1975 Evinrude 50hp not top end speed

[Jacob645]

I've been asking around everywhere and still can't figure out what wrong with this motor. It starts fine and idles GREAT! When I give it wide open throttle, it runs at about 10 mph. It never planes out the boat. I just bought the boat so this is the only way its ever run for me, but i know it should go faster!
Compression:98 on both cylinders
Spark:Good
Carburetors: Rebuilt
Reed valves: Good condition
Would it be beneficial to Decarb? Does decarbing really help that much? I've been told that the compression should be 160 plus!
Please help!!

 

[bowhuntrrl]

Re: 1975 Evinrude 50hp not top end speed

You make no mention of what size boat it is on !!! Maybe the boat is too large for the motor size. Could also be a prop problem. Do you have any idea of the rpm when you are at WOT (wide open throttle ) ??? The 98 lbs compression is on the weak side, has the boat been sitting for a number of years ????

 

[Jacob645]

Re: 1975 Evinrude 50hp not top end speed

It's on a 15' 4" Fiberglass 1985 Gator Fishing boat. Its a triple hull design. The boat is rated for 60hp max. No idea about the RPM except that it is low. I believe its SUPPOSED to run between 5000 and 6000 and it's definitely not getting there. The boat is said to have been sitting out for a couple of years, but someone had obviously done some work on it. It had a brand new fuel pump and water pump. Brand new fuel lines. Carburetor were in excellent condition. Extremely clean.

 

[tashasdaddy]

Re: 1975 Evinrude 50hp not top end speed

Jacob, is it possible the boat has some extra weight. such as water saturated foam under the floor? you can find the correct dry weight of your boat and motor, at nada boats. then have the complete rig weighted at a public scale.

 

[Jacob645]

Re: 1975 Evinrude 50hp not top end speed

I couldn't find my boat on NADA! I can't find any info on Gator Boats from Bossier, LA. All I can find is ProGator and Gator Trax. I just did a decarb and by the look of the sludge coming out, i think it needed it. I used Deep Creep. Is that a good brand?

 

[Jacob645]

Re: 1975 Evinrude 50hp not top end speed

If the foam is completely saturated between the floor and the hull, what do you do?

 

[Jacob645]

Re: 1975 Evinrude 50hp not top end speed

The bottom coil on the motor i've found is cracked! Could this be the problem? Is it possible that at low speed it has enough spark to work, but at high speed the coil is cutting out that cylinder?

 

[tashasdaddy]

Re: 1975 Evinrude 50hp not top end speed

yes, that could be the problem. did you check for spark, on both cylinders. just start it on muffs, and with insulated pliers remove the spark plug. if it they are firing, the rpms will drop. if they are not firing, there will be no difference. have you checked compression. let's rule out the motor before tear up the floor.

 

[Jacob645]

Re: 1975 Evinrude 50hp not top end speed

I decarbed the motor with a couple of cans of deep creep. I also replaced the cracked coil! It ran great! The only problem occurs when I try to pull it back from WOT. It tries to drop a cylinder. Maybe fouling the plug temporarily?

 

[tashasdaddy]

Re: 1975 Evinrude 50hp not top end speed

do a link n sinc on it, this adjust the carbs, and spark so that they work together.

 

[Forsaken]

Re: 1975 Evinrude 50hp not top end speed

so jacob, you cleaned everything with deep creep. did you actually rebuild the carbs, or just take them apart and clean them then put them back together afterwards. and you had a cracked coil that you replaced... did you do anything else at all. i ask this because i have a 75 70hp that is doing the same thing.

 

[Jacob645]

Re: 1975 Evinrude 50hp not top end speed

I bought a carb kit for one of the carbs only to find that it was insanely clean! I cleaned it with carb cleaner anyways and the other one too. I ran two spray cans of deep creep through the carbs while it was running at high idle. Halfway through the second can we shut it off. We went inside for about 20 minutes and then came back out to restart it. It smoked alot!! Then we sprayed a bit in the spark plug holes and let them sit until the next day. Then we changed the cracked coil. Thats it man! Good luck! Let me know if you have any more questions!