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'72 Johnson 4hp Runs for 5min then dies.

T

Tpotter1100

New member
Hello everyone,
I am a novice to the boating world and have just purchased my first lil Jon boat. Along with it came this sweet lil 1972 Johnson 4hp with the weedless drive. The only history i have is that it ran about a year and a half ago, and it leaks a little on the fuel pump cap.

So...Here is what i have done so far.....

I purchased new plugs, new impeller, carb kit, fuel pump kit/cap/filter, installed new gear oil.
At the moment, using the owners gas tank and primer bulb.

Installed new impeller. (the impeller seemed slightly larger than the cover, meaning that i had to turn the shaft Clockwise while installing the cover to bend the tabs enough on the impeller to allow the cover to go on) Is that normal??

New plugs, new gear oil (installed from bottom port).

Removed Carburetor and all components found that the jets were severely clogged, and cleaned with carb cleaner really good. (i unfortunately do not have a compressor) I installed new bowl gasket, float, needle, and gasket over middle jet. I also installed 2 small gaskets inside each chamber for the high and low lean/rich ports. Is this correct?? the parts diagram seemed to show 2-3 gaskets stacked inside?? but when i cleaned it out, it only looked like two were inside but however they were all crumbling apart when removed.
I set the low speed adjustment 1 1/2 turns out, and high about 1 turn out.

**One thing i am now seeing after further research was that i failed to do was remove the little plug that is on the bowl cover**
But i believe this is for low speed circuit in carb??

I have removed the fuel pump, and found a tutorial on how to rebuild it. after rebuild verified that the check valve inside was working properly by blowing through the inlet, and not able to blow through the outlet. Now i have no leaks when the bulb is pressurized, yay!

I have now taken the boat to my nearest lake and tried a test run. Prime the bulb (tank does not require a vent to be released), pull the choke, Set to start, and give a couple yanks and it starts!! i push the choke in and she sounds nice and smooth. I start to give it more throttle and she sounds Great!! a adjust the mixture on the high side a little to lean and she sounds even better!! As i got about 200 yards away from the dock i hear the tone of the motor start to change and then she just died......

i pull the cover off to find it smoking, and HOT! i tried to crank and it felt like it almost locked itself up. took a hard pull (not yank) to get the flywheel to turn. once i freed it up i yanked on it, but nothing.

After about 30 minutes of letting it cool down, it started and did the same thing.

Any thoughts? or ideas??

Thanks,

Ty
 
When running, that engine should be emitting a water spray out those small holes you see halfway down the long exhaust housing. The engine is obviously overheating to a point whereas it is seizing up!

Did you have the copper water tube perfectly aligned with the water tube so it the tube did not hit the edge of the rubber grommet and fold it over to create a shut off flipper?

At any rate, drop the lower unit again and dismantle the water pump as something is wrong in that area. The pin missed the impeller slot, something!

HINT... Have the impeller housing upside-down in your left hand... the impeller in your right hand... spin the impeller into the housing in a "Counter Clockwise" motion. Now, either slide the housing and impeller assembly down the driveshaft OR slide the driveshaft into the housing and impeller assembly, whichever if feasible (some driveshafts have a pin through the top portion)... making absolutely sure that the pin engaged the impeller slot.
 
Roger that! will do. I was afraid of that! didn't know if there was any 'pee holes' located on this motor. so i should definetly see water coming out of the 6 or 8 holes in the middle of the drive shaft casing?? i mistakenly thought they were exhaust holes. or am i not in the right spot?

Man i'm really hoping i haven't damaged the cylinders as i have tested this with same results about 4-5 times:( but each time i have let it cool down for a good 30-hour+

I will update the thread as soon as i can tear it apart and investigate.

Thanks in advance for the help!
 
Tpotter1100 said:
Roger that! will do. I was afraid of that! didn't know if there was any 'pee holes' located on this motor. so i should definetly see water coming out of the 6 or 8 holes in the middle of the drive shaft casing?? i mistakenly thought they were exhaust holes. or am i not in the right spot?

