318 running like a dead goat

-
T

TurboGrimace

Member
Joined
Aug 31, 2010
Messages
15
Reaction score
0
Location
Maryland
my 318 was built by the previous owner. IIRC from nearly a decade ago, it has a mopar purple shaft cam in it (the biggest he could get of course), 340 heads (doubtful probably stock), rpm performer dual plane manifold, avs 650 carb, and an electronic ignition box.

back in the day it ran strong. the cam is incredibly lopey and idle is rough. I just got it running after sitting for two years, which only took some cleaning and some fresh gas. before i packed it away two years ago, it was starting to become a dog, so I checked the timing and set it to 12 BTDC and it ran even worse. I continued to advance the timing until it ran a little better, but it required a significant amount of advance to get a little power. Still really weak though. The timing advances with increased RPM, but there is no difference in timing with the vacuum line hooked up or taken off.

Clearly (for me) part of my problem is an untuned carb, but I wanted to get the timing set correctly first before i started screwing with the carb. It originally had a 750 cfm eddie with weighted secondaries. I'm tempted to put that back on and use that because I liked the way it ran with that.

I know this is a lot of information and there are a lot of potential issues, but I was hoping that I could get some guidance on where to start, what to do, what to change. Even some info on what may work better with my mysterious combination.

Thanks a lo guys!
 
"but there is no difference in timing with the vacuum line hooked up or taken off."

You need to solve this issue first. If the vacuum advance diaphram is torn it could be causing a vacuum leak. I would either replace the vacuum advance can or replace the entire distributor with a known good distributor. You are having to dial in a bunch of initial advance to make up for the missing vacuum advance. Check your vacuum source and make sure it isn't a ported vacuum source.
 
sledger46 said:
"but there is no difference in timing with the vacuum line hooked up or taken off."

You need to solve this issue first. If the vacuum advance diaphram is torn it could be causing a vacuum leak. I would either replace the vacuum advance can or replace the entire distributor with a known good distributor. You are having to dial in a bunch of initial advance to make up for the missing vacuum advance. Check your vacuum source and make sure it isn't a ported vacuum source.
Click to expand...

my vacuum port is right off the carb. Your comments make sense though. I can hear the diaphragm moving if I suck on the vacuum line to the can. So the first logical step would be to try a new can and then reset the timing?
 
TurboGrimace said:
my 318 was built by the previous owner. IIRC from nearly a decade ago, it has a mopar purple shaft cam in it (the biggest he could get of course), 340 heads (doubtful probably stock), rpm performer dual plane manifold, avs 650 carb, and an electronic ignition box.

back in the day it ran strong. the cam is incredibly lopey and idle is rough.
Click to expand...


What is the static compression (compression gauge reading with spark plugs removed and throttle wide open) and exactly which purple cam is in the motor ?

You would probably be much happier with a smaller cam .
I like the MP.528 solid for my average street 440 . (intake ,headers,and mild port job on factory heads)
 
I'd definitely be happy with a smaller cam. This one is clearly eating up some potential power, but for now I just want to get it running like it used to.

I checked the vacuum can and it's not leaking. I don't notice any movement in the distrib though. And i dont think the vac advance is kicking in. At 3k I only have 30* of total advance with 10* BTDC at idle. I should be getting more and that extra bit should be from the vac. If the vac advance can is good what might be the problem for the vac advance?
 
If you are running such a big cam, what torque converter are you using? A stock torque converter will make a big cammed motor fall on its face. Did you drive it before you bought it?
 
I've had it for almost 9 years. I drove it with the original transmission, a beat 904 with a stock converter. When that gave out I put in a 727 with a 2400 stall and a shift kit. It wasnt as perky as the 904 (different gearing).

I'm thinking the vac advance is shot, but it's not the vac can.
 
TurboGrimace said:
I'd definitely be happy with a smaller cam. This one is clearly eating up some potential power, but for now I just want to get it running like it used to.

