1976 75 HP Evinrude help.

[Shadow662]

I have an 1976 75 HP Evinrude that I cleaned up and took out for the first time today. Out of the water the engine runs great. When throttled up runs around 7K RPM's. We get it out on the water and push the throttle forward and she stalls out so we took the cover off and noticed that the spring wasn't pushing the timing advance so we moved it by hand. She ran at full throttle at around 6-6.5K RPMs for about 15min. Then she cut down to 3.5K RPM's at full throttle. We checked the throttle linkage that is good, checked spark that is good.

So I have 2 questions is there a way to lube the timing advance to free it up so the spring can push it forward or is the spring bad?

And why did the engine drop to 3.5K RPM's at full throttle and still won't go to max RPM's at full throttle?

Timing advace only works if you advance it by hand in the water. But why does it run good without the timing advancing out of the water?

Any help would be great thanks.

 

[rsimmons42]

Re: 1976 75 HP Evinrude help.

your spring will still be good. It takes alot to take the force out of a spring. They are baked in a oven to give them there strength. The timing base is sticking, there is a good chance that there is some contaminants up on the inside. First I would recomend taking 2 cycle engine oil(the same for the engine, and put it around the ring. Do not use WD-40 as this will further gunk up the problem. Only place it around the ring. If this does not fix the problem. I would recommend taking the throttle assy apart and cleaning it. YOu can do this without changing the timing, or throttle/shift linkage. Pull it apart paying close attention to where all of the grommets go. Clean everything down to nothing, then re-grease with moly-lube(get at your local marine store) IF this does not fix the problem, then you need to pull the Flywheel and take a closer look. The timer base should have molly-lube around the brass fitting where it makes contact with the crankshaft, put enough on there to lube it, but not tomuch that it comes out of the top. Then place it back together, making sure that the retaining ring on the timing base sits flush on the crankshaft housing. If it does not something is holding it up too high. If this is the case, your upper main bearing may be sitting high, causing the binding.

Let us know what you find.

 

[rsimmons42]

Re: 1976 75 HP Evinrude help.

your problem with the throttle only going to 3ooorpm is most likely your carbs gumed up on the high speed jet.

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

your problem with the throttle only going to 3ooorpm is most likely your carbs gumed up on the high speed jet.

As soon as I got this motor I took apart the carbs and cleaned them up real good and after we got back from the water we started it in the yard and can get to full throttle RPM's out of the water.

If you belive that it could still be the carbs gummed up tell me and I will clean them again.

I will also do as you suggested with the timing advance.

Thank you.
Hopefully I can get her to run as good as she was for that 15 minutes of happiness that everything was working.

 

[rsimmons42]

Re: 1976 75 HP Evinrude help.

first things first, in your driveway, you should never rev the engine to more than maybe 2000rpm. A engine will always run different in the driveway than in the water. with the motor under load the engine is looking for the correct mixture of fuel/air.

I would take one more look at the carbs. It doesn't take long.

Did you just clean them or did you use a rebuild kit?

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

I just cleaned them they sat for awhile. I did notice that someone before I got it installed rebuild kits or cleaned because they installed the floats upside down. I will clean them out again and try if that doesn't work I will get rebuild kits. Is there anyway to narrow down which carb could be the culprit?

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

Ok I took the carbs off and they didn't look bad but I still went threw and cleaned them even the jet in the bottom of the bowl. I replaced the spark plugs also. We took the boat out today and it was running good then the RPM's dopped to 3.5K again.

Is there some kind of a rev limiter on it or something else? Or do you think it is still fuel related?
Is there something on the engine that slows the RPM's if it over heats?

I also fixed the timing advance.

But can you please help me figure out why it ran good at first then dropped RPM's again?

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

Took the boat out again today after a couple hours of sitting this time she didn't bog down to 3.5K at full throttle. She got up to normal RPM's then started chugging and wouldn't go past 5K not sure if this was part of the original problem or a new one. Before she would just drop to 3.5K and get anymore RPM's. So I am going to order the carb rebuild kits and replace the fuel lines and see if that helps any.

