1000 RPMs - Runs Rough - Force 150 HP

[arriva2001]

Hi,
Any thoughts what might cause the engine to run "rough" right around 1000 RPMs? It starts fantastic, idles great around 750, and if I'm cruising around 3000-4500 RPM, it also runs great. But right above idle around 1000-1200, it just runs a little 'stuttery' or rough feeling. If i increase or decrease the throttle, it smooths right out. No hesitation when pushing down the throttle. Any ideas?

I'm running a brand new tank of non-ethanol gas with Quicksilver 2 cycle premium plus oil, and some sea foam in the gas.

Anything i should look for, or is this normal behavior of the engine?

Thanks,
Adam

 

[SkiDad]

mine ran like that around 1500 rpm - i think what you are saying is normal. I do remember my engine didn't like sea foam - maybe it will be a little smoother once you run that out.

 

[jerryjerry05]

Always include a year and model#

Still test for water.
Dirt in the carb?
​Install a filter between the last fuel pump and carb.

​Like Skidad said, Seafoam might be a problem?
​About the only additive you need is Sta-Bil then only if you let the boat set for extended periods.

 

[arriva2001]

Thanks guys. It's a 1994 H150412PE Pacemaker. I have about 6 gallons of the gas with sea foam in it left, so I'll burn that out and not use the stuff again. I was hoping it would remove any carbon buildup that might. Be in the cylinders.

I do have the inline fuel filter before the carbs. It was new this year. Maybe I need to replace again if the Sea foam loosened up some gunk or something??

Seems weird that it only runs a little rough at 1000-1200 Rpm. maybe above that, the high speed jet takes over?

 

[kbh121956]

Some love "Seafoam additive". I put it in my tank and ended siphoning it all out! It made for hard starting and it didn't run smooth at all. Just my 2 cents worth.

 

[pnwboat]

I've seen a few Force 120HP and 125HP motors run slightly rough or maybe sounds a little different right around 1100 to 1400 RPM's. I think I remember Frank, one of the Forum members that's no longer with us mentioning at that RPM, the throttle plates are transitioning past the idle speed ports in the throat of the carburetor to the normal high speed operation, and you may notice a slight roughness. If the motor is running well other than that, I'm not sure I would spend a lot of time trying to fix it.

Definitely run that tank with Seafoam out and fill it up with a fresh tank of gas and see if that helps.

I soaked an old used carbon covered piston in a can of some Seafoam overnight and it hardly made any difference.

 

[jerryjerry05]

Run it.
I did the same thing pnwboat did with the SF.
DID NOTHING.
If you want to clean the fuel system.
​I use a 1 gal can and mix 1/2 gal. fuel and a 8oz.jug of Chevron"with techron" fuel injector cleaner.
Don't forget the right amount of oil in the mix.

​I run that for about 5 min and let it set for 1 hr.
Then run another 5 min.
Then switch to the main tank and make sure the fuel is clean and no water.
You need to run the fuel just like they call for 50-1 and no more.

 

[arriva2001]

Thanks again for your advice, guys. I'll run the tank out of the seafoam-treated gas this weekend. I'm only noticing the roughness in that 1000-1200 RPM, so if that is related to the change over to high speed operation, that makes sense, and I won't worry about it that much. Especially if fresh gas fixes it.

I do want to clean the 'carbon' out of the outboard, because I have read so many horror stories lately on these boating forums (I should really stop reading--sounds like all engines are designed to fail), so that is why I used the sea foam. I have no 'evidence' that my outboard is carboned up....but from what I read, how do I know that it is not??? And carbon can be what causes the need for a rebuild or repower, which I cannot afford right now.

I have used Quicksilver Power Tune engine cleaner in the past, and it smokes like crazy...but I have no evidence that it did anything other than pollute the air and water around me...so i was hoping the SeaFoam in the gas while operating would work some magic without killing all the fish!

I'm interested in your suggestion, Jerry, about the Chevron Techron. I used that stuff in my old 03 Nissan Xterra...and after one tank, my mileage increased from 13 to 16 MPG. It seemed like a pretty big change to me, and also the acceleration seemed improved. I just didn't know it would be something I could use on an outboard!

 

[jerryjerry05]

The Power Tune is a cleaner carbon remover.
​It's gonna smoke like crazy but the results are worth it.

You don't need to run it through the fuel system.
Start the motor, get it hot.
​Then spray the PT(lots) in through the carbs until the motor smokes and has trouble running.
Then shut it down QUICK.
Then remove the plugs and tilt the motor up and spray a bunch of PT in each cyl.
​Rotate the motor, making sure the PT is coating the pistons and then add more.
Let set for 36-48 hrs.
​Add more and move the flywheel a bit.
Then after it sets.
Start it up and let the PT burn away.

PT is a cleaner and has NO lubricating properties.
​Spray 50-1 pre mix in the carb if you have trouble starting.
Clean the plugs or replace.

 

[arriva2001]

Thanks. I will try the PowerTune again. is it safe to leave it in that long? I wasn't sure if it could damage any gaskets or non-metal parts that might be in there?

 

[jerryjerry05]

ANY cleaner/ soak can melt plastic and ruin seals.
PT ruins cork gaskets!!

It won't hurt the head gasket.