Neptune Outboard afraid of water

[Buccaneer]

Tried my 1936 OB34A 4hp Neptune twin the first time today after going
through it. Had it on the outboard stand, and it started in three
pulls, sounded great. I only let it run about 10 seconds, and killed it.
Then promptly Baptized it in the test barrel with "not so Holy water".
What I expected at this point was it starting with one pull, and pumping
water like Old Faithful. I now have a blister on one hand, and a cramp
in the other from pulling on it. The longest run in the test barrel was
about three seconds 🙁
It seem more promising after cutting back the high speed jet,
and sometimes better when I retarded the mag from what I guessed
was "start" position.
The carb is a Tillotson MS-88A. Anyone know the initial high speed
setting? I don’t remember seeing an adjustable low speed setting.
It has a twist grip throttle. Should it start with the throttle closed,
partially open, or?
I have not checked the compression yet, but will do so before I tinker
any more. Anyone know what’s acceptable compression on an old
opposed twin like this?
Thanks, Buccaneer

Prepare to be boarded!

[b-morrison]

Try starting with the prop off. If the rings are stuck or worn, it may start and either loosen up/free the rings or….. I had an old evinrude where I did this..

[The Boat House]

• This reply was modified 6 years ago by The Boat House.
• This reply was modified 3 years, 9 months ago by The Boat House.

[joecb]

It has an underwater exhaust tube , yes? Should be pressure relief holes in the Exhaust tube that are above the water level. Are these holes clear and open? or all plugged with carbon and "goop". back pressure on the Exh will make for difficult starting.

Joe B

[RICHARD A. WHITE]

you can run it longer than 10 seconds, check cylinder temps with your hand, probably get 20 seconds or so. Use that time to get carb set. Mine also with MS88A carb. Do this a few times let it warm up then completely cool down, do it again, until it starts easy every time. As I recall I used about half choke to start and that helped alot…

hope this helps

Richard

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[Buccaneer]

Said Neptune was completely torn apart, de-carboned, cylinders lightly honed, new gaskets, etc.
I did think about the back pressure on the exhaust tube. One of the tubes has a 3/8" hole
high above the water line, but I think it’s the drive shaft tube. Not sure if the exhaust has
a hole or not. It did not magically re-start after I took it out of the test barrel and put
it back on the stand, but by that time I was pretty much tired of pulling, lol.
My choke is spring loaded to stay open. It’s a chore to pull the rope with one hand,
hold the choke closed with the other, and use the third hand to keep the lower unit from
flipping up! Will check compression soon, but have to go eat Easter Bunny tomorrow.
Happy Easter! Bucaneer

Prepare to be boarded!

[mr-asa]

New rings as well? Maybe they need to bed in before it will run well?

[eltoquad]

I had the same problem with a twin Neptune and it was caused by loose main bushings. It’d start out of water but not in. I repaired them and it started fine there after. If it starts in water without prop on (motor will spin over faster) that’s probably your problem.

[Buccaneer]

Eltoquad, The mains seemed pretty good for an 79 year old motor, but
I did replace both bushings in the lower unit, which were shot for sure.
I used some heavy camshaft installation lube on the mains when I
put the crankcase back together, so it’s possible that it started on my
first try, but not after the cam lube "thinned out".
Did you have to line ream your new crankshaft bearings, or just
install them?
Hopefully will have time to play with it tomorrow!
Thanks, Buccaneer

Prepare to be boarded!

[Buccaneer]

Had a little time this afternoon to work on the Neptune. Checked
the compression, and both cylinders were at 60 psi. They’re the
original rings, but maybe the compression would come up a little
after the rings re-seat after the cylinder honing?
Put a new condenser in it. Fired right up on the stand. Ran it
about 30 seconds, tried tuning a little bit, but really not enough time.
Put it in the test barrel, positively thinking it would fire right up
this time….. WRONG again! Would hardly fire.
Next time I’ll take the prop off and the exhaust tube and see
if it runs in the water.

Prepare to be boarded!

[Author]

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