 

[kenmyfam]

Re: 1976 75 HP Evinrude help.

When it does this did you squeeze the primer bulb to see if it picks up ???

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

Yes primer bulb remains hard.

I was thinking it could maybe be a gasket or something. I'm a mechanic and on a car usually chugging can be a worn intake manifold gasket and is usually fuel related. But that wouldn't explain why it runs fine out of the water other then there isn't any load.

I have spark at all cylinders.
New spark plugs.
Fuel tank is full of fresh fuel.
Fuel filter is clean.
Carbs were cleaned- going to get rebuild kits.
Fuel lines look to be in ok condition however old so I'm going to replace.
Anything else I should check out?

Got this engine for free guy who owned it died. So if I put some money into I think I will still be making out good.

 

[billy4hp]

Re: 1976 75 HP Evinrude help.

Yes primer bulb remains hard.

I was thinking it could maybe be a gasket or something. I'm a mechanic and on a car usually chugging can be a worn intake manifold gasket and is usually fuel related. But that wouldn't explain why it runs fine out of the water other then there isn't any load.

I have spark at all cylinders.
New spark plugs.
Fuel tank is full of fresh fuel.
Fuel filter is clean.
Carbs were cleaned- going to get rebuild kits.
Fuel lines look to be in ok condition however old so I'm going to replace.
Anything else I should check out?

Got this engine for free guy who owned it died. So if I put some money into I think I will still be making out good.

How about starting out with the basics, what's the compression like? Not looking for a specific number just as long as they are above 100 psi and close to each other they should be fine. Also you should read the "Top Secret" file about reviving old outboards that have sat, decarbing, lync and sync, etc...

FYI max loaded engine RPM on your 75hp should be around 5800rpm, anything over that could obviously cause bearing / piston damage as well as issues with the reed valves as they aren't designed to operate above that RPM as well... Revving over 2000k rpm unloaded out of the water is just begging for a runaway engine scenario with catastrophic failure as a result...

If you did actually run the engine ouy of the water for 15 minutes at WOT unloaded at the rpm's you stated 6000 to 7000 rpm I would imagine some damage may have resulted...

It will run completely different out of the water because (1) there is no load on the prop and (2) there is no resistance or back pressure on the exhaust. My 1978 70hp idles a full 300 rpm less in the water compared to on the muffs in the driveway...

Good luck with your project,

Billy

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

I didn't run it out of the water at full throttle. The tach has to be wrong if the max rpm's is 5800 on that motor. At 5k accoring to the tach I go 20mph and not on plane. When the tach is at around 6k I'm on plane and doing about 35mpg at full throttle. Will check with timing light. Do you know the RPM's at idle?

I will get the compression tester from work and check compression.

I did notice some black oil like stuff around the prop before taking her for her first trip. Wasn't lower end unit oil. Search the boards and found it is probably carbon being burnt off with some un burned fuel. So I will do the sea foam as well.

 

[billy4hp]

Re: 1976 75 HP Evinrude help.

I didn't run it out of the water at full throttle. The tach has to be wrong if the max rpm's is 5800 on that motor. At 5k accoring to the tach I go 20mph and not on plane. When the tach is at around 6k I'm on plane and doing about 35mpg at full throttle. Will check with timing light. Do you know the RPM's at idle?

I will get the compression tester from work and check compression.

I did notice some black oil like stuff around the prop before taking her for her first trip. Wasn't lower end unit oil. Search the boards and found it is probably carbon being burnt off with some un burned fuel. So I will do the sea foam as well.

Black "spooge" around the prop / exhaust hub is more than likely unburnt fuel / oil, sea foaming will clean it out real well.

