Place fuel pump, where?

[25horses]

Hi

I have an old Johnson two-stroke two-cylinder 25 hp in my possession (25R69D). This spring I aim to get it up and running in a proper way. I've done some small repairs during this winter but there is one big question left. Where do I place the fuel pump. There are two nearly identical places to put it outside the lower or ouside the upper cylinder.

As the new fuel pump was a bit bigger than the old one it seemed better to put it in the upper position, most preferably when this made the lid possible to close ond of course open. But, sadly this lead to that the engine died if I wasn't quick enough on the prime pump.

No I've noticed that the two chambers isn't identical. The upper chamber seems to have another function then the lower one as it has some connection with the carb.

What do you folks have to say about my story? Do I have to mount the pump in the lower position?

Cheers
Roland

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[racerone]

It does not matter.-----The motor has 2 separate crankcases and each one operates with the exact same pressures.----Fact there is not much that can go wrong with these pumps !!-----Why the new pump ??----I would maybe install a new $4 diaphragm , but not a new pump.----The pump runs with a + PRESSURE pulse not vacuum as some folks think.-----When those 2 covers are off what do the pistons / rings look like ?----What does a compression test show on this motor ?-----If the engine dies with a new pump then test run run with a different tank and hose.-----Simple testing is the path forward !!----Or bring it over as I have all the bits / pieces to fix that fine motor on the shelf.

 

[F_R]

They put it on the lower cylinder at the factory, but it really doesn't matter. That other hose is the crankcase drain and is supposed to go to a special fitting in the lower right corner of the lower bypass cover.

 

[25horses]

Thanks for your answers, it is very much appreciated. So if I stick to placing in the upper position I have to figure out why it runs pretty bad. As I mentioned I have to be quick at the primer bulb to keep it running even though the fuel pump is new.

That brings me to a couple of other thoughts. What kind of gasket should seal between the two housing and the cylinder head? If the motor sucks air instead of fuel that could be part of the explanation to the poor result.

There is a little hose going from the lower part of the engine to the upper part near the flywheel. I noticed that it was in a very bad condition with lot of cracks so i replaced it. Can you guys please tell me the function of that hose? The new one is blue and I send a couple of pictures where you can get a glimpse of it.

Thanks, I apologize for my english. I'm a Swede.

 

[Crosbyman]

the hose recirculates oil back to the top bearing thanks to the crankcase pressure build up when the piston is on the down stroke .

by the way a new fuel pump ...can be defective/weak did you go Chinese ? did you install the base gasket


remove the pump and give it a blow test air should pass "IN to Out " but NO AIR should pass Out-->IN

if air passes OUT TO IN… the internal check valves are not doing their job

 

[Crosbyman]

[No message]

 

[racerone]

I have said it many times.---Most fuel pumps that are replaced are in very good working order.----Saw on a website that the " number sold was 1153 "-----I can't believe that these simple pumps failed on a 1000 motors.-----Diaphragm is only $4.00 or so.-----Pull the flywheel and inspect ignition system.----Make sure high speed jet in carburetor float bowl is clean.----Roland , does spark jump a gap of say 7 or 8 mm on a test device , yes or no ?

 

[25horses]

Thanks again, I will check the sparks. And yes, I installed the base gasket and as far as I know it´s not a chinese pump. But what about the gasket or not between the pump housing and the cylinder head?

 

[racerone]

Those 2 wee covers on the side of the block ( not the cylinder head ) do require gaskets.