still no power

I've posted in the last month or so about very little power on my 71 50hp Evinrude model 50173s. I had a spark issue which I resolved with a new coil pack. However still no power. The more weight the less power output. With just me onboard there's still a huge lack of power. So here's where I'm at, carbs are very clean, everything removed and thoroughly cleaned. Compression is 160 on top cylinder and 155 on bottom. Spark jumps a 7/16 gap no problem. Motor starts and idles nicely. At Wot each bore of carburetors has what seems like identical fuel delivery. There is quite a bit of fuel left on spark plugs every time I pull them after running WOT. Tonight I tried removing each plug wire while running in water. The top cylinder had some change but not much. The lower cylinder was extremely noticeable upon removal. So that got me thinking reeds. Pulled carbs again to inspect and the reeds look great. Checked with timing light and timing checks good. Hit the spark plug wires with timing light also, which indicates they are sparking the same. The top cylinder barely knocking the motor down when pulling the plug wire baffles me. Carburetors are doing their job, I have good spark and good compression. So why is my motor not cranking out any horsepower? Am I looking at a timer base issue, sticking? Any input is appreciated!

Yes with throttle lever all the way back both butterflies are fully closed. This is where it gets tricky though. This boat is a 15 for trihull given to me after my grandpa and a couple uncles have had their hands in it. So I can't be sure what has been monkeyed with or not. After reading other posts I looked at the cam and roller situation and no matter what the cam is always in contact with the roller and is already past the mark to begin with. I also see that with very little advance with the throttle the butterflies are already opening. This isn't something I have changed and the motor always ran top notch with plenty of power. The prop is 13x3/4/15 and is same prop ran for twenty years and is in good condition. I'm on vacation and have no access to a manual. How do I go about getting things synchronized again. Also need to point out with all the hands on this motor previously I can tell that at the pivot where the throttle arm comes from, forgive my terminology there, the angled plate the set screw stops at had been turned about 45 degrees and I imagine the screw adjusted as well.

Before I make any adjustments here's how things sit currently: with throttle lever all the way back to idle the cam and roller are in contact and the mark is right at dead center of the roller. Any advancement moves the mark below the roller not to mention the butterflies began to open almost immediately. So there is barely any movement at this time for adjusting the roller to the cam if the mark needs to be slightly above the roller at idle. So that raises a question for me then, at idle does the roller need to be in solid contact with the cam, or should there be a slight gap until cam meets roller and line pass's dead center opening butterflies?

Looking at how things sit now, should I be starting from scratch and setting the idle with the set screw and working my way forward to the cam and roller meeting? Then making any smaller adjustments to idle using the nylon nut on the cable after setting slow speed on carbs?

So I adjusted the roller so the mark passed dead center and butterflies began to open. Zero change to power of motor. Not sure where to go next with this.

have you checked the timing at WOT? I don't know what the specs are for the motor, but it should be on a sticker on the air box.

No I haven't checked the timing at WOT yet. We're at our lake cabin away from any real tools but will check it out in a few days when we get home again.

DON"T try and do it running on the muffs!! You either need a test wheel, or do what I do, and that's make sure the boat is well strapped to the trailer at the ramp, and get the motor just far enough into the water so it's pumping water. One guy on the timing light, one guy on the throttle. You need to get to at least 3000 rpm in gear to check it correctly. If your parking brake on the tow vehicle works, make sure you use it

Appreciate the advice! I'm not a big fan of the muffs for anything other than small testing. I will post results as soon as I get a reading. This issue is driving me nuts!

I ran into a very similar problem a few years back on a motor customer brought me. Long story short(along with hair pulling) some one had resealed the lower unit and had installed bearing carrier upside down as it had a solid bottom and it was blocking off the exhaust thru prop cause extreme backpressure.

No work on the lower unit aside from gear oil changing. I'm stuck on the issue of the top cylinder having very little change when spark plug wire was removed, then the lower almost killing motor off when removed. It acts like a one and a half cylinder and the power of 25 horse instead of a 50. There's good spark, good compression, and good fuel delivery. What am I missing?

Yes I've swapped plugs and swapped coils around seeing if problem followed even though both coils are new. I know that new doesn't exactly mean anything anymore so I tried it. I'm going to try switching brands of plugs cuz my uncle chewed my butt for running champion brand.

