Same Motor, Same Prop, Losing speed??

[carrier82]

Besides compression, the problem can be in many places. Is the carb still the same? Are the ignition components the same? Is the ignition timing set up correctly? 10% ethanol might require a bit richer mixture, but should't dramatically affect engine performance.

 

[Steamboatbonner]

That's good to know. I always try for ethanol free but its hard to acquire now days in this neck of the woods. I will be checking timing, compression, and hopefully actual RPMs over the holiday break if all goes according to plan. Will report back Sunday or Monday night.

 

[steelespike]

Well this weekends maintenance didn't go the greatest. The compression gauge I had was not in functioning order. I did notice that the plugs looked to be burning very clean and evenly. With the long weekend coming up I will be borrowing a new set of gauges and doing the test before heading out on the lake for the 4th of July festivities.

Just curious, how much change in performance should I expect to see between 87 grade with 10% ethanol, and 89 grade with 0% ethanol?

The 89 octane will be harder for the motor to burn. As far as performance I don't think you could tell a difference unless you make careful note.

 

[Grandad]

I recently had the motor replaced with an identical 3.0. Before the motor swap I could cruise about 40-42 mph (Speedo AND GPS). Since the motor swap I have a hard time getting past 32 mph. (Speedo AND GPS). The Tach is also reading a lot higher on the new motor but Im thinking the tach is no longer accurate and needs replacing. Any insight on where my speed loss is coming from???.

There seems to be some assumptions here that could lead you off into the weeds looking for a solution. Why not confirm that your tach is either accurate or not and replace it if it isn't. If it is reading correctly, the new engine is performing well as evidenced by the high(er) RPM. If the RPM is high and your MPH is low, then the problem is likely something like a slipping prop. - Grandad

 

[Steamboatbonner]

Okay........ : Had someone stop by and test the compression. all 4 cyls read between 129 and 131. Timing seems to be correct, and tachometer wiring was fixed. His tach and the tach on the boat are now agreeing with each other for the most part. Out on the water, WOT rpm is reading just about 4800 rpm (needle shakes a little bit).. The only thing I DID find was the prop is starting to show its age, and will hopefully be replaced in the next few weeks. And this weekends BIG DISCOVERY was a very small hole in the hull. about the size of a pea. It has been previously hidden by the trailer rollers. Due to its small size, I opted for a small marine resin repair kit which seemed to cover the whole quite nicely. I have no clue how long the hole has been there. My concern now is that the foam is beginning to waterlog, which is where my speed loss is coming from. :facepalm: