Blown exhaust gasket and rough idle?

H

Heimer308

Junior Member
I just acquired a stock '30 Sedan that had a mild restoration done sometime in the 80's. It runs but its a really rough idle and backfires real bad, even after adjusting the distributor timing, points, and GAV. It does have a pretty bad exhaust leak on the exhaust manifold at cylinder #1 and starting on cylinder #2. I didn't think of this at the time, but is it safe to say if the exaust is leaking then the intake on #1 is also leaking and causing a bad air-fuel ratio? Would it be wise to spray starting fluid on the intake and see if the idle note changes?
 
Heimer308 said:
I just acquired a stock '30 Sedan that had a mild restoration done sometime in the 80's. It runs but its a really rough idle and backfires real bad, even after adjusting the distributor timing, points, and GAV. It does have a pretty bad exhaust leak on the exhaust manifold at cylinder #1 and starting on cylinder #2. I didn't think of this at the time, but is it safe to say if the exaust is leaking then the intake on #1 is also leaking and causing a bad air-fuel ratio? Would it be wise to spray starting fluid on the intake and see if the idle note changes?
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Sure but if you know its leaking why not change it out with a good copper one.
 
Just bought the car a few weeks ago, I bought a copper intake/exhaust gasket to take care of the exhaust leak but haven't had time to install it yet. Not super familiar with inline engines that share intake/exhaust space, so I was curious if the leaking exhaust could also affect the intake mixture.
 
When the two manifolds are bolted together the surfaces that mount to the block have to be in the same plane and flat. Put it on a flat surface such as a marble slab and look to see if there are any gaps. The best way to get the surfaces flat and in plane is on a milling machine, but a shade tree method is to glue a piece of emery paper to a flat surface and slide the bolted together manifolds back and forth until you get a uniform pattern.
 
If your planning on keeping the car and drive it regularly here's my suggestion.
Buy a New exhaust manifold. Clean the block surface as clean as you can get it. When attaching the intake,leave the two bolts loose. When you tighten the manifold use a 3/8 drive ratchet with your palm over the head of the ratchet. Snug it up. Now attach the exhaust pipe snug.
Now using the ratchet give each nut a 1/4 turn. I Never use a torque wrench on exhaust.
Be sure to replace the carburetor gasket. Go to my YouTube channel for more details on installing exhaust manifold. Hookemfair garage
Wick
 
I just fixed one today for a lady friend of mine and my wife's. New copper gaskets properly installed and she couldn't believe how well it went. I was pleased too.
It sounds like your leak is as bad as hers was. Not only did it leak exhaust badly but the inlet was leaking. There is no way a motor can run properly like that.
Replacing those gaskets is EASY on a LHD car so don't be reluctant to go for it.
 
Like the head gasket, the manifold gaskets will take a set and have to be re tightened several times. Suggest after the initial heat and cool, then after 100 miles, then after 300 miles. These don't have to be exact miles but the point is to re tighten the manifolds.
 
my method of finding leaks in the inlet or exhaust train is to duct-tape the positive-pressure side of my vacuum cleaner (Hoover?) onto the carburettor or exhaust. then i use leak-detection spray and foam any joints. You will be able to find the smallest of leaks, this is a far more sensitive method than the 'WD40 on inlet manifold' method.
 
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