Evinrude missing on bottom cylinder

[jonboatwarrior]

Hi guys,
I just bought my first boat and have a problem with the motor. It is a 1977 70HP Evinrude. It starts and runs but I believe the bottom cylinder is missing. While it is running in the driveway, I pulled the spark plug wires one at a time and when I pull the bottom one, nothing changes. When I pull the middle one, it dies. When I pull the top one, it runs rough. I switched spark plugs of the bottom cylinder and the middle one and the problem stays with the bottom cylinder. I pull the bottom spark plug and attatch it to the wire and it is getting spark. When I first pulled the bottom plug, it was black and wet. I cleaned it off, put it back in and tried again but still no luck. Everytime I pull the plug, it is wet.

So I have used a spark plug that I know works.
It is getting spark
The plug is wet so I am getting fuel

Could I be getting too much fuel and be flooding it?
What tests can I do to narrow down the problem?

Thanks in advance for all you help.

 

[AlTn]

Re: Evinrude missing on bottom cylinder

cdielectronics.com will have a trouble shooting guide for your ignition....marineengine.com..boats.net...shop.evinrude.com will have diagrams and prices for your motor...the electronic troubleshooting will require a dva meter or a dva adapter for your multimeter. Using an airgap spark tester..$10 or less at most auto parts stores...set at 7/16" the spark should be blue with a good snap from each sparkplug wire. To eliminate the coil for that cylinder, try substituting a coil from a working cylinder. Would recommend you purchasing an OMC Johnson/Evinrude Factory manual for your motor if you plan on keeping it....find them on ebay or outboardbooks.com. Seloc and Clymers may be too general depending on your experience.

 

[jonboatwarrior]

Re: Evinrude missing on bottom cylinder

Thanks for the reply. It sounds like you are saying I may not be getting a good enough spark. I will try switching the coils. I do remember when I pulled the wires off the spark plugs of the 2 top cylinders, I could definately hear the spark jumping from the wire to the plug....not so much with the bottom cylinder. I will let you know what I find.

 

[jonboatwarrior]

Re: Evinrude missing on bottom cylinder

More information....not sure if this will help. I switched coil packs with another cylinder and the problem stays on the bottom cylinder. I put a rag over the bottom air intake to choke it while running and the motor acts up. When I remove the rag, the exhaust gets real smokey for a second and then the motor goes back to running the way it was. Not sure if that tells you anything.

 

[AlTn]

Re: Evinrude missing on bottom cylinder

did you check the air gap spark?...if less than 7/16" on this cylinder, more testing using a dva capable meter is necessary..post back on air gap test

 

[jonboatwarrior]

Re: Evinrude missing on bottom cylinder

Just checked it and they are all sparking well. Thank you for the continued help! What's next?

 

[jherlyn]

Re: Evinrude missing on bottom cylinder

I realize that you said that the bottom plug is wet, but I was wondering if you would take some premixed fuel in a spray bottle and spray it into the bottom cylinder while the motor is running to see if the cylinder picks up

 

[Daviet]

Re: Evinrude missing on bottom cylinder

Have you checked the compression on the cylinders, what are your readings?

 

[jonboatwarrior]

Re: Evinrude missing on bottom cylinder

I will try the spray bottle thing this evening. I haven't checked the compression yet. I don't have a gauge. I am trying to locate one though.

 

[jonboatwarrior]

Re: Evinrude missing on bottom cylinder

Ok, So I tried the spray bottle thing and it seems to rev up for a sec and then back down combined with some white smoke out the exhaust. Does the same thing when I first choke the one cylinder and again when i stop choking it. So my thinking is that it isn't getting gas unless I spray it in or put on a full choke to create more suction. I imagine the choke only works for a second in the beginning because it runs out of air and then works for a second when I remove the choke because it gets the air back but then runs out of fuel. And the white smoke is like when you first start it. Does this make sense? Is my fix going to be cleaning up the carb? I haven't done a compression test yet but I think I know where to get a gauge if need be.

 

[AlTn]

Re: Evinrude missing on bottom cylinder

a compression test,if nothing else, will establish a baseline for the future. Its main purpose now is a health check/ what needs fixin' type question.W/O knowing for certain what's going on compression wise, it's hard to say what to do next. Realising that you may well have found the trouble, you may have something else going on as well. It does need to be done..for peace of mind if nothing else.

 

[jonboatwarrior]

Re: Evinrude missing on bottom cylinder

compression test results:
top 120
mid 115
bot 110
Is this ok?

 

[jonboatwarrior]

Re: Evinrude missing on bottom cylinder

Cleaned the bottom card and it started working. So took it for a test drive in the river and it is lacking power. That 70HP should have pushed a 16' aluminum boat a lot faster. When I gunned it, it would slowly rev up. It was slow getting out of the hole and if my wife (small) sits next to me in the back, it would not get out of the hole. It's like it had no power. Not sure what to do next. Any advice would be greatly appreciated.

 

[Daviet]

Re: Evinrude missing on bottom cylinder

Did you overhaul all the carbs or just the bottom one?

 

[AlTn]

Re: Evinrude missing on bottom cylinder

agree with Daviet...if you'll go to marineengine.com you can find diagrams for your engine...word of advice on the carb rebuild..do one at a time as it's easy to get jets mixed up and often, not sure in your case, the carbs may have different jets depending on their position...compression numbers are ok and a decarb procedure may well even them up some....are the carbs the only problem?..hard to say, but they do need attention before going further...a factory workshop is invaluable if you want to diy....seloc and clymer may be too general depending on your experience

 

[admlofton]

Re: Evinrude missing on bottom cylinder

Check your bottom carb float. Could be dumping too much fuel on the cylinder!

 

[jonboatwarrior]

Re: Evinrude missing on bottom cylinder

cleaned the other two carbs and took for a test run. Much better. was able to get out of the hole with my wife and her dad sitting next to me in the back. Running much better. I'm not sure if it is running at a 100% but it runs good. Thanks for all the help. I really appreciate it. Now if I can just get the reverse to engage, I will be ready to go fishing. I tried adjusting the cable but can't find a happy medium between forward and reverse.