1989 Johnson 40 hp 2 stroke idle problems

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
OldKenT
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1989 Johnson 40 hp 2 stroke idle problems

Postby OldKenT » Thu Jun 09, 2016 6:34 pm

I have a 1989 Johnson 40 hp VRO which will idle indefinitely when on muffs in my yard, but stalls between 5 and 20 seconds after I start it at the dock at a lake. It stalls whether the fast idle lever on the remote control is set in the run position (as you do before shifting into gear), or advanced to higher RPMs (as you do when starting a cold motor). After reading the postings in the old forum, I have increased the idle RPMs by adjusting the idle screw on the linkage to about as high as I can make it with the expectation that the back pressure from being in the water can cause stalling when it is in the run position, although I don't know why this would matter because it already is stalling even when I have the fast idle lever advanced to an even higher level of RPMs.

Does anyone know the cause of this problem? Can back pressure affect fuel supply or combustion? The mechanic confirmed to me last fall and again this spring that compression is ok.

Here are some background facts (I don’t know whether they matter): From last August until November when it was winterized, the motor sometimes had problems starting. It turned out that the VRO pump failed, and he confirmed that this year when he did the spring tune up.
I have all of the original Johnson service manuals for this motor, so I did the work myself - replacing the VRO pump and the pulse limiter. After this, the motor started without a problem, and I ran it on muffs for at least 2-3 hours – first on premixed fuel to be sure that oil was feeding from the oil tank to the new pump, and then on high test gasoline to help clean the carburetors of any excess oil. When I then saw that the carburetor gaskets were looking like they were leaking, I installed new carburetor kits (float, needle, O-rings, gaskets, etc.), and a new inline fuel filter. The only other work I did after that was to replace the primer solenoid. All new parts are BRP OEM parts. The gasoline tank and all fuel lines and fittings are less than 2 years old. I treat all gasoline with Stabil and K100. The carburetors have had Sea Foam injected while running on muffs. I have not replaced the separate 10 micron fuel filter since the VRO pump replacement as that was replaced in March. Thanks for your help.

Oldslowandugly
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby Oldslowandugly » Thu Jun 09, 2016 7:57 pm

That's a real head scratcher. Firstly, there is an idle bypass port on the rear of the motor, right below the engine cover, on the midsection. It's purpose is to allow the exhaust gas an escape because, as you surmised, the underwater pressure will stifle the exhaust. Once the motor is running fast enough the exhaust goes out the through-the-prop exhaust. When you ran the motor, was exhaust and cooling water coming out of the bypass? Secondly, that motor uses a fixed idle jet in the carburetors so verify that the jets are clean. I know you had the carbs apart, but did you shoot carb cleaner through the low and high speed jets? Thirdly, did you test for a good strong spark? A motor on muffs has no load at all and will run with little effort. But even a small load like being in a barrel or on a lake may cause a weak spark to fail. Instead of using muffs, try using a large plastic barrel to run the motor in. That would duplicate the condition at the lake. Just some ideas to think about.

OldKenT
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby OldKenT » Thu Jun 09, 2016 8:42 pm

Hi Oldslowandugly, Yes, there is water and exhaust coming from that rear port - far more at the lake than on the muffs to be sure. When servicing the carbs, I removed and cleaned all parts and used air pressure to be sure all passages were clear, so I do think I have that covered, but I may do it again if there is no other solution because it does seem like a fuel supply problem. The carbs had also been cleaned by the mechanic I used, and when I disassembled them I found nothing to indicate blockage. Both spark plug wires have good strong spark - that was my first test.
There is an intermediate air bleed orifice at the top back of each carb. Do you know what that does? When the air silencer cover is removed, there is an opening in the silencer itself through which access can be made to that air bleed orifice. I don't know why that would be there unless access might be needed without removing the silencer. Has anyone here ever had a problem with that?

Oldslowandugly
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby Oldslowandugly » Thu Jun 09, 2016 10:07 pm

That does just what it says- it is an air bleed and needs to be clean- nothing more. I looked at your motor online and in my book and I see that both our motors have a slow speed needle that is factory adjusted. It will either be flush with the carb body or sticking out of an adapter. I forget about it because you are not supposed to mess with it. When you disturb the carb the procedure is to make a mark on the carb housing as a reference. Count the turns as you slowly turn the screw in until it lightly seats, then write down the number so it can be returned to that setting. If you did not do that, then the book says to screw it in until it seats lightly, then unscrew it two full turns for initial setting on a 40hp. Start motor and let it get warm idling in gear. If it is lean, it will sneeze and backfire. If it is rich it will run rough and unsteady. Only make adjustments to the screw in 1/12 increments and allow 15 seconds for the motor to stabilize each time. Continue until you reach the highest consistent rpm. When satisfied, run at high rpm and return to idle in gear to see if the idle stays smooth. If not, repeat the adjustment. Hope this helps.

