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1988 Johnson 20HP idle head scratcher

E

emilkob

Member
I have a 1988 Johnson 20HP (J20ECCA), which has the electric primer. Rebuilt the carb over the winter. This spring it is idling well. However, I noticed that turning the low idle adjust screw has no effect on the idle. I read some threads on models in this year range and realize that I mistakenly put the plastic needle bearing seat in (was included in the rebuild kit. I took the plastic seat out, put the needle screw back in and till find that the screw has no effect ( and engine is idling well!!) I can understand that there could be some type of obstruction of the perfect configuration that is metering the gas when the screw is turned out, but how the heck can the engine remain in perfect idle when the screw is turned ll the way in? Could my primer system be leaking into the cylinders at the perfect rate?
 
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As you've discovered, the 1988 20hp model does not use that very small white plastic bushing/bearing on the slow speed adjustable needle valve.

Indeed, that engine should come to a halt with that needle valve turned all the way in.

Did you forget to install the small round gasket on the brass center high speed nozzle of the upper body?
 
Thanks for the response Joe. I went out and fooled with the engine again. It will eventually sputter and die out if I turn the idle adjust screw all the way in. However, once I turn it out 1/4 turn (or much more) the engine will idle around 800RPM and smooth. Turning the screw once it is 1/4 turn out has no effect on the RPM's. I did not dismount the carb and check for the gasket which you have pointed out.

It currently idles and runs "very well", and my inclination is to leave it alone for the season, and take the carb off and apart and clean and re-assemble over the winter.

I feel fortunate that it is idling well (no matter what I do) versus idles rough (no matter what I do). I am wondering if I am pushing my luck every time I go out this summer?
 
The final adjustment on idle should be on the water and in gear,when lower unit is submerged there is back pressure involved
 
Good point are you running it in a barrel of water at least 5 inches above the cavitation plate in forward gear? As long as it is getting plenty of fuel you always want to run slow needle a tad rich. The final adjustment on the water is go from slow to WOT quickly if it hesitates add 1/8 turn rich and try again. Once you get a nice clean hole shot then adjust idle speed at around 600-650rpm in forward gear. Running rich helps with cold starts as well. Keep a close eye on the spark plugs the first few times out you want the center insulation a nice toasty brown. Also did you check/adjust engine sync between throttle opening and spark advance? Easy adjustment you check every time you rebuild the carb.
D-4 line the follower roller center of the two marks on the throttle cam it is at that point the throttle butterfly begins to open as you advance the timing. Loosen the clamp screw on the shaft on the carb to make the adjustment. To get it exact put a alligator clip with a straight wire on the throttle shaft on the carb that will tell you exactly whe the carb begins to open.
 
(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.
 
Guys, thanks for the info and apologize for the delayed response. Just getting back to the boat. Took the carb apart and cleaned. Yes the circular gasket on the high speed nozzle is in place.

I understand the initial setting of the S/S needle, and how to perform the linknsync.

How should I initially set (and adjust) the thumb wheel on the throttle linkage, and also the small nylon idle stop screw?

Also, I have clear tubing from the electric primer to the two injection points. When running the engine, I can see some flow of gas (not a full flow, but a slow movement of bubbles) out of the primer and into the injection points. Is this normal? I assume there is some level of vacuum from the cylinders pulling on the primer lines, is it okay that there is this small level of gas escaping from the primer?
 
Testing is what you do.------Pinch off the fuel supply to the primer and test run the motor.-------Any change in behaviour ?
 
If your asking the way to adjust the throttle cable disconnect the cable and make all the slow speed adjustments then adjust the cable to fit at idle speed.
 
Thanks Kim. i won't get on the water until late this week. will report back then. I have read that this engine should max out at 5000 rpm at WOT. If it is over/under is there an adjustment for that? What does the spark adjust screw (item# 17 on the Cylinder/Crankcase drawing, which goes through the starter bracket) do / how do you set the adjustment?
 
#17 is max spark advance and should be good if you have not messed with it. The way to adjust WOT rpm is by changing the pitch on the prop. Let us know how the sea trials go.
 
Okay, played some hooky today and got out on the water this morning. It's idling smoothly at 680PRM in gear. Is that too low? WOT is at 5100 RPM which is slightly above spec, but it was only me on the boat. Strange thing is that turning the S/S idle mixture screw continues to have no apparent impact on RPM's until a point when it stalls. I have it set, turned out from seat 1-1/4 turns. Further turning of the screw (CW or CCW) seems to have no impact. It starts, idles and runs great. No hesitation going from idle to full throttle. I am just concerned that it could be idling lean or rich and I don't know it. I ran forward idle for a good 20 minutes. The engine stayed smooth. If it was running lean, wouldn't it overheat? My over-temp horn isn't working, but that is another issue.
 
This " lean running " thing is something that has to do with full throttle / full load.-----No damage can occur at idle speeds if impeller / cooling system are in good condition.
 
So how do I know if it is running lean or rich at full throttle (there is no high speed mix adjustment, just the synchnlink). Whats the use of the S/S screw if it doesn't do anything. I set the idle speed via the idle stop screw, the S/S mix screw seems to have no effect.
 
emilkob said:
So how do I know if it is running lean or rich at full throttle (there is no high speed mix adjustment, just the synchnlink). Whats the use of the S/S screw if it doesn't do anything. I set the idle speed via the idle stop screw, the S/S mix screw seems to have no effect.
Click to expand...

