Fuel pump and tuning issues 1962 28hp seahorse

[kevinwd1]

Tested the boat today for the first time .The motor ran quite well but wouldn't rev out, if we backed the throttle off a little bit the motor seemed to rev a little better. So we adjusted the high speed needle using the knob and got the best results with the adjustment at full lean setting, but still not revving out .From this we assumed that we needed to screw the high speed needle in further than the fine adjustment would allow .So we tied up against the pier and removed the adjustment knob and screwed the high speed needle in so more. Problem was that we couldn't restart the motor and noticed fuel leaking from the fuel pump. So it seems that the fuel pump diaphragm has broken (probably should have replaced it as the motor hasn't been used for about 10 years)
So my questions are
1- Would a faulty diaphragm make the motor very hard to impossible to start (pull start only)

2-Would it seem that we are on the right track in adjusting high speed needle

Regards Kevin

 

[kfa4303]

Re: Fuel pump and tuning issues 1962 28hp seahorse

G'day Kevin. Yes, a faulty diaphragm could make starts difficult inasmuch as the motor won't start without enough fuel. However, I'm not sure if that particular model of fuel pump can be rebuilt. If it is a small, square shape you should be able to find a kit. However, if it has a square body with triangular top, you'll have to buy a new pump. As for the carb settings, you generally wan the hi speed needle to backed out about 1 full turn from lightly seated for starters. You'll then need to fine tune it at WOT on the open water. Here are some links that can help you with each of your issues.

Rebuilding the OMC Fuel Pump

(Carburetor Adjustments - Two Adjustable N/Vs)
(J. Reeves)

Initial settings are: Bottom high speed = seat gently, then open 1 turn out. Top slow speed = seat gently, then open 1-1/2 turns.

Setting the high and low needle valves properly:

NOTE: For engines that DO NOT have a shift selection, obviously there is no NEUTRAL position. Simply lower the rpms to the lowest setting to obtain the low speed needle va /lve adjustment.

(High Speed) Start engine (it will run pretty rough), shift into forward gear, take up to full throttle. In segments of 1/8 turn, wating for the engine to respond between turns, start turning in the bottom high speed needle valve. You'll reach a point whereas the engine will either start to die out or spit back (sounds like a mild backfire). At that point, back out the needle valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest setting.

(Low Speed) Slow the engine down to where it just stays running. Shift into neutral. Again in segments of 1/8 turns, start to turn the top needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Eventually you'll hit the point where the engine wants to die out or it will spit back. Again, at that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustments, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

1962 Johnson RX-10 28 hp Outboard Motor Parts

 

[kevinwd1]

Re: Fuel pump and tuning issues 1962 28hp seahorse

Have just ordered a new diaphragm, should turn up on Tuesday. Can't get a kit here in Australia just some individual parts

 

[kevinwd1]

Re: Fuel pump and tuning issues 1962 28hp seahorse

Just out of curiosity are there any fuel pumps that you can retro fit to this type and size motor?

 

[kfa4303]

Re: Fuel pump and tuning issues 1962 28hp seahorse

Hi kevin. Yes, some folks use Briggs & Stratton fuel pumps off of motors of similar hp. However, they can be a little bulky to retro fit on the smaller hp models, but I think you should have enough room under your cowl. Mikuni brand is also very popular and a bit more stream line, but a bit more pricey.

MIKUNI SINGLE FUEL PUMP from Aircraft Spruce (I think you might need a slightly larger one for your 28hp)

 

[kevinwd1]

Re: Fuel pump and tuning issues 1962 28hp seahorse

Thanks kfa4303.Will replace the diaphragm and hopefully it fixes the problem .The motor was running well for its first time in the water and was starting after 3 or 4 pulls so I’m hoping the extra load on the fuel pump caused the diaphragm to fail. We stripped it down and their seemed to be a tiny perished area? Pulled the spark plugs at the pier and they looked dry. It seems a little strange that we couldn't get the motor even to fire when trying to restart it? If anything else in pump needs replacing then retro fitting a different pump will be the go as parts are very expensive here in Australia.