In need of more power

[Nelsonjer]

I have a 1971 Evinrude 50Hp Lark, Model 50173S with a 13.75x 15 RH Alum. Prop. on a 1971 15' Crestliner trihull Muskie. I am the second owner of this boat which was used as a ski boat. I took the seats out and installed pedstal seat for fishing. The motor has plenty of power when I am in the boat by myself, but if there are other passengers it really dogs. Certainly not enough power for sking. Compression is 125 psi on the upper cyn. and 150 psi on the lower. Time for a new motor? Thanks for your help and assistance. Really in need!

 

[phatmanmike]

Re: In need of more power

well if you sell that motor simply beacause it dogs, ill second your opinion... phatmanmike@yahoo.com

 

[JB]

Re: In need of more power

"Really dogs" expresses your opinion very well, INOG, but it tells a technical helper almost nothing.<br /><br />Do you have a tach? What rpm are you getting while alone and with passengers? Do you have a speedometer or a GPS? What speeds are you getting?<br /><br />Your compression numbers are not good. The difference of 25psi is about 20% (should be 15% or less), but 125psi on the low cylinder is high for a bad cylinder, and 150psi is high for a 33 year old engine.<br /><br />I suggest a new compression check, with care that both readings are taken in exactly the same way, with a screw-in guage.<br /><br />You may be over propped for what you are doing, but we need rpm figures to diagnose that.<br /><br />Let us know what you find.<br /><br />If you just need a rationale to buy a new engine, you have it: You want one? That is good enough.<br /><br />Good luck.

 

[DJ]

Re: In need of more power

In need of grace,<br /><br />The two cylinder 50 hp. John/Rudes are are no powerhouse when it comes to dragging things around. They do OK, yet lack some in overall low end ability.<br /><br />First off, what is you wide open throttle RPM? Perhaps you can prop down, when pulling toys.<br /><br />Also, do a decarb, on that engine. It may balance your compression readings.<br /><br />Read this.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000016

 

[Nelsonjer]

Re: In need of more power

Really dogs means I can't pop a skier out of the water, as well as, if I have thre or more people in the boat I plow water rather than get up on top of it. No tach, when by myself I can reach a speed of 24-25. Thanks for the decarb tip DJ. How do I get to the carbs? They're not apparent when the cover is removed.<br />Thanks everyone.

 

[phatmanmike]

Re: In need of more power

to find the carbs do this.. <br /><br />with hood off, look at fromt of motor,(side facing the boat) you whould have a rectangular aluminum plate with two inch size holes, remove the outer screws from that plate, also called your airbox cover. and there you will find two carbs. when you spray the DECARB into the motor, people usually do it through the plug holes and through the carbs. make sure your choke and throttle plates are 100% open when you spray it in. then just follow directions of bottle and be on your way<br /><br />that motor is identical to mine, but mine is a 72... you need any engine specific help on that thing, lemme know<br /><br />phatmanmike@yahoo.com

 

[OBJ]

Re: In need of more power

I'll second the opinions posted on compression and decarb. You may also want to consider the engine set up on the boat. Not having Trim and Tilt don't help much either. If you find the decarb brings the compression together better, try adding a Whale Tail to the engine and setting the tilt bar out a hole or two. This may help with getting the boat on plane when pulling a skiier.<br /><br />EDIT: And try and get some RPM readings. This will tell you if the engine is over or under proped. Keep us posted....thanks.

 

[Nelsonjer]

Re: In need of more power

Hey Guys, I used the seafoam on my 71 Evinrude 50 hp and brought the upper cylinder compression to 150 psi, which matches the lower cylinder. Pretty happy about that. Thanks Roscoe, DJ and JB. Now I want to get a RPM reading, but don't know how to go about it. Is it worth buying and mounting a tach? Where in the world do you hook it up?<br />I appreciate the help!<br />Still in need of Grace

 

[OBJ]

Re: In need of more power

ING...150psi compression is really remarkable for a 71' twin popper. But glad to hear both cylinders read the same.<br /><br />Check iboats for tachs. This is really the single most important gauge a boater can have. It will tell right now if the engine is doing it's job.<br /><br />All you need to hook up a tach is a hot wire (12V), a ground and a signal. The signal wire can be connected to the Yellow/gray stripe wire coming from the rectifier. This is the AC lead from the stator under the flywheel. Be sure to follow the instructions that come with the tach.<br /><br />Keep us posted....thanks.

