Johnson 4R72S revive?

[Grem]

Hi everyone.

I bought a little 14' alu fishing boat yesterday which came with an untested 4R72S. I bought the boat primarily to row, but of course the o/b would give me much more flexibility. This is my first ever boat and consequently first ever o/b. I've had dozens of motorcycles over the years.

There is no manual included (the start procedure label is still attached to the engine) and I'm running on a tight budget of money, time, tools and space.
(I'm staying with my g/f in an apt in Birmingham AL for abt the next six weeks).

The engine turns over via the rope (slow return) but that's as far as I've got. My plan is to progress step by step but abandon the project if major work or expense looms.

There is no fuel tank, but I bought a connector plug at Wallymart yesterday. I won't bother spending another $45 on fuel lines and tank if she won't even rumble.

I've read most of the q+a for these motors and note that the pump impeller should be replaced if the motor has been standing for years, but again, I don't want to start on that if she appears to be dead.

I'm going to remove the plugs, check for sparks and run some fresh gasoil through the carb and bores. The I'm going to gravity feed the fuel via an old oil bottle attached to the fuel line.

So, can anyone walk me through a test run, starting from the point where I get a large bucket of water (how big?) to stand it in...?

Thanks in advance!

 

[JB]

Re: Johnson 4R72S revive?

Howdy, Grem.

Welcome to iboats.

You have one of the greatest little outboards ever made. It is worth bringing her back to life, but short cuts are a very bad idea.

First, do a compression check. If she gives you over 60psi in both cylinders and they are within 10% of each other she is basically healthy mechanically.

Go to the library and study a Service Manual for a 1973 Johnny 4. If they will allow it, check it out.

Then go to the Engine FAQs Forum and do "Awakening a sleeping outboard."

Let us know what you are finding. There are several here who would qualify to be called "The little Johnny whisperer". You can get her purring with our help.

Good luck.

 

[Vic.S]

Re: Johnson 4R72S revive?

You might like to start by reading the advice in "Awakening a sleeping outboard" in the Engine FAQs if you have not already done so.

 

[kjdunne]

Re: Johnson 4R72S revive?

Welcome to iboats, you'll find a lot of knowledge and helpful people here.

Go to the "Engine Frequently Asked Questions" section and find "awakening a sleeping outboard" post. It is pretty comprehensive for what you should do.

I'm not too sure I like the oil bottle fuel tank idea. You'll need to vent it for fuel flow, I guess you'll need to poke a hole in it. Ask around and maybe you can borrow a real fuel tank for your test.

I would use a regular trash can (30-35 Gal.) for the water. Make sure the water level covers the water intake by at least 6 inches.

If it fires up, or even if it dosen't, do a compression check. AutoZone and some other parts stores will rent a compression gauge for only a deposit or very little rental fee. This test is one of the most important factors to determine whether the engine is worth your time and effort.

Let us know how you make out.

 

[Grem]

Re: Johnson 4R72S revive?

^^^^^

Thanks for the welcome!

The project is frustrating for the constraints I mentioned and accordingly if the prospect is a large expense of time and money I will have to pass.

I'm going back to the UK in abt 6 weeks where I have more tools than Sears. Here I have a strip of sockets, a pair of pliers and a screwdriver!

It would however be nice to get some use from the motor even if it's not performing to its full potential.

If I can't find a manual in the local library, could someone advise me how to locate the pump impeller?

I was intending to attempt a short run and if successful, change the pump internals and buy a fuel tank and lines. Then when I come back in March, perform a more thorough service.

Incidentally, how does one decide what angle to run the motor at on the transom? It has an adjustable bracket.

 

[Grem]

Re: Johnson 4R72S revive?

Well I had a look under the cover this morning.

Everything is pretty clean. The fuel pump and lines look new, as do the plugs. I removed them and determined that I have fat sparks and compression. I'm wondering if indeed the water pump impeller has been changed too. How do I access it and what am I looking for?

The rope start returns very slowly. Is this common and is there a non-replace fix?

Incidentally, is the groove around the flywheel designed to accept a rope for emergency starts?

 

[Vic.S]

Re: Johnson 4R72S revive?

To access the pump you have to drop the gearcase off the leg as it is mounted on the top of it.

If you go to the BRP Parts website enter the details for your engine viz Johnson, 1972, 4 hp, and then choose your model number you will be able to access exploded diagrams.
No substitute for a manual but will show you the pump etc in the gearcase diagram and give you some idea what is involved.
AFAIK there is not a telltale on that engine. If you go to the trouble of inspecting the pump impeller it is false economy to refit the old one IMHO.

The problem with the rope start mechanism may just be that its got a bit stiff and needs cleaning up or maybe the rope has been replaced and the spring not properly pretensioned. If you start dismantling it take care not to let the spring escape. Its like a caged tiger waiting for someone to open the cage door.

It does look as though there is provision to wind an emergency rope onto the flywheel.

 

[Grem]

Re: Johnson 4R72S revive?

^^^^^

Thanks for that!

If I take out the impeller, what would suggest that it's worn?

Would it be good or bad to apply some WD40 to the rope start mechanism? It kind of has that 'gummy' look and feel.

 

[Grem]

Re: Johnson 4R72S revive?

Can someone also tell me the difference between 'weedless' and 'standard' motors?

 

[Rick.]

Re: Johnson 4R72S revive?

