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what the heck?

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durwin

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I have a 25 hp 3 cyl 2 stroke evinrude, motor starts and idles great off start then after a minute or two of driving or I exceed 3/4 throttle engine will start jerking then engine will start running rough I will come to a stop and motor is idling terribly I will attempt to throttle and will get no response,then I will shut engine down and restart and engine will run normally again until I attempt to full throttle. Please help first time engine owner.
 
If when you apply full throttle, it feels like you're hitting a submerged object... engine jerks bad on the transom, that would indicate that the engine is jumping out of gear then back into gear.

Saying that you get no response when you apply throttle means very little to us.... it dies out, it simply continues to idle... you need to explain exactly how the engine reacts.
 
durwin said:
I have a 25 hp 3 cyl 2 stroke evinrude, motor starts and idles great off start then after a minute or two of driving or I exceed 3/4 throttle engine will start jerking then engine will start running rough I will come to a stop and motor is idling terribly I will attempt to throttle and will get no response,then I will shut engine down and restart and engine will run normally again until I attempt to full throttle. Please help first time engine owner.
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When you use the squeeze bulb does the carb flood? Does the bulb seem to build pressure?

If you try the squeeze bulb at 3/4 throttle or with the engine running rough, does it temporarily correct the problem or make it worse?

Take a hard look at the linkage, ie with the engine not running open the throttle to full and back a few times, make sure that all linkage parts are positively moving back/forth with the throttle. I assume this engine ran fine in your experience and now you see this problem, or is it a new engine for you?

My suspicion is you have a fuel delivery issue, ie fuel pump not keeping up and the carb runs out of fuel at higher RPM. This could be an air leak in the fuel line leading up to the pump or the pump parts are going south... Another possibility is some pumps can fail and leak fuel into the crankcase (since they actually run off a pulse from the crankcase), flooding the engine out. The squeeze bulb tests will help check this area while also checking to see if the carb is flooding.

What doesn't make sense to me is that simply starting the engine again makes it run right - that doesn't strike me as a fuel thing unless you are squeezing the bulb again in between.

Jon
 
Have you looked at the water pump ?------Is your motor overheating ?--------S.L.O.W. system kicking in ?-----------Is this motor still running with oil injection system or was that taken off and thrown away as it should have been long ago ?-------Run with a timing light hooked up and observe spark when motor falters.
 
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I think you nailed it because on the first start of the day motor will run great,then while motoring engine will start jerking and almost wanting to stall then as I keep on throttle it try's to correct its self every so often,then I will squeeze bulb and it builds up pressure and engine attempts to again correct its self occasionally ,engine also has new power pack,thermostat,waterpump and all three carbs have been serviced and kill switch replaced,how many fuel pumps are there I see two identical units behind air silencer/ breather I guess it's called.
 
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durwin said:
I think you nailed it because on the first start of the day motor will run great,then while motoring engine will start jerking and almost wanting to stall then as I keep on throttle it try's to correct its self every so often,then I will squeeze bulb and it builds up pressure and engine attempts to again correct its self occasionally ,engine also has new power pack,thermostat,waterpump and all three carbs have been serviced and kill switch replaced,how many fuel pumps are there I see two identical units behind air silencer/ breather I guess it's called.
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What year is it? You can look it up on this site in the parts area. I'd be surprised if there is more than a single fuel pump but there would either be one per carb or one total.

If it's a fuel delivery issue you will be able to make it run normally just by pumping the bulb.

Jon
 
There were 2 pumps installed on these 3 cylinder motors !!!!!------------Need to run with a timing light to see if it is ignition related.---------Could be as simple as carefully cleaning the optical bits under the flywheel.
 
You said all 3 carbs serviced. Was the problem what made you service it or did it start after you got it back? I'm thinking carb problem. Clogged jet in one of the carbs?
 
I have a compression tester what should I be reading on all three cylinder?and timing light I don't have and don't know how to use one when I do get one please explain would like to learn
 
Thanks people I will try all suggestions and test where I can I am on a remote First Nation settlement in northern ont and I just got the motor back from a service shop to be tuned up and cleaned I was told carbs where cleaned and a few other things done like I had mentioned and motor ran good first day I got it back then everything went to ****,like I said will run normally for quite a while then then she starts running like crap one ther thing I am running mixed fuel no injection been removed
 
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I don't know why in the world all these difficult tests and troubleshooting suggestions are being offered.
I always, always do the easiest troubleshooting step FIRST, then move to the more work intensive.

He is clearly describing the function of the SLOW mode, or at least it seems so to me.

So, simply disconnect the tan wire from the temp sensor at the head, and retry the boat.
There should be a disconnect bullet very close, if not follow the wire til you find it.

If the engine performs correctly, BE SURE TO REMEMER that it is overheating, or at minimum, the temp sensor is defective.
At any rate, it is a quick, easy test to eliminate SLOW as being the "problem" .
Also....be absolutely sure you do not run it hot. Have you had the cover off, and felt around on the head to see if it is hot?
Have you used a IR temp gun to measure the actual temps?

Remember, SLOW is not a problem....the overheat that is triggering it is.

If this is not it, then proceed with other suggestions.
 
The poster says that oil is being mixed.---------These motors used an oil injection unit driven by fuel pressure hence the 2 pumps I believe.----------Does not use an oil pump like VRO units.
 
If it is remote electric start it will have an electric primer with a red lever.-------Manual start uses conventional choke flappers.
 
Thank you for all the helpful diagnosis,have eliminated most suggestions but one it is said my prop is no good causing motor to rev to high causing s.l.o.w to engage I have taken motor out and stay at low rpm and did not have any issues, so guess I will wait for new prop and see what happens
 
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