1983 70hp evinrude a dog

[shaggy rat]

Howdy! Long time reader/first time poster. I just recently purchased a 1987 14' sylvan sportster(aluminum runabout) with a 1983 evinrude 70 hp hangin off the back. I had the carbs rebuilt the first week I had it because of lack of speed/takeoff. After having the carbs gone through, I actually lost about 3mph. I am only hitting about 30 mph, which seems a little slow for a boat as light as this with a 70 on it. It seems like it just doesn't seem to hit WOT. Any suggestions on how to release the horses this little motor has to offer, or is this all I should expect? Thanks in advance, Troy.

 

[DJ]

Re: 1983 70hp evinrude a dog

What RPM are you getting at wide open throttle.<br /><br />Without knowing that, anything else is a guess.

 

[shaggy rat]

Re: 1983 70hp evinrude a dog

I don't have a tach, so I don't know. I decarbed the motor just now, and noticed that when I put my hand over the bottom carb, nothing noticibly changes in the way it idled, but when I put my hand over the top or middle carb, the motor quickly starts to die. After I ran the whole can of stuff through the motor, I pulled the plugs to see what they looked like. The top and middle weren't that bad, but the bottom was covered in a oily black soot. Hmmmm.?

 

[DJ]

Re: 1983 70hp evinrude a dog

What is the compression on all three? Maybe the bottom hole is dead.<br /><br />Or, the bottom carb is fouled.

 

[shaggy rat]

Re: 1983 70hp evinrude a dog

The bottom two were 120, and the top read at 125. I just picked the boat up from the marina this morning. They rebuilt all three carbs, and put a new oriface in one of them, so I don't think it's a carb problem.

 

[shaggy rat]

Re: 1983 70hp evinrude a dog

I took the boat out this morning with my fingers crossed hoping that the decarb would do the trip. Didn't happen. I did notice the thing was drinking gas like crazy. I went through 3 gallons in about 20-30 minutes of run time.

 

[DJ]

Re: 1983 70hp evinrude a dog

Without knowing your top engine RPM you, and me, are really guessing. If it using a lot of fuel, you are probably lugging it. Meaning it is overpropped. That will destroy that particular engine as sure as running it out of oil.<br /><br />You need to find out your rpm's.

 

[shaggy rat]

Re: 1983 70hp evinrude a dog

Could it really be that overpropped pushing a 4-500 lb 14 ft. aluminum boat with one person in it? I would think I would be able to run a 23 pitch prop on this setup with better results than I am getting now if the motor was running right. I am working on getting a tach right now.

 

[voodoo]

Re: 1983 70hp evinrude a dog

that prop does seem awfully big<br />If there was no change in the lower cylinder when you covered it and it eats gas it may be a leaky fuel fump flooding # 3

 

[shaggy rat]

Re: 1983 70hp evinrude a dog

Ok. Today I hooked up a tach from my old boat and headed to the lake. I am only hitting 4700 rpms at wot with me and the wife in the boat. I found out my prop is a 13x19. While I was out there I hooked up a timing light to make sure I was getting a spark from all three under load.I was. Then, I took the silencer cover off and at full throttle squirted a little fuel mix into each carb, each made it slow down. I noticed at idle, if I took off the spark plug wire off the bottom plug almost no change, middle plug a significant drop in rpms, and the top plug removed quickly killed the engine. Please someone help, I am going on my vacation this saturday to lake cumberland and I think going to a lake w/o a boat will definately ruin my only weeks vacation!

 

[voodoo]

Re: 1983 70hp evinrude a dog

did you try switching the plugs?

 

[shaggy rat]

Re: 1983 70hp evinrude a dog

I have gone through two new sets.

 

[voodoo]

Re: 1983 70hp evinrude a dog

I have a 13x17 on my 15 foot Doral glass with a 1990 65 that hits 5900 @33 (on the speedo I will bring gps next time) mph with 400 lbs of load in it.<br />How does it idle? Maybe you should focus on the # 3 cylinder.<br />Is the # 3 plug dirty compared to #1 & #2

 

[shaggy rat]

Re: 1983 70hp evinrude a dog

Nope. The number three plug looks just like the others.

 

[voodoo]

Re: 1983 70hp evinrude a dog

Try a 13x 17 prop.. my motor makes it's max hp over 5000 if you are not getting there.<br />Always good to have a spare anyway.<br />The hand over #3 thing still bothers me.<br />Ask someone else if the vro can pull oil alone to #3

 

[angus63]

Re: 1983 70hp evinrude a dog

Shaggy<br />Your fuel consumption of 3 gallons per 1/2 hr is on target for running at or near wot. Expect 7 gallons per hour wot. Is your cav plate even with the bottom of the boat? Is your wot timing per the manual?