1963 Johnson 18hp surging, backfiring and stumbling

[SuperEnzo]

Hi I have a 1963 Johnson 18hp that Ive been working on for a little while. I bought this motor off craigslist from a guy that had trouble with it running at high speed and had disassembled the carb so we couldn't run it. I bought it for cheap and immediately set to work on diagnosing the problems.

I put in the oem johnson carb kit with a new float, took out the welch plug to clean the orifices and the entire carb with wires and cleaner, reinstalled welch plug, replaced high and low speed packing washers, new gasket between carb and powerhead. I synced the carb with the cam follower so that the butterfly just starts to open as the cam follower is centered on the line.
Adjusted the needles 1-1/4 turns out for the low speed and 1/2 turn out for high speed.

Running 24:1 fuel/oil ratio

Cylinder psi is 90 in each cylinder

I replaced the spark plugs and checked the gaps on the points (.020"), checked for good blue spark, made sure the leads aren't crossed or anything

replaced the impeller and lower gear oil with new seals on the screws

I rebuilt my original Johnson 6 gal tank (single line) and put in all new o-rings and things since it was leaking (you can see what I did in my posts about the gas tank)

Now I got ready to start her up: pulled full choke, set it in my large water bucket, primed the bulb until it got hard, set the the throttle to a little past the start mark and after 4 pulls she fired right up and idled very high with the choke on, probably about 3000 rpm so I disengaged the choke and let it start to idle down and it started missing and popping out the exhaust. What its doing is at idle, with no choke, is the motor is idling to about 1200 rpm then it will backfire with a decent pop out of the exhaust and then the rpms fall like the engine is shutting down and then the rpms will start to rise back to 1200 rpm and the cycle starts all over again. The motor will continue to do this until I shut it down. Also interestingly is that enriching the low speed needle by even 1/2 a turn out has no effect (as i had thought that it could be a lean sneeze). In addition to try and get the idle rpms down I unscrewed the idle screw all the way out and even removed it and it had no affect on idle rpms.

I tried the boat on the lake yesterday to see if the problem was related to running in my bucket but the same symptoms showed. I even tried to throttle up the engine and the stumbling and all over the place rpms followed as I increased the throttle. At one point while trying to get the boat up to mid throttle (trying to slowly roll up the throttle to speed) the motor completely died and backfired so violently that It rotated the motor from one side of the boat to the other (picture the tiller handle swinging from port side to starboard). Also the motor was severely underpowered it felt (perhaps running on one cylinder) and we were barely moving in my 14 footer with me and my buddy who are light even though I had the motor pinned at mid throttle and the rpms were up around 2500. The motor starts pretty easily with cold or hot (like 3 pulls cold and 1 hot) but runs like crap cold and hot (after idleing for like 5 minutes).



Possible problems: these are what I'm thinking but I wanted some opinions from members here.
1) Running on one cylinder/ one cylinder is intermittently cutting in and out = electrical problem

2) air leak - this would explain the surging and the crazy high idle with the choke on (I had a 2 stroke motorcycle with a base gasket leak that did this)

3) clog in the carb - I highly doubt with these simple carbs at this point

Im pretty stumped with this, I can get a video of this later if you need me to. Thanks for any help
-Ethan

 

[oldboat1]

approach seems good. Doesn't seem close to prime time yet -- would guess #2 and #1, in that order. In addition, it would be worth checking the reed valves (and might cure an air leak in the process). A broken leaf can produce strange stuff. You might mist a little carb cleaner around the the base of the powerhead and around the joints behind the carb -- see if engine speed changes (testing for air leaks). Hold up a newspaper or something at the side of the carb when testing to shield carb intake a little.

Not clear how much ignition work was done, but coils and condensers might need replacement. Need to test spark with an adjustable tester when trying to diagnose ignition issues.

 

[lindy46]

You didn't break the tip of the low speed needle off in the orifice, did you?

 

[tomhath]

Have you tried squeezing the priming bulb while it's running? Might be a weak fuel pump.