Just out of curiosity can a reed valve look good but be faulty? With the top cylinder getting spark but performing poorly I paid special attention to that particular reed. All 8 ports seemed to seat down nicely. Just wondering if anybody had ever encountered such a thing

Regardless of what your uncle's opinion is... OMC has always recommended the Champion L77JC4 spark plug, gaped at .040 for that 1971 50hp model. This is the spark plug you should be using, especially when trouble shooting!

You have stated that you have compression psi figures of 160 (top) and 155 (bottom), and that you have spark that will jump a 7/16" gap on both cylinders. This spark... is it a strong blue lightning like flame, a real SNAP!?

If indeed the compression and spark are as you state, that leaves the fuel system in question.

Also, you state that while underway in the water, you pulled both spark plug wires (one at a time) from the plugs and that pulling #2 resulted in quite a change (drop of power)... BUT... pulling the top cylinder (#1) did not. With proper compression and spark, this points to a top carburetion problem.

Do this......................

Have the carburetor face plate removed so that the carburetor throats are accessible. In the water, underway, at full throttle, stick two fingers into the top carburetor throat (acting as a manual choke). If the engine rpm increases, that proves that fuel is not flowing thru the carburetor as it should.

Since you did get a proper response from the bottom carburetor, sticking two fingers into the throat of the bottom carburetor should result in having that cylinder flood out.

Now, if indeed the top carburetor experiment resulted in a increase of rpm (power), I would suspect that the "horizontal" high speed jet is fouled/clogged. That "HS Jet" is located way behind the float chamber drain screw/bolt, in the center bottom portion of the float chamber. Clean it carefully with a piece of single strand steel wire as cleaning solvent just doesn't do that job properly.

Let us know what you find.

The following is simply for my reference if needed later on.
HS 308977 - 328543 - .058
Idle 3 - +/- 1
High 19

Joe I did have both high speed jets out and cleaned thoroughly earlier this week. I looked down both barrels at full throttle with a flashlight and there was equal spray. But I'm going to give it a try with the two fingers in the throat after rain slows down. If that doesn't indicate anything I'm going to verify spark again, think there's enough items at the cabin to make a homemade tester.

Spark tester...... Since the engine can be cranked over via the electric starter... this tester setup would suffice.

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark.

I was only able to perform the spark test as the weather here it's not conducive for boating. The spark however really jumped the 7/16 gap with a bright blue lightning like snap. The weather looks good for tomorrow so I'll post results with the carb test ASAP.

No I swapped coils around but have always been cautious to keep proper plug wire with proper cylinder. Weather is good today so will be trying carb test soon and see if it's truly a carburation issue. I won't have decent tools to work with until home tonight.

Ok I stuck two fingers into the throat of the top carb and lost some RPM's. I then stuck two fingers into the lower carb throat and again lost RPM. The kids were hounding me about tubing even with very little power to pull. I stuck the two smallest ones on the tube and just myself and a mirror on the boat. Things started off sluggish and powerless. After about fifteen minutes I noticed on gradual turns of the motor it would pick up RPM and gain some power. I held it on a gradual turn and let it wind up higher and higher until it seemed to quit climbing. At that time I had a fair amount of power but not full power yet. I realize towing will cause some drag but not this bad. After tubing I took two adults for a cruise around the lake and it was right back to being doggy again. An extra three hundred or so pounds doesn't seem like it should change things so much. I had my passengers move their weight around the boat some with no change. So I don't know at this point with the fingers in the carb test not telling me much if perhaps spark is not as strong as I'm believing it to be or what. Any idea's? I should mention with the tubing as soon as I straightened out again the RPM's would drop off again.

The trim pin was always in the lowest hole since the boat was handed to me. I did move it up to the third/center notch since I talked to you. When you say over propped does that mean I would go down a prop then. My current prop is 13x3/4x15. My grandpa always referred to having a power prop and a speed prop. I have and older beat up spare that is hard to make out the numering but appears to be 13x1/4x17.

I'm not so much worried about speed. Where I initially noticed the power loss is when three of us jump in the boat to buzz out on the lake for some fishing. Never had a problem cracking the throttle and skipping across the lake before. We don't do a lot of tubing or skiing but there again never had an issue with any of that. I understand it's only a 50hp but it had a lot more power than it's cranking out now. I don't have much knowledge on propping, is the 13 in my 13x3/4x15 the pitch? Or what does the 15 mean? I guess I'm not sure what the numbering really means.

