Hello all,

I just joined; but I wish I had been aware of this club years ago. I have a 1954 14′ Penn Yan Swift that is nicely restored and the transom has been reinforced. I have run it with vintage Mercury Mark 55 and 58A, and Merc 400 motors, both short and long shaft.

I just bought a Merc 400 short block for only $100. Turns out it has very good compression (at least 105 psi at 7000′ above sea level) and the end seals are very good. The other parts – mag, carbs, starter, and fuel pump, are from my original Merc 400, which has two stripped spark plug holes.

I have started up the motor in my water test tank. But it will only run with the throttle advanced as far as it will go in neutral. When I start backing off the throttle, it quickly stalls.

I cleaned the carbs and ran sealer around the flanges when I reinstalled them. The idle jets are set at the original setting – about 3/4 turn from closed. When I change that setting it has only a minor effect. I then replaced the carbs with another pair that were totally cleaned. Same result.

I can back off the throttle and get it to run a little slower by applying some choke, but not very much slower.

I wondered if I had an air leak somewhere, but I can’t trace it. I replaced the bleed line and fittings, but that did nothing. I get a good spark when I crank it, so the mag seems OK. Plugs are new.

I checked to see if air is blowing out of the carbs, indicating reed valve problems. But I couldn’t detect any. But could it still be the reed valves? I sure hope not. Could it be some crud stuck on them, and could I get it off with some additive?

As I said, it runs fine at medium rpm – with the throttle pushed up to the stop in neutral. But it stalls once I try to close the throttle even a little.

So I’m at a loss. I sure hope one of you can help.

Thanks, Bob