Engine slows when #1 is hooked up

[gearloose]

The problem is as follows. 1929 with lots of miles still running with original wiring. Engine at idle, spark up, remove #1 spark plug connector from the distributor and the engine speeds up , make contact back to the cap and the engine slows down. Any thoughts? The head is off and shows no blown gasket between 1 & 2.

[Mitch//pa]

i would have liked to have seen some more diagnostics done before exploratory surgery

[1955cj5]

Did you try the same test with any of the other plugs/cylinders?

[gearloose]

yes they were normal

[gearloose]

Originally Posted by Mitch//pa

i would have liked to have seen some more diagnostics done before exploratory surgery

what would you have liked to have seen?

[Mitch//pa]

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Originally Posted by gearloose

what would you have liked to have seen?

a compression and leak down test...
ck for a vacuum leak at the intake manifold
switch the spark plugs around
ck for proper spark intensity to all the cylinders which gives you an indication of a secondary issue
to name a few

when you remove a plug connector off a running motor the connector should be grounded so the spark does not back up into the dist body which can play hell with the other cylinders. i like to do it by grounding it with a screwdriver to the head

[P.S.]

My guess- Arcing inside the distributor body (the bakelite housing with the 4 terminals across the top) between contact #1 and #2.

Internal arcing happens when they get old, cracked, etc.

[blgitn]

You can check number one intake valve, clearance & seat as long as you're in there.

[Tom Wesenberg]

Originally Posted by P.S.

My guess- Arcing inside the distributor body (the bakelite housing with the 4 terminals across the top) between contact #1 and #2.

Internal arcing happens when they get old, cracked, etc.

That was my first thought also. Number 3 and 4 are the usual trouble spots, but it can also happen on the first two.

As Mitch said, more test should have been done before removing the head. Also, as Mitch said, you should use a screwdriver to ground out the plug, and never leave the coil high voltage with no place to go.

[P.S.]

Originally Posted by Tom Wesenberg

That was my first thought also. Number 3 and 4 are the usual trouble spots, but it can also happen on the first two.

As Mitch said, more test should have been done before removing the head. Also, as Mitch said, you should use a screwdriver to ground out the plug, and never leave the coil high voltage with no place to go.

Agreed.

As for leaving the coil with nowhere to discharge... That is how I test them for internal arcing or dielectric breakdown.

[Mike V. Florida]

My first thought was a bad plug.