2.5 Mercury 260 running super rich and stumbling

[jdb35]

Last weekend I took the Ally out for a run on the river. I am running a 2.5 Mercury 260 and it ran fine leaving the landing, I ran it up to about 5000 rpms and had to let out of it to meet another boat. When I tried to accelerate again it started stumbling and would barely make it to 3000 rpms. I could not plane the boat. I idled back to the landing and loaded the boat up. After I removed the cowl I found one of the vacuum lines off on the side of the motor by the fuel rail. I replaced the vacuum line and hooked it to a hose, the problem was still there. I am running a bracato computer and have had a similiar problem before. The last time I had to remove the horn and clean out the vacuum line going to the computer, I hope this solves my problem again. If anyone has any other suggestions please feel free to let me know. I appreciate any help with this problem before I resort to taking it to the shop.

 

[chad202]

Could be that or lost a pack. Could you tell if its was firing on all six?

 

[jdb35]

Chad, I pulled all the plugs and they all looked the same. It seemed like it was trying to pick up the other cylinders at times. That is why I thought the computer went super rich when the vacuum line came loose and loaded up the motor on fuel

 

[K.Kiser]

Yeah, if the tygon hose from the computer to the intake gets clogged or thwarted the computer will go rich to protect the engine..

 

[ziemer]

I have to clean that small nipple on the horn before every trip out. You can thank this chit ethanol fuel for that...

I never cleaned it prior to ethanol. I've run both Klotz and Alisyn oil and it does it with both.

I keep a small bread twist tie, and piece of Tygon in the boat, in case it happens while I'm out.

 

[mdevrow]

Corrupt fuel map!! Tony just repaired mine!!

 

[Luketrician]

speaking of corrupt fuel maps...better be sure your rectifier is okay..actually just spend the 20 bucks and replace it.

I lost a good merc ecu to a bad recitifer, they will screw up a good ecu/acu quick.

If you did not replace the recitifier it could corrupt the ecu again...that's how I found out anyways..

 

[mdevrow]

Thanks Luke I will replace mine.

 

[jdb35]

Today my brother Paul (aka H20skier30) and I think we found the problem. The tygon tube from the horn to the fuel regulator was completely stopped up. After cleaning out the tube the motor ran a lot better, but is still loaded up with fuel. I will have to run the motor under a load to clear it out, learned this from past experiences. Will keep posted on what I find.

 

[jdb35]

Got my motor running right again. I appreciate all the replies and good advice I received on my motor problems. Got to give credit where credit is due, Chad202 was right on the money. I had a switchbox going bad. It was hard to pinpoint because when I put a spark checker on each plug it showed all plugs were firing. What tipped my brother and myself off was on the starboard side the motor actually tried to crank on that bank of cylinders but not on the port side. I had problems with a switchbox on a promax one time also, they are hard to diagnose but definitely worth looking at first if you have firing problems.

 

[K.Kiser]

We're gonna need an onboard vid of a wide open pass of a couple miles or so, just to prove that you've really fixed it..

 

[jdb35]

If it don't quit raining here soon, I will be able to do it in my yard.:beer:

 

[99hawk]

My 260 did the same thing good spark but no go at 3500 rpm. Ended up being the switchboxes.