3.5 ob won't start

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3.5 ob won't start

Postby boatfreak » Mon Nov 02, 2009 7:27 pm

I have one of the early model 3.5 outboards, it came with a black carb, I purchased it new 20 years ago, I've never been able to start it. Two years ago I got back into the hobby. I have printed and read the manual, tried suggestions from other forums, I purchased a new gold carb and plugs from mecoa this year but still it won't start. I can see fuel (25%) going to the carb. The starter is going in the correct direction. The glow plugs are glowing, I bought a new ignitor with a meter that looks good. Everything seems right, just doesn't start.

I have cleaned the carbs, taken the lower half off to lubricate but the engine itself has never been taken apart. Still has a lot of compression. Overall in great shape.

I have another inboard that starts with no problems so I have a little idea of what I'm doing.

I really want to get it running.
Please help
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Postby SteveM » Tue Nov 03, 2009 8:42 am

Just to confirm, you are using an electric starter on the flywheel cone and you are spinning the motor in a clockwise rotation. The black carb has a smaller bore diameter and should work just fine. 25% nitro fuel is also fine.
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Confirmed-

Postby boatfreak » Mon Nov 09, 2009 6:31 pm

Thank you for replying so quickly, and sorry I took so long to respond-

Yes, I double check for the correct rotation each time. It is a positive to negative connection for my starter. I also verify by looking at the prop to make sure it going in a direction that would be pushing water.
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Postby SteveM » Mon Nov 09, 2009 6:51 pm

I seem to recall that the original 3.5 OB motors used a short glow plug. What fuel are you using?
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Postby boatfreak » Mon Nov 09, 2009 9:33 pm

Yes, it does use a short plug, though the new ones I got from mecoa don't have the idle bar ( they were out). It should start without the bar just not stay running once in the water as I understand it. Long plugs will strike the piston.

Fuel is Byron Fuel 25% from the local store mostly, I've also tried Blue Thunder 20%, these are what I use in my other nitro engine.

Would a higher nitro content help?

Someone on another forum suggested verifying the piston sleeve is oriented correctly, it appears to be correct.
boatfreak
 
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Postby SteveM » Tue Nov 10, 2009 4:32 am

Idle bar glow plugs are not usually used in marine engines, but I suppose they will be fine.

I used Byron 25% nitro fuel so you are fine there.

Is your 12V power source giving full power to the starter? All bolts on the motor tight and no leaks? Ball bearings in the motor all good and no rust?

I'm running out of ideas.
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Postby USMC » Tue Dec 01, 2009 9:36 pm

Has this engine ever be started at all?
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Postby HappyOne » Wed May 05, 2010 7:09 pm

I picked up the same motor late last year, original 3.5, short plug, water cooled, black carb.

Close the needle valve down (just to where it stops) then open it 3 1/2 turns. Attach the glow driver then put the starter on the cone (going backwards to the direction that the starter is designed to go) and cover the carb with your thumb for a second or so to choke it. Once you remove your thumb, she should start up soon after.

The carb should be open about 1/3 of the way.

Good luck.
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