'79 V4 85hp Evinrude Compression spec

[CaneCutter79]

My motor was loosing RPM's after it was warmed up. I don't have a tach but I am estimating the motor runs around 5K at WOT. After about 5-7mins, the RPM range dropped to around 3,500-4,000RPM and the motor sounded like it was struggling or bogging down.

My boat mech. ran compression tests and said all I needed was new plugs. The gap on the old plugs were over-double the factory spec and the plugs are probably over 10yrs old. (former owner rarely changed them)

So my compression was 130psi in 3 cylinders and 135 in the last cylinder. Is that good for a 30yr old outboard that has never had a tune-up? I plan on getting a tune-up and de-carb this winter.

I haven't tried the new plugs yet but I have a feeling the boat will perform much better.

 

[wilde1j]

Re: '79 V4 85hp Evinrude Compression spec

"Tune up" has nothing to do with compression and those numbers are great.

 

[CaneCutter79]

Re: '79 V4 85hp Evinrude Compression spec

"Tune up" has nothing to do with compression and those numbers are great.

So those compression numbers are very strong for a motor of that age?

Thanks for the help!

 

[wilde1j]

Re: '79 V4 85hp Evinrude Compression spec

... of any age.

 

[tashasdaddy]

Re: '79 V4 85hp Evinrude Compression spec

if this is how you did your test the #'s are fantastic. http://forums.iboats.com/showthread.php?t=313884

don't wait till winter, do the decarb and change the plugs now. the i know i need to do it syndrome can be very expensive.

also you could be running hot, causing your problems. seeing the previous owner did not change plugs, i doubt he ever changed the impeller.

 

[CaneCutter79]

Re: '79 V4 85hp Evinrude Compression spec

The pee stream is very strong. That doesn't mean the impeller is not doing what it should though, I realize that.

I'll keep an eye on the motor temp. I agree, the tune-up is definately needed. I did change the plugs. That was cheap. The tune-up is what's holding me back. Just don't have the extra cash. Tune up is about $300. I hope to do it as soon as possible.

 

[kenmyfam]

Re: '79 V4 85hp Evinrude Compression spec

The pee stream is very strong. That doesn't mean the impeller is not doing what it should though, I realize that.

I'll keep an eye on the motor temp. I agree, the tune-up is definately needed. I did change the plugs. That was cheap. The tune-up is what's holding me back. Just don't have the extra cash. Tune up is about $300. I hope to do it as soon as possible.

Check the head temp's after a good run. If you have no other way then you should be able to hold your hand on the head for 3 or 4 seconds before it gets "too hot" to leave there. Not overly accurate but a good guideline.

 

[emdsapmgr]

Re: '79 V4 85hp Evinrude Compression spec

You may be dropping a cylinder after it warms up. Not unusual for ignition problems to show up once the engine reaches normal operating temps. Use an inductive timing light and check each plug wire when the engine is under load. It will show misfires and no fires.

 

[CaneCutter79]

Re: '79 V4 85hp Evinrude Compression spec

Check the head temp's after a good run. If you have no other way then you should be able to hold your hand on the head for 3 or 4 seconds before it gets "too hot" to leave there. Not overly accurate but a good guideline.

Isn't there an audible safety peizo horn or something that makes an audible noise as a warning of over-heating even on a 79 model motor? I know I've heard one on a newer outboard but not an older one like this one.

I have noted the flywheel was really warm. I might could hold my hand for 2-3 seconds if I remember right. I never tried the block itself.

 

[emdsapmgr]

Re: '79 V4 85hp Evinrude Compression spec

Your engine has a temp switch in each head. When they sense 212 degree temp, they will go to ground and set off the horn in the control box. Once the engine cools back down to 175, the horn will silence. You can get a hot horn from just one head, or both. Normal idle temps for that engine are between 145 and 155.

 

[tashasdaddy]

Re: '79 V4 85hp Evinrude Compression spec

i keep one of these in my boat bag, just in case, i suspect overheating.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93983

 

[CaneCutter79]

Re: '79 V4 85hp Evinrude Compression spec

Well, the new plugs solved my problem. Motor runs strong and sounds stronger. Motor is running best it has so far since I got it a few months ago. I still need a carb kit, tune-up, and an engine de-carb. That should clean out the 30yr old motor and give it something it needed years ago. Fuel economy on the boat is really good but it will be even better after the tune-up.