81 4HP starts but cuts out after a min or two

[evinrude81]

Hi All,

I'm a newbie here, and to outboards really, so my lack of knowledge is vast! I have just acquired a 1981 semi-working 4HP (2 cylinder, 2 stroke) motor that really hasn't ben used for the last 10 years. Not being entirely useless mechanically I plan on seeing what I can do to restore this thing to its former glory.

Could I ask the favor of suggestions what may be causing the problem? Things I know is that It does have new gas, the water pump works fine, and the guy I bought it from wasn't well versed in these matters so it could be simple or not, but one way or another I plan on learning how these things tick

All suggestions gratefully received.

Thanks,
Mark

 

[i386]

Re: 81 4HP starts but cuts out after a min or two

You might want to read the articles in the FAQ forum for starters. Even if you don't immediately do all the stuff written there it's good information.

You need a steady supply of fuel.

You need a good spark on all cylinders at the right time.

You need compression.


Others will surely be along to provide more information. Good luck.

 

[Vic.S]

Re: 81 4HP starts but cuts out after a min or two

I believe that model has a coil and breaker ignition sysytem so that rules out a fault occuring within an electronics module as it warms up.

If it starts easily and runs OK at first that more or less rules out any other faults with the ingnition, but it would be wise to check/clean/regap the plugs and reface or replace and reset the breaker. As it stars OK the condenser is unlikely to be faulty.

The most likely problems are with the fuel system. Again because it starts OK and runs OK initially it is unlikely to need a carb strip and clean but it is something to consider later.

You need to ensure that there is an unobstructed flow of fuel to the carb. The symptoms you describe are typical of a blocked fuel tank vent so check that or simply try running with the cap off.

If that motor has a built in fuel tank then check for a good fuel flow to the carb.

If it has a remote tank then check the fuel pump as well as the tank cap and fuel lines. Pumping with the primer bulb will keep it running if the fuel pump is faulty. A small air leak in the fuel line from the tank will also cause this problem. The connector being a suspect point but again pumping with the bulb will keep it running.

In either case check the tank for debris and that the filter is clean

If it stops firing quite suddenly as though you had pressed the stop button concentrate on the ignition system. If it dies more slowly perhaps sounding a bit different or speeding up slightly before stopping concentrate on the fuel system.

Let us know what you find.

 

[tashasdaddy]

Re: 81 4HP starts but cuts out after a min or two

this will help, sitting 10 years replace the water pump .

http://forums.iboats.com/bbBoard.cgi?a=viewthread;fid=36;gtid=1035575

 

[Tommo]

Re: 81 4HP starts but cuts out after a min or two

Hi, I have a simular Johnson a 1985 and I had the same problem it would cut out after a couple of minutes.
I believe the problem is very simple, if you have an internall tank you must release that small valve ontop of the fuel tank cap. It allows air back into the fuel tank to replace the fuel thats been sucked into the carb. Or you could just open the fuel cap slightly.

A few more things

Also OMC changed its recomendation from 100:1 to 50:1 fuel oil ratio. So use 50:1 of quality oil.

It may sound obvious but never start the engine out of water, in a bin of water is acceptable.

Also never tip the motor upside down to drain fuel out, any water left in the gearcase will rush into the powerhead causing major damage. I learnt this the hard way.

Tell us how you go

Good luck

 

[Fishstick1962]

Re: 81 4HP starts but cuts out after a min or two

I had a small engine that would start and run fine for 3-4 mins then die like i turned the key off. Turned out to be the coil. When the coil was cold it worked fine, when it heated up it just quit. But I would start with the fuel system as the other posters suggested.

G-Luck!

 

[Vic.S]

Re: 81 4HP starts but cuts out after a min or two

When the coil was cold it worked fine, when it heated up it just quit

Yep ,I logged back in to say look at the condition of the coil especially if the ignition system becomes the prime suspect.

I believe the problem is very simple, if you have an internall tank you must release that small valve ontop of the fuel tank cap. It allows air back into the fuel tank to replace the fuel thats been sucked into the carb

Thats what the vent valve is for. It applies to both integral tanks and remote tanks alike

 

[evinrude81]

Re: 81 4HP starts but cuts out after a min or two

Just wanted to say thanks to everyone. I tend to agree that it's likely a fuel supply problem so I'll take the suggestions and work my way down.

Great item on reviving dormant motors. I'll be running through that list.

Much appreciated and I'll report back - it would be great if this proves to be as simple as a gummed fuel line or blocked vent. If it is, it'll be one of the better $70 I've ever spent!

 

[evinrude81]

Re: 81 4HP starts but cuts out after a min or two

Latest scoop - haven't done anything mechanical yet but did a bit of better diagnostic work. The vent is OK (I tried running with the cap off too and it's the same). Tonight's discovery is that it's easiest to start with the normal settings but choke on whether hot or cold, and throttle set in the 'fast' position. I ran it like this for 4-5 mins, experimented with turning off the choke, and richening the mixture and RPM's went up nicely and it seemed to run fairly smoothly.

The problem seems to be as soon as I back off the throttle below a 'slow fast', towards the start setting, the engines stalls out. I have to leave it 5 mins or so as it seems flooded. I can't get it to run below the 'start' position, even leaning it out as I go.

All that said, I haven't yet taken the sage advice offered yet other than the vent, and inspecting the tank interior which looks good. I guess I will have to crack the case and start poking about and work my way down the fuel system. I also suspect that because of the years of inactivity, the plugs, points etc must be pretty tired so will need replacing.

Perhaps the overall problem is the years of storage - there must be some gumming and I can only imagine that the electricals need freshening up. Perhaps a darn good thorough service is needed. The work will continue as I get time....

