Problem with late 80's 135hp Mercury - no high rpm, no power..

[Pachanga_rick]

Late 80's 135hp Mercury outboard.

Problem -
Won't rev much over 4000-4400 rpm.

Feels slow revving and lethargic when in neutral. Not sure if that's normal for these older outboards to rev like this .

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Quick history.. I was given my Dad's Crest pontoon that he replaced the little 50hp with a late 80's Mercury 135hp engine I had sitting around.

Before running it the carbs were cleaned, fuel lines replaced, primer bulb replaced and fuel filters.

Motor started up and ran (runs) nicely.. just won't run much over 4000-4200 rpm.

My dad figured the pro was wrong so he found a smaller prop..same performance, but he didn't care as it was a canal cruiser.

Well the Pontoon is now mine and I need this engine fixed.

[LakeFever]

Check the plugs and compression first. If that all makes the grade id guess stator but this is some old stuff here and while the hard parts like the block/rods/pistons and whatnot are solid items the electrical stuff doesn’t age as well. So budget wise you have to decide if you want to find the exact cause and change that up only or what i suggest is new stator, new spark boxes, new plugs, clean carbs and replace the needles and seats at minimum or do full rebuild
kits although in my experience needles and seats are usually enough and reuse the old gaskets if careful, then replace ALL the fuel and rubber hoses under the cowl along with new fuel filter. As said if the compression is good? This will get her singing beautiful music again and last a good while too. I have sourced some reasonably priced electric parts with some careful searching.

hope this is of some help

edit: ditch the oil injection and delete black boxes too. Run premix. Last a looooooong time if you go this route

[Pachanga_rick]

Compression is perfect, this was a pretty low hour motor.

I did notice my volt guage was only at 12 from low to max rpm..

[LakeFever]

I’m not an expert by any stretch but my left toe says it’s the stator. You can buy or build a meter to test the stator but even then it’s a little tricky to figure out. Spark boxes need to be replaced in pairs so if you did both and the stator you’d almost surely be grooving well again. One thing I’ve noticed over the years is not running car batteries keeps the electrics working a lot better and longer. Something about the voltage being slightly different with the non deep cycle type. Maybe urban myth or coincidence but it helped me keep some old motors running strong for long

[Merc 2.5]

So when u checked plugs did they all have same color or close , or does 1 or 2 of em look real black ? Have you looked at you link and sync and see what timin is set at. Im not sure about the 135 but the old 150 ran and rev nice a set of 200 carbs will help that motor breath.

[Pachanga_rick]

Ok, spoke with my dad this morning and asked him exactly what was done to the engine after I gave it to him. ...

• He pulled the carbs and had them cleaned and rebuilt (local old mercury guy did it)
• Rebuilt and cleaned fuel pump
• Replaced all fuel lines and filters (even ran the boat from a portable tank)
• Replaced the Stator
• Replaced both CDI / switch boxes

It's hard to tell from the video, but at idle she has the "lean sneeze" every 10-30 sec'.

Also she revs VERY slow, I'm used to a 2.5/280 or my 300xs. Without a load I can run up to 6300 rpm, but it takes a while to get to.

and last the VOLT thing.. unsure if the gauge is bad or the system is only charging at 12 volts... this will be added to the list of "to check" later this week.

[Stoker1]

Dang, is it good to rev an engine that high w/no load? Always thought that was a no-no. If its alright, then I'm happy to go twerk the neighbors a tad

[Pachanga_rick]

Dang, is it good to rev an engine that high w/no load? Always thought that was a no-no. If its alright, then I'm happy to go twerk the neighbors a tad

Maybe it is, maybe not...

[LakeFever]

Are you using the fast idle arm to rev that thing up or is it in gear using the main control?

[Pachanga_rick]

Are you using the fast idle arm to rev that thing up or is it in gear using the main control?

Everything is stock from Mercury, so I'm guessing its the standard arm. I have a list of things to check this weekend...

The first is the back of the Tach, I don't think its set on the 6 cylinder setting, next is prop side and last is engine height.


But First first is I need to adjust my boat lift to hold the pontoon.. lol, I plan on winter boating until my Canal freezes up.