Thrust, hp, and weight comparisons

[Charles Myers]

An update

I have tinkered and tinkered with the synchronization.  Maybe it is right; I’m not sure.  I do know, though, that loosening the two bolts for the throttle cam and trying to reposition that cam did not seem to modify anything.  The short linkage rod (not the long one with the collar) on the throttle butterfly axle was bent, which kept that axle from moving all the way to its stop.  I straightened that rod.  I also adjusted the knurled knob on the throttle cable (the cable from the front of the boat next to the driver).  Those actions achieved a perfectly horizontal throttle butterfly at full throttle.  I then adjusted the collar on the long throttle rod on the port side.

On Saturday, October 28, 2023, we had an 83 degree day in Richmond.  My son and I took the boat to the lake.  The motor started, although the throttle control beside the driver had to be set much farther forward now to get the motor to start.  (That was a surprise.)  On the water and underway, at full throttle, the fast needle did what was expected.  It had a sweet spot for the fastest speed.  But when backing off on the throttle, no amount of fiddling with the slow needle achieved smooth idle.  The motor never quit, but it loped badly.  Interestingly when I got it to the best it could do on the slow needle, a minor turn of the fast needle achieved a steady (no loping) idle).  That was fine s long as we only wanted to move slowly, but the moment we gave it full throttle, it was necessary to re-set the fast needle a bit to resume best speed.

Best speed continues to be much slower than the boat moved in previous years.  Even so, I think we are making progress.  During the trip before this one, we got stranded on the lake, unable to get it restarted at all.  We had to be towed.  So our experience on October 28 was an improvement over that.

I am suspicious about the slow needle packing.  After we got back home, I added another packing washer and re installed the needle.  Cold weather is coming, and I have now winterized the motor.  So unfortunately it will be next spring before we get to go to the lake again to test it out.

What I need, I think, is to find an old timer who knows the 1956 Evinrude Lark 30 hp very very well and knows how to set everything correctly.  Does anyone know of such a person within 150 miles from Richmond?  I am definitely not ready to give up on this motor.  And keeping this 1956 motor married to this 1956 boat is a priority for me.

Thanks, everyone for all your help.

[fleetwin]

OK, well you might be onto something with the packing on the low speed needle.  Many of these carburetors have a pesky threaded sleeve that the low speed needle threads into.  This sleeve can just rotate in the carburetor casting when you turn the needle if the packing is not tight enough.  Perhaps the threads are messed up as well.  So, even though you are turning the needle, the needle may not actually be moving in and out due to the spinning sleeve.  I wish I knew why the carburetor was designed this way, it can be very frustrating indeed.   It is not abnormal to have the low speed running quality affected by making adjustments to the high speed needle.  Usually the high speed needle is dialed in first, then the low speed needle is adjusted.

OK, it sounds like you have the linkage set up pretty well, seems like the carburetor is opening all the way.  Good for you discovering that the throttle cable trunnion may not be allowing the throttle linkage to advance fully!

You still feel that performance is off/low.  Have you replaced the propeller lately?  If so, perhaps you have the wrong “pitch” prop.  A propeller with too much “pitch” won’t be able to develop full power, it may lug at full power and not perform well due to low full throttle RPM.  Think of propeller pitch as the various gears in a manual shift car.  Think of how your car would react if you pushed the accelerator to the floor at about 20MPH in high gear.  The engine would probably stumble, bog, ping/knock, and would be very slow to respond until the car got up to speed.    Now think of the other extreme, let’s just say your prop pitch is too low.  Think of how your car would respond if you just left it in second gear while accelerating onto the highway.   The engine would just scream/over rev and the car wouldn’t go very fast.

There is also a trim rod adjustment on your engine on the bottom of the stern brackets.  The boat will plow through the water at high speeds if the trim pin is in too far, and not perform well.  Trimmed out too far, the boat may be hard to plane off because the bow pops up during acceleration, the boat may “porpoise” up and down at high speeds as well.