Man i'm really hoping i haven't damaged the cylinders as i have tested this with same results about 4-5 times:( but each time i have let it cool down for a good 30-hour+ . I will update the thread as soon as i can tear it apart and investigate. Thanks in advance for the help!
Click to expand...

Those 6 or 8 holes (whatever) actually do let some exhaust escape BUT the majority of it is blown out at the propeller area. It is the exhaust pressure that causes the water spray to be blown out those small holes.

Running the engine to a point whereas the aluminum pistons are seized to the steel cylinder walls is not a really good thing to do BUT some boaters get lucky... hopefully you are one of them.

Be sure to tighten all the bolts, nuts, screws on the powerhead as the heat will have loosened them... especially the head bolts.

Once the overheat problem is solved, we'll see if there'a any resultant damage.

Here's the carburetor adjustment setup for when you get ready for your next test run.

******************
(Carburetor Adjustments - Two Adjustable N/Vs)
(J. Reeves)

Initial settings are: Bottom high speed = seat gently, then open 1 turn out. Top slow speed = seat gently, then open 1-1/2 turns.

Setting the high and low needle valves properly:

NOTE: For engines that DO NOT have a shift selection, obviously there is no NEUTRAL position. Simply lower the rpms to the lowest setting to obtain the low speed needle valve adjustment.

(High Speed) Start engine (it will run pretty rough), shift into forward gear, take up to full throttle. In segments of 1/8 turn, waiting for the engine to respond between turns, start turning in the bottom high speed needle valve. You'll reach a point whereas the engine will either start to die out or spit back (sounds like a mild backfire). At that point, back out the needle valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest setting.

(Low Speed) Slow the engine down to where it just stays running. Shift into neutral. Again in segments of 1/8 turns, start to turn the top 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. Again, 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 adjustments, 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.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
********************
 
I'm guessing that the copper tube is either not seated properly or pinching the grommet, as described. OR, i just didn't install the impeller correctly. I will open it up this afternoon when i get off work for sure. i'll try to post pics as well of what i'm doing to further help.

Thanks.
 
Best to do a compression test now.---------Doing this 5 times may have done damage.----Gas and oil is mixed at 50:1 on this motor.
 
already ahead of ya! went to harbor freight and picked up a compression test kit, if i can make it through traffic should be home in about an hour!
 
So i'm pretty sure i found the issue, when i removed the lower unit from the motor, i immediately saw that the copper tube was not in the rubber grommet. total mistake on my part..:( So now i am running a compression test to see how bad i've torched this lil motor........

Top cylinder 1 = approx 20lb. psi

bottom cylinder 2 = approx 30lb psi

i'm no mechanic, but that doesn't seem good AT ALL!!! :(

Should i even try to start this thing and see if the water pump works?
 
Update:
I removed the impeller and inspected. no damage that i could see. I used the method as described on inserting the impeller into the housing 'counter-clockwise'. I then re-installed everything and then ran a drill on the drive-shaft and put the lower end in a tub of water and tested the water pump and it shot right out of the rubber grommet! so I was good there. That's when i reinstalled (MAKING ABSOLUTE SURE that i installed the copper pipe in the grommet) I began the compression test.

I did not remove the head yet, because i want to order the gasket first.

I did however remove the engine from the boat and place in a water bin and start it. and she fired right up. Purred like a kitten, and would you know it, spitting water out of those holes!! I let her run at low and medium speeds for about 10-15 minutes. i didn't push her all the way because of my water supply. she sounded great!! i know i will have $hI&!@ for compression but, will i hurt anything to run it as is for a season and then do something to enhance the compression later??

Thanks for the input guys!
 
Before locking yourself into overhaul mode....... getting a engine that hot (more than once) in all probability has damaged the head gasket. Remove the cylinder head and carefully clean the sealing surfaces of the head and the block. Then install a new head gasket, torquing the head bolts to their specific tightness as per your manual after which check the compression again.

