1961 40hp big twin

[robnwendy]

Newbie here I got the boat last year,(1968 silverline in good shape) having idle problems in neutral.If I leave choke out half way it stays running. Took notice the idle adjust screw is nylon and was broken replaced it but bending new one to.Put in metal bolt but doesn't seem to do the trick.I was read on here about high and low speed adjustments on carb.,but don't know if that's the problem or not.I'm going to rebuild the carb.but going out today.Is there a quick fix for now,and need suggestion for long term.Also it's a pull start so not fun when it dies.

 

[jay_merrill]

Re: 1961 40hp big twin

Rebuilding the carb is very likely exactly what you need to do. If the motor will continue to run partially choked, you may not be getting enough fuel from the low speed needle valve/jets. This can be caused by a dirty carb. Basically what is going on is that you are not getting enough fuel to create the proper fuel/air mixture to sustain normal combustion. When you partially choke the motor, you are correcting that imbalence and matching the air flow to the fuel flow that you do have, which is apparently enough to keep the motor running.

Go ahead and thoroughly clean the carb and rebuild it. If you don't have a service manual for your motor for instructions on how to do this, you can buy one here at iboats, or may obtain one from other sources.

 

[Willyclay]

Re: 1961 40hp big twin

Welcome to the iBoats Forum. The experts here, which I am not, can help you with any problem. I previously owned a 1959 Johnson 35HP which is almost identical to your motor. I had idle problems that caused me to clean the carb three times before I finally got ALL the gunk out of the passages. The last time I found a tiny amount of trash in the idle screw inlet. The experts will tell you to strip and soak the carb body in cleaner overnight to help dissolve the deposits. Good luck and let us know how you do!

 

[robnwendy]

Re: 1961 40hp big twin

Could I adjust low speed needle valve for now.And are rebuild kits for that motor avilable at most marine shops.

 

[Willyclay]

Re: 1961 40hp big twin

It will be a crap shoot whether or not adjusting the low speed mixture will fix or help your problem but try it and see. Turn the needle valve 1/4 turn at a time and pause to let the engine respond. Sounds like you need more fuel, so start by turning it out or counter-clockwise. The idle screw you described in your first post above sounds like the idle SPEED adjustment screw if it was originally nylon. The one you want, the idle MIXTURE screw, is brass with an indicator cap on the accessible end. Yes, carb rebuild kits are still available. Maybe another member will post a recommendation on that soon. Good luck!

 

[robnwendy]

Re: 1961 40hp big twin

Thanks, I'll give it a shot. Appreciate everyones help.I will get a manual and a rebuild kit for carburator.Sould I get original owners manual or is Selco manual better.

 

[jay_merrill]

Re: 1961 40hp big twin

Aftermarket manuals will do in a pinch but they usually aren't very good. Their main "sin" is that they most often cover a very wide range of OMC motors and don't cover any of them very well.

The first thing that I would do, however, is to make sure that the low speed needle valve is adjusted properly. On most OMC motors of that vintage, this is accomplished by screwing it in until it seats - do this gently so that you don't damage the taper on the needle valve - and then back it out 1-1/4 turns. Use this position as a starting point to set the idle speed at the correct value, per the manual.

If you do this and the motor still doesn't run properly, you may as well accept the inevitability of rebuilding the carb. Don't be afraid of doing so - it really isn't all that difficult.

 

[tashasdaddy]

Re: 1961 40hp big twin

what is your model # so you can get the correct OEM service manual. Seloc is very general, and not specific to your motor.

 

[Willyclay]

Re: 1961 40hp big twin

Just sent you a Private Message regarding a service manual.

 

[itstippy]

Re: 1961 40hp big twin

"I'm going to rebuild the carb.but going out today.Is there a quick fix for now,and need suggestion for long term.Also it's a pull start so not fun when it dies."

Get the service manual and go through that old girl top to bottom, maintenance-wise. First, look it over very closely for wear marks on the moving parts & linkages. They're easy to spot on a dirty motor. Then clean out any 47-year-old grease that's turned to putty and replace with grease from this millenium. Clean, clean, then oil & grease. New impeller. Fresh lower unit oil. Carb kit. Compression test. Spark test. Seafoam decarb. Get the old fishing line off the prop shaft. Read the "awaken a sleeping outboard" writeup and make sure you've done all that stuff. It will run forever if taken care of; it will wear out and die if you just do a carb job and get it "running good" but don't do the other stuff. You will love that old motor if you take the time to clean it up and observe how it all works. It's like an old Detroit V8 - simple and powerfull and solid and "sits well" during periods of non-use and sounds awesome and drinks gas like it's 1961.

You could install electric start quite easily and cheaply. Big Twin starters & brackets show up on eBay often because so many of those motors were sold and so many get parted out. If your flywheel has a ring around it with teeth on it like a big gear that the starter gear would engage, you're in buisiness.

Can you tell I love the old Big Twins?