Sorry, don’t know any members in your area, hoping someone will chime in for you….  Don

[Charles Myers]

Good thoughts about the prop.  The prop that is on the motor is the same one used from the beginning of Mom and Dad buying the boat and motor back in the 1950s.  It is the same one that used to give a speedometer reading of about 29mph.  Now we are getting about 15mph.  (That is a pitot tube reading, and the pitot pickup that sticks own in the water has been changed, hoping that maybe that at fault.  But we get the same result with the old and new pitot sensor.)  What the numbers are on the speedometer in MPH, of course, is less important than whether the boat is really moving as fast as in the past.  We used to water ski behind the boat, but I’m not sure that would be possible at its current speed.  It is just not as fast.

That is a good tip about the trim rod adjustment.  I will investigate that.

A new thought is that we have noticed that at full throttle on the water, if we press the throttle cable really hard, the beveled gear at the bottom of the port side that is turned by the cable will move just a little bit more.  That, in turn, will move the vertical shaft that reaches up under the flywheel a little more, and the speed will be a little bit faster.  I am thinking that the gear that is turned by the cable may be “off” by one tooth.  I want to study some about how to re-position that. I know, already, that the gear at the bottom of the vertical shaft will sit in a groove only one way, so I am guessing that the beveled gear that is turned by the cable is the one that would have to be re-positioned.

[joecb]

29 to 15 MPH is a pretty dramatic change, have you considered prop hub slippage as a cause? It’s an old prop you said.  To test, mark the prop and hub, then after a run check for misalignment of your marks.

Joe B

[fleetwin]

OK, well you can test your theory statically.  Simply shift into forward gear, remembering to spin the prop to ensure proper clutch dog engagement.  Push the throttle lever all the way forward, you shouldn’t have to “jam it”.  Now go back and look at the throttle linkage on the engine.  Is the mag plate hitting its WOT stop?  Is the carb butterfly opening all the way?  Take pictures is you need clarification..

I usually don’t put much stop in speedometer readings, not very reliable.  But, I do put stock in you complaint about not being able to pull a skiier.  OK, so the engine has the original prop, still might have been the wrong prop from the start.  Don’t think it would affect performance that much though.  The OMC part number along with the prop diameter and pitch is usually stamped into the propeller right behind the plastic hub.  So, you could post the number/size here if you like.

Let us know if your theory about the control/linkage not working correctly has merit, hopefully this is all that is wrong.

[Charles Myers]

Thank you for your help.  I am still tinkering with the motor settings.  Here is my latest attempt at making settings.

1. Motor in forward gear (not running of course).
2. At max throttle, the arm on the port side of the carb for the axle of the throttle butterfly is all the way against its stop. The butterfly is fully open.
3. The “mag arm” (as you labeled it in your second photo and where the spark plug wires attach) is not against its stop. I can, by hand, press against the port side of that arm to try to move it to its stop.  (Is it supposed to be movable by hand?)  It is springy, but does not move all the way to the stop. (Interestingly, the Evinrude parts diagram and list just calls the “mag arm” the “H.T. lead to armature plate anchor.”)
4. I then release the collar on the long throttle arm (that term is from the Evinrude parts diagram and list, although some are referring to that as an “economizer”). That causes the arm on the port side of the carb to spring back, and the throttle butterfly closes.
5. At this point I can push against the “mag arm,” and it moves all the way to its stop.
6. Holding the “mag arm” against its stop, I then press the long throttle arm forward to rotate the arm on the side of the carb and open the throttle butterfly fully. I tighten the throttle arm collar.
7. At this point everything seems OK. The butterfly is open; the arm on the side of the carb is at its stop; and the “mag arm” is at its stop.
8. As at test, I pull the throttle all the way back, and then advance it to full throttle. Something has changed, the “mag arm” no longer reaches its stop, and the collar has to be moved a little to restore a fully open throttle butterfly.