If you have no service manual, I can look up the torque specification tomorrow. Let me know.
 
Tpotter1100 said:
Yes that was more my plan!! Unfortunately i do not have service manual yet.
Click to expand...

Okay... You might want to print this out, make a note, whatever.

Flywheel Nut - 30 to 40 Foot Pounds

Connecting Rod Screws - 60 to 66 Inch Pounds

Cylinder Head Screws - 60 to 80 Inch Pounds

Spark Plugs - 17.5 to 20.5 Foot Pounds

Tighten the head bolts in the following sequence whereas every number is a bolt.

9....10
5.....6
1.....2
4.....3
8.....7
 
Awesome thanks! took a screen shot and saved it. How do i go about cleaning the cylinder walls and pistons/ head without taking it ALL apart? i've seen where you take a sanding block with 80 grit, and take the head and sand on flat surface to remove any warpage. but as far as inside the walls and on the piston head, what do you recommend? just regular degreaser? carb cleaner? WD-40 and scratch pad?
 
Simply wipe the cylinder walls with a clean rag... perhaps one with a little WD40 on it. Don't be sticking sandpaper in there as you'll never get it all out of there and that residue will tear a aluminum piston to pieces.

Use a sharp edged putty knife or a blade type edger (same but thicker blade) to carefully clean the head and block surface. Be sure to have both pistons at the same level so as to keep the exhaust and intake ports closed.

You can use #220, #320, #400 wet/dry sandpaper, laid on top of something you know is absolutely flat (a sheet of glass preferably)... whatever works for you, then spray some mineral spirits on the sandpaper to enhance the cutting action. Now, after cleaning the cylinder head with the scraper, if you feel there may be a warpage, rotate the head on the sandpaper in a figure 8 fashion so that all areas are covered evenly.

I strongly suggest that you DO NOT sandpaper the block sealing surface in any manner that would allow grit to enter the cylinders. If this is absolutely needed, be sure to stuff rags into the cylinders so that grit cannot enter and gain access to the port areas.
 
Thanks joereeves! Glad you cleared that up, as i would have probably done exactly what you said not to do. haha

Is it possible that i could gain more compression by simply cleaning the walls and piston heads?

I know that i may gain more if i replace the head gasket, (fingers crossed) especially if it is blown or leaking inside. but i was curious if maybe installing new piston rings would give me any more compression? I know that i have obviously done a little damage, but now i'm curious as to how i can bring her back to peak performance by not taking the head apart and going to machine shop/honing the cylinder/ and getting Bigger rings, etc. I am not scared to take this lil motor apart and put a New set of rings on it, if it will benefit me at all, but i am scared of the cost to take it to a shop.

If you have any other suggestions on how i can improve performance, IM ALL EARS!
 
For the time being, just go the clean up route, then take the engine for a test run... you may be one of the lucky ones.

Should the compression be poor... keeping in mind that the compression psi will relate to the speed in which the engine is cranked over... and you feel you must tear that powerhead down, it's really not that big a deal, it's lightweight and sort of like working on a big watch, nothing strenous!

Hopefully the pistons aren't samaged and can be cleaned up. New rings would be a must. The glazed cylinder walls can be redone to a cross-hatched finish with (black) #400 or #600 wet/dry sandpaper and mineral spirits or a small hone in your power drill. Check the top of the pistons... if they're oversized, the size will be imprinted upon them. If STD size, there will be no markings (order the proper size rings).

Clean up of the block and what have you... clean with mineral spirits, then soapy water, then rinse with clear water, then compressed air... after which immediately brush on oil to any parts that would be subject to rusting... cylinder walls, crankshaft, whatever.

FYI... If you don't have one, Harbor Freight has a very nice parts cleaner for about $80 or so and mineral spirits can be bought in bulk at many places.
 
I took the boat out yesterday and the motor ran GREAT!! i'm not sure really what to expect as far as speed and power as this is the first lil outboard i've ever owned. But it didn't seize and overheat, didn't sputter, started right up every time i asked it to!

