#2 cylinder problem on 1978 70 hp

When disconnecting the plug wires from the plugs cylinder 1 and 3 will sputter and the engine will quit. However when #2 wire is disconnected the motor continues to run as if there is not even a cylinder there, no sputtering or stalling. All wires show a current when I put a timing light on each wire, and the plug in #2 shows a spark when removed and the motor turned over. What is my problem?

Re: #2 cylinder problem on 1978 70 hp

#2 has a problem with getting and compressing fuel.

Usual suspects are carb, compression, scavenging.

Re: #2 cylinder problem on 1978 70 hp

What is scavenging? I have rebuilt the carbs but never tested the compression.

Re: #2 cylinder problem on 1978 70 hp

Sounds to me like your coil Is misfiring on that cylinder that would do it, or your power pack misfiring your coil, get a timing light and try your coil wires and the power wires out of power pack to your coils.then you should see . You might even check your stater it should kick 6 amps.

Re: #2 cylinder problem on 1978 70 hp

Scavenging is the pumping process by which fuel/air is drawn into the crankcase, then pumped into the cylinder, JZE.

For scavenging to work, the reeds must seal, piston seal on both downstroke and upstroke and all gaskets must be sound.

Re: #2 cylinder problem on 1978 70 hp

Would a crack in the intake or the reed plate cause this problem with #2 cylinder?

Re: #2 cylinder problem on 1978 70 hp

After doing a spark plug test the next step is to do a compression test. If one cylinder is low(or they all are) you next remove the head and look at inner cylinder for cracks or holes etc that are making the pressure low. When you get this far I believe the problem will be seen. The reed value lets gas into the cylinder before it compresses it ,if all cylinders show good compression (80 to 110) I would next check the reed. Im no expert but thats the way I would zero in on how bad its broken.

Re: #2 cylinder problem on 1978 70 hp

I wouldnt think so but you can take and spray a little starting fluid on the crack and if it changes idle it is sucking in air, I dont see the reed plates doing that I think you have a bad power pack or a weak stator, I would get a timing light and check the spark and amp meter and test the stator

Re: #2 cylinder problem on 1978 70 hp

Check compression and tell me reading on all three. On a much used 70 should be at least 100-125 psi.

JZEVINRUDE said:

When disconnecting the plug wires from the plugs cylinder 1 and 3 will sputter and the engine will quit. However when #2 wire is disconnected the motor continues to run as if there is not even a cylinder there, no sputtering or stalling. All wires show a current when I put a timing light on each wire, and the plug in #2 shows a spark when removed and the motor turned over. What is my problem?

Click to expand...

Re: #2 cylinder problem on 1978 70 hp

I just went through very much the same problem, and found I had problems if I didn't approach things methodically and logically. You need spark, compression, and fuel (but not too much fuel!)

First off: what does the #2 plug look like? Wet/black -- cylinder is getting fuel but not firing or firing very weakly; Dry and gray/white -- cylinder is starved for fuel.

So, you start with spark, which you have done (read the first post people -- he already did the timing light!). If plug is wet, you should make sure you continue to get good spark when the motor is hot, b/c coils sometimes flake out when hot. However, if you know the cylinder is failing despite good spark, move on.

Now you're down to compression or fuel. Compression is easy to check, as Sandhammaren05 suggested, so do that first. Bad compression in that cyl means most of your easy solutions are out. :-(

If compression is good, then that cylinder is either getting too much fuel or too little, and the plug should tell you that. My problem was a flooded cylinder due to gunk in the carb float valve.

AFTER you get an idea of what you think it is, try to swap ONLY THAT PART with another cylinder, and see if the problem follows the part. Unfortunately, you can't swap that carb, but if you suspect weak spark you can swap a coil with another cylinder (making sure you switch both the plug wires and the leads connecting coil to powerpack; don't want #2 firing when #1 is supposed to!) One of my problems was not following this advice and assuming that a wet plug meant a spark problem, so I changed the coil unnecessarily before doing the switch test.

Good luck, and let us know what that plug looks like!

Re: #2 cylinder problem on 1978 70 hp

I will try out the suggestions from everyone today, i appreciate all of the knowledge and interest, thank you. Talk to everyone later

Re: #2 cylinder problem on 1978 70 hp

JZEVINRUDE said:

Would a crack in the intake or the reed plate cause this problem with #2 cylinder?

Click to expand...

Yup. That is an example of a trouble that interferes with scavenging.

Re: #2 cylinder problem on 1978 70 hp

Okay, here are my test results so far. I have tested the coils and the powerpack for misfiring and the timing light showed no missing. The plugs all look the same, wet and slightly black. I then did a spark test and all the plugs jumped the gap with a strong blue arc. Next I did a compression test and showed #1 @ 115, #2 @ 115, and #3 @110. Started the engine and the cylinder still not working, which is what I expected since I have not done anything but testing. I then sprayed the intake manifold and around the carb gaskets with starting fluid. The #2 carb would choke the motor when i sprayed that area. So... now I have the carbs off the manifold and when I turn them upside down and blow in the gas port the float has closed the valve (good.... right?)I will now look for any cracks in the manifold and reed plate. I need help!!!

Re: #2 cylinder problem on 1978 70 hp

Don't use starting fluid, JZE. That stuff is dangerous and contains no lubricant. Use premixed fuel.

Re: #2 cylinder problem on 1978 70 hp

thanks for the tip. I still do not have the motor running, are there any more helpers out there?

Re: #2 cylinder problem on 1978 70 hp

JZEVINRUDE said:

thanks for the tip. I still do not have the motor running, are there any more helpers out there?

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Just curious, other than you believing there is a problem, what issues are you having when the boat is in the water? Poor performance, planing issues, etc?

Reason I ask is I believe early outboards run a little snotty at idle especially on a hose, just because you don't hear the engine slow down doesn't mean it isn't slowing down somewhat so are you using a tachometer to verify this lack of drop in engine rpm when you remove the plug wire from cylinder #2?

I too have a 1978 Johnson 70 hp and was sure I had a issue with my engine regarding cyl #3, I checked the compression, did the same pull the plug while it's running test your doing which performing, etc... Long story short after replacing the spark plugs and a short sea trial I had no issues at all and the boat runs 3 mph faster than the PO said it would for him...

Just sharing my own experience...

Good luck,

Billy

Re: #2 cylinder problem on 1978 70 hp

billy,
You make a good point about the rpm. I have not put a tach on the motor when I disconnect the #2 wire but there is not any noticible change to performance compared to the other plug wires when disconnected. Regarding on the water performance, it barely wants to go at slow speed and many times stalls unless choked. Once I get through the lower rpms it catches and flies.

Re: #2 cylinder problem on 1978 70 hp

JZEVINRUDE said:

billy,
You make a good point about the rpm. I have not put a tach on the motor when I disconnect the #2 wire but there is not any noticible change to performance compared to the other plug wires when disconnected. Regarding on the water performance, it barely wants to go at slow speed and many times stalls unless choked. Once I get through the lower rpms it catches and flies.

Click to expand...

Sounds more like a carb problem than a dead cylinder (perhaps a carb problem just on cylinder #2?) what does the spark plug look like on cylinder #2 compared to the rest, clean and lean or oily and fuel fouled?

HTH

Billy

FWIW, I have been told the early power pak ignition systems don't like to have the spark plug wire disconnected and be ran for very long and have the power pak survive and I have the factory shop manual and it doesn't have the removing the plug wire as a diagnosis tool so you might not want to do it very often as all that voltage has to go somewhere (power pak isn't a cheap part)....