Need more power from 75 hp Evinrude

[rivertripp]

Well I finally got my boat in the water after all this time. The boat ran very smooth and I loved it. However the motor does not feel like it is running at its top performance. I have a 1980 75hp Evinrude 3 cylinder 2- stroke outboard, and it felt like I was only topping out at about 25 mph today on the water. When I put her into full throttle it planed off very quickly but felt very sluggish getting to max speed. The motor is on a 16' aluminum boat and for this size boat this is the max rating for outboards. When I put it in the water all three carbs were completely rebuild by a professional mechanic along with new spark plugs, new fuel pump lines, and a new throttle cable. The prop is not too small for the outboard either after checking the size. Any suggestions as to how I can get her to run faster when on the water? I feel like this motor could move the boat a lot faster.

 

[bktheking]

Re: Need more power from 75 hp Evinrude

Have you checked for spark on all 3 cylinders, might be running on just 2.

 

[Chinewalker]

Re: Need more power from 75 hp Evinrude

If the motor is healthy, your 75 should be into the mid 30s at minimum and may even touch low 40s depending on the boat. What are you running for a prop? Has this motor ever performed well on this boat? As BK noted, check to make sure you're running on all three cylinders - don't just check for spark - confirm that it is actually running on those cylinders.

 

[tashasdaddy]

Re: Need more power from 75 hp Evinrude

proper set up, engine height, proper prop (pitch and diameter), proper load placement in the boat. all of these have to be right inorder to get optimum, out of your motor.

how do you know it was topping out at 25 mph? speedometer on the boat, gps?

what are you wot rpms, this is the most important part. it should be turning 5500-5800 rpms at wot. if not you need to find out why. timing, linc n sinc, poor boat engine set up.
long shaft on short shaft boat.

 

[kenmyfam]

Re: Need more power from 75 hp Evinrude

Agree with TD,
Need more factual info to proceed further.
Start with the basics.

 

[rivertripp]

Re: Need more power from 75 hp Evinrude

Thanks guys I will check those things out

 

[rivertripp]

Re: Need more power from 75 hp Evinrude

Took the boat out again and this time I had a second person with me. The boat to about 3 to 5 min. to finally plane off and I was able to do that by playing with the trim. At wot the boat would only top out at 24 mph at around 3000 rpm. We checked all three cylinders and all three are firing good. The engine is not a short shaft outboard and the prop size is a 13 3/8 x 17 for a 1980 75hp evinrude. As I am reading I should be in the 30's for speed and rpm in the 5000's. When I would initally put her in full throttle the motor would only run at around 1800 rpm and after 3-5 min with playing with the trim would I finally get the engine to only around 3000 rpm at 24 mph. Any more suggestions?

 

[Chinewalker]

Re: Need more power from 75 hp Evinrude

Either your boat is waterlogged to the point of being severely overweight, or something is wrong with your motor. Do not run it any more until you determine what it is, as it may be a gummed up carburetor, in which case the associated cylinder is not getting any lubrication and you could be damaging it by running it more.

How did you determine that all three cylinders were firing good? Did you just check for spark or did you one at a time remove a plug wire and note a difference in engine RPM? What are your compression readings?

 

[rivertripp]

Re: Need more power from 75 hp Evinrude

The boat is not water logged, the weight we had on the boat did not come close to the max weight recommended. Carbs were cleaned and rebuilt by a certified outboard mechanic, and we checked the cylinders by checking for spark and rpm change. Not able to check the pressure we were on the lake working on all this and only had simple hand tools to work from. However the father in law took the prop to the prop shop for me and told them my situation and the said the prop looked to be in good shape and a good size, but when taking a closer look they saw that the clutch was only holding 5 lbs of pressure when they said it should be holding closer to 2500 lbs. They are going to put in a new clutch and I will take it out again. Hopefully that will be the answer to the problem. I will let you guys know what the outcome was, and thanks for your knowledgable help and if anyone has anyhthing to add in the mean time I am all ears!

 

[tannedman]

Re: Need more power from 75 hp Evinrude

Im not sure if this will help but have your power pack looked at i went thru the same thing i had good spark but no speed i took it to a local guy it checked it all out tried a used power pack for intament spark reasons and the motor worked great with it being replaced

 

[rivertripp]

Re: Need more power from 75 hp Evinrude

Thanks tannedman. Let me ask you, how much did that fix run you if you don't mind telling?

 

[Tim Frank]

Re: Need more power from 75 hp Evinrude

The boat is not water logged, the weight we had on the boat did not come close to the max weight recommended. Carbs were cleaned and rebuilt by a certified outboard mechanic, and we checked the cylinders by checking for spark and rpm change. Not able to check the pressure we were on the lake working on all this and only had simple hand tools to work from. However the father in law took the prop to the prop shop for me and told them my situation and the said the prop looked to be in good shape and a good size, but when taking a closer look they saw that the clutch was only holding 5 lbs of pressure when they said it should be holding closer to 2500 lbs. They are going to put in a new clutch and I will take it out again. Hopefully that will be the answer to the problem. I will let you guys know what the outcome was, and thanks for your knowledgable help and if anyone has anyhthing to add in the mean time I am all ears!

