Johnson Seahorse 15 hp 1975 Fuel pump

[lywtrte]

I bought a seahorse 15 hp 1975 that has problem with fuel pump. I clean out the fuel pump and tested it with a bycicle pump and confirmed that the pump works. I am unable to see the fuel coming out of the outlet port by pulling on the pull cord. I am wondering if I am having problem with the pulse from the engine block. I connected a clear tubing onto the engine port and fill it with water. I was able to see only about 2 inches of water movement. a very week pulse pressure. Does any one know how much pressure the engine create to drive the pump? The engine seem to have good compression. How much pulse pressure does it need to power the diaphram fuel pump?

I would appreciate any information you can provide to trouble shoot this issue.

Thanks

 

[fdrgator]

The engine supplies alternate pulses of pressure/vacuum from the crankcase as the piston moves up and down. Nobody expects it to work at cranking speed. You have filled the carburetor with fuel by squeezing the primer bulb. That is all it needs to start and run a few seconds. Once running the fuel pump takes over, keeping the carburetor full. If you want to test it, tee a pressure gauge into the line between pump and carb. Should run with a pound or two of pressure (while running).

 

[lywtrte]

The engine supplies alternate pulses of pressure/vacuum from the crankcase as the piston moves up and down. Nobody expects it to work at cranking speed. You have filled the carburetor with fuel by squeezing the primer bulb. That is all it needs to start and run a few seconds. Once running the fuel pump takes over, keeping the carburetor full. If you want to test it, tee a pressure gauge into the line between pump and carb. Should run with a pound or two of pressure (while running).

Fdrgator, Thank you greatly for the reply. Your explanation about the alternate pressure / vacuum helps greatly. I stopped worry about the engine pulse and worked on different area. I tried elevate the fuel tank above the engine and tried staring the engine with the help of starting fluid. I was able to get the engine to run for few minutes and cycle through forward and reverse before the engine stopped. I think i might have a poor fitting at the quick disconnection which might have let air entering the fuel line and interrupted the pump operation. I will replace this connection first before I trouble shoot the hard start problem. I am sure I will check back at this forum for more question. Your answer opens the door for me to try the next step. I am so new at this. I will post the result when I get the engine running.

This a great forum and i appreciate the help.

 

[SuperT]

Never use starting fluid to start you motor. You risk scoring the piston and cylinder. It needs the oil in the gas to lubricate the internal parts.

 

[joereeves]

If you pump the fuel primer bulb constantly (acting as a manual fuel pump), the engine runs like it should... that indicates a bad fuel pump, assuming there are no fuel/air leakage points

 

[lywtrte]

SuperT ,You warning about not using starting fluid makes sense. I just never thought of it. I guest starting fluid must be designed only for 4 stroke engine. Do they make starting fluid that has oil in it so 2 stroke people can use them safely. I was able to get the motor start reliably. I am still having difficult keeping the engine running smoothly. Engine run a little smoky, a little rough, and having difficulty idle at slow speed. I will need to look up on the carburetor forum for tip on this.
My current concern is the water port. I see some water discharge from the water port but not by large quantity. I saw a few video in youtube when the engine running on the lake, the water seem to shoot out like jet. could some one comment on how much water should be coming out of the water port at idle, high rpm, and with gear engaged. Does the water pump run the same way with gear engage and in nutral? Is low water discharge an indication of bad water pump or impeller. Many thanks

 

[joereeves]

(Exhaust Relief Ports - Exhaust Housing (Inner/Outer)
(J Reeves)

The long housing between the powerhead and the lower unit is called the exhaust housing. There is a inner housing within it that has a heavy duty seal around the bottom of it, or heavy duty seals around a inner extension between the housing and the lower unit.


The red hot exhaust travels down thru that inner tube and out the propeller with a somewhat supply of water to cool the propeller hub. A good amount of water surrounds and fills the space between the outer and inner tube, otherwise the outer housing would get so hot that the paint would burn off.


Some water pumps, for some reason (differing even when new) exert a great amount of water pressure, and if the exhaust housing seals are in perfect condition, the water fills the tube to a point of overflowing.

This brings into play those two holes or slots, whichever the engine might have, at the top rear portion of the exhaust housing just below the powerhead.

Now, if those two holes/slots weren't there, water would continue to flow up into the cylinders. Water not flowing out of those holes is no concern for alarm UNLESS that outer housing suddenly becomes extremely hot..... the warning horn should sound long before that happens.


The main reason for those holes being there (exhaust relief holes) is that when at an idle, there is an extreme amount of resistance encountered by the exhaust trying to escape due the fact that the outlet via the propeller is now blocked by a wall of water. The escape route in this case is for the exhaust to escape out those two holes, otherwise the engine would slow down quite quickly and die. If exhaust cannot escape, air/fuel cannot gain entrance to the engine.

 

[kimcrwbr1]

The fuel pump may have a hole in the diaphram if in doubt just get a rebuild kit and see if that solves the running issue. Cold start issues ar almost allways with the carb try setting the slow needle a little rich. Once you get it running good and the slow needle adjusted wait a day and see if it starts first pull. If not adjust the slow needle out 1/4 turn and try again. It is allways best to run the idle air rich to protect the motor running at slow speeds and it helps with the hole shot and cold starts.