1972 20hp johnson not running properly

[jwilkey84]

Re: 1972 20hp johnson not running properly

Well I tried to make her run again tonight. It took me about an hour to get it to start. I rechecked some things: spark is good, and I think the fuel pump is good, it shoots fuel out about 3-4 inches, is that enough or dooes it need more pressure? I tore into the fuel pump last weekend and everything looked good as far as I could tell. I also replaced every inch of fuel line and put new hose clamps on everything. The needle valve is 1&1/2 turns out. It finally started when I had the throttle opened a little. I think I had it flooded at first, so I took the plugs out dried them, and also blew the cylinder out with compressed air. Anyway after it was running: it will not idle but will run if I keep the rpm's up. adjusting the needle valve does not seem to make a difference. I also put some grease around the shaft that controls the butterfly on the carb, didn't seem to make any difference. Prettymuch I am done monkeying with this thing, and I usually don't give up, but this has me so frustrated. I think I will wait for a few reply's and then it is going to a mechanic. So any more ideas would be helpful and appreciated.

 

[HighTrim]

Re: 1972 20hp johnson not running properly

Did you try spraying pre mix into the carb throats to isolate your problem?

Choking it and having it pick up indicates faulty jets to me. Were the carbs completely dissassembled and bathed/rebuilt? Fuel bulb get hard when primed?

I would ensure the carb is spiffy clean, rebuilt, set the idle under load in gear, then link n sync as stated.

 

[jbjennings]

Re: 1972 20hp johnson not running properly

Jwilkey,
I really think that your float valve is sticking or your float is not set right. When you pump the bulb, will it get firm? If you pump it too much, will fuel start pouring out the carb. vent? If you are not getting the right amount of fuel in the carb bowl, it could cause what you decide. If you have a new float valve and seat, I would try cleaning the old needle and seat and using it just one time, with the float VERY slightly leaning down when it seats the valve and closes the fuel off. I had a similar problem and someone recommended trying a different needle and seat and it did solve a lot of problems.
Just a thought,
JBJ

 

[jwilkey84]

Re: 1972 20hp johnson not running properly

The bulb gets hard, I start it and it goes a little limp, but I thought that was normal. I dont notice fuel pouring out of the front of the carb. Not for sure what you mean by vent. Although I did notice sometimes after it has run for a little while that when I go to start it again the bulb needs pumped again. It is almost like sometimes the bulb stays fairly hard and other times it gets soft, but regardless it never runs right and the needle valve adjustment seems to make no difference at this point. Is that even possible for the primer bulb to stay hard sometimes and go soft other times?

 

[jbjennings]

Re: 1972 20hp johnson not running properly

There's a hole in the carb on the starboard side--that's the vent.
My brand new float and needle didn't work worth a flip. When I put the old needle in it seemed to be a little higher sticking out the seat and my float was able to be set nice and straight like it should be. I'd check it out and try it. I was having problems similar to yours and put one of my other carbs on it and it ran perfect. I think it may be POSSIBLE that your float needle may be incorrect, but I'm no expert. If I'm having trouble with one, sometimes I like to get mad and say "poot on it" for a few days and kind of relax a little. I usually figure it out after a little break from the stress. It does eat on me having to worry about it when I can't figure it out. But it eats on me more to be wondering what the bill will be when I take it to a mechanic.
One more thing you might try:
Get a meter and put it on ohms and check the resistance on the plug wires while the wife flexes them all the way down the wire. You may find a wire broken in the insulation. Moving the armature plate would flex it and it may seem to have good spark on one wire but after adjusting the throttle it may open the break. This is very rare but mine had that exact thing recently.
BTW, the bulb shouldn't be totally firm when it's running, but shouldn't be limp either.
Good luck,
JBJ

 

[jwilkey84]

Re: 1972 20hp johnson not running properly

I don't think i have the old needle and seat, but I can check. If I remember right, according to the carb rebuild chart, the float should normally hang down 1/4" when in a vertical resting position. Is that right. I guess I don't know how to tell if my float is adjusted correctly other than going by the measurement on the carb kit chart. If you could, please explain to me how to correctly adjust the float and what exactly that does to the fuel flow. Thanks!!

