Evinrude 250 running rough at mid rpms

[deb0650]

Hi. 2001 Evinrude 250. Model E250FPXSIF. S/N 4930668. Outboard has about 170 hours. Just returned from a Baja trip where my outboard was running rough between 3,300 to 4,100 at part throttle (less than full throttle if that makes sense). At idle and low speeds it ran perfect. Then I would accelerate to plane just fine and if I backed off to an easy cruise at between 3,300 and 4,100 it would run real crappy. When running rough it sounded like a ratty carbed 2 stroke. No smoke or smell. I checked the plugs and the gap was .038 to .040 so I regapped to .028. Didn't seem to make a difference. I run the new style QC10WEP and they have about 45 hours on them. Also upgraded the thermostats and blow-off valve to etec specs. It is propped correctly and usually runs fine. I changed both fuel filters about 25 hours ago. I use BRP 50 oil and carbonguard in the fuel. Fuel is not too old and was treated. I ran the outboard the entire time on the water with a lot of idling in between running from spot to spot. Like I said, it sounded perfect at idle and low speeds until it got on plane and reached about 3,300 or so and then if I increased my speed and rpms to 4,200 or more it would run good. It seemed like it didn't want to run at a lighter throttle setting but was fine with a heavier throttle setting. Any ideas?

[ELGIN]

We will need more information to help answer your question.

Cylinder head temps at idle would be a good start.

How old is "Fuel is not too old and was treated" and what treatment?

[deb0650]

Fuel tank is 135 gallons. 80 gallons was added in December and the remaining was from October. I always treat it with carbonguard and stabil (red) in the designated quantities when I pump in fuel. The check engine light did not come on. The outboard started fine and never stalled. Like I said, it seemed to run perfectly at low rpms and high rpms. Just did not like a light cruise setting. I had a heavy load of four big guys, full bait tank, and large ice chest. The boat is a 26' Seaswirl Striper. The prop is a rebel 14 3/4 x 15 and revs out to 6,000. The ocean temp was 61. Don't know the cylinder head temp. Like I said it has new thermostats and blow-off valve from etec so it should be running hotter than stock. I ran the boat two weeks ago and it ran fine. Never noticed any roughness until the last three days down in Baja. Thank you for your help.

[deb0650]

One more thing I should mention. The EMM was repaired by DFI in September for the ignition capacitor. Got it back and the regulator went bad after a couple tuna trips. Sent the EMM back and they replaced the regulator. Ran it once after that and it ran fine. Then the problems in Baja. After the first EMM repair I did check the timing and set it properly. I didn't check the timing the second time. Didn't expect it to be any different.

[ChampioNman]

I may be way out there but did you pick up a load of fuel in Mexico? If so that may be your problem.

[deb0650]

Nope. Good ole' US gas. Same station I fuel my cars at. I will replace the plugs with new ones and see where that takes me. Would a fuel issue cause the erratic running I'm describing? What confuses me is the great performance at idle and slow running (not on plane, just pushing water). I did not detect any roughness or missing. It accelerates to plane fine. Then when I back off to maintain a moderate speed on plane is when it runs rough. When I speed up and give it more throttle it cleans up and seems to run strong. I've always understood that if the injectors work, they work. They don't selectively pick a particular rpm to do stupid stuff. Is there another condition that could cause the injectors or spark to be erratic at a particular rpm? Thank you for your help.

[ChampioNman]

Sure messed up fuel will really show in a 2 stroke motor. Although your motor may not have posted a H20 in fuel a good policy is to replace the on board fuel filter yearly, and your plugs every 100 hours, more if you are idling/trolling.

[deb0650]

The plugs and both fuel filters have been changed in the past 45 hours/6 months, but I will change them again. I still don't see how water in the fuel would not impact the outboard at idle, low speed and high speed. Thanks again for the input. Would water in the fuel create white exhaust? I didn't detect any smell or visible smoke at all.

[ELGIN]

You need the dealer software, run the engine to the RPM where the problem occurs and richen the fuel injectors, see if that helps.