Popping out Passenger side Exhaust
 

Not my car but trying to help out.
12v negative earth H & H flathead fitted with electronic ignition. Fitted with new 4 barrel 390 carb. Distributor is mechanical advance only. Checked advance and only shows 3 to 4 at idle and only around 12 at 3000 rpm. Know it should be around 24 degrees.
Pops out passenger side only mainly at low speed.
To check firing by removing a lead to see where the popping occurs I understand you need to ground the removed carbon lead t avoid damage to ignition unit? Hope to locate cylinder and go from there.
Plan is a compression test, lead down check to locate the cylinder at fault.
Possible this may be valve train related, sticky valve, a vaccum gauge at idle should show this up?
Appreciate all comments.
Phil NZ

Re: Popping out Passenger side Exhaust
 

just check your manifold bolts are nipped up , might just be a vacuum leak. Your vacuum gauge will bounce a few Hg. if its a burnt valve it will be a lot more . just clip a timing light on each lead and watch it thats easy enough done too.

Re: Popping out Passenger side Exhaust
 

stuck exhaust valve-try shorting out one cylinder on bank at a time to determine which cylinder

Re: Popping out Passenger side Exhaust
 

This would be my guess as well . . . can be as simple as an adjustable lifter with too little lash.

Re: Popping out Passenger side Exhaust
 

Drizzle some Marvel Mystery Oil down the carb when
it's running to free the sticky valve. G.M.

Re: Popping out Passenger side Exhaust
 

Thaks the kind of thinking i'm looking for . Understand adjustable lifters ar in use but screwed in to accomodate the use of the slightly longer chev valves.
And this can be confirmed with shorting out, vaccum gauge, and compression and leak down testing right? Also could be caused with a crossed HT lead.
As its electronic distributor carbon core type wires are in use.
To short out one cylinder at a time requires the lead to be earthed to block? Right?
Thanks,
Phil NZ

Re: Popping out Passenger side Exhaust
 

Compression test --- quick and easy.

Re: Popping out Passenger side Exhaust
 

lead to block-correct, can be done easy if no insulator on plug wire, otherwise pull off one lead at a time till the popping stops. in a very rare instance you might get a crossfire if the wires are old or jammed together

Re: Popping out Passenger side Exhaust
 

i understand with electronic distributor you need to earth pulled off lead to block to avoid damage to unit? when checking for popping.
Phil NZ

Re: Popping out Passenger side Exhaust
 

As Flatjack mentioned, a compression check should check it. Don't make it harder then it might be. Granted sticky valves can show up under load and speed also. But at speed I'm not sure your pulling sparkplug wires. Then sticky valves underload... maybe mmo it a few times. (could use some diesel fuel bottle fed, but I prefer mmo over time or for results. Don't fill the tank with diesel!)


Vacuum gauge would show a dip or flutter. Compression gauge might lead to the cylinder it's happening.


Not saying you can't with a open hood and someone sitting on the fender. My pops and uncle drove a car with the uncle running the throttle on the fender and my dad driving for a few miles to get it home. Different time. Compression checks are easy and should be done on any engine.


If after you check vacuum and compression (standard mechanical diagnostic tools for old engines). It could be a miss fire from the electric ignition. I'd check the earlier first. Easy tools and checks.

Re: Popping out Passenger side Exhaust
 

Consider wrapping the spark plugs in tin foil from the base to near the tip, about 1/4 inch below. When the engine is started the spark shouldn't take that path but as you remove the lead the spark should jump to the tinfoil.
I'm not sure how an electronic unit works but but if you can remove the plug at the coil/distributor end and have a spark gap to jump to it may be easier.

Re: Popping out Passenger side Exhaust
 

A combustion engine is just a air pump. Well with a bit of fire! But if you pull a plug wire and it doesn't do it. well......


Best of luck!

Re: Popping out Passenger side Exhaust
 

Normally i just pull off the plug wire for checking with copper wire plug leads.
But read somewhere with carbon leads and electronic distributor it can cause damage to electronic unit. This is the point I am trying to clarify.As the car is a couple hundred miles away from me and want to be sure all options are considered.
Thanks
Phil NZ

Re: Popping out Passenger side Exhaust
 

pull off the boot that is not supposed to be there and use a screwdriver to short out the plug--the fire/electric discharge will go to ground

Re: Popping out Passenger side Exhaust
 

So don't do that!. Lots of ways to skin the hypothetical cat.