I have received my new head gasket in the mail, and i removed the cylinder head last night and began to clean it up. I didn't see any major issues, the gasket wasn't in terrible shape but definitely needed replacement. i laid a straight edge on it and noticed that between the 2 pistons was down a little so i gently sanded the head down in a figure 8 pattern as described. until the high spots came off and the entire head had a nice clean surface.

Am i supposed to use a gasket sealer? how do i apply? i don't want to clog up the water passage holes. I've read in other forums that some gaskets now don't require sealant. how do i check?

This one is green and came from iboats. http://www.iboats.com/Sierra-18-384...B1ebUNyD2TeK4uDLzAVhLcBoUwhddHibdIaAroV8P8HAQ
 
If the gasket has a coated shinny surface, it will be a self sealing gasket and will probbalt have the print on it stating "Do Not Use Sealer" and as such, do no use anything to seal it. If it looks simply dull as a material gasket might look, simply coat it with oil and install it. See that little notch at one end...match that up with the head.
 
ok, yea this one is kind of dull and has print on side, but not shiny. I'll coat with oil, install and update on the compression readings (fingers crossed).
 
Well i have finally got some free time and changed the head gasket. I torqed the bolts to spec and without starting the motor, re-tested the compression. I saw a very, very slight increase, but not much at all. Do i need to run the motor and 'break-in' the gasket first/re check torq, before i try to get a decent compression reading?

I wiped and sprayed down the cylinder with wd-40 and wiped a light coat of motor oil to prevent rust until i got a chance to fully replace it. could it be that it is highly lubricated at the moment?
 
I would not trust your compression gauge. I bought several from Harbor Freight. Fancy ones with all sorts of attachments to make my life easier and none of the gauges would read above 60 pounds. I went to auto zone and purchased a compression tester and it registered over 100 lbs on the same engine.
 
Bullie said:
I would not trust your compression gauge. I bought several from Harbor Freight. Fancy ones with all sorts of attachments to make my life easier and none of the gauges would read above 60 pounds. I went to auto zone and purchased a compression tester and it registered over 100 lbs on the same engine.
Click to expand...


Ooh, very good point. I'll see if a buddy has one i can borrow before i take it back. I plan on test driving this weekend.

Thanks!
 
Jumping over a few posts that have been made since... you stated "I took the boat out yesterday and the motor ran GREAT!! i'm not sure really what to expect as far as speed and power as this is the first lil outboard i've ever owned. But it didn't seize and overheat, didn't sputter, started right up every time i asked it to!"
*****************************

Sounds like a winner to me. Brings back that old adage..... "If it ain't broke, don't fix it!"

After the engine has a few hours on it, check and re-torque the head bolts. That should do it.
 
That engine would not even run with compression as low as you are reporting.
Either operator error on the compression test, or a bad gauge.
 
daselbee said:
That engine would not even run with compression as low as you are reporting.
Either operator error on the compression test, or a bad gauge.
Click to expand...


Yes i agree. I watched a few you tube videos to double check myself on the operator error check. lol. I think the gauge is junk.
 
joereeves said:
In complete agreement with Daselbee.
Click to expand...


Hey Everybody. I have a hard time starting the motor after stopping it, it's happening more and more and hoping to help me diagnose what the issue is. On a cold start, i can usually pull the choke out and pull it once, and then push the choke in and pull it and it'll start almost every time, and run great at top speed. when i get to where i want to stop i slow the motor down and bring it to a stop. Now when i go to start again, i have a really hard time getting her to fire back up? I'll usually keep the choke pushed in and set the throttle to start and fire it up and it seems like it's almost flooded... I have found that if i pull the choke out, pull it once or twice and 'Clear' it, that i can push the choke back in, and she will fire back up and run.

My thought is that i don't have the low circuit in the carb dialed in quite right.

Thoughts? suggestions? tips?


Thanks in advance for the help!
 
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