If it is critical for the “mag arm” to be all the way against its stop, what am I doing wrong?

[fleetwin]

OK, not quite sure I understand all you are saying….

The mag plate may not advance fully if the economizer linkage is preloaded, the vertical arm can not push that horizontal throttle rod past the wide open position.  So, if the engine was run like this, you wouldn’t achieve full advance ignition timing resulting in a loss of power.

So, you are saying that once the economizer linkage is adjusted properly, the mag plate won’t reach its raised boss/stop on the block.  Are you pushing the throttle arm manually or using the remote control?

[Charles Myers]

Thank you for your continuing help.

The first sentence of your last message is interesting.  While the “mag arm” is all the way at its stop, I have been setting the collar on the throttle rod all the way back while the throttle rod is pushed all the way forward (opening the throttle butterfly fully).  Am I doing that wrong?

During all my efforts, I got tired of walking all the way forward to the remote gear and throttle levers while working on the settings.  So at the motor I detached the push/pull gear cable and the push/pull throttle cable to make the throttle setting manually.

At one time, I considered the possibility that the throttle notches might have been “off” in the remote control box, but as it happens, the max throttle lever position on the remote places the push/pull cable for the throttle in exactly the same spot as setting the max by hand.

From your comment, I gather that the failure of the  “mag arm” to reach its stop during maximum throttle affects timing and may account for why the motor does not run fast enough at maximum throttle.  Am I understanding that correctly?   A clue may be as follows: A Johnson Service Manual says that the pivot for the “mag arm” includes a spring (304220) that may not be strong enough to advance the “mag arm” all the way to its stop and that a revised/ stronger spring (304656) should be used.  I have the stronger spring on order.  Unfortunately, installing it probably will require removing the flywheel – which I have been unsuccessful doing so far.  Pulling the flywheel off is scary.  I have a substantial fear of cracking the flywheel or stripping out some threads while trying to pull it.

Another theoretical possibility for the problem is that the throttle cam may be out of position.  It is bolted in place by two tiny bolts reaching UP from the bottom of the cam.  Synchronization instructions say to loosen those bolts and to move the cam to enable the roller to touch the cam in the right place.  Getting a 5/16/ wrench on those tiny bolts is really difficult, and I have tried that, but I don’t dare to loosen the bolts so much that they fall out.  But, so far, the loosening that I have done seemed not to enable repositioning the cam at all.  So I re-tightened the bolts.

A third possibility, (not likely, I believe) is that the gearing at the base of the vertical throttle arm is off by a tooth.  I can remove the vertical arm, but it has a rectangular base that fits into its socket only one way, and I don’t see a way to adjust the throttle gear to mesh with the vertical arm in another gear notch.

[vintin]

Charles Myers wrote:

Thanks to everyone who has commented and especially for encouraging me to hang onto the 1956 Evinrude Lark 30 hp.  A photo of the boat with the motor is attached.  I will search for a local service pro who knows this motor as a step toward evaluating its speed/ synchronization/ etc.

Look into a new Tohatsu 30 hp 4 stroke. Tilt and trim included. 127 lbs and will cut your fuel use at minimum in half. You can’t hear it run! Way better for the environment too.

[fleetwin]

OK.  We are not making much progress here, the written word can be confusing.  Can you post some pictures?  The only thing I can say is that the cam roller pick up adjustment will have little/no effect on WOT performance.   I agree about the flywheel, do not attempt to remove it.  This requires a very specific flywheel puller tool from OMC, trying to use substitutes can cause injury and broken parts.

Who has cared for this engine in the past?  A local marina/shop?  Perhaps they could look at these adjustments quickly for you, unless you don’t have much confidence in their abilities.

So again, please post pictures/videos.  I realize this website limits the size, making things tough, you can always post a link here.   I fear we all might be confusing an otherwise simple situation….

[Author]

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