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1959 Mercury Mark 35a - Engine starts, then dies

B

Boatsnhoes

Contributing Member
Hello again everyone,

I've gotten the lower unit in pretty good shape, so it's back to working on the motor for now. A problem I've noticed is that the motor starts, runs hard for maybe 3 seconds, and then dies on me.

A few thoughts:
1) Fuel delivery issue? I currently have it running without a fuel pump just to test it, so I'm pumping the primer bulb hard, starting the engine, and then the engine dies before I can pump the primer again (it's on the other side of the motor). The reason I don't think this is the issue is because it dies out so fast - within 3 seconds. Do the carbs run through a full bowl that quickly?

2) Advance issues? - I have the timing set appropriately according to the timing marks, but I'm concerned a PO pulled the flywheel and put it back on offset. The reason I think this may be the case is that I get a better start and slightly longer running time by opening the throttle and therefore advancing the timing. Now that I type it out this one seems kind of silly, but still, thoughts are appreciated.

3) Fuel:Air mixture - The reason I think this may be the issue is that when I pull the plugs, they're covered in a sort of grainy, flaky black crud. No idea what that is or what it means, but I suspect it has something to do with a rich or lean mixture (or maybe bad spark timing leading to incomplete combustion???)

Let me know what you all think!
 
..."Do the carbs run through a full bowl that quickly? "

No. A full carb runs at least twice as long.

If the timing is right at WOT, then the timing is right. Have you buzz box timed it?

Jeff
 
I haven’t buzz boxed it, and I’m not sure what that is. All I did was line up the timing marks in accordance with the manual.

Any thoughts on the plug? I don’t know why it would be building up carbon so quickly
 
Is the fuel pump installed? If not you've left the hole in the crankcase open which is causing a dangerous lean condition! The flakes on the piston could be carbon coming off.
 
Pump is NOT installed. Didn’t know this was so dangerous! If I’m honest I did suspect but was being lazy.

Can i just cork the hole and continue to test this way?
 
Cut a piece of thick cardboard to match the footprint of the pump and bolt the housing on top of it, this might not last long as fuel will soak it I don't think that trying to run it without all the systems working is going to help you, they all work together. The controls should also be hooked up so you can control the speed (don't rev the crap out of it unloaded) and set the idle etc.
 
Alright maybe I'll just throw the pump on there but not connect the fuel lines. At least it'll have a seal then.

I'm not wild about testing again in this cold but I might just have to pull the trigger.

Thanks for the advice!
 
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