Anyone got any other thoughts that may be helpful.

Once again,
Many thanks,
Mark

 

[mikesea]

Re: 81 4HP starts but cuts out after a min or two

It probably has a screen where the fuel line enters the tank.Sometimes the shutoff valve gets debris in it. What is happining is you have a restriction,it wont keep up with demand for fuel. Take the whole system apart from tank to carb,it sat too long and by fixing a bit here and there will frustrate you to the point you give up,or in and do it right

 

[Scaaty]

Re: 81 4HP starts but cuts out after a min or two

I did a 2 horse (also had a 84 4hp I sold to my neighbor) that was giving me fits. Turns out way deep inside the fuel shutoff, was old gummed up tar like crap from old gas. Take the fuel line off at the carb, then open the petcock. You should have a steady flow. If not, try new hose first. If still a dribbler, take the petcock out, and soak it in carb cleaner over night. Blow it out with compressed air. If you don't have compressed air, use a can of computer duster air (believe me, don't know how I got along without that little can of air...use it for all kinds of clean up operations). Still have trouble, try taking the low speed jet out, and spray carb cleaner in there. Let us know the results. Good motor, we'll get it running for ya

 

[Scaaty]

Re: 81 4HP starts but cuts out after a min or two

Jeeezzzz, I forgot to ask...does it have a built in tank? I really can't tell from your post?

 

[evinrude81]

Re: 81 4HP starts but cuts out after a min or two

Indeed - it's a built in tank. All very useful thoughts so much appreciated. Next steps crack open the housing and dismantle the fuel system to make sure it's clean all the way. One small step at a time. Watch this space!

 

[cobra 3.0]

Re: 81 4HP starts but cuts out after a min or two

Most probably a fuel issue. I had the same motor that was tempermental every spring after storage. Check all fuel lines right through the filter to the carb. Take the carb off and give it a good cleaning with a spray can carb cleaner product. It's probably varnish in the lines, filter, bowl and small orifices as mentionned above by others.

 

[Vic.S]

Re: 81 4HP starts but cuts out after a min or two

Because it runs fast OK do not be surprised if you find no obstruction in the system between the tank and the carb.

You seem to believe it is flooding so look at the float and its valve. They can stick or there may be some debris in the valve stopping it closing properly.

After that I guess you will have to look at cleaning the main jet assembly and the slow running passages. I clean jets by poking through with soft copper wire as that will not damage brass but others will say I should use something softer, such as a brush bristle. Maybe nylon monofilament fishing line will do it. Before you remove the slow running adjustment needle note its setting ie how many turns it is open (1½ IIRC), but on reassembly you will adjust it to the best running position before refitting the knob.

If you have not found them you may find the parts diagrams on the BRP website useful.

I'm sure its been mentioned already but don't run the engine dry, even briefly, or you will destroy the water pump impeller

 

[freddyray21]

Re: 81 4HP starts but cuts out after a min or two

I agree sounds like a sunk float or a needle valve not shutting the fuel off. When it is running at high speed you are using enough gas to keep the float bowl from flooding. When you idle it back it isn't and it floods. Rebuild the carb with a new float

 

[evinrude81]

Re: 81 4HP starts but cuts out after a min or two

Today's news - some good, some not so. I did get as far as pulling out the fuel filter which was partially blocked, flushed the tank, replaced the gas, replaced the fuel line, and can now confirm I have a nice steady flow of fuel. I also pulled of the carb and gave it a good cleaning inside and out with carb cleaner - though it did look pretty clean so no obvious evidence there, but then again, I hate carbs as they can look so normal yet...

I also replaced the aged plugs with some nice new ones, and sprayed a little WD40 on some of the tighter joints, with some marine grease where I could get at.

So where are we now. Well, I seems I've taken a few steps back. I can't get it to fire up at all now. Since it got to be twilight, I pulled the plugs to check for spark and not a thing from the lower cylinder, though the upper sparks well (tried swapping the plugs to make sure it was a problem somewhere from the lead up.

So there we have it - while I have done a few needed things, there's still a mystery to solve. I didn't think to test the electrical before so I don't know if I've somehow introduced a problem (I have a hard time seeing how but perhaps I did something stupid?).

So suggestions as to next steps? How do you get the magneto cover off these things without breaking the casting? I know my problem lies in there somewhere (and I did want to get to that part before too long anyway so I could replace the electrics in there as they're no doubt rather crusty) but figured I'd best stop before I did something stupid in haste this evening.

Thanks
Mark

 

[evinrude81]

Re: 81 4HP starts but cuts out after a min or two

Adding a comment - since I used WD40 in the vicinity to free up a few stiff joints, a buddy of mine just suggested this may kill a magneto? Thus no spark? Is this likely anyone? Perhaps I killed it myself?

Thanks,
Mark

 

[i386]

Re: 81 4HP starts but cuts out after a min or two

If your ignition has breaker points I'd say it's possible. You'll need to pull the flywheel to get to them. If it was the WD-40, just cleaning the points should do it. Might as well check the point gap while you're in there.


You'll need a special tool to pull the flywheel off. It's called a harmonic balancer / steering wheel puller. They're $15 or less at most autoparts stores. My puller didn't come with the right size bolts for my flywheel. For mine, I needed 3 3" x 1/4" grade 8 bolts and some washers. If you can find flange bolts, you shouldn't need the washers.

Now might be a good time to get a manual too. It'll tell you more than you ever wanted to know about your motor.

 

[evinrude81]

Re: 81 4HP starts but cuts out after a min or two

I believe it does - according to the original handbook (yes, I have that), it refers to breaker point gap being 0.020 so, yes and yes. That's a nuisance though I suppose I had it in in the back of my mind to take a look around in there anyway