35hp not running right

[don_61760]

I bought this 1987 35hp last fall. Ran it a few times and ran great. This spring it ran fine in the driveway took it to the lake and put it in the water. ran fine circling back to the dock and the died. Refused to start. Back home checked it and had no spark. Tested everything and replaced the switchbox. Got it running but when we took it out again it would be running fine but start bogging down for a few seconds and then recovering. Has to be fuel right? Took off the carb, it looks fine. What's next? Rebuild fuel pump. I'm stumped. BTW fuel is good.

 

[Texasmark]

If you still have OEM original hoses both inside the engine and to the engine for your fuel distribution, your problem could easily be degraded fuel lines which could be cracked, letting air in, or dissolving allowing rubber parts to clog your fuel lines/filter. What you said would give your engine time to do a nice job of distributing such and collecting in the fuel filter would be a good place for that. I guess they had fuel filters in the engines in '87....look for one and change it if you have one and the bulb also when you change your engine to tank line. Other thing, might as well do a fuel pump kit too as the diaphragm in it could be cracked.

 

[don_61760]

The motor didn't have a filter on it but I have ordered new line, pump kit, and a filter. I replaced the primer bulb already. I didn't see anything in the carb bowl but that doesn't mean it's not there. The service manual mentioned air bubbles. What does that do, just prevent the pump from moving enough fuel? I assumed any air would just vent out of the carb. It's really discouraging to go out and worry about your motor quitting and not getting back. If only I could afford a new four stroke bigfoot.

 

[Texasmark]

The pump forms a partial vacuum on the fuel line when the engine is running. It has to have fuel present to pump satisfactorily, and is the reason for the squeeze bulb. Bubbles in the fuel would decrease the density of the fuel it is trying to pump and starve the engine at that particular rpm where present. For what it's worth, in 50+ years of boating I never had an air bubble problem in a fuel system.

Fast forward to today: Cracked fuel lines seem to be more common than years ago. As such you have a source for sucking air (aka bubbles) in the fuel. Other thing is pieces of fuel line will migrate down the line and into the carbs and clog things up....had it happen on my 2002 90 in the year 2010, and it had an internal filter............On the internal filter, matters not the position of the filter but the orientation is important.....fuel flows with the arrow because of the way it's made internally.....filters a lot more crud before it needs changing. Put it as close to the carbs as is reasonable.

 

[don_61760]

Thanks for your help. Waiting for the fuel filter and pump kit. Hope that does the trick.

 

[Texasmark]

Thanks for your help. Waiting for the fuel filter and pump kit. Hope that does the trick.

Open up your fuel lines and have a look inside your fuel lines. Bend them as you look in an attempt to expose cracks that may not be visible when relaxed and also pieces/chunks of hose missing.

 

[don_61760]

Worked on the fuel pump today. The first check valve was really bad. Part missing. Pretty sure that was the problem. The lines were in pretty sorry shape so I went ahead and replaced them all. Haven't started it up yet but I'm99% certain the pump was the problem. Thanks again for your help Texasmark. I really appreciate it.

 

[Texasmark]

Worked on the fuel pump today. The first check valve was really bad. Part missing. Pretty sure that was the problem. The lines were in pretty sorry shape so I went ahead and replaced them all. Haven't started it up yet but I'm99% certain the pump was the problem. Thanks again for your help Texasmark. I really appreciate it.

Good luck