 

[SuperEnzo]

To oldboat1: I have reciepts from the previous owner for brand new coils and condensers 10 years ago
To lindy46: the low speed needle is sharp and pointed at the tip, not snapped off
To tomhath: when i was on the lake yesterday, squeezing the bulb did not help the motor at all

I went out to the garage an started getting into my troubleshooting. I set up the motor to run it in the tank today and when I went to prime the bulb, I noticed that pumping it was not filling. I did some checking and it seemed that the bulb was not pushing fuel but just pushing air. Weird. I had to take the fuel barb off at the engine side, squeeze the bulb, put my finger over the end of the fuel hose and let the bulb suck up gas that way to get fuel to pump through. Once I did that the line was pushing gas again. I re-hooked the line up and pumped the bulb and this time for the first time I was able to completely fill the glass bowl and keep it that way. I must have had air in the lines from an air leak I just fixed. The motor seemed to run okay after I did this.
Here is a video after doing this, it seems okay: https://youtu.be/EO8yJ_t6Eqw
Also, notice in the video how much my motor is shaking? is this normal? My last 1977 7.5 hp mercury never shook this much at idle. any ideas?

So heres what I troubleshooted:
1) used my in line spark checker to check if a cylinder was dropping = Both cylinders were firing consistently even with revving of the engines

2) checked spark plugs after idling for a minute = both plugs black, slightly wet and sooty from idling, seems like they're both getting fuel and burning it

3) pulled the flywheel to check for sheared flywheel key = key is intact

4) pulled the carb and reed cover to check reeds = all reads in tact, no cracks

5) I pulled the carb bowl because why not and it was totally clean like I expected


Im starting to think the lean backfiring and what not was possibly cause by the air that was trapped in my fuel primer bulb, does anyone know how I can make sure that it is all expelled?

Also is there any timing to set with the magneto plate and everything?

Tomorrow I will go through the entire electronics system and check the resistances and whatnot

 

[oldboat1]

You're a methodical guy, SuperEnzo. Think I would buy a motor from you (well, maybe not the 18hp quite yet).

Good to have the video. I think the lower unit isn't deep enough. If you sink it about half way up the leg, you will run safer (water pickup) and quieter. That exhaust popping can be misleading. My sense, though, is that it's running pretty well. Shaking is pretty normal with the period motors I've had, some more than others. I think you might be able to dial it in for a little smoother running. I would try tweaking the idle adjustment a little (the air/fuel mix -- top needle). I would try to lean it out just a bit. If you get a lean sneeze or stalling, richen the mix a little (maybe 1/4 turn counterclockwise, maybe less). That lean sneeze will come from the exhaust port on the leg, by the way, and you might not pick it up if you are getting exhaust noise from the prop area. As you lean it out, rpms will likely rise -- throttle it down, and continue adjusting the mix. Technically, you're looking for about 650 rpms in gear at idle, but you can tell by sound. Sinking the leg deeper should increase back pressure a little as well, and that in itself may give you smoother running (certainly a better chance at dialing it in correctly).

You're on track working on the idle. It's a pretty big motor to idle down low and slow, but think it's got a chance. You may still want to readjust points (that's your timing), but think I would work at dialing in the carb first and go from there.

​Nice looking motor.

 

[lindy46]

Motor runs pretty good IMHO - but if adjusting the low speed needle has no effect, something is wrong in the idle circuit.

 

[Chinewalker]

From the sound in the video, it very much sounds like it's running on one cylinder. My Johnny Cash 18 idles quite smoothly and doesn't shake nearly that much. A cylinder drop test would be a good start. Pull the plug wires one at a time to see which cylinder it is not running on.

 

[SuperEnzo]

I found something when I removed the magneto plate to check the electronics: the upper crankshaft is slightly oily.
Also there is zero play in the crank so I think the bearings are just fine



I haven't replaced this seal before so I'm wondering if this is enough oil to warrant a replacement and it could indicate why my motor is running poorly. Any ideas? I want to address this first and then I'll respond to everyone who has suggested fixes
-Ethan

 

[racerone]

Does spark jump a gap of 5/16" in air, yes or no ?----Does throttle plate open at the correct time.----There is a line on the throttle cam and throttle must open there.

 

[Chinewalker]

You may be able to visually check the seal at the top by lightly spraying it with soapy water. Put the flywheel nut on and turn it over with a wrench. Note whether any bubbles emanate from the seal area.

