SOLVED: 1963 Evinrude 40hp Lark V only firing on one cylinder

[SteveVT]

I thought I was home free today on this engine after getting the water pump working. Previously I had replaced the magnetos, points, and condensers, and plugs. The engine runs but when I pulled the plug wire on the lower cylinder, no change. Pulling the plug wire on the upper cylinder, and the motor stopped. I've tried carefully adjusting the idle mixture over the full range from killing it lean, to killing it rich, but except for an occasional brief burst from the lower cylinder, I'm still only running on the upper.

I did a compression test on both cylinders and they both read 80 lbs on my compression tester. I get a hot fat spark on the missing lower cylinder. Just to make sure of timing I pulled the flywheel again and checked the point gaps. Both were .020".

Seems to me the carb ought not to be the problem, since it feeds both cylinders and one cylinder is fine. I see unburned fuel in the lower, so I don't think it is starved. I've switched plugs in case one was bad, but no difference.

I'm starting to suspect the plug type itself, and oil fouling (standard 24 to 1 mix). This engine originally called for J4J plugs -- but they aren't made any more. I was told that were replaced by J4C at the auto parts store. But I've read elsewhere that the bar electrode was shorter on the J4J to prevent plug oil fouling.

I also saw a suggestion to file the bar back to the center of the rod electrode. I haven't tried that. The other possibility would be to try a hotter plug.

Any other suggestions about possible causes and solutions?

 

[boobie]

Are the reeds okay ??

 

[lindy46]

You say you have a "hot fat spark" on the lower cylinder - is that with a spark tester or with a spark plug? Did you try switching the plugs around? J4C or J6C are the correct plugs. Also, 80PSI is pretty low compression. Should be 110+ for that motor.

 

[SteveVT]

Thanks Lindy, I checked with a spark tester and with the plug itself, and I also switched the plugs.

Also with the plug tester inline with the plug in the cylinder and a running engine, the neon was firing.

And even with the tester on the plug wire but no ground at all it the tester lighting up. I could feel and hear the snap vibration at the end of a plastic plug puller, just holding it in the air, no ground.

boobie, I hadn't thought of the reeds. Guess I'll have to check that. That would make a difference, one cylinder to the other and a real possibility.

Think I'll test a J6c in the lower cylinder -- should be a go or no-go test, and then I guess I'll dive into the reeds. Or maybe throw the motor into the reeds!

 

[SteveVT]

re. reeds -- one thing noticed ....no fuel comes out of the front of the carb on this one.

re. 80 lb compression -- I wouldn't count on the ultimate figure as accurate, since it's quite an old tester with about a foot long rubber hose connection.

Rather, the main thing is that the readings are the same.

One cylinder is running fine also, at what ever the compression actually is.

 

[SteveVT]

Also, not quite sure I understand the safety components and connections on this engine that prevent over-revving. Could a problem in that system be a possible cause?

 

[SteveVT]

I changed out the lower cylinder plug with a J6C and it started firing.

Emptied the tank (with some Seafoam added).

Off to get fresh gas and oil and check low speed tuning.

 

[oldboat1]

Was glad to see you got the water pump issues resolved. The J6Cs should work (J4Js -- now J4Cs -- are the recommended plugs. Think you're right about the electrode length, but not sure how much difference it makes in a good running motor. You can probably find some NOS J4Js on Ebay, or could try an ad on the AOMCI site). Gap is .030 (.020 for the points). Run 24:1 mix. Flywheel nut torque is 100-105 ft lbs., and important.

I'm not a fan of regular use of Seafoam in the tank -- think it sometimes creates more issues than it resolves. For carb maintenance, need to disassemble and soak if you have running issues. Initial needle setting (idle needle is 1 and 1/2 turns out from seated -- should get you up and running. Fine tune after warm up. Need a tank or the lake for fine tuning, as you need back pressure.

Hey -- Get it running. BTW, best spark tester is the open air adjustable type, not an inline. Spark should be a solid 3/8", but will probably get more than that with fresh ignition parts. Replace coils if the casings are cracked -- I usually just start with fresh coils, points, condensers and wires (7mm solid core).

 

[SteveVT]

Hi Oldboat, thanks! have already done most of what you mention (new coils,points, condensers, flywheel torqued to 105 ftlbs, plugs gapped to .030, etc.) It's a definite runner, but the initial problem was running on the upper (No.1) cylinder only, with an occasional beat indicating the No. 2 kicking but no sustained running. The seafoam was not intended for a regular usage, but a one-shot deal.

After changing its plug to J6C on the No 2 (and fresh gas/no seafoam, still 24:1 mix ratio)) I'm getting sustained running of the number 2 cylinder for awhile, but it can cut back out at times.

The wiring is not the greatest and in particular the white wires have some frayed insulation issues, as well as being held tightly under sharp metal clips. These are part of the cutout/safety switch circuit, which I'm beginning to suspect as a possible culprit.

This cutout circuit is connected to the No 2 points, and is intended ground out the spark on that cylinder on conditions of high crankcase vacuum, advanced throttle, and shifter in gear. There is a vacuum switch, and a microswitch on a cam.

If any of these (or the wiring) goes to ground it intentionally cuts out the spark on the No 2 cylinder -- which has been the problem cylinder I'm dealing with. So it is possible that an intermittent short in that circuit or a bad vacuum switch could be the culprit.

Tomorrow I am planning to rewire and test that whole circuit.

I'm still concerned about the compression readings. I checked both cylinders more carefully today and got 84 pounds in each with my old uncalibrated compression tester. Tomorrow I want to calibrate it and if I still get a low reading, add oil to the cylinders to see if it bumps them up.

