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1984 70hp need help!

R

rbr

New member
Hey guys
I've been reading through posts for a week trying to fix my problem and nothing seems to be working. When I start my boat runs beautiful. Get on the water and on the plane once. As soon as I Throttle Down I can't get above 1200 RPM without bogging down. It's a 1984 Evinrude 70 horsepower outboard. Revs fine in neutral with no load. I've replaced the power pack and rebuilt the fuel pump. Still have the exact same problem. Compression on all three cylinders is within 10% of 135 PSI. I have spark. Only thing I haven't done is rebuild the carbs because it's something I can't personally do. If it was a carb problem how would it run beautifully on plane the first time I give it throttle after starting it. Any help would be greatly appreciated. I've read similar post but people don't seem to update their post with information on whether what they tried worked or not.
 
When did the problem start? Slowly came on, or suddenly. Do you have a plastic or a steel fuel tank? Could it be struggling to suck fuel from the tank. Maybe the tank vent is not working and vacuum is building too strong for the fuel pump to overcome.
 
I ran it with the gas cap off. i always get one good run at wot but when i throttle down i can't get back up again. motor is new to me.
 
So it's done this since you bought it? How long will it run at high speed? As long as you keep it on step? Or will it eventually slow down on its own?
 
Yes I bought it like that. I never saw it running in water when I bought it. Not sure if it would do it on its own. It has lost power wide open throttle once. All the other times it was because I had Throttle Down and couldn't get it back up. Because it runs so beautiful Full Throttle on the first pass it pushes me away from a fuel problem and makes me think it's an electrical problem that only appears when it gets hot. However my motor is too old to have any kind of overheating circuitry
 
Is that fuel pump the original "No Warning" VRO that has no wiring leading from it... a updated VRO with the warning wiring harness... or a small regular fuel pump as used with models before the VRO came into existence?

When this problem takes place, or better yet, before it takes place... have someone constantly pump the fuel primer bulb, acting as a manual fuel pump. If this cures the problem when you go through your stated routine, you either have a fuel/air leak somewhere between the engine and fuel supply OR the fuel pump is still not functioning properly.

If the fuel primer bulb has a tendency to collapse or flatten out somewhat... a fuel restriction exists somewhere between the engine and fuel supply.

You state... "I Have Spark". That doesn't really mean very much to us. A proper spark test is to have "all" spark plugs removed and to be using a spark tester whereas the spark will be forced to jump a 7/16 air gap. The spark should be a hot, wide, blue flame... a real SNAP jumping across that air gap. This is a must!

No tester? They're available at most auto part stores... or easily build the following.

********************
(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

This can obviously be modified to a 6 or 8 cylinder setup tester.

********************
Let us know what you find.
 
its pre vro. I will get a spark tester and check. when I throttle down and lose the ability to return to high RPM the primer ball is only half full. Does that tell me anything?
 
Yeah, "pre vro", I know, but 1984 was the entrance date of the VRO on the higher horsepower models, and being something new... some boaters began a converting club so to speak, so I had to ask. Your reply suggests you have the original "small" fuel pump.

Normally the fuel primer bulb is laying horizontally on the deck somewhere and as such the fuel level will drop down to the halfway point... this is normal.
 
yes old style I just redid it. can you think of any fuel issue that will work perfectly and then crap out?
 
Maybe water is leaking into the boat? Ha! Its happened to me. Seriously, how long does it take to "cool down" before you can get the motor to run WOT again?
 
That was actually the first thing I checked. I've only been able to get it to come back once. The rest of the time it's never let me come back to open throttle
 
Place hand in telltale stream to see if she's running warmer than it should, you should be able to keep hand there indefinitely.Telltale should be slightly warm.
 
This is an excellent challenge. It seems like it can't be true. If it was overheating you could get fired up on step after a short cool down. Have you done your stator and trigger tests in ALL throttle positions? Secondly and less a concern to me......but just checking.....mix ratio? Integral fuel tank? Fuel line collapsing? Primerbulb punky from alcohol? How long is the fuel line overall, from tank to motor? 3/8 inch or 5/16? This is one that I would love to take for a ride. Additionally, we have all seen stator, triggers, powerpacks, act up and/or fail at different temps. Also, perhaps water is leaking into the cowling area, causing the problem electrically. Have you tried running it with the cowling off during your tests? This will let some components run slightly cooler, then if you get a longer run time, we may be able to close this case.
 
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I just ran to the time. The long weekend is coming up for us here in Canada. So I'm just taking it to the marina tomorrow morning and going to have them do a troubleshoot on the water. They said they would tell me what's wrong and then I can just do the repairs myself. I'll let you guys know what it ended up being. This problem has consumed my thought process for 2 weeks. Just to clarify it is running smooth on all cylinders when I get stuck in low RPMs and just wants to bog down when I throttle up. I am only struggling with the fact that I get a good 15-minute pass out of it. If it was timer base or stator wouldn't I have misfires?
 
No, not necessarily. If one of the good techs here could try your boat on the water, I guaranty you a repair answer. Where is your home in Canada? I have 2 properties in NW Ontario, near Dryden.
 
So..... Did you ever try pumping the fuel primer bulb, acting as a manual fuel pump as suggested in post reply #6?

Also in post reply #6, I stated: "If the fuel primer bulb has a tendency to collapse or flatten out somewhat... a fuel restriction exists somewhere between the engine and fuel supply."

Was there an answer??... I may have overlooked it.

Good luck with the troubleshooting marina.
 
just got the boat out of the shop. they are baffled. they ran it till it failed and tested the spark and compression. they were both perfect. they said its fuel but can't find it. they guessed crank seal but said they can't guarentee
 
so the way I'm getting it to work is bringing the prop just out of the water and throttling to 5000 rpm as I trim it back down. works everytime. it seems to only have trouble at about 1500 rpm under load
 
When they tested the spark at "low power mode".......
.did they check the timing? This could be the result of trigger, stator or even power pack defect at high temps. Did you show them all these posts. Total expertise here is hundreds of years experience. EDIT: Just noticed your last post. So you only have to do this when it is fully warmed to max operating temp? Did you try running without the cowling on as I asked in my earlier post?
 
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Cowling doesn't matter. On or off the boat does the exact same thing. I got one good pass if I don't sit at the dock and idle too long. After that I have to use my work around
 
I still think it is a result of heat affecting an electrical component.......in this case we can most likely eliminate the power pack or anything in the fuel system.
 
You don't have to listen to me, however, when I first laid hands on an outboard, 2 stroke oil hadn't been invented yet.
 
Just fixed the wife's car yesterday, 2007 Caliber. 2 shops looked at it, said plugs/coils. Common sense told me it was "drive by wire" foot feed. Turned out it was engine side, in other words electronic throttle valve at engine. Put a used one on it, runs great....at least for now. This is old school solving new school. Just don't drop a strong magnet on the floor next to the foot feed. What the he#% was wrong with throttle cables?
Did you fix your 70 yet?
 
I was on the water for the whole long weekend. my buddy gave me one of his old props and the problem went away.i can't explain it.
 
Dann!!!! That was what I should have said. Truthfully, I was thinking the prop was too much for your load and driving habits. I have a 115 Merc on an Alumacraft Trophy 170. Constantly freighting in Canada. Got 2 props. Always pushing the edge of when I can pull the step. Get up, throttle back......save gas, you know the story. Non oxy in Canada is almost 5 bucks a gallon. Thinking on slowing down and going back to using a sail.
 
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