high lift cam or vacuum leak?

[GearAddict]

Ok, so I'm sad to say that after buying my 69RR 383 4spd over a year ago, I've finally re-wired the entire car, recreated the interior from scratch and procured and mounted every piece of missing chrome...but I know nothing about the motor. The car was set-up to drag (shallow gears, frame connectors, ext..) but the motor seemed fairly stock (from looks alone).

I've finally flushed out all the bad gas, replaced carb (edlebrock that was on it was un-rebuilable), checked compression, new plugs and checked the dizzy. Now I'm working on getting the engine running reliably.

The car fires up without a problem every time, but has a super choppy idle (shakes the whole car) and only reads 3-5 Hg (the needle dithers between 3-5). I was thinking vacuum leak, but cannot find one unless it is leaking at the manifold... So I started thinking radical cam? The engine smooths out relatively when wound up

Any other quick tips on determining leak or cam (I know it sounds like a stupid question even as I'm typing it), short of pulling the valve covers and measuring lift (or more importantly duration)?

Also, if measuring lift is the answer, is it true valve lift/duration at the valve stem side (post rocker ratio) or at the pushrod side?

anyway, sorry for sounding like such a noob..any help is appreciated.

 

[derrickmanx1]

Spray carb cleaner around the base of the manifold (not in the the carb) while it is idling. If there is a change (dip) in the rpm you found the leak if there is one.

 

[GearAddict]

Spray carb cleaner around the base of the manifold (not in the the carb) while it is idling. If there is a change (dip) in the rpm you found the leak if there is one.

Sorry, I should have said that I did that already... I checked all hoses (PCV and advance) and sprayed around the manifold to head on the top side...haven't tried squirting under the manifold yet...but I was using starter fluid and was worried about fire. I'll try with carb cleaner.

 

[bigmanjbmopar]

Ok, so let me make sure I am reading your post right, first you say the car was set up to drag, then wonder why it has a choppy idle? lol sorry not being mean or anything just getting a kick out of this. I am glad you are working so hard to get it all back to original looking. that is tough I know.

Let's start with replacement carb, please give us details on it? cfm brand etc. how is it hooked up? then we move to electrical. spark plugs, wires, dizzy etc. if it was set up to drag does it have old points or electronic ignition? Have you done a compression check?

Pics pics pics want to help you but you have to show us what we are dealing with

 

[GearAddict]

Ok, so let me make sure I am reading your post right, first you say the car was set up to drag, then wonder why it has a choppy idle? lol sorry not being mean or anything just getting a kick out of this. I am glad you are working so hard to get it all back to original looking. that is tough I know.

Let's start with replacement carb, please give us details on it? cfm brand etc. how is it hooked up? then we move to electrical. spark plugs, wires, dizzy etc. if it was set up to drag does it have old points or electronic ignition? Have you done a compression check?

Pics pics pics want to help you but you have to show us what we are dealing with

Ok, I suppose my comment was a little comical

It has a Holley 650, vacuum secondaries, electric choke (purchased with a wrecked Eldelbrock 1407, never seen a carb that looked like that inside, baffles rusted)
Offy manifold
iron heads (not sure of the casting)
Stock mopar electronic distributor, MSD 6A and blaster coil (I have a new MSD dizzy, just haven't dropped it in yet). Cap and rotor replaced
Wires Accell, look good but old... new ones on their way
Plugs...I can't remember, new but nothing special, old ones were soaked and burnt up.

Checked compression at around 120 +/- 5psi on all 8

Pics to come

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I should say, it doesn't blow smoke and now that I got rid of the weak electric fan and put a fan, clutch and shroud on it, it runs relatively cool and steady temp.

 

[bigblock]

Cam!!!

 

[A383Wing]

you sure you got firing order & plug wires on correct?

 

[67Satty]

With the vacuum gauge hooked up, did you slowly turn the distributor back and forth to find the highest vacuum reading? Then after that, set the idle mixture screws for the highest vacuum reading. Then after that, set the idle?

 

[GearAddict]

you sure you got firing order & plug wires on correct?

This is one of those questions that make me want to check it again (strange form of firing order OCD, I'm always convinced its wrong) but it was correct the first 3 times I looked.

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With the vacuum gauge hooked up, did you slowly turn the distributor back and forth to find the highest vacuum reading? Then after that, set the idle mixture screws for the highest vacuum reading. Then after that, set the idle?

To be honest...no, I set the timing by ear then checked it with timing light...I just put the vacuum gauge on it for the first time yesterday and was shocked by the low reading. I can try this tomorrow.

On a seperate note I lived in Oceanside/Vista for 11 years... I miss a good Carne Asada burrito and hunger for one about every other day...Cali will ruin you on all other Mexican food.