The standard prop is mounted 90 degrees to the leg where the weedless is more like 110 degrees. Check out the brp site mentioned above and you will be able to tell which one you have. Rick.

 

[Grem]

Re: Johnson 4R72S revive?

^^
Rick- Seems she is standard.

Well had a chance to run her up this morning.

After a few pulls she began to run, but seemed reluctant off choke then stalled. I checked for fuel flow, open the choke up a bit and after a few more pulls she started to run quite well and I slowly got her off choke. The bad news is that after she ran quite well for about a minute, she stalled and the flywheel felt tight, suggesting a partial seizure. I let her cool down, disconnected the fuel and gave her a few more pulls. She seems free enough again and if anything I think the compression has improved (unstuck rings?) The good news is that the rope start has freed up and returns perfectly now.

So now I know she will run, I guess I will go ahead and order a water pump kit. Where is the best/cheapest place to get those spares? Do the kits come with instructions?

 

[Rick.]

Re: Johnson 4R72S revive?

Glad to hear it ran but the piston stiffness is concerning.

You really must get a repair manual for your specific motor. I always get them via Ebay and they are quite commonly for sale. If you can't find a johnson an evinrude for the same year/model will work. The impeller won't come with instructions but it is strait forward enough once you unbolt the gear case. A manual would walk you through it. Your rewind is probably in need of a good cleaning but it would be best left until you have a manual. I cleaned one before I had a manual and it was horrible and to be honest I'm not sure I put it back together properly but I know it is still working. Your nearest dealer should have that impeller in stock. Your need to do a compression check and I would suggest sooner than later. Best of luck. Rick.

 

[Grem]

Re: Johnson 4R72S revive?

^^^

Thanks for the advice. Now I know it runs I will go ahead and spend some money on a manual, fuel tank/lines and the pump repair. The BRP catalogue lists both an impeller kit and a pump kit and I'm not sure what I should order.

The partial seizure was a bit of a blow but with no 'tell tale' I assume there is no way to know if the pump is functioning? My first motorbike at 16 was a little 50cc 2-stroke single which seized solid on a regular basis when I ran it flat out (as you do) and that always ran fine again once it cooled down, so fingers crossed!

 

[Grem]

Re: Johnson 4R72S revive?

Should I order the pump kit or the impeller kit?

 

[Xcusme]

Re: Johnson 4R72S revive?

The condition of the water pump you have now dictates if you'll need just the impeller or the whole kit. If the wear plate and pump cup are worn or badly grooved, the whole pump is needed.

Remove lower unit bolts and it should drop down to expose the pump. Replace the pump assembly as needed. When you reinstall the lower unit, grease the drive shaft splines and be sure water tube is inserted into the pumps rubber grommet. Be sure to run motor with water in barrel high enough to cover the pump assembly and then some. A water spray will shoot from the small holes in the midsection while running. That spray IS your tell tale that the pump is working.

 

[Grem]

Re: Johnson 4R72S revive?

^^^^^

Ah great - thanks for the headsup!

Is it best to have the motor mounted on the boat to drop the lower unit, or lay it on its side?

 

[Xcusme]

Re: Johnson 4R72S revive?

I find it easier to mount the motor on a motor stand and tilt the motor on it's transom bracket to a 45 degree angle. Mounted on the boat (out of the water) is just as good. Either way, having the motor mounted in a stable way should make dropping the lower unit (and re-assembly) a breeze.

Make sure to grease the drive shaft splines and fit an 0-ring in the groove below the splines (if groove exists) to keep water out of the spline/crank junction to prevent rust.

 

[Grem]

Re: Johnson 4R72S revive?

I went down to NO for a while, so Monday was the first chance I had to work on the engine. When I removed the lower unit I was dismayed to see that the pump housing was held in place with two slotted machine screws. Needless to say they were corroded and difficult to access with the shaft hitting my knuckles and the lower unit wobbling around. Are these screws standard? Why on Earth would they not use hex-heads or Allen screws?
Sure enough, the impeller was toast. The blades were perfect and supple, but the centre section was mashed allowing the shaft to spin free.
At the local dealer, the impeller was in stock but the housing screws and oil seal were not and although those three little parts totalled to nearly $20 with tax, they wouldn't place orders for less than $50. I was running out of opportunities to get this done and get out on the lake so I had a rummage at Lowes. I found a pack of screws for 87 cents and some mixed O-rings for $2.xx. Everything went together really easily and 20 minutes later I was testing in a trash can. She fired up and issued a stream of warm water such as which any octogenarian would be proud.
The motor was subborn to run smoothly off choke, but by the time my dish-wash bottle of fuel (courtesy of the weed trimmer) was gone and I'd fiddled with the jet screws it seemed good enough for a lake trial. I picked up a nice 3 gal tank and fuel line at Academy for abt $40 and hit the lake today.
Man, was I impressed! With fresh gas, she started after about 6 pulls and was soon running perfectly off choke. I ran at various speeds for about 40 mins then shut off. I tested a hot start - one pull. Then I rowed and fished for an hour or more and she started from 'cold' in two pulls. Thereafter she ran faultlessly at all speeds and started when required with one pull. I used less than 2 gals of fuel all day.
I'm a very happy boater and going back to the lake tomorrow.
A big thanks to all of you guys who were kind enough to help getting me started.

 

[Grem]

Re: Johnson 4R72S revive?

Thar she blows:

http://www.youtube.com/user/Slurrricane