1977 Evinrude 70hp - Low RPM and not power - Help!

[Cougar_15]

Ok guys, I need some advice. I just got back from the lake, it was my first trial run for my restoration/rebuild, and I'm having trouble with the motor. A little history, the motor is a 1977 70 hp Evinrude (70773s). I recently installed a new water pump and rebuild the carbs and replaced all of the fuel lines.

As mentioned in the title, I'm experiencing low RPM and lack of power from the motor. It's a little hard to start but once it's going it idles fine. According to the new tach (boat never had one before and hopefully this new-used one is correct) it's idling at about 1000 RPM. At 2000 RPM it purrs like a kitten. It accelerates to 3000 RPM with no problem but that is as far as it will go. If I try to go past 3000 it give a little surge then drops back to about 2800 and continues to surge a little.

Any ideas what could be causing this? The only thing I can think of is maybe the floats are not adjusted correctly and it's starving for fuel? Or could it be something with the high speed jets?

 

[Brokeback Johnson]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

Sounds like the high speed orifices are obstructed.

 

[Cougar_15]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

The high speed jets were removed and cleaned (as well as the passages in the carb body) during the rebuild. I suppose some gunk could have dislodged from somewhere and stuck in one or more of the jets... I guess I'll have to pull the carbs again and go over them to look for obstructions and check the float levels.

Any thing else I should check while I'm at it?

The other thought I had was could it be a problem with the fuel pump, could it be having trouble keeping up with the fuel flow on higher acceleration?

Any one have any other ideas as to what could cause this issue?

 

[ezeke]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

Is the fuel fresh?

Do you have a water separating fuel filter?

Did you install clips between the float arms and the float valve needles?

You might want to take the float bowl plugs out one at a time and give the primer bulb a squeeze or two to flush the float bowls.

 

[patrick4266]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

Are you sure your throttle is opening up all the way? Did you do a link & sync?

 

[Cougar_15]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

Yes, the fuel is fresh and has marine stabil added.

No water separator yet but wouldn't water in the fuel affect the idle/low speed as well?

Clips? There were no clips when I took it apart and did not see any clips in the new parts...

Yes, the throttle is opening all the way, as far as I can tell the linkage is correct.

I also checked the spark plugs and all 3 looked fine...

 

[ezeke]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

Clips are in all new carburetor kits for the last 25 years or so.

 

[Cougar_15]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

OK, I looked at my leftover parts and I did find something that looks like the picture you supplied but I only found two, I must have lost one . Are these clips essential? Do you know if they can be purchased separately or do they only come in the rebuild kits?

Is there any good way to test for fuel flow problems (plugged jet, stuck needle/float, etc...) before dismantling the carb?

I was also wondering if there is any way to test an outboard at 4000+ RPM safely without being in the water (while running on muffs)?

Thanks for all your help guys, I am new to motor repair and a lot of these kinds of tips and tricks are not covered by the OEM manual.

 

[ezeke]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

OK, I looked at my leftover parts and I did find something that looks like the picture you supplied but I only found two, I must have lost one . Are these clips essential? Do you know if they can be purchased separately or do they only come in the rebuild kits?

If the needle drags or sticks, the clip helps to pull the needle down with the float.

Is there any good way to test for fuel flow problems (plugged jet, stuck needle/float, etc...) before dismantling the carb?

Turn the carburetor upside down and you should not be able to blow through the fuel inlet. There is no way to test all of the possible flow problems without removing the carburetor.

I was also wondering if there is any way to test an outboard at 4000+ RPM safely without being in the water (while running on muffs)?

No, you need a test wheel and a test tank.

 

[Cougar_15]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

Well, I finally found some time to run some more tests:

• Spark: spark is good on all three cylinders, will jump a 1/2 inch gap.
• Compression: reading are 120,115,120, so looks good to me.
• Cylinder drop test (pull plug while running): top and middle very noticable change in engine perfomance, lower carb only small differance...
• timing light on each plug lead: all three had a consistant pattern at idle and the pattern appeared to be the same for all three as well.
• Carbs: dismantled and checked the jets, none were pluged, re-adjusted the floats the middle carb was set a little to high.
• Installed new spark plugs
• Adjusted the linkage

On the muffs it starts up nice and idles fine. I won't be able to test the higher RPM's until next weekend on the lake. Can anyone think of anything else I should test or look at before takeing it to the lake for another trial?

