question on two fuel pumps 1999 25 johnson 3 cylinder

[tracygriffith]

hi all, new to this forum, thanks in advance for help. i'm trying to figure out why this 25hp 3 cylinder johnson (99) stalls out when giving gas. several mechanics have been unable to id problem. carbs have been gone over, look good, new power pack didn't fix problem, it's baffling. will typically start right back up, idle fine, etc, until throttling up to get on plane.
i'm wondering if it may be a problem with one of the two fuel pumps, as manual shows them as "pumps which cannot be switched"; as if they are two different from one another. they look exactly the same and I see no identifying markings. anybody know this motor/pumps and have any ideas?

[Joe Reeves]

Having retired in 1991, I can't answer your fuel pump question.

However....... Having any engine die out when throttle is applied is normally the result of one of three causes (or all of them)..........

1 - The timer-base under the flywheel on many models has been known to stick as the spark advances, and that results in a retarded spark scenario.

2 - The cam that slides against the roller that opens the throttle(s) icould be engaging the throttle roller too soon. The scribe mark on the cam should align with the roller dead center at a specified idle timing degree... low, something like 2,3,4 degrees, whatever the manual states.

3 - The high speed jet that lies horizontally in the bottom center of the float chamber, way in back of the drain screw may be somewhat fouled, clogged, gummed.

[tracygriffith]

thanks Joe

Thanks for the ideas Joe, I've wondered about high speed jets and will check them tonight. Cam roller I'll check also. Not sure what to make of timer base stick idea...can this "timer stick" be seen without removing the flywheel?
thanks again, i'll update tomorrow, hopefully with good news

[Joe Reeves]

The sticking timer base could always be plainly seen as of the year I retired (1991) but I have no knowledge of the later models design. I would thing it could still be viewed... BUT... the habit engineers have of jamming everything together (sigh!).

Pertaining to the throttle roller.... for more years than I can remember, the roller was one piece, about 3/8" wide. THen somebody in power got the brilliant idea of making the roller smaller and having a transparent cover over it to bring the 3/8" diameter up to par. The result of that is the transparent cover cracks away, causing the roller to be the wrong (too small in diameter) size which throws the entire throttle/timing synchronization off. It should be 3/8 dia...... check it.

[tracygriffith]

thanks again, helpful to hear ideas to check. high speed jets look all clear, took them apart and saw no signs of clogging at all. carbs look great. waiting for new carb bowls to arrive, as two had small cracks and leaks. pretty sure the cracks had nothing to do with running problem, and that i cracked them couple weeks ago.
i'll check sticking timer base and throttle roller cam when i put the carbs back on, hopefully this weekend, depends when parts arrive.
thanks again!

[NautiBuoys]

"i'm wondering if it may be a problem with one of the two fuel pumps, as manual shows them as "pumps which cannot be switched"; as if they are two different from one another. they look exactly the same and I see no identifying markings. anybody know this motor/pumps and have any ideas?"

They are indeed different: One pump is designed to draw fuel from the tank; the second delivers fuel under pressure to the fuel mixing unit. Switching the pumps around will result in poor performance, and if the mixer is still there (which everyone recommends one remove), possible engine damage.

The pumps are serviceable (how to clean filters, how to function test, suction pump test, pressure pump test) and best to get the engine manual. One can get them cheap on ebay.