Just as a reference for you, my 1978 70HP with a 13 1/4 X 17 prop pushes my 16' runabout to 36mph @ 5300 rpm, boat with all my gear and 2 people weighs in @ 1400lbs / freshwater / sea level. I use a Tiny Tach for my tachometer / hourmeter. Neat little gadget and you can't beat the price...

Good luck,

Billy


http://www.tinytach.com/tinytach/index.php

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

Ok, I bought the sea foam going to use it tomarrow. Going to use the "top secret" file for instructions.

Also I am unsure of the prop size on my boat I belive it is factory because of color. The boat I have is a 1964 18' Starcraft Holiday. The guy that sold it too me took a 2007 Yamaha 50HP off of it before he sold it. The tach is a yamaha and belongs to that motor. I changed the poles to 12 poles as that is what a manual for a diffrent company says to put it at for their tacks.

Thanks for your help. Will post any follow up questions or if the sea foam works tomarrow.

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

Well I ran the sea foam threw didn't do anything to help with my problem but from all the smoke I'm sure it cleaned it up real good. I took a the spray bottle that I used for the sea foam and put fuel in it. When the engine droped to 3K again we sprayed fuel into each carb and found that the bottom carb is the culprit. Thinking maybe the float is getting stuck in the up position. It's the only thing that makes sense because if you let her sit for a while and take her out she will run fine untill I think the bowl is low on fuel and since the float is stuck up the carb doesn't refill. So I will be taking that apart again. Thanks for the help.

 

[Sandhammaren05]

Re: 1976 75 HP Evinrude help.

Sounds electrical. I disagree with one statement above: 5800 is not the limit if the motor's in good shape (good rod, wrist pin and main bearings), those motors were used in racing (same powerhead on short and longshaft models) and turn 7000-8000 RPM (in the water under load, not in the driveway or in neutral as is stated by another helper!!) problem free, so long as you run double oil . From 6000-6500 RPM run 1.5x normal oil. However, 100-120 psi means bad rings, LOW compression on that motor is 130 psi, a good compression is 150-155 psi.

Well I ran the sea foam threw didn't do anything to help with my problem but from all the smoke I'm sure it cleaned it up real good. I took a the spray bottle that I used for the sea foam and put fuel in it. When the engine droped to 3K again we sprayed fuel into each carb and found that the bottom carb is the culprit. Thinking maybe the float is getting stuck in the up position. It's the only thing that makes sense because if you let her sit for a while and take her out she will run fine untill I think the bowl is low on fuel and since the float is stuck up the carb doesn't refill. So I will be taking that apart again. Thanks for the help.

 

[Shadow662]

Re: 1976 75 HP Evinrude help.

Finally got her working correctly. It was the bottom carb high speed jet clogged up again. Seems like a bad spot for that jet considering all the gunk falls to the bottom. When I got the motor it was full of mouse nests and the intake is on the bottom so I think it sucked up some more of what I didn't suck out with the vaccum and clogged it.
I ran her at WOT for about 30 min with no problems. She push's my 18' Starcraft 35-40mph at 6.5K RPM's. Thanks for everyones help.

 

[mustangrich]

Re: 1976 75 HP Evinrude help.

Shadow662 -- Is your motor still running well? It appears I have the same problem on my recently acquired boat (same motor as yours). What was the final "magic" that got it working properly ... was it a problem with the float or did the bottom carb just need to be cleaned out again? Thanks.

 

[billy4hp]

Re: 1976 75 HP Evinrude help.

Shadow662 -- Is your motor still running well? It appears I have the same problem on my recently acquired boat (same motor as yours). What was the final "magic" that got it working properly ... was it a problem with the float or did the bottom carb just need to be cleaned out again? Thanks.

Read up one post, there was a plugged HS jet in the bottom carb....

 

[mustangrich]

Re: 1976 75 HP Evinrude help.

Thanks Billy4hp -- I was just verifying with Shadow that after 2 months the culprit really was the clogged carb. I have the same issue he described, but seems like every other outing the motor works fine, then the other times it stalls out over 5mph ... very frustrating!