OldKenT
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby OldKenT » Fri Jun 10, 2016 5:08 am

The O-ring on the slow speed needle is replaced and the needle cleaned when the carburetor is rebuilt, so the needle adjustment has to be done again after that. I followed those instructions, Oldslowandugly, and mIne now idles best (on muffs) at 3 turns open. It stalls if set at 2 turns to 2-1/2 turns, and runs too rich at 4 turns. Thanks for the guidance on this problem.
It seems like this problem would have to be related to the back pressure. Can the back pressure of the water on the exhaust at the prop limit the fuel intake from the carburetors to the cylinders?
Also, the pulse limiter is new, installed as part of the new VRO kit. That plays a role, I think, in how quickly the VRO pump cycles and delivers fuel to the carburetors. And I think it runs off the compression in the crankcase. Does that make sense to anyone?

Oldslowandugly
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby Oldslowandugly » Fri Jun 10, 2016 8:43 am

OldKenT it looks like you covered just about everything. Like I said, a real headscratcher. I know nothing about VRO as I have a 48SPL and I mix my oil in the gas tank. What I do know is that a lot of guys get disgusted with it and remove it entirely. The exhaust back pressure really doesn't affect the incoming air/fuel mix unless it is blocked so badly it stifles the motor. Think potato jammed in an exhaust pipe. But you said the bypass is working and that is plenty of relief. I looked at the troubleshooting chart and there are about 3 dozen fuel related problems, most of which you have addressed. What caught my eye was "plugged pulse limiter fitting" , "damaged VRO unit" , and "fuel leaking through primer solenoid". I had a bad primer solenoid once and it would work/fail whenever it felt like it. Try disconnecting and plugging the primer feed hose, and choke the carb manually, just to eliminate that. Also check the little red flip switch on the solenoid. It may have been left in the manual feed position by accident.

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dg22
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby dg22 » Fri Jun 10, 2016 11:28 am

Even though your mechanic said the compression is fine, I would double check the compression. My guess would be low compression, possibly caused by a worn head gasket. 20 years ago, I had a snowmobile that would run but it would constantly stall and lose power and the problem would get worse as it warmed up. The problem turned out to be a worn cylinder head gasket. Best of luck.

OldKenT
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby OldKenT » Fri Jun 10, 2016 1:31 pm

dg22, that makes sense and I will do that with a different mechanic to see what he says. My usual mechanic is quite skilled on Johnson / Evinrude products, and in business for many years, but he is not a dealer. So I will go to a dealer to see what he says.

Seahorse
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby Seahorse » Fri Jun 10, 2016 2:44 pm

That 2 cylinder design would often scuff the bottom piston, especially if run with a stuck open thermostat or without one. Compression readings may test OK but the scuffed piston could be discovered by performing a leakdown test.

Two other items that affect the low speed operation when everything else looks good are a sheared flywheel key where the flywheel has barely moved, or a spun inner timing magnet on the flywheel.

OldKenT
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby OldKenT » Fri Jun 10, 2016 6:01 pm

Hi Seahorse, I haven't heard of a spun inner timing magnet and can't find a reference to it in my service manual. What is that?

OldKenT
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Re: 1989 Johnson 40 hp 2 stroke idle problems - the answer

Postby OldKenT » Fri Jun 17, 2016 6:02 pm

The answer or solution is that I failed properly to clean all orifices in the carburetors on my first rebuild. The lesson is that EVERY opening and passage needs to be cleaned thoroughly.

After several efforts at adjusting the idle screw and the slow speed needle on the carburetor, none of which solved the problem, I decided to remove the carburetors again and to clean every orifice again. The cause of the problem was with the intake tube on the lower carburetor, which had been blocked, at least in part, by the excess oil thrown by the old VRO pump. I ran a thin wire through the intake tube and the high speed orifice, and that solved the problem.