 

[SuperEnzo]

Alright I'm back. I did alot of troubleshooting but first ill respond to everyone:

To oldboat1: Thank you for your kind words, I greatly appreciate that. Since I'm young (20) the internet is kind of a no "judging a book by the cover" since you cant see who the poster is... most people at the parts stores and dealers laugh me off and don't treat me well because they don't think I know anything or I'm just a 'kid', but I've been rebuilding engines since I was 15. Anyways I bought a garbage can to run my motor in and it is now in about 4 inches away from the exhaust port. The motor is still running kinda shakey but has calmed down with backfiring and is running okay since I purged my gas lines of air; which would result in the excessive backfiring and whatnot. I have adjusted the lean idle screw to get the motor idling consistently without backfiring (still kindy shakey but I believe you that these older motors run shakier at idle). Points have been adjusted and the whole ignition system has been checked and everything proved to be in good condition.

To lindy46: The air in the gas line was what was making the screw ineffective, I purged that air and the screw is controlling the engine like one would expect.

To Chinewalker: I dripped oil onto the top of the upper seal with oil and turned the crank with the plugs in to pressurize the cases and no air escaped so I bleive the seal is good. I did not perform a cylinder drop test yet. I found something else on the motor that requires attention and may explain the weird running... see below

To racerone: The igniton advance plate has been synced with the throttle butterfly valve. I have great blue spark, and I have not physically used a spark gap check tool yet. I went through the whole ignition system and checked all the resistances and everything is perfect like it should be

Troubleshooting: So here's all I did in the last 2 days. I re-went through my carb to make sure the passages and everything was clear. Then I went through everything on the magneto plate (coils, condensers, spark plug wires, points) and the condensers and coils passed the resistance tests; continuity on primary windings and condensor, 4600ohms on secondary windings and I even snipped of a 1/4 inch of spark plug wire on each end to get to new clean copper (spark plug wires proved continuous). I reinstalled all of the components and torqued down my flywheel nut to 45 ft-lbs. The motor fired right up and ran the same as it did...

Now heres where we get to the weird stuff: As I had the motor idling in my bucket I noticed that after about 5 minutes of warming up the engine I noticed a steady drip of water coming from a screw on the water jacket/exhaust cover. a whisp off steam came out of the cover as the engine began to warm up also. So naturally I went "well there has to be a gasket under there thats 40 years old" So i started to undo the bolts to pull off the gasket and this is what I found:











It definitely looks to me like water is leaking from the jacket and getting into the cylinder. Any thoughts on this?

-Ethan

 

[racerone]

Judging by the piston rings this motor was rebuilt or it is " just broken in " ----Have seen those maching marks on 40 year old motors and that is bonus.

 

[flyingscott]

One thing in your video I don't see any water coming out of the exhaust.

 

[SuperEnzo]

Interesting well that's awesome news. I see what you mean racer one, the lines on the piston rings, I didn't even notice.

The leak is not seen in that video, I actually got a bigger bucket to run my motor deeper in the water and it started to trickle out very fast in the deeper bucket probably from the increased water flow. You can see all the water at the bottom of the water jacket cover in my pictures

 

[SuperEnzo]

Did anyone have any other thoughts on this water in the cylinder? I'm still kinda wondering if i should be worried or not

 

[AlTn]

if the piston top doesn't appear to be "steam cleaned" I wouldn't worry that much about it having had water ingestion. Going forward, what was your plan if the water problem was obvious?..do you want to pull the powerhead for a tear down and inspection?

 

[oldboat1]

I'm not seeing evidence of water intrusion. Plugs don't appear to be washed. I think there is a possibility that you could be running hot, though -- think I would pull the l.u. again and push some water up the tube with a hose and some kind of fitting. Let it exit normally, and you might flush it out some in the process. Your motor has a thermostat up at the top of the head, and you may need to replace it -- good to pull it out and check it, anyway. With the t.stat cover off, flush both from the bottom and the top just for good measure.

Operating temp should be about 130 or 140F (Can be lower, but shouldn't be over 160F). You should be able to touch the top of the head while running, maybe hold the heel of your hand on it for a few seconds at least.