 

[Meep-Meep]

I'm thinking you have some other problems. Sure it's possible you have a hot cam but even with some high overlap street cams I was able to get 8" Hg at idle in neutral. 120 PSI isn't very good and could be a result of the hot cam. Ditto on checking firing order and general health of the ignition. Set initial timing to 10-15 BTDC. See how it runs now.

 

[bigmanjbmopar]

I would say either firing order is off 1 or plug wires are crap or you have a voltage leak in one of the wires to ground. either replace them all or go through them one at a time to ground to make sure they have a good spark.

Basically pull plug wire use a piece of copper in the end and hold to the block, crank the motor and see if there is a spark at each one. Rough idle is usually either fuel or spark.

High lope'r cam will net you less vac for sure but that's not your problem rough idle is right? pics!!!!!!!!!!! lol

 

[Propwash]

Wow...That's low Vacuum. Real low. These guys bring up some good points. Comparatively speaking, I run a pretty healthy solid lifter cam and i'm pulling 9HG borderline 10. One would think that if the prior owner did in fact shove in a big honking cam, you would see other modifications to the top end to accommodate the new lift/duration. Nicely ported Iron or Aluminum heads, adjustable rockers, a good flowing intake, pushrods, springs, a larger and more tunable carb ect..ect.... If not, and it was a radical cam, it would make a better door stop than anything else. That being said, folks do it all the time.

I've got a lot of great advice from the folks off this site, including a few on this thread. I'd definitely side with what they have to say above, as well and take a look at the current dynamics of the engine and it's components before settling on the notion there's a monster cam in it. Could very well be, but never hurts to take a look at the basics first.

 

[Herr_Poopschitz]

Adjustable rockers? If so, run the valves...

 

[Xp29h]

Gearaddict,

I certainly feel your pain. Same type of issues with my 69' 383. Low Vacuum, p.o. stated put in big cam. etc... looked everywhere for vacuum leak(s), Nothing found yet..
well it wasn't the cam! I replaced that with a milder one (numbers escape my old memory right now, but will post later if you need) Still didn't fix vacuum. couldn't get timing set timing right due to old worn distributor so setting at right degree for most vacuum wasn't possible. Here is a list of what i have done to somewhat correct my issues: maybe it will help you out!!

- New Cam - (info coming later)
- new valves - they were oversized but the valve seats were ground at wrong angle allowing for them to stick open. exhaust back into the carb. Not running good, get timing set right, tough!
- 906 heads redone for the seats and springs
- New Roller Rockers and adjusted correctly (made a big difference) don't by cheapies though! with new pushrods too Ratio 1.5
- A whole new ignition system - just ordered 3 days ago an MSD 6 AL2 programmable, blaster ss coil and Pro billet 383 distributor (mech advance) with new wires too. We will see on this.

It came with an Edelbrock performer 383 with Holley 650 mech secondaries and no choke. not sure the intake matches the motor, but have a single plenum tm6 that I will try once timing is set. May try performer 383 rpm too.

Sorry for all that but wanted to show that I went back to the beginning. I believe my car was heading in the drag/street racing way. I have found that probably with all engines but certainly with the 383, things need to be together. In time and proper geometry for the valve train. I am making progress but still not all there yet. I am hoping that after the ignition and timing set up, vacuum will be at least in that 9 -12 inches category, hopefully more.

When you buy a car from someone else, we never know what they have done and it seems that it is a lot of trial and error to get set right not knowing everything they did.

Again sorry for long post but Hopefully some of this will help you out in some way. Also, the people here are very knowledgeable and certainly will hop in to help! Good luck and I hope you can get it faster than I have.

 

[GearAddict]

I would say either firing order is off 1 or plug wires are crap or you have a voltage leak in one of the wires to ground. either replace them all or go through them one at a time to ground to make sure they have a good spark.

My new wires got here today! I'll swap me out and check the order when I do it.

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I'm thinking you have some other problems. Sure it's possible you have a hot cam but even with some high overlap street cams I was able to get 8" Hg at idle in neutral. 120 PSI isn't very good and could be a result of the hot cam. Ditto on checking firing order and general health of the ignition. Set initial timing to 10-15 BTDC. See how it runs now.

It set at 12 deg now and runs as described.... Heavy chop at idle then smooths out when revved. I'll see where I'm at after the wire replacement.

