Old OMC motor - new fuel & ignition parts but won't idle!

[Swell]

Re: Old OMC motor - new fuel & ignition parts but won't idle!

Here's an update on this one. I finally got round to fully testing the fuel pump. I used a gravity feed to the carb and ran the motor - the pump worked fine.

Also, the lack of idle was still there with the gravity feed.

I also ran it using the gravity feed but with the fuel pump removed and with a plug in the pulse hole. Again, exactly the same - idles for a short time and dies, so the fuel pump diaphragm is not leaking and if there is a crankcase leak it?s not there. I think that pretty much removes the fuel pump from the equation.

Is there any point in the cycle at which the crankcase is fully sealed i.e. when the motor is not running? I did try blowing into the pulse hole via a length of tube and rotating the flywheel to see what the back pressure was like. There seemed to be no point at which there was a total seal ? I could hear air escaping via the exhaust in certain positions, and through the carburettor in others, but there did feel like there was a reasonable back pressure in all positions. Not sure if that test is in any way valid, but I thought I?d mention it.

So, I?m back to re-checking ignition and I may remove, clean and re-build the carb. Other than that I?m out of ideas!

 

[kfa4303]

Re: Old OMC motor - new fuel & ignition parts but won't idle!

These may help with the ignition and carb job. These links aren't for the exact same model as yours, but the basics are all the same:

http://www.outboard-boat-motor-repa...on 3 HP 1952-1967 Ignition System Tune-up.htm

http://www.outboard-boat-motor-repa...hnson 5.5 HP 1954-1964 Carburetor Tune-UP.htm

 

[Swell]

Re: Old OMC motor - new fuel & ignition parts but won't idle!

All now fixed!!

It's slightly embarrassing as the problem was with the idle jet setting. I'd followed the guidance and wound it out 1.5 turns, then tried winding it in to find the right spot, but the problem was that the required setting was 1.75 turns! At 1.5 turns it was just too lean with not enough fuel getting through. Whether this implies that there is another underlying issue I'm not sure, but either way the engine now runs fine in all respects so I'm over the moon about that.

Seems obvious now but there you go - put that one down to experience!

Thanks for all the tips - at least now the motor has been tested exhaustively!

 

[jmendoza]

Re: Old OMC motor - new fuel & ignition parts but won't idle!

Your low compression could be nothing more than a slightly faded head gasket, try replacing it and you can also scrape the carbon off the piston crowns while you are at it.