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Motor bogs down at full throttle

gone_fishing We have a 98 25hp Evinrude that has an annoying habit of intermittently bogging down or losing power when we run at full throttle. One of the problems is that it is completely unpredictable as to when it is going to happen. When it happens we stop the motor take it out of the water for a minute or so, start it back up and it works fine. (At least until the next time.) Does anybody have any idea what this could be? 2001-04-16
J.B. Cornwell Howdy, gone_fishin'. Sounds like fuel starvation to me. Check that the air vent on your fuel tank is open and not blocked, that there are no air leaks in your tank-to-motor hose, and that your fuel pump is in good shape.

Another possibility is overheat Check out your cooling. Have a good stream of lukewarm to hot water (no steam)from your tell-tale? probably okay.

A blocked or closed air vent on the tank will look unpredictable because how long it takes to starve the engine depends on how full it is. An unvented full tank will develop a vacuum pretty quickly, while a near-empty tank may take half an hour to do the same.

Hope that helps.
JB

2001-04-16
richk I have a 1996 25HP Evinrude that I bought new in 1998. I have the exact same problem as you described. I will be cruising along at full throttle, then, without warning, and very abruptly, the motor slows down almost to a stop. After about a second it goes 2001-04-18
gone_fishing Thanks richk!

Yeah, it sounds like we are having the exact same problem. You are a lot farther along in the leg work than I am though. At least I know what NOT to try. Let me know how the fule pump goes.

2001-04-18
sony2001 gone_fishing and richk possibly that model
developes a vapour lock in the carb and by tilting the motor it unlocks. Additives have
been developed to prevent it. To mechanically
adjust something I would guess changing float
height.

------------------

2001-04-18
richk sony2001,

My motor clears itself without tilting it. I have checked the float level while in the process of rebuilding the carburetor. So, I don't think that would be a problem. Thanks for the suggestion, though,

richk

2001-04-18
Thewizard80 I have a 1984 Yamaha 50hp, 3 cyl, oil injected, outboard motor, low hours, and is in fairly new condition. At full throttle, it bogs down. I've changed the gas lines, tank, and fittings. The water pump works fine and the water is luke warm. The repair manual doesn't help either. 2001-04-19
J.B. Cornwell Hey, wizard. Most likely fuel starvation, but could be ignition timimg or spark strength as well as more obscure causes. Stop buying and replacing stuff until you zero in on the real cause. You could end up broke and still have a misbehaving motor.

Quic

2001-04-19
Mikael-Block Hello all
I can see a lot of possible errors, I have one more.
My guues is the plugs. They might get overheated, maybe an cooler or warmer type than the standard.
I no mechanic, so maybe I'm wayout.
Mikael
2001-04-20
richk An update on my 1996 Evinrude. I put a new fuel pump on a few days ago, and took the boat out to a local lake yesterday. I ran the motor wide open for about 20 minutes straight, and it never flinched once. I'm not going to break open the champagne yet, because I've been down this road before; where it looks like it's fixed, but two weeks later it acts up again. All I can say now is "So far, so good". 2001-04-20
ned white I have a 92 ,50 hp yamaha, with Jet drive, the boat sat for 4 years, Then I got a chance to work on it. Took off the bowls and cleaned out the jelly, dumped the fuel and started fresh, new plugs, new oil, Nothing, got the carbs rebuilt, new fuel pump, new oil pump, Now it will run, choppy, then overheat, ? I put on a new fuel line with new bulb, no good, The boat ran fine 4 years ago, then went kapoot, all the time I have been blaming the gas, but I think it's time to blame something else. Any Ideas??? thanks. 2002-02-02
Fouled Plug Ned, what compression readings does your Yammy have? 2002-02-02
Ned White Thanks for the note, never checked the comp, just going by the fact that it ran great before it was parked. The only info I get out of the book that I haven't checked is the adj jet settings on the sides of the carbs, top one is one turn, second one is 1 1/2 turns, etc. or something like that. I will check the comp, what am I looking for??? 2002-02-02
gone_fishing Well, my problem turned out to be nothing more than a gummed up carb. We took it in to the shop after putting in a new fuel pump didn't work. All they did was spray some Mercury Power Stroke in the carb, etc... And Wholla! Anyway, feeling dumb now... 2002-02-05
12Footer No, GF..Don't feel dumb. You did good.
When the carb is gooed-up,this just means the original problem made it all the wayt thru your fuel system.
Now, with clean fuel tanks, fuel lines,filters, fuel pumps and carb,
2002-02-05
Fouled Plug Ned, I would hope to see at least 100# of compression, and the cylinder should be within 15% of each other. The compression test should be done on a warm engine, but a cold reading will let you know if something is really wrong (a reading of 0# would not be good at all) 2002-02-05
mgortel Could be a bad fuelk hose between motor and tank. Replace hose and try. I had this happen to me before....the hose was old and kept collapsing under the vacuumn draw that the motor was creating when it was trying to suck a lot of gas at higher RPM's. 2002-02-12
Ned White OK back to the choppy engine. i broke down and took the boat to the shop. I was on the right track, He replaced everything I replaced. But,,,, after i had rebuilt the carbs, they were never reset properly, so they did them again, This time they were set right. And guess what, They are finicky little boogers. Total cost was $500, but it works. I was getting nowhere by myself. Good luck. 2002-04-07
wayne c. I agree with all the posts on this problem, theres one other item u might look at. A friend w/a 50 hp Yamaha had same problem. If pitch on your prop is too small you may be hitting the rpm limiters at wot, just an idea. 2002-04-08
hair426 gone fishing
i have an 85 that does the same exact thing and it's drivin me crazy!!!!!!!! if u here anything let me know
later
2002-04-09
honsey I too am having the exact problem...any answers yet? 2002-06-28
fireman 757 Don't know about the Yamadogs but the evin sounds like an ignition coil breaking down. As soon as it bogs down shut it down and pull your plugs. If one is wet or more carboned than the other I would suspect a coil. When you shut it down and tilt it up it could be cooling down sufficiently to run right on startup. I'm not saying this is it for sure but you seem to have eliminated the other things it could be. You can always spend eighty bucks and about 15 minutes replacing them. 2002-06-29

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