Help with 88 Evinrude 70hp won't come down to idle

[rheine]

Evinrude 70 VRO. First it needed a power pack and I got spark. Then I see one carb was dripping fuel on bulb squeeze. Rebuilt all three. Changed the plugs to NGK marine gapped at .040.
Compression 100, 92, 90. Tank drained and fresh mixed gas. Used inline plug tester. All sparked.

I finally stumbled on a starting procedure that worked. It has to have good strong throttle and a couple key pumps. When I get it going and back it down to 1500 it peters out in 15 seconds. Another clue: It seems like at 2000 suddenly another cylinder will kick in and she roars, screams.

I am chasing ghosts now so I elevated to my friends here. Thanks

R

 

[Rustywrench]

If those compression numbers are correct I might pull the head before I spend anymore money. You may find scored cylinder?

 

[jbuote]

Nowhere near a pro here,
Not sure I like those compression numbers, but I'm used to older engines, so it may be good..
At least they're within 10% of each other it seems...
(Edit: and Rustywrench addressed that while I was typing... lol)

One thing that jumped out a me:

Used inline plug tester. All sparked......
Another clue: It seems like at 2000 suddenly another cylinder will kick in and she roars, screams.

That inline tester.... It's just the kind that lights up if there's spark right?
Have you tested with an adjustable open air spark gap tester?
Should jump a gap of 3/8" (pretty sure is the min) or greater with crisp blue SNAP!! If not, need some ignition troubleshooting...

cdielectronics has a good troubleshooting guide at the top of their page for that...

The pro's here can/will guide better, but to me it seems like there still may be a spark issue which could cause stalling at idle, and then what seems like sudden power with rpm...

Hope it helps..
Will follow to see how you make out..

 

[Rustywrench]

10% rule doesn't do you much good on these little 2 & 3 loopers. They have huge port area & when they get scored or heavy wear then compression leaks by causing a poor idle that just fades away. Usually will continue if you choke/prime it a little. May require choke/prime to restart. That is wet sealing the cylinders for a short time. Just didn't want you to chase your tail or spend more money before you find the possible true problem? Easy to pull head & have a look.

 

[jbuote]

^^^ See what I mean? I got to learn something too! Thanks Rusty!
You're in good hands rheine!

 

[rheine]

A couple day ago after the carb rebuild I was able to key pump and start right to an idle on the muffs. It idled clean and crisp. Monday I had a hard time starting on the water but finally it went and I had to hurry up and get it in gear. I cruised for 2 hours at 2500 but I felt maybe not all three were working. The vibration seemed off. Do I have a crazy fuel pump, wacky coil pack? Water in the tank? Need more test advice.

 

[fireman57]

Really? You need more advice? They could tell you to replace the coils as they might be bad or tell you the crank seal is bad etc.... They could tell you to throw money at it which I think is what you want them to do. They are telling you to make sure it is worth going farther on by pulling the head. Such an easy job and takes almost no time at all. If you have a bad cylinder nothing is going to help.
Why do people ask advice because they don't know what to do and then say that is the wrong advice. Sorry for the rant but I feel for these guys on here that enjoy helping people and know what they are talking about basically be told that they are wrong.
Rant over. Mods if you feel the need to delete this then please do. And sorry if I broke the rules.

 

[fireman57]

You also should not run NGK plugs in these engines as they were literally built around Champion plugs.

 

[Dmpaul89]

Sounds like you have a missfire at low rpm. With those compression numbers i wouldnt invest anything into it until you do as others have said and look in the cylinders. Might just have stuck rings from sitting. Might be junk. Dont know till you look.

 

[rheine]

Wow, all I can say is it used to be a friendly place. You can close out the thread.

 

[oldboat1]

Would go to Champion plugs, like suggested, at .030 -- or at least try .030 with the NKGs. Would also check to see if there is in fact a cylinder drop when it is acting up (ignition related) -- use a timing gun and see if and when it flashes (or stops).

Not much margin for error with compression numbers -- might experiment with higher idle setting.

At some point need to pull the heads, but can do some cheap tinkering in the meantime. (Might get lucky, and find a new head gasket and resurfaced head will get some improvement.)

 

[flyingscott]

Those compression #s are horrible. The 10% applies only to a workable compression #. Those motors new will be about 140 psi. A good used one will be 100 to 120 psi. Your motor needs an internal inspection.

 

[oldboat1]

Clinging to optimism just a bit longer, try another compression tester (preferably a known good one) and see if you get similar results.