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One would think that if the prior owner did in fact shove in a big honking cam, you would see other modifications to the top end to accommodate the new lift/duration. Nicely ported Iron or Aluminum heads, adjustable rockers, a good flowing intake, pushrods, springs, a larger and more tunable carb ect..ect.... If not, and it was a radical cam, it would make a better door stop than anything else. That being said, folks do it

This is why I was leaning towards leak and not cam, I would have thought the motor would have been built up more if it was running that aggressive of a cam

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Gearaddict,

I certainly feel your pain. Same type of issues with my 69' 383. Low Vacuum, p.o. stated put in big cam. etc... looked everywhere for vacuum leak(s), Nothing found yet..
well it wasn't the cam! I replaced that with a milder one (numbers escape my old memory right now, but will post later if you need) Still didn't fix vacuum. couldn't get timing set timing right due to old worn distributor so setting at right degree for most vacuum wasn't possible. Here is a list of what i have done to somewhat correct my issues: maybe it will help you out!!

- New Cam - (info coming later)
- new valves - they were oversized but the valve seats were ground at wrong angle allowing for them to stick open. exhaust back into the carb. Not running good, get timing set right, tough!
- 906 heads redone for the seats and springs
- New Roller Rockers and adjusted correctly (made a big difference) don't by cheapies though! with new pushrods too Ratio 1.5
- A whole new ignition system - just ordered 3 days ago an MSD 6 AL2 programmable, blaster ss coil and Pro billet 383 distributor (mech advance) with new wires too. We will see on this.

It came with an Edelbrock performer 383 with Holley 650 mech secondaries and no choke. not sure the intake matches the motor, but have a single plenum tm6 that I will try once timing is set. May try performer 383 rpm too.

Sorry for all that but wanted to show that I went back to the beginning. I believe my car was heading in the drag/street racing way. I have found that probably with all engines but certainly with the 383, things need to be together. In time and proper geometry for the valve train. I am making progress but still not all there yet. I am hoping that after the ignition and timing set up, vacuum will be at least in that 9 -12 inches category, hopefully more.

When you buy a car from someone else, we never know what they have done and it seems that it is a lot of trial and error to get set right not knowing everything they did.

Again sorry for long post but Hopefully some of this will help you out in some way. Also, the people here are very knowledgeable and certainly will hop in to help! Good luck and I hope you can get it faster than I have.

Wow...best of luck, I hope my problems are not that deep, but it wouldn't surprise me if they were either. "Buying someone else's motor is like a box of chocolates....you never know what you're gonna get"

Thanks everyone for the posts, I'll check for manifold leak, replace wires, check order and set timing to highest vac then carb mixture and see where I stand.

 

[70bigblockdodge]

Cam is in retarded, a inherited problem of sticking cam in without degreeing crank keyways are cut inaccurately from factory, my 2 cents

 

[khryslerkid]

If you have power brakes don't forget to check the booster. Just remove the hose and plug it. You'll see a big difference if you have a bad one...

 

[GearAddict]

Ok, so I had been storing up parts that I had intended on using, so this weekend I will be installing...

New MSD plug wires (hopefully sort the firing order and good/bad wires question
Edlebrock RPM Intake with new valley pan (solve manifold leak question)

Check vaccum
Check timing
set timing with vaccum
set mixture with vaccum

I'll post results/findings

I do also have a new MSD distributor, but wil hold off on install until I've gone through everything else.

 

[GearAddict]

ok so here's a sunday afternoon update. I just started the teardown and removed the old intake. A couple of observations....

1. The old valley pan gasket seal looked like it was not so good, real messy, glooped on RTV...used both on the end rails and around the ports.
2. a few isolated signs of rust in the lifter valley, directly below the water jacket for the intake crossover. Not horrendous, but there non the less.
3. It appears that the cam is a Mopar Purple cam... not sure which one, but could explain the choppy idle, along with the possible vacuum leaks from the manifold as described above.
4. From a layman's inspection of the cam, I don't see any major condition issues, the wear appears to be very even. I'm going to rotate the crank manually next, just to be sure there are no appearant stuck lifters.

Thoughts? I'm not new to motors but I have generally run pretty stock cams over the years...what should I expect for vacuum from the mildest grind of the purple cam?

Also another couple checking questions...

1. Are the intake manifold bolt holes open to the water jackets in the heads, the same way they are on a chevy? meaning they need a teflon sealer on the threads?
2. I have read a few posts on how best to seal the Valley pan gasket, but I have seen conflicting comments... gasket sealer around the ports...no gasket sealer. Everyone does seem to agree on High Temp RTV to seal the ends of the valley pan.

Any advice is appreciated.

Here is an old pic from when I first started on the car... hadn't even got the chrome on it...she's come a long way, but still lot's to do. As soon as I resolve some of the motor issues, I'll pull her out into the sunlight and post some better pics.



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[A383Wing]

no intake bolt goes into water, sounds like yer cam might be too big for street diving? I had purple cam in my 66 long ago....did not like it, way too choppy and no vacuum for brakes

sealer on end rails only, (under pan rails, none on top of valley pan, no silicone or sealer around intake ports....