If they mean that the hub is slipping, that would increase RPM as the load would come off...

 

[Dhadley]

Re: Need more power from 75 hp Evinrude

I believe what you call the clutch is the hub. If the hub were spinning the rpm would be much higher, almost out of control. If you are at only 3000 rpm we have an issue that's more than a simple prop problem. Most likely an engine problem combined with a set up issue. Taking 3 to 5 minutes to plane is horrible. should be more like 5 seconds.

 

[Tim Frank]

Re: Need more power from 75 hp Evinrude

The boat is not water logged, the weight we had on the boat did not come close to the max weight recommended.

Is there a floor?...and is there foam that might be waterlogged?
Is the boat and motor new to you or have you had it a while....and if so has the performance dropped off markedly?

 

[rivertripp]

Re: Need more power from 75 hp Evinrude

Sorry the guy I was talking to kept saying clutch, but yes the hub. When we looked at the hub it looked to be in very good shape. The boat is old along with the motor. The guy I bought it from did not "winterize" the boat at all and the carbs we extremely gummed up. We took the normal steps in awakening the motor by having the carbs rebuilt, new spark plugs, new fuel pump lines, lower unit grease changed out, water pump in good shape, and a new throttle cable. So no the boat and motor are not new by any means, but the boat does have an aluminum floor in it.

 

[jay_merrill]

Re: Need more power from 75 hp Evinrude

Sounds to me like you are propped about right. I have a 15" pitch prop on my 65hp Johnny and get 29 mph (GPS) on a much heavier boat, at 5,100 rpm. If I were looking for WOT at the top of my range, I would run a 13" pitch to get 5,500 rpm, but I am comfortable with being somewhat overpropped. I don't the exact WOT range for your motor, but its probably what mine is - 4,500 to 5,500 rpm.

I agree that you need to be careful in running the motor - if you are getting insufficient or no fuel to one of the cylinders, you will not be getting adequate lubrication to it.

Beyond that, you can check ignition for intermittant problems with an inductive timing light. I sometimes do this while underway. I just tape the trigger shut, put the sensor on one spark plug wire at a time (stop and shutdown the motor while changing leads) and place it on the floor of the boat. This makes the light easily viewed by an assistant, or just be turning around to look at it every so often. If you have an ignition problem (timer base, powerpack, ignition coil, wire), this should reveal it.

One thing that you did not mention, is the fuel pump. If the motor sat around for a long time, a failing diaphram is a striong possibility. You could suffer from insifficient fuel flow and could also have pieces if shedding rubber clogging up your newly rebuilt carbs.

How about fuel? Did you start out with fresh fuel in a clean tank, with no water or debris in it? Once again, this could be a source of problems and coud clog up those rebuilt carbs.



???

 

[rodbolt]

Re: Need more power from 75 hp Evinrude

sounds to me like you need to find a dealership with the correct test wheel or a dyno to test your motor or you will most likly post about a smoked piston.
your rig, your choice.
if the engine can spin the test wheel at the OMC posted RPM or it can pull the correct pressure on the dyno ,go fight prop/hull issues.
if it cant find and fix the engine issues BEFORE you post about smoked pistons and scored cylinders.
trust me.

 

[tannedman]

Re: Need more power from 75 hp Evinrude

Thanks tannedman. Let me ask you, how much did that fix run you if you don't mind telling?

My motor was running at 5600 max rpm and i was getting 36mph before i had the problem then dropped to maybe 20mph when problem started and 2000rpms had the power pack replaced like i said and while it was in the shop he noticed my motor was mounted higher then it should be dropped it down to its lowest point and not only did it pick back up to the 36mph i gained 5mph and top speed with the same 5600rpms was doing 41mph Try and find a good used parts guy he might test a used 1 on it for you. Hope yours is as easy of a fix

 

[rivertripp]

Re: Need more power from 75 hp Evinrude

Thanks tannedman, and also do you remember the total cost of that fix? I will see if I can get my hands on a timing light and also check the cylinders again. Another thing I found was that when we pulled the spark plugs out one at a time it appeared that they has a light coating of lubrication/ grease on the end of them, like they were getting lubrication. Is that one way of telling if the cylinders are working? The fuel pump is good, when i first got this boat that was one of my first projects and the diaphram checked out to be good, but the hoses that were dry rotting were replaced with new ones. i also chunked the old metal gas can and replaced it with a new 12 gallon plastic can along with a new fuel line and fuel connecters, so I know that can be omitted out for now. When i get the prop back after a new hub replacement I will take it back to the mechanic and ask him about running the test. Thanks again for everyone's imput!

 

[tannedman]

Re: Need more power from 75 hp Evinrude

Mine was a cheap fix since my machanic has old motors and lots of used parts he only charged me an 1 hour labour 25.00 and 50.00 for the used power pack but he found the problem quick. He checked compression first then spark plugs then spark and found 1 inconsitent so he tried switching the wires and that changed where ti inconsistent spark was which led him to the power pack