Vacuum leak hunting party

[popinsmoke]

Greetings and thanks for taking the time to read this,

I purchased a 1978 Dodge Magnum, 360 2bbl W/Auto trans (904) the lean burn system has been removed and a knock off of the Mopar Performance Electronic ignition made by proform was installed in its place.

As I do with any car I buy used; I check the compression and change the oil and give it a tune up.

Compression was good so I changed the oil and preceded with the tune up as the car idled very poorly.

Checked the mechanical timing at it was 10 degree's, checked manifold vacuum and it was about 8 inches, so the hunt for the vacuum leaks began.

I chased the hoses with propane torch and ended up finding about 6 different leaks, replaced the offending hoses and checked vacuum again.

After replacing some leaking hoses the vacuum gauge would show 15 inches and had smoothed out some.

I have tried smoke, propane, wd-40 and blood sacrifice to find where it is still leaking, if I hand choke the carb the vacuum jumps to 24 inches and picks up rpm and runs smooth as glass.

WD-40 the intake gasket areas, base of the carb, checked brake booster fitting, I am running out of idea's of where to look?

Yes I posted this in another section but it doesn't see as much traffic, my apologies to the mods please feel free to merge the posts.

Thank you in advance for any and all advice.

 

[mopar 3 B]

PVC valve, charcoal can, vacuum control lines for AC/heater or anything with a vacuum can at the end of a hose can leak vacuum.

 

[eagleone1983]

Sorry to butt in but I'm just interested, what do you mean by chased with a propane torch? I'm not familiar with any tricks of the trade to find vaccum leaks so can you elaborate so I can add that to my list of items this site has helped me with.

 

[popinsmoke]

Eagleone,

First thank you for your service, chasing a leak with a propane torch is pretty simple. First you put on a smaller tip on the torch like a brazing tip, then attach a length of vacuum hose to the tip about 2 feet is fine. Second start the car and crack the torch valve open and use the end of the hose you attached to the torch to follow your vacuum lines, base of the carb, between the intake manifold and head, anywhere you think there could be a leak.

A vacuum leak will suck up the propane and you with hear your idle change so you know that you have found your leak, the length of hose attached to the torch with slow the propane discharge and allow you to pinpoint things.

Other methods include spraying starting fluid, carb cleaner, etc I prefer propane as IMHO it's less likely to start a under hood fire.

 

[idrivemopar]

Maybe dodge1972 will chime in here. I had an interesting conversation with him recently talking about a 79 Magnum I used to own and he was telling me there is some sort of air sensor on the lean burn systems where the pipe gets plugged up causing it to run rough, not sure of the details, but maybe he can provide more details.

 

[Hugh Jass]

I didnt hear you mention checking the egr valve, valve hung open causing vacuum loss, sometimes removing the egr and looking if the valve is cocked is the only way to be sure. . Also Worn valve guides will in some cases show good compression but cause rough running. Sometimes its good to use a needle nose pliers and pinch off each hose close to the vac source, one at a time and look for idle to smooth out. In some cases a vacum amplifier or brake booster leaks vacuum internally and your propane enrichment wont pick up the leak.

 

[67 coronet]

I would just unplug each line to vac source and plug it up.one should show a jump in signal and you will at least know which line its on.a cracked carb can cause the problem you stated as well.

 

[popinsmoke]

Gentlemen thank you for the replies it was a combination of a intake gasket leak and a plugged idle circuit on the carb.

Since the intake had to come off I am replacing the intake and the 2bbl and going with an Air Gap manifold and street demon carb. I will update after the install.