 

[jay_merrill]

Re: 1972 20hp johnson not running properly

The fact that the motor tries to keep running when you choke it suggests to me that it is either sucking air into the carb body somewhere or it isn't getting enough fuel at idle. Since you have tried the grease trick with no change, the problem probably isn't the throttle butterfly shaft/carb body problem.

The huffing sound as it dies suggests too little fuel. If opening the LS needle valve doesn't help, the problem is somewhere else in the carb. An improperly adjusted float valve could be the culprit but I think it is less likely than the possibility of still having some junk in the carb. When you rebuilt the carb, did you remove the core plug on the top of it? Unless the passage underneath, and the holes that spray fuel into the top of the carb, are completely clean, you would still have problems.

Hang in there, we will get this figured out and the good news is that you will learn a lot about this motor in the process of discovering what the problem is.

 

[G DANE]

Re: 1972 20hp johnson not running properly

In my experience, a poor ignition on that model will often act like carb problems. Looking at the spark in a plug, outside in the air only tells you it has spark. Do a spark check - place a nail in the spark plug boots once at a time, hold 5/16" from ground with an insulated plier, and let itturn with both plugs out. Will both jump the gap with a clear blue snap ?? If it doesnt. it can be from various reasons. bad condensers, bad points or bad set points, drive coil installed with too much clearance to flywheel, bad connections/ground, bad coils. Check that first. That motor will run fine with worn butterfly shaft and lots of other small problems, lots doo

 

[jwilkey84]

Re: 1972 20hp johnson not running properly

if a core plug is the round thing that resembles a dime that you pound in with a dowl, then yes I took those out of the carb and cleaned in there, even though it looked pretty clean to start with, and replaced them with the ones proviede in the kit.

 

[jwilkey84]

Re: 1972 20hp johnson not running properly

Update....I got the motor out tonight after work and took the carb off again. I looked everything over really well and found nothing. Well I was putting the old needle valve back in to try that, I noticed that the brass piece that the needle valve sits in had a slightly different sized hole in it than the new one. The old brass piece had a slightly bigger hole than the new one that came with the kit. I installed the old brass piece and the needle valve which sits in it and put it all back together. I started the motor and it ran pretty rough at first, would not idle. I kept it running by opening the throttle a little bit. Several times I would try to let it go back to idle, but it would just die. Well I played with the SS needle valve a little and the motor decided that it would run idle on its own, so since it would idle and I had two free hands I started to bend and wiggle the plug wires trying to see if that would make it miss or anything, but it did nothing. The motor continue to run on its own. I probably let it run for about 10 minutes continuously, and even put it in gear a couple of times and it didn't even die! I am excited but I don't want to get to confident. Do you think the small diffenence in the the hole size that lets gas into the carb made the difference? I don't know. You will remember that I had it running good in the barrel one other time after cleaning the points and later took it to the lake to be disappointed by a motor that would not run. So I guess I will take it to the lake and see how it does.

 

[jbjennings]

Re: 1972 20hp johnson not running properly

I wouldn't think the size of the hole would make a big difference on idle but the distance the needle sticks out of the seat I think would. I think that is a fixed jet carb, right? No adj. for the high speed? It will be interesting to see if it runs wide open good. If it's not running smooth, though, I'm skeptical. When you get one of those right, you usually know it's right. When you crank it up cold on choke, does it run plenty long enough for you to push in the choke and then it smooths out nice? If it won't, it's not fixed. Having your slow speed adjustment make a difference in idle is a really good sign, though. If it were me, I would spray a little carb cleaner around the intake manifold and carb base to check for leaks. It will smooth out if there's a leak. A handy trick taught to me on the forum is to take a little propane torch and open the gas valve and let propane flow out to the manifold and carb and such while it's running to see if it smooths out, indicating gasket leaks.
Holler back and tell us how she runs,
JBJ