Dumb Question

[Robert1050]

Dumb question from a Newb....

I thought I was pretty up on Mopars, having owned several over the years, but since I've never had a 440 Magnum, I just have to ask:

I just picked-up an original, numbers matching 1970 Challenger with a 440 Magnum, 727 that was owned by the proverbial little ole' lady.  It has 73K miles on it, has received regular maintenance, no go-fast goodies, but it has the lumpiest idle of any factory car I've ever driven.  Last Sunday, I put new plugs, wires, cap & rotor onto it and the plugs that came out all looked good (slightly rich, but otherwise, no surprises).  The carb had been re-built last year and does not appear to be leaking fuel, or have any vacuum problems.

It idles at about 800 RPM and once you drop it in gear & go, the lumpiness settles out & there is no mid-range, or high-speed miss to it.  Since I don't know anyone in my immediate neighborhood to ask, I thought I'd pick everyone's brain here.  Just how lumpy is a stock 440 cam?  I've ordered a factory service manual that will be here next week, so I can trace the vacuum lines, but everything looks good right now.  Once I have the manual in my hands, I'm going to use a dial indicator to check the valve lift - anyone else have any thoughts on this?
Robert

[GoodysGotaCuda]

I've driven about all the 'hi-po' motors. All restored originals, and nothing what i would consider very lopey. I'd be looking for vacuum leaks and such. Is there power brakes? Maybe the brake booster has a leak and when you hit the brake pedal/hold it to put it in gear in is enough of a vacuum leak to kill the motor? 

[farmboy70]

 

[JS27N0B]

Magnum cams are usually very smooth idling. I would check for vacuum leaks.

[BIGSHCLUNK]

Only thing I know of with that lopey idle "stock" is that funny lookin' spark plugs in the valve cover motor.. 

[Robert1050]

Well, you were all absolutely correct on this one!  I got the service manual a week after I posted this question and started to check all of the vac lines.  All were routed correctly, but several had minor exterior cracking near their appropriate fitting, so I cut the hoses back to eliminate the cracked areas, fired the motor up & didn't notice any changes to the idle.  Hooked up a timing light (had to borrow one from my boss, I had tossed/sold all of my old ones off a long time ago) and found the timing dead on.

I was still stumped.

My boss walked over to the car with a can of carb cleaner & sprayed it around the base of the carb, no change in idle.  He sprayed it onto the driver's side intake manifold/head joint & still no change in idle.  Then he sprayed it onto the passenger side joint & the RPM shot way up.  Oh, that told us something.

Called our local Mopar dealer, no valley tray/intake gaskets in stock (what kind of a dealer are they?), so I called the local NAPA auto parts store.  They had 1 in stock, $18, picked it up.  Took 45 min to get the manifold off, found that a previous owner had used the stock valley tray/gasket along with a set of aftermarket paper gaskets - that along with no sealer produced intake leaks in about 6 different areas that we could easily see.

An hour later I had it all buttoned back up, fired the motor back up - it idled just fine!  No lopey idle anymore.  The carb still had a significant hesitation (accelerator pump doesn't seem to squirt much), so I spent some time the next day finding & ordering a newly re-built Holley 4360 to replace the tired Carter (in my conversations with the lady I bought it from, the R/T originally came with a Holley, but she had it towed into a shop to fix a 'wouldn't start' problem & they tossed the Holley & installed the Carter).

I'll let everyone know how it runs after I get the Holley bolted on.  Then I'll order a rebuild kit for the Carter & I'll go through it & see what's wrong with it.

Robert

[MEK-Dangerfield]

Robert,

  One step at a time. It is a sloooow painful process, but you are getting there. 


  Mike

[JS27N0B]

Glad to hear you are making some progress.