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?

 

[JB]

Re: motor bogs down at full throttle

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.<br /><br />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.<br /><br />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.<br /><br />Hope that helps. <br />JB

 

[richk]

Re: motor bogs down at full throttle

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 back to full throttle. It is very intermittent; sometimes it won't happen for weeks, other times it happens 3 times in an hour. Here's what I have tried: I cleaned and rebuilt the carburetor (twice), replaced the fuel tank, fuel hose, primer bulb, checked all electrical connections. I have tried bringing it to a so-called "Authorized Repair" shop. The mechanic told me I had carbon in the cylinders. He replaced the head gasket, charged me $105, and did NOTHING to fix the problem. I just took the boat out Tuesday for the first time this spring, and the problem is still there. I bought a new fuel pump yesterday. This week I will install that and try the motor again. This has been very frustrating! It's nice to know that someone else has experienced this problem. Keep me posted, and I will do the same.

 

[gone_fishing]

Re: motor bogs down at full throttle

Thanks richk!<br /><br />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.

 

[sony2001]

Re: motor bogs down at full throttle

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

 

[richk]

Re: motor bogs down at full throttle

sony2001,<br /><br /> 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,<br /><br />richk

 

[Thewizard80]

Re: motor bogs down at full throttle

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.

 

[JB]

Re: motor bogs down at full throttle

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.<br /><br />Quickie fuel pump test: Pull the fuel line off of one carb. Place it in a can or plastic bottle and turn the engine over for a few seconds. If you get strong pulses of fuel in the bottle (about 1oz. per second)your pump is probably okay. If they are weak, overhaul your fuel pump. Do this in the open, away from any source of fire or spark.<br /><br />Carb/ignition narrowing test: You say the engine bogs. Do all three quit or could only one be cutting out? If it is only one, find which one by pulling the plug wire and listening for changes. When you have isolated which one is cutting out, swap the ignition parts for that cylinder with one of the good ones, one part at a time. If the trouble moves to the new cylinder, replace the last part you moved. If you can't move the trouble this way, try moving the carb. If the trouble moves, overhaul that carb.<br /><br />If it is all cylinders failing, check that your ignition timing is being advanced smoothly with the throttle. You can do this by inspecting the linkage while advancing the throttle without starting the engine.<br /><br />If the above fail to isolate the problem, tell us what you did and what you found out. Then we'll try again.<br /><br />Good luck.<br />JB

 

[Mikael-Block]

Re: motor bogs down at full throttle

Hello all<br />I can see a lot of possible errors, I have one more.<br />My guues is the plugs. They might get overheated, maybe an cooler or warmer type than the standard.<br />I no mechanic, so maybe I'm wayout.<br />Mikael

 

[richk]

Re: motor bogs down at full throttle

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".

 

[Ned White]

Re: motor bogs down at full throttle

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.

 

[Fouled Plug]

Re: motor bogs down at full throttle

Ned, what compression readings does your Yammy have?

 

[Ned White]

Re: motor bogs down at full throttle

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???

 

[gone_fishing]

Re: motor bogs down at full throttle

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...

 

[12Footer]

Re: motor bogs down at full throttle

No, GF..Don't feel dumb. You did good. <br />When the carb is gooed-up,this just means the original problem made it all the wayt thru your fuel system.<br />Now, with clean fuel tanks, fuel lines,filters, fuel pumps and carb, you should be back to normal.But keep it running by running it often,and not lettting old fuel go bad in the clean tanks. Try to run them close to dry before switching-over to the full tank, and carry a one gallon can with enough 2 cycle oil (6oz) to mix in the event you do not make it to the dock.<br />In other words, don't run the risk of running out of fuel, but also,don't allow gas to sour in the tanks, by figuring fuel consumption,and keeping a resrve you can dispose of at the end of the day, by using it in your tow vehicle.<br />I've never had to use my reserve in the engine,but I've also never returned with more than 3 gallons of fuel in my boat's tanks.<br /><br />

 

[Fouled Plug]

Re: motor bogs down at full throttle

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)

 

[mgortel]

Re: motor bogs down at full throttle

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.

 

[Ned White]

Re: motor bogs down at full throttle

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.

 

[wayne c.]

Re: motor bogs down at full throttle

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.

 

[hair426]

Re: motor bogs down at full throttle

gone fishing<br /> i have an 85 that does the same exact thing and it's drivin me crazy!!!!!!!! if u here anything let me know <br /> later