You're going to need to remove and dismantle the carburetor again... If there is no response when adjusting that slow speed adjustable needle valve... either the small hole that the needle valve sits in is clogged... OR... the small brass tube that sits off center within the larger vertical brass high speed "nozzle" is clogged, gummed, fouled. Either of which would result in NO fuel flowing through the slow speed passages.

It's also possible that someone has tightly screwed that slow speed needle valve in so tight that the tip broke off and is jammed in that hole (it happens).
 
Joe, thanks for hanging in there with me...... When I cleaned the carb last week, I removed the welch plugs and the lead shot so I could be sure that all passages were clear. I put a long needle through all passages and shot carb cleaner to be sure that they were unobstructed.

Is it possible that the electric primer is leaking some fuel during idle? It's the only thing I can think of. As I mentioned in an earlier post, there are some bubbles which flow towards the injection ports (at least the one on the top of the carb), but not a steady flow of fuel while idling.
 
You mention "Is it possible that the electric primer is leaking some fuel during idle?"... after which you said that you see some bubbles flowing towards the injection ports. Injection ports I assume are the primer fittings on the carburetors in back of the throttle butterflies... OR... the primer fittings on the intake manifold.

Those fuel primer hoses are supposed to be small diameter solid black rubber hoses... I assume you're using clear plastic hose? Regardless, to test to see id the primer is leaking, simply remove a hose from the intake manifold or wherever it's attached to to see if fuel is flowing out of it. Remember that the RED lever must be turned so that it is pointing at the other end of that primer solenoid.
 
I went out today to video the engine idling. It was idling around 700RPM, with water fed through clean out muffs as I was in the driveway.
As the video shows, at idle, there is flow through the primer tube. The S/S needle is turned out from seat around 1-1/2 turns.

Turning the S/S has no effect on RPM. Is the engine idling off the flow from the primer tube? I took the primer apart and put back together. All looked good, and the primer feeds gas when powered. I imagine that the primer plunger, gasket or plunger spring is bad? One more note, while idling I pulled the tube off the top of the carb and it keep idling smoothly. Getting more confused, but happy that the engine has decided to find a smooth idle on its own......

https://youtu.be/8dt31h4IYn0
 
Yeah, apparently the primer solenoid is leaking and feeding fuel through that small line to the eintake manifold... proven by taking the line off, as you state, and having the idle smooth out.

Why the solenoid is leaking?.... Either something internally which you will descover or that RED lever isn't where it belongs.
 
Here are my latest tests, recorded on video:

(Idle 1): with primer lines disconnected, there is no gas being pushed through the primer (red primer switch not in manual mode) Primer line to top of carb clears, engine stays running smooth. If I close off the open line that connects to the primer with my finger, vacuum from top of carb starts pulling gas from the line that inserts below the carb into the intake. Is this normal?

Idle 1 https://youtu.be/gD0yW91UOw8

(Idle 2): With both primer lines disconnected (one that inserts behind the gas pump, and one that goes to a T which then goes to the top of the carb and under the carb into the intake) the engine continues to idle smooth . Turning the S/S needle has no effect until the carb starves. What range of RPM's should I expect? There is maybe a 30-50 RPM increase when I turn the S/S needle in from 1-1/2 turns. Is that all I am looking for? Turning out from 1-1/2 seems to have no effect at all.

Idle 2 https://youtu.be/isyKcXdj38E

Maybe I've been looking for more sensitivity in the S/S needle than I should be expecting? Also, I have read on some posts where folks need to turn the S/S needle out three or four turns to get a smooth idle. I have not tried that far out, but will next time I get to the boat. Interested in opinions whether my current idle is considered smooth or rough? I thought smooth, but I clearly don't know what I am doing.....
 
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You state: (Idle 1): with primer lines disconnected, there is no gas being pushed through the primer (red primer switch not in manual mode) Primer line to top of carb clears, engine stays running smooth. If I close off the open line that connects to the primer with my finger, vacuum from top of carb starts pulling gas from the line that inserts below the carb into the intake. Is this normal?

NO, this is not normal and it makes no sense at all! Something on that engine is screwed up proper and without being there, I have no idea what it is and can think of nothing new other than to advise installing the proper fuel lines.

Fuel is being fed to that engine via some other route besides the carburetor. Check the fuel pump diaphragm as follows.

********************
(Fuel Pump Diaphragm Test)
(Two Hose Type Only)
(J. Reeves)

Note: This pertains only to the regular Two Hose type fuel pumps.

Leave the hoses attached to the fuel pump. Remove only the two screws that attach the fuel pump to the powerhead. Re-insert those two screws and install a nut to each of them so that the fuel pump is securely clamped together. With the fuel line attached to the engine, pump the primer bulb while observing the pressure/vacuum operating hole on the back side of the fuel pump. Should any fuel leak out that hole, the diaphragm is faulty.

If the diaphragm is faulty, the fuel pump will require rebuilding or replacing. Note that repair kits are not available for all fuel pumps, in which case replacing the pump would be necessary.
 
Did you take the lines off at the manifold and carb and plug the ports to each or take the "T" apart and plug lines.?You would not get any gas recirculating like what seems to be occurring and see how it runs.With the needle open far it would seem like you would be flooding at idle or running very rich.Once the needle is backed way out from the seat I would think it is a non factor at that point and going out further would do no good.If the engine idles good at a very rich level would this be compensating for air leaking in somewhere or another problem?
 
Thanks Joe, newyota, I will be away from the boat for a long weekend. I'll get back to you once I am back next week and can try your recommendations.
 
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