One thing I'm not sure of is the differance in response to the cylindar drop test mentioned above. When the top and middle plugs were pulled the differance was very obvious. When the lower plug was pulled and replaced there was a small change but it was much less than the upper two. Should I be concerned about the lower response from the bottom carb? Does the lack of strong response indicate a problem or could it be normal for one carb to be less active at idle?

 

[Cougar_15]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

I just thought of another question, if the problem is still present is there any tests that I should/need to perform while I'm at the lake on the water? I am planning on going out this weekend and any advice would be appreciated.

 

[patrick4266]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

Did you do the link and sync exactly as your omc manual tells you?

 

[Cougar_15]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

I followed the OEM manual as best I could...

The thing I'm most concerned with is the lack of response from the bottom cylinder when the plug wire is pulled while running. It has compression, spark, the float bowl fills with fuel and the jets have been verified clean and clear, what else could be wrong? Is there any other way to tell if that cylinder is running or being dropped? Last night I pulled the new plugs and compared the bottom one to the other two and they all look pretty much the same, basically clean and dry. So it sounds like the bottom plug is firing or it would be black and oily right?

I'm really at a loss here, I've tried every suggestion I've found here on the forum (both this thread and other similar threads) and I've run out of ideas ... I only have a little experience with outboards and I've used that up so I'm really hoping someone out there has a tip or trick they can share to help me figure this out...

 

[Cougar_15]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

Ok guys I'm getting desperate, I really need some more good ideas!!

This weekend I'm going to try swapping the lower coil with the middle coil to see if it makes any difference. I'm not expecting much since they all appeared to have good spark but at this point I'll try anything. If that doesn't change anything, I'm going to take the carb apart (again) and triple check that everything is clean and open. While it's off I'll double check the reeds too.

I'm at the point that I would take it in and have a professional mechanic work on it but every shop I called said it would be 2 -3 weeks before they could even look at it which pretty much rules out the rest of the season. So if I can't get it fixed myself, I guess I'm out of luck until next spring....

 

[Cougar_15]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

I took the boat out again this weekend and the problem is still present but I was able to narrow it down to fuel flow. When I open up the throttle it will get to 3000 rpm and start to surge as described above but by repeatedly bumping the choke I was able to get to 4000 rpm (went from 10 mph to 20mph and got on plane). So it looks like I'll be taking the carbs apart again, it must still have some kind of blockage in the high speed system... The jets were clean and open when I checked so I'll focus on the passageways between the jets and the carb throat for starters...

 

[bmstang]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

you need to have those clips on the floats. Those jets hang from the clips it's a must and no you can't buy them separate they only come in the kits. I had the same problem with mine it may not solve your problem but i know those jets have to hang from the clips

 

[sonshinesmuscadines]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

I took the boat out again this weekend and the problem is still present but I was able to narrow it down to fuel flow. When I open up the throttle it will get to 3000 rpm and start to surge as described above but by repeatedly bumping the choke I was able to get to 4000 rpm (went from 10 mph to 20mph and got on plane). So it looks like I'll be taking the carbs apart again, it must still have some kind of blockage in the high speed system... The jets were clean and open when I checked so I'll focus on the passageways between the jets and the carb throat for starters...

my 1977 70 evinrude did the same thing its the coil pak .You need a coil pak if buy it from the evinrude dealer and he installs it. 1 year warrantty . you install it no-warrantty . these motors are notorious for this.

 

[rlcairns]

Re: 1977 Evinrude 70hp - Low RPM and not power - Help!

What RPM should this engine turn? what rpm should I cruise at? How big of a deal is a small nick on the prop? I have another one, but I don't know if I should swap, repair the old one, or swap and fix the old one as a spare. Any idea how fast my 1977 Starcraft Supersport aluminium 18 should go? Never had much done to the engine, but it seems to run fine.