Getting frustrated... Best way to trouble shoot an old big twin in a tank?

[Bigkat650]

So my 1958 Johnson 35hp is not running right. From what I have read on here, it sounds like it's running on only 1 cylinder. It idle's OK, not great at first but good enough to keep it from stalling. It idles better after running for 5 minutes.

I thought everything was OK so I take it out on the water and start it up, same sort of deal.I let it warm up a few minutes, then shift into forward--and it felt like it immediately wants to stall, so I give it a bit more throttle, now i'm at about 2/3 throttle and its just enough to get me moving about 5-6mph approx. I push it open to WOT, and all the motor does is gain a slight bit more RPM (maybe 200 more rpm?), my boat goes a couple MPH faster, but the motor is noticeably running rougher and vibrating more. The carb was recently serviced, as were the coils and points--has to be the plugs or wires I assume.

I have read that the simplest way to make sure both cylinders are firing OK is to run the motor in the bucket, and while its running, disconnect 1 of the 2 plugs. if the motor is operating correctly, it should still run on 1 plug, but run rougher--It should be a noticeable difference. If that cylinder was not firing and you pull the plug wire, I will not notice a difference when I unplug it. Likewise if that cylinder was the only one firing, and I unplug it--the motor will simply quit.

My questions are: Does this hurt the motor at all to do this? Also, if it turns out that both cylinders have spark--what else could cause the motor to run this badly? I know the high speed needle could play a part, but I believe it it relatively close to where it should be (I started at 1.25 turns out from closed and played with it from .75 turn to 1.75 turn, and still ran just as poorly. I did this on the lake while giving it almost full throttle). Could it be gas? The fuel tank had 1 year old/bad gas in it when I got it. I siphoned that out, filled it up with 2 gallons of fresh 87 octane and siphoned that out as well, then filled it up 100% (6 gallons) with new 89 octane at a 24-1 oil ratio. So I figured the gas is good--but I suppose there could have been an ounce or two of residual junk fuel that got mixed in with the new stuff.

I plan on testing the plugs tonight. Any thoughts? Thanks

 

[HighTrim]

Re: Getting frustrated... Best way to trouble shoot an old big twin in a tank?

Well until some tests are done, we are merely guessing.

Start with compression, always. What are the readings on both cylinders?

Next, you must have an inline/adjustable spark gap tester if you are going to troubleshoot outboards. The spark must be able to jump a 3/8" gap with a bright blue ZAP!!

What plugs are you running? Have you tried different?

You say the carb and ignition was serviced. By whom? What did they do? If they replaced the coils I would assume they would replace the 50 year old plug wire while at it?

You will not hurt anything by pulling plug wires, but be aware, use proper grounded plug wire pullers, or youll get a shock. If you dont have any, get the wife to pull them.

The starting point for the high speed needle is 3/4 turn out from lightly seated, you then screw it IN, clockwise to fine tune.

 

[F_R]

Re: Getting frustrated... Best way to trouble shoot an old big twin in a tank?

Well, to begin, your high speed needle is open way too far. It is going to 4-cycle at such settings (fire every other revolution). Start with 3/4 turn open, and turn it in till it starts to lose power, then back till it regains power (on a boat, on the lake, in gear, full throttle)

Pulling plug wires while running shouldn't hurt anything----IF the coils are in great condition. It could damage marginal ones. It can also knock you out of yuor BVD's. (I hate getting shocked) Better test is to unplug and ground each wire at a time, then start the motor and see if it made any difference.

EDIT: BTW, are you trying to run it in a tank with the hood on? Futile. Remove the hood. Also, you simply cannot expect it to run at anything more than fast idle in a tank unless it is a professional test tank and using a test prop.

If it is the Super Sea Horse (Super Quiet) model and it won't run on the boat on the lake with the hood on, you have a smoke inhallation problem. Most likely cause---the o-ring seal (and/or spacers if long shaft) is missing from the top of the water pump cover.

 

[Bigkat650]

Re: Getting frustrated... Best way to trouble shoot an old big twin in a tank?

1. The motor was completely serviced by the guy I bought it off of. He rebuilds outboard motors as a hobby, and when I asked him about this motor, he said he had replaced the coils, points, and condensers; new plugs; new impeller; new lower gear lube; and cleaned/resealed the carb. I do not know if he replaced the plug wires. He did a compression test last summer and was just under 100 in each cylinder, something like 98 in top, 95 in the bottom. Not ideal, but should be serviceable. He also said of the dozens of motors he had, this was the one he ran on his boat the majority of the summer last year. I asked him what he thought it could be when I described the symptoms, and he said it was most likely the high speed needle just needed adjusting.

2. My local NAPA only had 1 inline spark tester I purchased on Tuesday. It is not adjustable, and has a bulb in it--not a gap. I plugged it inline with the spark plug and had my wife watch it while I pulled the manual start line. I got absolutely nothing on either cylinder, so I assume the tester is not functioning correctly... that was frustrating because I was hoping it would help shed light on the problem, not create more questions. I took the bulb out, and it looks like its a 250v bulb... I just assumed its not designed to work out outboards, or the bulb is blown. It only cost a couple bucks, so it's not even worth returning.

3. The plugs are correct for the motor, however I have purchased replacements at NAPA that I will test soon. I hope with changing the plugs, and dialing in the high speed needle's the motor will run to it's potential. Unfortunately I won't know until I get it on the water. The only other thing I have thought could be a problem is the gas. Based on my description of how the motor is running, and how I cleaned out the tank--is it possible the gas is bad?

 

[F_R]

Re: Getting frustrated... Best way to trouble shoot an old big twin in a tank?

Is it possible the gas is bad??? Well all things are possible. But I doubt that is the problem here. I think you have zeroes in on the two most likely---running on one cylinder or carb adjustment.

Point number one, about having been serviced doesn't impress me much. If it is in such perfect shape, why doesn't it run? Even if it was perfect last time it ran, that was then and this is now. Stuff happens.

 

[Bigkat650]

Re: Getting frustrated... Best way to trouble shoot an old big twin in a tank?

Is it possible the gas is bad??? Well all things are possible. But I doubt that is the problem here. I think you have zeroes in on the two most likely---running on one cylinder or carb adjustment.

Point number one, about having been serviced doesn't impress me much. If it is in such perfect shape, why doesn't it run? Even if it was perfect last time it ran, that was then and this is now. Stuff happens.

Yeah, he's a mechanically inclined hobbyist that has done this for years and enjoys doing it--not a professional outboard mechanic. With that being said, I was (and still am) confident that he did a good job on the rebuild. It is a 55 year old motor, and I bought it knowing it would probably have some minor issues and require some TLC--and like you said, stuff happens.