Won't run on all cylinders HELP

[RalphS in NE Oregon]

Helping a friend get his 1915 running after a 20+ year sleep. With difficulty with coil box he got it running poorly on 2 cylinders. All new wiring. Rebuilt Patterson coils. We can short out cylinders 3 & 4 and just about kill the engine. Slight effect on 2, no effect on 1. We can see spark on all 4 plugs when shorting them out. Seemed like it had to be bad plugs so we switched the front two to the back two. Same result; back two will kill the engine when shorted out, front two no effect. Tried replacing the #1 plug with one from a known good running engine. Still no effect on engine running. What in the heck is going on? Any ideas will be appreciated.
Ralph

[Susanne]

Hanging valves, maybe bad wires or a bad timer (tho if you're getting spark to the 1 & 2 plug...) maybe a mouse nest in the intake manifold... manifold leak... we KNOW it's not the coils. Do a compression test on all 4, let us know what the readings are.

[Charlie B in N.J.]

At last. Someone, probably with experience, recommends a compression test. 2 thumbs up. My persnal favorite diagnostic tool. Wet & dry don't forget.

[RalphS in NE Oregon]

Forgot to mention that we had done a compression test. 40psi on all cylinders wet and dry. Don't see how it could be timer since we have spark on all four. Idea of plugged intake manifold worth checking out.
Ralph

[Scott_Conger]

You are describing a vacuum leak at the forward port of the intake manifold.

You will likely see the engine pick up some if you direct a propane torch (unlit) to the forward intake. Any positive change in running will ensure the diagnosis is valid. It is possible to have a leak and not be able to focus the propane stream correctly, so even if there is no change, that does not ensure that there is no leak, so keep that in hip pocket as still being part or all of the problem.

Any time I start a car after many years of storage, and that is a pretty good number of cars, I have invariably found cheap/crap paper intake/exhaust gaskets which fall to pieces when manifolds are removed. Those things were big sellers to cheapskates in the '70's and 80's. I have found that there is NO point in attempting to resurect a car without simply starting with a rebuilt coilbox, coils and carb and good intake/exhaust gaskets (and usually a repro exhaust manifold unless the car is 1916 or earlier).

[RalphS in NE Oregon]

Great suggestion Scott. He will try the propane torch check next. He did replace the head gasket and freeze plugs already because he had coolant seeps. So the manifolds were off and gaskets replaced with new gaskets from Langs. But there still could be a poor seal. Car came with a Holley G on it which ran poorly and leaked so he has one of my useable, but not rebuilt NH carbs on it. Although it is not running on all cylinders, other things are good enough that we have had numerous free starts.
Ralph

[Scott_Conger]

Ralph, it doesn't take much of a "ding" on the gasket to injure it, particularly if wrestling with a bent exhaust manifold at the same time.

Best of luck to you two. You'll get it figured out.

[RalphS in NE Oregon]

You nailed it Scott. He couldn't find a leak with the propane test, but he took the intake manifold off and found a misalignment with the gasket and reset it. It's running on all four now! And he took out the magneto post and cleaned and it's running on mag now too, which it wouldn't yesterday.
He and his son took it out for a short ride this afternoon and reports that it runs and drives well.
Thank you Scott and the Forum.
Ralph

[Scott_Conger]

Ralph

I am very pleased to hear you all had such a successful day!