1989 40 evinrude intermitent stumbling

[wetboy86]

Hey guys, my 1989 rude 40 runs great but will suddenly fall on its face at or near wot. it does not stall, I pull the throttle back and it idles fine. if you throw the gas back up it will surge then stumble as long as you want. I found out if I turn it off and wait just a second it will fire up and run wot again. it does not do it everytime I go out, and you can be running for 10- 15 min at wot with no problems then fall off. It has the vro disconected, the bulb is hard,I have replaced every fuel line on it, a brand new fuel tank and the carbs have been gone through 3 times by yopp marine who thought it was trash in the fuel system. it is weird cause some days it dosent do it at all, just once or several times an outing. shut it off and it will take off everytime. any ideas?
thanks in advance for your input........SW

 

[jl_photo]

Re: 1989 40 evinrude intermitent stumbling

have you checked the fuel pump?

what kind of fuel tank do you have? is the air vent open and unclogged.

is the fuel pickup tube in the tank drawing air?

quick connect fittings ok? they can leak air and not fuel.

is the fuel clean? free of water?

can you borrow a different tank? borrow a different hose while you're at it.

 

[wetboy86]

Re: 1989 40 evinrude intermitent stumbling

thank you for the reply,I started with a new, clean and dry tempo 12 gal tank, I changed all the fuel lines including the tank line and bulb so the fittings are new. maybe the pump? it was a vro job but it disabled when I got it so I have to pemix. yopp bros marine couldnt find anything wrong with the pump but I guess that dosent mean its good. since it only happens after several miniutes at wot or near that, maybe the demand is greater than it can keep up with somewhere in the system. but that dont explain why it keeps doing it untill shut off and restarted.

 

[wetboy86]

Re: 1989 40 evinrude intermitent stumbling

Answer, took apart vro pump and found diaphram deteriorated to the point that the black rubber material was flaking off the fiber material and traveling to carbs, blocking the jets. How it ran in this condition for 2 years I have no idea. You could actually read through the diaphram. solution replace VRO pump with a manual pump.
hope this helps someone else