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93 Johnson 25hp Lacks Power

K

Klink

Regular Contributor
I have a 1993 25hp Johnson J25RETS on a 2008 Stumpnocker 14' with a brand new 10x13 aluminum Solas prop, rebuilt carb, synch & Link, Joe Reeves timing set (set the timing at 4 degrees less than the factory specified 30 +- 1 degrees, per Joe Reeves method. I set it at 27, because the screw would not go lower than 27. It was at 30 degree when I started the test. In other words it was at 30 degrees before I adjusted it to 27 degrees). Compression is 123 lbs on both cylinders.

Took out the boat this weekend and wide open with 2 adults (425 lbs) and 6 gals of fuel plus two batteries and electric motor and equipment (same or less than both tests below) I get 4400-4500 rpms and 16-19 mph, measured on a GPS.

Creekman at microskiff.com says he gets 30 MPH with the same boat, engine, and weights http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1343782844

The Evinrude Performance reports with 25hp ETEC that weighs like 60lbs more than my engine says it gets 27mph http://www.evinrude.com/Content/Pdf/neutral/performanceReports/PE857.pdf


The engine does not feel like it is running at full power, sometimes it would not rev past 4200 rpms. I had to run near wide open all day to run a round trip distance of like 32 miles.

Will pull plugs tomorrow to look inside and test spark and timing again. Is is possible for the engine to run that fast on just one cylinder?

Any suggestions?
 
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Tested the spark with a spark tester and they both jump 3/4" (hard to see any blue color, as it is daytime. ). Though the bottom spark plug does not "look" as direct and strong.

The bottom spark plug was clean, looks like it did no work, while the top spark plug was full of soot. I had cleaned them just before I went out and ran them only for like 8 hours running time.

The clean bottom spark plug also has the outside body steel clean, like it has not been used much (no heat?). While the top, the dirty spark plug has a tad of corrosion color on the surface.

A) I will test the boat tomorrow on the water, pull one spark plug wire at a time and ground it with an alligator clip and run the engine to see if it does the 16-19 mph WOT on one cylinder. (Amazing to me)

After that I guess I'll go one step at a time from easy to harder solutions:

1) swap the spark plug wires
2) swap the plugs.
3) put in new coil I have
 
Took it out today, ran it on one cylinder with disconnected spark plug wire attached to a grounded spark tester. At idle it ran on one cylinder, but you could tell that it was on one cylinder. Did it to both cylinders and they ran the same by themselves at idle speed. Tested one cylinder at a time at WOT and it went nowhere, it ran like a regular 2 cylinder engine doing like 2000 rpms. BOTTOM LINE - the engine can't run like I described above (at 16-19 mph and 4200 - 4500 rpms) on one cylinder.

With two 180 lb persons, 8 gallon of fuel, 2 batteries, a MinKota bow mounted motor, anchor, rode and hardly any other equipment, it did 4600-4800 rpm and 24 mph. Will test timing again tomorrow.The speed this time was measured by a speedometer on a jet ski that ran next to me.

It may just be that with all the added weight of the other day, the engine just can't push it faster than 16-19 mph.
 
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The culprit - incorrectly set timing

Bought an Actron CP7527 Inductive timing light which advertised as having "a strong Zenon light that works even in sunlight". And went and tested the maximum spark advance on the water with the boat going WOT. It was not hard to do since the timing on this engine can be set from the front of the engine. I just sat in the back bench and red the mark I had made at 26 degrees (30 degrees minus 4 degrees, the Joe Reeves method) , and it read the same 26 degrees. It should have read 30 degrees, but there was no difference between the maximum spark advance set with the Joe Reeves method with the starter motor, and the real world reading in the water. It appears that on my 1993 Johnson 25hp, one has to set the Joe Reeves method at 0 degrees off the factory specified maximum spark advance. P.S.- the timing light did show my white mark in the sun, it was not as bright as in the dark, but I could clearly see it. The inductive pickup is a big step up compared to my 40 year old timing light, which I will now retire.

I re-set the maximum spark advance to 30 degrees minus 0 degrees with the Joe Reeves Method and will re-test the boat tomorrow in the water at WOT with the timing light.
 
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Klink said:


I re-set the maximum spark advance to 30 degrees minus 0 degrees with the Joe Reeves Method and will re-test the boat tomorrow in the water at WOT with the timing light.
Click to expand...

Tested the maximum spark advance in the water at WOT, it was at about 28, so I advanced it to 30 (the factory spec) on the water at WOT.

BOTTOM LINE: Looks like on my engine one has to set it at +2 over the factory spec using the Joe Reeves method, then finish it in the water at WOT.
 
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