I did forget to have throttle full open when checking, and choke off, so I'll re-check properly tomorrow.

Anyway small progress.....

 

[oldboat1]

Sounds like progress to me. Don't think throttle and choke are important to compression testing, but -- on the other hand -- try it as suggested, and see if there is a change. I haven't run into issues with the vacuum switches, but think there is a history with them. Would like to hear what you find.

Best...

 

[lindy46]

Cut-out switch is usually working or not. Shouldn't cause intermittent problems. You can temporarily remove it from the system (disconnect the wires) and see how the motor runs. Or you can test it with an ohmeter. Switch should normally be open. Apply vacuum to it and the switch should close. Make sure the wires are good and not grounding out somewhere.

 

[SteveVT]

Thanks Oldboat, Lindy.

More investigation today:

Calibrated the compression gage and it was 5 pounds under, a bit of something white fell out of it -- like a styrofoam bead or a bit of paper as I was changing its fitting to do the test. I also noticed a bit of surface rust on the quick connect between hose and gage, so I cleaned the and put a tiny wipe of white grease on it.

To teste the cylinders, I opened the choke up but couldn't open the throttle while cranking because of the ignition switch lock out.

But anyway, compression check read 100 lbs on the top (No 1) cylinder and 96 lbs on the No. 2. Adding 5 pounds correction gives 105 and 101 lbs for the cylinders respectively with throttle at Start. So, I'm going to stop worrying about compression for now.

I rewired the frayed bits in the safety switch and vacuum switch circuits. I decided to check the safety switch adjustment. When I did I found a definite problem:

The safety switch is held to a bracket by two screws, and the bracket is held to the power head by a bolt in a slot in the bracket for adjustment.
When I started to adjust it, I noticed that after tightening the bolt, the switch could still be moved. I unbolted the bracket, and looked at the switch. One of the two 4-40 screws that holds it to the bracket was missing. So it could pivot on the other screw. The remaining screw was tight, but it wasn't enough the keep the switch from moving out of position under pressure or probably vibration.

I just added a new screw and Loctited a nut on the bottom this time instead of relying on the thin tapped sheet metal bracket as originally made. I'll adjust the set point per manual. I think it was way off...

Hoping that's the smoking gun.......

 

[SteveVT]

Fired up great after the rewire, safety switch repair and adjustment, and ran perfectly at various throttle settings -- thought I had it made.......but a few minutes later starting to miss and then... back to single cylinder operation.

After trying everything, carb idle tuning, etc. as before, I put the neon spark tester inline with the No 2 spark plug while it was missing. The light was flashing, but dimly. Then a sudden burst of firing and the tester flashed very brightly, then back to dim flashing and single cylinder operation.

Soooooo.....it has to be an intermittent somewhere in the new ignition components.

I pulled the plug wires and measured the coil resistance to ground (secondary winding). Both coils were 8.27 kOhms, measured through the spark plug wires. This tells me the coil secondaries are not broken, and that the plug wires are making good contact with the magnetos.

This leaves the capacitors and points as possible problems. I guess I have to pull the flywheel one more time.

I'll check the point gap, yet again. And trade the capacitors to see if the cylinders trade problems.

Well, it could also be an arcing problem in the plug wire, or the coil windings.

I could trade coils, but not plug wires, and I don't have wire to make up new plug wires.

What do you guys use if making wires from scratch? Do you just buy a universal copper auto set and use the wire? There's no bulk wire available locally.

 

[SteveVT]

Waiting for wires to arrive, I decided to open up the fuel pump and carburetor to replace old parts with new. I also pulled the flywheel to get ready for changing out the spark plug wires.

I found a bunch of problems, all corrected now.

Fuel:

The packing in the idle adjustment jet was a chewed up mess. The aluminum bushing that the jet needle screws into had a mashed starting thread. Idle adjustment had been difficult and weird. That was the reason. Someone probably overtightened the packing nut to keep the bushing from turning with the needle. I pulled the bushing and found it was a 1/4-28 thread, so I chased it. Now the needle rotates smoothly. New packing and washers and just a slight tightening of the packing nut is all that is needed.

The float valve had a piece of debris in it, and also the needle was worn. Needle and seat replaced.

The float was old and a bit fuel soaked. Replaced.

New gaskets all around and the idle passages checked and cleaned.

Fuel pump diaphragm was badly stretched and the membrane had actually pulled in from the sides. It looked from tiny discoloration like a pin leak of air might have been able to get in on the vacuum side through one of these pulls.

Ignition:

The most important problem of all was a small shiny copper spot I found on the number 2 cyl condenser wire. Apparently a short kink had been rubbing on the flywheel and wore through the insulation -- barely noticeable just that the sun caught a tiny glint of copper. But that would definitely block the number 2 cylinder. It also explains why I got a good spark before tightening the flywheel down, when after that it became iffy. I'm thinking that's got to be it! Well there were other earlier ignition problems too. But that one seems like it matches the sometime firing issue perfectly.

But, I'll wait for new spark wires too. Just might as well have everything right before putting the flywheel back, and trying again. Feeling hopeful.....

 

[lindy46]

Yeah - make sure you tuck all the wires under the flywheel down so they can't rub on anything. Not an uncommon problem - seen it many times.

 

[SteveVT]

Okay, all back together. Ignition works fine after moving condenser wire and re-insulating it, changing out to new spark wires, resetting the points, adding the missing screw to the stop switch so it will stay in position, adjusting its position and the throttle ignition advance, per book values.

And fuel delivery and idle adjust seems good after rebuilding the carb and fuel pump. Both cylinders firing.

Water pump repair is delivering water. So finally marking this one solved!

Thanks to all who offered suggestions and help.