I was able to set the idle screw on the carburetors at 2-1/4 turns open, as recommended by the service manual, and to return the idle screw on the linkage to its original setting! Thanks to all who offered advice, and to Jim for this amazing web site.

Oldslowandugly
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby Oldslowandugly » Sun Jun 19, 2016 5:54 am

Sometimes it's the simplest thing. I'm glad you figured it out.

JRDIII
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby JRDIII » Fri Jul 08, 2016 11:03 pm

I'm also glad you were able to figure out the cause, as idling problems are often hard to pin down.

I have a 1990 Johnson 40-HP on my 13-footer that I bought about four years ago with the original VRO still in place. Right after I brought the boat home I began having very similar idle problems. [The engine] would idle fine on muffs, but not in the water.

I rebuilt and thoroughly cleaned the carburetors, and that did the trick. But, then about six months later, I began having the same problem again.

I removed the carbureotrss and found that the same jets I had cleaned six months earlier were now clogged again. In the meantime, I had been reading a lot about this motor on-line and about various user experiences with the VRO. There are many who advocate that the motor is designed to run with a VRO and that is the way it should be. But there are just as many, if not more, who advocate that the VRO eventually is going to cause a problem--perhaps a very serious problem--and keeping it just isn't worth the risk and trouble.

While cleaning the carburetors for the second time in six months, I crossed over to the latter camp, and I've been happy ever since. I have to say the biggest relief is simply the peace of mind knowing that since I've been mixing my own fuel and oil my engine is being properly lubricated.

When the VRO was hooked up there was always a subtle but uncomfortable doubt in the back of mind: what if?

What if this thing decides to quit when I'm running open throttle across a big lake or out in the ocean?

What if my 22-year-old VRO has been sending a poor ratio of oil to the engine over the last few years and without even knowing it my compression has been destroyed?

I had no interest in finding out the answers to those questions, but at the very least I was pretty convinced the VRO was the source of my carburetor problem, so I tossed the VRO and haven't looked back.

I consider mixing my own fuel and oil a pretty minor inconvenience, but another huge benefit of ditching the VRO is reclaiming the extra space [the external oil reservoir tank] takes up in the back of the boat, not the mention the aesthetic improvement that comes with removing a smelly, sticky oil case with unsightly wires and lines attached.

I keep a gallon of oil and a measuring cup in my boat box, and every time I fill up the boat's fuel tank I do a quick calculation and add just the right amount of oil (plus Seafoam). It takes five minutes, but provides complete peace of mind. Oh, and I haven't had to clean my carburetors since that last time, more than three years ago. The engine has been running like a top--knock on wood--ever since.

By all means, do what works best for you and if you love the VRO and the minimal convenience it provides stick with it. But if you keep having carburetor trouble, I would encourage you to go the same route I did. I don't think you will regret it.

jimh
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby jimh » Sat Jul 09, 2016 12:52 am

My 1992 Evinrude 225-HP V6 had six carburetors. It had its original OMS pump, which worked fine. I never had any problems with carburetor passages or jets clogging. The convenience of the OMS or Oil Mixing System pump was a great asset for my boat operation. With a 77-gallon fuel tank, and adding fuel in increments of more than 30-gallons at a time, going to pre-mixed fuel would have been a big drawback.

Engines that run off 6-gallon fuel tanks are easy to use with pre-mixed fuel, but not engines that run off tanks with more than ten times that capacity. Pre-mixing is a big pain with fuel volumes like that. OMS is a good system and works just fine. Removing a working OMS system fuel pump would be a mistake.

OldKenT
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby OldKenT » Sat Jul 09, 2016 6:43 am

JRDIII, the parts needed for the VRO Johnson outboards are readily available and easily installed, so if you ever want to go back to the VRO pump it is very easy to do. I was simply not thorough enough in cleaning the carburetors after installing the new VRO pump. Now, this 27 year old outboard hums.

JRDIII
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Re: 1989 Johnson 40 hp 2 stroke idle problems

Postby JRDIII » Sat Jul 09, 2016 9:00 pm

Good point. Mixing in larger volumes would definitely be a hassle. I have a 9-gallon tank so it's not a big deal, and since the OP mentioned his motor is a 40 hp I assume he has a pretty small tank as well. If that is the case, I definitely recommend that he ditch the VRO, and I speak from the experience of having done it both ways. Glad it's worked for you, though.