1964 40hp carb question

[broncos730]

I have a '64 40hp big twin 2 stroke. I've never had it running more than 30 seconds at a time before it starts stalling, missing, kicking back, and then just up and dying.

I've changed the plugs, points, condensers (coils looked ok). I have a good blue spark with a 1/4" gap.

I've cleaned and rebuilt the carb but didn't replace the cork float. One thing I noticed is the orifice plug (as called in the manual) that installs in the bottom of the bowl (high speed orifice?) was snugged down and I re-installed that way. A lot of the documentation here on iboats say to back it off 1 full turn.

Could this be the cause of my problem? The problem with this motor has never been idle vs. WOT just running in general but at this stage I'm looking at everything. If the orifice is to be backed off 1 turn what's to keep it from loosening/tightening during engine running due to vibration?

 

[tx1961whaler]

Re: 1964 40hp carb question

The high speed orifice in the bowl should be screwed in tight. It is not adjustable on the 1964 40 HP. The low speed needle at the top is adjustable. On some motors both are adjustable. The carb has to be absolutely clean to work. There are a few tiny passages that have to be blown out with compressed air to make sure they are open. The plug on top must be removed and the idle air passages cleaned out. When I clean my carb I soak it in Berryman's for a few hours, then spray and clean with aerosol carb cleaner, and finish it off with compressed air. Even with all of that, I have had to do it over again. Also, if you have old fuel lines, you may want to replace them. Modern gas seems to be breaking down the old fuel lines from the inside and causing carb fouling. They also crack and cause air leaks, which could be contributing to your problem.

 

[broncos730]

Re: 1964 40hp carb question

Thanks! I'll pull the carb again. I've tried bypassing the fuel system entirely and put a tank above the motor gravity feeding the carb and still it only runs for 30 secs. Seems like a fuel delivery problem. Do the floats ever go bad on these? Also what about reeds? I'm not getting any backfiring through the carb but nobody ever seems to be discussing the possibility of the reeds (or whatever they are called on an outboard 2 stroke) failing.

 

[tx1961whaler]

Re: 1964 40hp carb question

Yes the cork floats do go bad. They will get saturated and sink, and the motor will flood badly. There is anecdotal evidence that ethanol will dissolve the shellac coating, but I'm not sure that 10% would do it. The coating on them did fail prior to ethanol coming on the scene. Reeds will go bad, but is is a rare thing to happen. I've only seen it happen once, and it had help from a loose screw getting sucked in through the carb.