the whole story, so this will be interesting, if nothing else leisurely.

Still working on locating degreeing gear.

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,

Glad your giving that combo another test. Your working around the cam problem pretty good. That question still needs to be addressed, but another day. As long as you can get it perform reasonably well in the mean time. You got a good work around.

Let us know how it went after you get back.

_________________
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

Short up-date for 57 jets with power valve plug in place, and lightest vacuum secondary control spring installed:

I have only driven the car about 100 miles since latest jetting configuration, and posting. Too soon for fuel mileage calculations, however by gas gage SWAG analyses looks to be better than 60 jets.

Performance is OK on the road, take-off thrust feels to be down from 60 jets. About half of 100 miles of driving was in town, the other 45 to 50 mph two lane country roads.

Spark plugs number: 2; 4; 5; 6; read as #14 & #13’s; #1; & 3 read as #11’s, according to plug[url=4secondsflat.com_chart.html]chart[/url].

Next weekend, weather permitting, I’ll be off on a 200 mile round trip to a car show and be able to evaluate fuel usage on one tank.

I did discover, was, with lightest secondary spring installed, the secondaries open at about 4400 rpm with no flat spot during transition, but with a surge of power. Unfortunately this secondary opening event is hard to test in a 45 mph zone that surrounds my location for miles, because I’m just coming on to 70 mph in second gear at 5000 rpm. That would equal a 200 dollar ticket if radar man were to observe this test, plus the three year kiss the insurance company would send in the mail…

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

4400 rpm seems a little late to me. This is the white spring you're talking about right? The white spring opens at around 2400 rpm on my engine. I guess my engine has more CID than yours but I wouldn't have thought that would make that much difference.

_________________
62 Valiant, 225cid Slant 6/PB 904 with lots of good bits

http://www.moparmarket.com/readersrides ... user=SV162

Sv162:
Yeah white, or chrome can’t remember, but what ever the directions listed as lightest I have installed.

4400 rpm is when I feel a surge of power, it could well be the secondaries are opening at a lower rpm. With out being able to look at the linkage attached to the diaphragm to see it move & when, I can’t tell. I can’t hear that howl like one can hear on some V8’s because my car is just too damn LOUD in the 2300 to 2800 rpm range.

Maybe that cam I have is just coming on in the mid 4000 rpm range. I just can’t tell. Mid 2000 rpm range is on the doggy side in comparison.

I wrapped a twist tie around the diaphragm’s linkage rod to show any movement, and it did, but not at what rpm.

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

SV162:
[quote]4400 rpm seems a little late to me. This is the white spring you're talking about right? The white spring opens at around 2400 rpm on my engine. I guess my engine has more CID than yours but I wouldn't have thought that would make that much difference.[/quote]

If 2400 rpm is the starting point for that light spring, than I need to pick a spring that will retard opening to some rpm slightly above my highest normal cruise rpm for better fuel economy.

From Mike Urichâ€￾s book: “Holley Carburetor Handbook 4150 & 4160 Selection, Tuning & Repairâ€￾ Page 35 shows a chart for 350 & 402 cid engine listing secondary throttle operation ranges.

Yellow spring on a 350 cid engine starts to open @1620 rpm, and full open @5680 rpm. The larger displacement 402 has 1610 rpm to 4960 rpm… These results are from a larger carburetor as well.

I wish there was a chart somewhere depicting a 390 cfm 4160 carburetor on a small displacement engine showing secondary opening rates.

I have to believe that your 2400 rpm start point is right on.

Are there any easy & inexpensive ways to determine when the secondaries start to open & reach full open without taking the hood off, and having my wife sit on a fender observing while motoring along a public way? --- Not that that would ever happen even several years after Hell froze over.

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

Yes, install a vacuum gauge on the secondary diaphragm.

_________________
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

Ted:
Hummm… Ted, I never thought of that.

Dead air while rusty wheels churn within cortex….

Aren’t all the vacuum passages that activate that diaphragm integral with the carburetor body, and no external taps exist to access them? Doesn’t that diaphragm get a vacuum signal from the upper portion of primary venturi? Or, am I missing some glaring concept here that will require, once brought to light, a slap to the center of my forehead with the palm of my hand, and some mild cussing in regards to a dumb guy wearing my shoes?

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

Primary/Secondary carbs (4 bbl, 2bbl) usually have a lock on the secondary barrels so that they won't open until you're 1/2- 3/4 open on primary barrels.

So you don't have to worry about the secondaries opening at cruise speed.

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Emsvitil / ED: So is why I feel the strong rush around 4400 rpm; because the primary throttle has reached a sufficient degree of opening, where the secondary throttle plates are unleashed, and allowed to open to whatever degree they can at that particular venturi vacuum level?

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

You'd have to pull the pod, lock the secondaries shut, and put a tap at the lone port that feeds that side of the diaphragm. My vote is using a set of radio shack parts that has a micro switch or contacts at the secondary actuator to light a LED in your car so you know it's opening or opened.

Back in the day before this was an option, my grandfather drilled the hood of his car and used a peice of coat hanger sticking out the top of the hood when closed to see if it was moving up or down....


-D.Idiot

I hear you there, it would be very handy. But I'm guessing they would be only ball park figures given the differing engine builds. I suppose sometimes a ball park is better than nothing.
I've run with different vac spring on the same engine and the only thing I had changed was diff ratio. 3.7 gears it liked the purple spring, 2.92 gears it liked the short yellow spring and now with 3.23's it seems to like the long yellow spring.
I can give you my findings with secondary spring opening points. These are what I've observed while driving, not on a dyno. I can feel and hear when the secondarys come in, and I've put a cable tie onto the diaphragm rod to tell me how much they open. These are just from quick glances at the tacho so please don't take them as gospel.

Spring..................rpm
White.................2400
Short Yellow.......2500
Long Yellow........2800
Purple................3000
Plain..................3500
Brown...............untested
Black................4700(I was surprised at this one, but the cable tie don't lie)
All except the black spring had allowed the secondarys to open fully.

I hope this is some help to you Bill, and anyone else.

_________________
62 Valiant, 225cid Slant 6/PB 904 with lots of good bits

http://www.moparmarket.com/readersrides ... user=SV162