 

[ledgefinder]

Re: In need of more power

Boy, we're all in need of grace - & some days more than others...<br /><br />I'd SeaFoam again, maybe even twice. The rings I see on maybe 50% of the old engines are just incredibly gummed up in the grooves. Once it's clean, then you don't have to do it as often...or you can just run the OMC Ficht oil.<br /><br />I get 150 on those early 50 twins also, compared to 125-135 on the same era V4s, so I think your motor's reasonably healthy. The 50 lower unit is geared way down compared to the V4, and at 15" pitch (if you're sure that's right) I doubt you want to go any lower. I think the 50 LU runs about 2.8/1 ratio, versus 2/1 ratio for the V4s. If you're not winding out a 15" prop, something else is amiss with the motor (unless the boat weighs a TON), & my first guess would be retarded WOT timing. Good mechanics will do that to give the engine an extra margin against overheating a cylinder, but it does cut power and maybe the 50 is particularly sensitive to it. It is a pretty highly-tuned engine, for it's day.<br /><br />Of course, being in LaCrosse, the problem is probably that the lake is still FROZEN...

 

[ledgefinder]

Re: In need of more power

BTW, if you can't borrow a tach, cheapest alternative is a "TinyTach". They're about $40 direct from the manufacturer (try searching on the web). They have their own battery, so you just wrap the wire around one spark lead and that's it. <br /><br />Is the prop banged up?

 

[Nelsonjer]

Re: In need of more power

Well the ice is off the water, although not too far north of here there is still 6 inches of ice. The prop is brand new. The boat weigh just over 800# - but hey I've lost 50#! Will use more Seafoam and will look for a tach. What do you think about the tachs sold in Cabela's?

 

[rickdb1boat]

Re: In need of more power

They also sell them right here on I-Boats site. Check them out and support this site...<br /><br /> web page<br /><br />or:<br /><br /> www.tinytach.com Best to call them so you get the proper Tach for your motor..

 

[Nelsonjer]

Re: In need of more power

Okay Guys, I now have a tach (Tiny Tach) on the 50 HP Rude and at WOT it reads 2500. I also put a whale tail on it and used Seafoam deep creep. In addition I bought a manual - which doesn't state what the rpm's should be. The prop is a 13.75 x 15 RH. What do you think?

 

[ezeke]

Re: In need of more power

Look in the "Specifications" page of your Owners Manual or Service Manual for "Full throttle operating range" for your WOT.<br /><br />Try setting the bottom of the motor closer to the transom.<br /><br />Make sure the hull is clean and smooth. A very little growth creates a lot of drag.

 

[Solittle]

Re: In need of more power

You need to double check how you have that tach connected. I don't know your motor but think the rpm at WOT should be in the neighborhood of 4,500-5,000 rpm - 2,500 ain't even close.

 

[G DANE]

Re: In need of more power

You should be able to get up clouse to 6000. Are you sure it is the correct tiny tach ?

 

[Bass Runner]

Re: In need of more power

I would say go to a 13 pitch prop or go to a smaller dia. 15 pitch, sound like you just don't have a big enough motor for the weight you are trying to push. Just like my girlfriend used to say bigger is better. HP that is.

 

[ledgefinder]

Re: In need of more power

The rpms are way, way, way off. Are you sure that tach is right?

 

[ledgefinder]

Re: In need of more power

You want to prop is so it turns ~5800 with your lightest load (you alone in the boat). Your id tag probably says 4500-5500 rpm range, but with today's gas it's best to really stay away from lugging the motor.<br /><br />You can check the TinyTach by testing it on a car that has a tach. Be aware that the TinyTach will, on a 4stroke (car), read HALF the actual rpm. 4strokes fire every 2 revolutions, 2strokes every revolution.<br /><br />If you are turning 2500 actual, and getting 150psi from both cylinders, something other MAJOR is wrong with the motor. I'd suspect one cylinder is getting no spark or gas.