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68' 40 hp johnson running terribly

T

tbirdguy

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I have what I think is a 68' 40 HP Johnson. Model # is RD-30 D, serial is J2858470. It doesn't have enough power to get out of its own way. I recently (about 2 years ago, & only 8 trips on the water since) had the ignition & carb professionally rebuilt. It ran phenomenally the first few trips on the water, then degraded a little. After first few trips, motor would run great at idle, in gear, and up to 90% throttle. At wide open, it would suddenly 'stumble' and not produce much power. If I backed off to 90% (estimated) it ran great again. The last trip on the water, it would start & idle fine, and initially ran well up to 90% or so. Then it started to 'stumble' at 1/2 - 3/4 throttle. Luckily we were on our way in off the lake. By the time we got to the dock, it had virtually no power. From idle in-gear to 1/2 throttle it would run ok-ish, but would surge up & then back down on its own. It still starts immediately and idles just fine in neutral.

I have good experience working on auto engines, but I'm completely in the dark on a 2 stroke out board. I REALLY appreciate any help! Thank you in advance.
 
Did it have 2 new ignition coils installed ??---------Run with a timing light to see how the 2 ignition systems behave.------Does the manual fuel pump go hard when you use it before start-up ?
 
High speed jet plugged up? You don't have to strip the carburetor down to check it. It is behind the hex head drain plug on the front of the carb bowl. But a special screwdriver is required. Or at least highly recommended.
 
I'm not sure if it had 2 coils installed. I just know that the 'ignition system was rebuilt', as it was worded to me. In hindsight, I wish I'd have pressed for more info at the time. To me, it also looks as though a plug wire is 'burned through' also.

The pump doesn't seem to get hard. I pump it up, and after quite few pumps it gets tougher to squeeze, but not hard. I stop at that point I stop because I get concerned that I'm going to flood the motor. Thanks.
 
Hex drain plug? Do I just un-screw it and check, then screw it back in, or does it require to be specifically adjusted? Thanks.
 
racerone said:
Did it have 2 new ignition coils installed ??---------Run with a timing light to see how the 2 ignition systems behave.------Does the manual fuel pump go hard when you use it before start-up ?
Click to expand...

Also, each cylinder has its own coil / ignition system? Or did I completely mis-understand that?
 
I typically run it out of gas every time. I did pull & replace the plugs (that's when I noticed the plug wire). The electrodes were pretty corroded.

I've got zero experience with points. The other problem I have is that I don't have a timing light, spark tester, or compression tester.
 
So, I was looking at it again and I definitely feel that one plug wire is arcing spark. I tried to follow them back, but I cannot figure out where the coils are to replace them. Also, I'm trying to see if both coils have been replaced or not when I had it worked on before. I wanted to get an idea of what I'm going into before I start disassembling things. Thanks.
 
It was quite common for those 40 HP motors to break the piston rings.--Compression test is required.----The flywheel has to be pulled to inspect the coils / points / condensers.----No test equipment ?----Then pull the 2 bypass covers on the port side of the engine to inspect pistons and rings.-Just cost you a couple of cheap gaskets.
 
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Just my $00.02 if you rebuild the carb make sure the little adjustment tab on the back of the float does not extend all the way to the needle's seat. Mine did and caused the carb to stick open and flood. Drove ne crazy trying to figure that out.
 
So I broke down and bought a compression tester & spark tester. Both cylinders averages at about 115 psi compression (highs of 120, lows of 110 / 108ish).

Spark tester revealed good spark on both plugs, which I was shocked to see on the one wire I thought looked burnt.

This would lead me to expect a fuel system problem. Is it possible that the ball pump from the tank has gone bad and is flooding the motor...or that the forever old tank I have(at least early 80's if not older) is building to much pressure and forcing to much fuel through the pump and then causing it to flood?

Thanks in advance for the help.
 
bdfwinn said:
Just my $00.02 if you rebuild the carb make sure the little adjustment tab on the back of the float does not extend all the way to the needle's seat. Mine did and caused the carb to stick open and flood. Drove ne crazy trying to figure that out.
Click to expand...

I would hope this wasn't the problem, as I had it professionally rebuilt. Also, it did run phenomenally initially and the first few times out.
 
I will look into the lines and pump and etc when I get a chance next in a few days. The place that worked on it and rebuilt the carb / ignition actually specializes in older out-boards, especially johnson / evinrude. I had called a few Marina's in the area to see what they'd charge and none of them would bother. However, all of them recommended the place I ended up going. Thanks for the help.
 
So, I got a chance to get it back on the water again this past week. The more I have time to run it and really observe what's going on, the more I feel it is timing related. As stated above, I know it has good spark and good compression. Carb wise, it starts up immediately and runs great at an idle and even just a nudge over idle. As soon as I try to throttle up over maybe a 10 - 20% over an idle, it falls flat on its face. I have to immediately throttle back to idle or it will kill the motor. However, even if it kills it, it will start back up immediately. Running at an idle, it will cruise indefinitely around without a problem...it's just un-godly slow!

At this point, I don't know how to check, test, and/or adjust the timing on this. This seems to be the most likely of causes to me. Thank you in advance for your assistance.
 
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