So you've got compression, spark, and apparently judging by the finger in the carb throat test... fuel flowing thru the carburetors.

Possibly the throttle butterflies aren't opening fully (flat horizontal) at full throttle... OR... the timer base under the flywheel is sticking, not obtaining fulll spark advance?

With the rig on a trailer, view the boat/engine from a side view.... the cavitation plate just above the propeller should be approximately 3/4" below the bottom of the boat and parallel (same angle of attack) with the keel (bottom of boat).

In the bottom center portion of the carburetor float chamber(s), way in back of the dain screw plug, there lies the High Speed jet. If this jet is slightly clogged, it will be impossible to obtain full power. The original part number is #308977 but has been superseded up to part #328543. The inner diameter size should be .058 and would have the number 58 imprinted upon its side.

The idle timing is 3 degrees - +/- 1 degrees. This is checked with the scribe mark on the cam dead centered with the throttle cam roller. It can be adjusted via the linkage between the vertical throttle arm and the cam.

The full spark advance of 19 degrees can be checked as follows:

(Timing At Cranking Speed 4°)
(J. Reeves)

The full spark advance can be adjusted at cranking speed,"without" have the engine running as follows.

To set the timing on that engine, have the s/plugs out, and have the throttle at full, set that timer base under the flywheel tight against the rubber stop on the end of the full spark timer advance stop screw (wire it against that stop if necessary).

Rig up a spark tester on the #1 cylinder plug wire. Hook up the timing light to the #1 plug wire. Crank the engine over and set the spark advance to 4° less than what the engine calls for.

It's a good idea to ground the other plug wires to avoid sparks that could ignite fuel that may shoot out of the plug holes. I've personally never grounded them out and have never encountered a problem but it could happen.

Your engine calls for 19°, set the timing at 15°. The reasoning for the 4° difference is that when the engine is actually running, due to the nature of the solid state ignition components, the engine gains the extra 4°.

If you set the engine to its true setting at cranking speed, when running it will advance beyond its limit by 4° which will set up pre-ignition causing guaranteed piston damage! You don't want that to take place.

No need to be concerned about the idle timing as that will take care of itself. The main concern is the full advance setting.

A fellow member from one of the various marine forums suggested having water supplied to the water pump (flushette or barrel) simply to provide lubrication to impeller. A worthwhile suggestion I thought, and entered here.

Be sure to use your own engines spark advance settings, not the one I picked out of the air here in my notes.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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You mentioned a lot of rain. Is that boat filling up with water under the floor?
Soaked flotation foam?
Exactly what is the boat and what does it weigh?

you might need a tach when fine tuning prop sizes, and a prop shop will ask for RPM's. Check out "tiny tachs" on line, works without connecting to wiring harness or battery.

The boat is a Forester trihull. The floor is very solid for being this old but I do try to maintain a good cover on it when it sits outside. Otherwise it sits in a garage most of the time. I believe the boat weighs somewhere between 1300-1400 lbs. I'm waiting for my timing light to return home so I can check full spark advance. I spent some time reading through the ignition section of my manual last night and performed a couple tests after work today. Think I have stumbled on to something but would prefer the more knowledgeable people on here to browse over my results. I did a low ohm check on the sensor coil by disconnecting the #6 and #7 leads on power pack. Desired result was 15 ohms and mine was 17 so is within range. Upon doing a high ohm test of either lead disconnected to a good ground which should indicate infinity one lead read 2.4 ohms and the other just over 3 ohms. This tells me the sensor coil is bad. Then I did a test of the charge coil. I disconnected the #1 lead on power pack and checked that to ground as indicated in the manual and got a reading of 847 ohms. The manual indicates a good reading is 750 ohms plus or minus 75 ohms. This also indicates a faulty ignition component. So could this mean I'm not achieving a true spark and be causing the power loss?

I did exactly as they specified for trouble shooting and that is what the manual called the low ohm test. It's when I did the high ohm test to ground the manual indicated I should get a reading of infinity. Any resistance would indicate a short to ground.

Yes both wires were disconnected from the power pack when testing. Perhaps tomorrow the flywheel will be removed and a good inspection done. How does one go about holding the flywheel stationary to remove the nut?

Sounds like the kind of method I would use! I will give it a shot and post any findings I come up with. Thank you for the help! What do you or anybody else make of the charge coil readings?

There is a slight amount of play up and down, about 1/16 inch I'd say.