I checked the vacuum can and it's not leaking. I don't notice any movement in the distrib though. And i dont think the vac advance is kicking in. At 3k I only have 30* of total advance with 10* BTDC at idle. I should be getting more and that extra bit should be from the vac. If the vac advance can is good what might be the problem for the vac advance?
Click to expand...
So what your telling us is you have a total of 20 * of mechanical advance (not including vacuum advance)....

10* at idle is not alot when you have a long duration cam . Try advancing the timing to 16* or 17* at idle . That would then give you 36 or 37 total degrees at 3000 rpms.

This will give greatly improved idle quality and more power from 3000 rpm's and up !

As far as the vacuum advance is concerned , you need vacuum for them to work Big cams don't make much vacuum ?

What is your vacuum reading at idle ?
 
Probably pretty low. What should I be looking for in terms of vac numbers? I can feel a slight draw on the tube at idle when I put my finger near the port.

Now I will say that it's a relatively recent issue in terms of my having the car. It didnt always have this problem and the cam has been in there since I got it.
 
I don't have time right now to post any pics (will try later) one of the mopar mags has very informative articles on setting up and modifying distributors + vacuum advance for stock and performance engines.

At idle (with a properly set up carb and distributor) there should be No vacuum to the distributor !
The vacuum advance only comes into play just past idle and also during part throttle conditions ....not at idle or during wide open throttle .
 
TurboGrimace said:
Probably pretty low. What should I be looking for in terms of vac numbers? I can feel a slight draw on the tube at idle when I put my finger near the port.

Now I will say that it's a relatively recent issue in terms of my having the car. It didnt always have this problem and the cam has been in there since I got it.
Click to expand...

The highest number you can get .

A stock granny motor may pull 18 to 22 inches.
A mild street motor may pull 12 to 15 inches.
And an all-out race motor may only pull 6 to 10 inches.


If you can feel a slight draw at idle that tells me the throttle plates are a little to far opened and are uncovering the slot that feeds that nipple .

To see what I'm talking about take another carb and flip it over and look at the primary throttle plates .

There should be one slot for idle mixture enrichment visible under each throttle plate with throttle fully-closed .

If you slowly crack open the throttle plates another slot should become visible just above one of the idle mixture slots , this slot is for ported vacuum for the vacuum advance (and should show zero vacuum at idle) .
 
thanks for the info. Im assuming that has to be in. of water. I'm going to set the base idle to 16 and then see about snagging a water gauge unless that's merc. I have some old merc gauges for multicarb goodness.
 
TurboGrimace said:
I'd definitely be happy with a smaller cam. This one is clearly eating up some potential power, but for now I just want to get it running like it used to.

I checked the vacuum can and it's not leaking. I don't notice any movement in the distrib though. And i dont think the vac advance is kicking in. At 3k I only have 30* of total advance with 10* BTDC at idle. I should be getting more and that extra bit should be from the vac. If the vac advance can is good what might be the problem for the vac advance?
Click to expand...
Get a hand held vacuum pump and hook it to your distributor . If there is no movement when vacuum is applied the advance mechanism is probably froze up and just needs to be oiled.
 
TurboGrimace said:
thanks for the info. Im assuming that has to be in. of water. I'm going to set the base idle to 16 and then see about snagging a water gauge unless that's merc. I have some old merc gauges for multicarb goodness.
Click to expand...
Just a regular vacuum gauge from an auto parts store (probably mercury?)
 
I'll see about lubin' the advance mech today. I dont think it's the can, I just dont see any movement after the diaphragm moves.
 
So I checked the vacuum and I was losing a crap ton through the pcv valve. I've plugged that up. The vac advance was actually working fine before this and I checked the voltage at the ballast resistor. On one side it's 10.5 volts and the other is 5.5 volts. This doesnt seem like enough. Are there any diagrams available for the proper wiring of the ballast resistor?

I bypassed the ballast resistor altogether and it was still running pretty funky. I'm wondering if the electronic ignition has failed in some way. I thought when they failed, usually the engine wouldnt even run though.

Thoughts?
 
You must log in or register to reply here.
-

Back
Top