'57 Johnson 18hp with a hickup.

[Hanr3]

Hola all,

I have been trying to get this motor back into great mechanical shape.
Things I've done.
New coils, condensers, points (.20), wires, and plugs (.30). Basically a new ignition system.
Rebuild carb with a new plastic float (the cork one has seen better days and was delaminiating), although I have some questions.
Is there an adjustment to the float?
The center brass thing that sticks up appears to be broken, purpose/problem?

Replaced the water pump, well was going to replace it, however the one in there looks almost brand new.

Pulled lower unit and cleaned out the gear assemble, new lube.

Onto my hick-up.
I adjusted the high and low speed needles. High is almost closed now, low is 1/8" off closed. Engine runs but has a hick-up, the faster I run her the less of a hick-up there is, more like a burb. IF I go too slow, the hick-up will kill the engine.
What could cause this, and more importantly how do I fix it?

I need to go fishing this weekend in my plaid and win the first tournament. :mrgreen:

 

[perchin]

When you rebuilt the carb did you remove the jets and double check that all the gum was cleared out. I've had to go as far as using a piece of tiny copper wire to clear out the jets before..... probably not your problem, but something to look at anyway.

 

[Hanr3]

yea, I soaked it overnigth is carb cleaner, used some wire and used my air compressor to blow it all out. I couldnt find so much as a finger print on it when I was done. :mrgreen:

Not saying I put it back together correctly, but its clean. :mrgreen:

 

[hossthehermit]

If you aren't already familiar with AOMCI ya might want to check their site, they've got a bunch of experts on the older OMC motors, good bunch of guys there. Actually, they steered me here.

 

[thudpucker]

Those were great running motors. Our family had 56 15Hp and a 57 18 Hp. Both would idle all day.

When you say Hiccup, do you mean a 'spit back through the carb' or are you talking about a 'mis-fire', just a plain mis-fire on one or both cylinders.

Dis your engine have the little Mercury switch on one of the Ignition grounding wires? That gave lots of trouble.
It was there in case you hit something and kicked the motor up, the engine did not run away at high RPM until you let it back down and the mercury switch let the coil start firing again.
If your mercury switch is still there, it might be bouncing. Causing one coil to short out....a misfire!

make sure your gas is mixed right. Those old Smokers were 25:1 mix.
Did you convert the engine to a modern single hose operation?
That two hose was dangerous.

You might have a vacuam leak somewhere.
Those jets shouldnt be screwed in so close (both start and 1 1/2 turns out, and the high speed may go as far as 2+ turns.

Yet you can get it to go at a high speed? That would mean you are getting fuel from the tank OK, and plenty of fuel.

One more horrible thought. A loose upper main bearing will cause miss's at various Rpm's.
If it's worn badly, upon increasing the Rpm, you get to a certain point and the thing wont hardly run at all. Misfires, back fires etc.