Johnson 2hp outboard - won't start-compression?

[PaulR]

Johnson 2hp outboard - won\'t start-compression?

our 2hp johnson dinghy outboard (now c 20years old!) lives in a cockpit locker during the season and in our attic in the winter and enjoys a fresh water flush and clean up when going into winter storage each year.

Last ran it during late summer but on trying to start it to flush it for winter - dead!

Good spark and fresh fuel but no run-popped into local o/b place where bod also checked spark, tried easy start straight into cylinder - still no start and then checked compression - said ought to be c100 and came in at 50- his diagnosis - throw it away and start again.

2 questions.

1. What should the compression figure be?
2. If 50 is low is there any economic fix or is it a throw away and start again job?

 

[jerryat]

Re: Johnson 2hp outboard - won\'t start-compression?

I'd whip the head off and check that the head gasket has blown or is leaking.

Most of these small engines corrode badly (over many years) around the waterways adjacent to the cylinder, and I've often seen this corrosion effectively preclude any chance of the head gasket making a proper seal.

Removing the head will give you access to piston, cylinder and surrounding waterway, and the problems may well be immediately apparent.

HTH's

 

[Norman_E]

Re: Johnson 2hp outboard - won\'t start-compression?

Jerryat gives good advice, but if it ran last time, and now wont run at all there may be a simple problem, like the timing having slipped. Does it even fire, without being able to run continuously? Not familiar with your engine but most small engines from the pre electronic ignition era have a small cam which works the contact breaker, if this moves on its shaft, or the contact breaker assembly comes loose you may get a perfectly good spark, but at the wrong point in the cycle. Check also that the plug itself is sparking, and not merely a spark from the lead to the cylinder head. I have recently had a lawnmower which showed a good fat spark when I took the lead off and held it close to the cylinder head, but the spark plug itself had failed internally. On most petrol engines compression has to be really bad before they will not run at all, low compression usually means lower power output, rather than total refusal to start. Usually before it gets so bad that it will not start you will have the situation where it will start and run, but lacks power and may even stall when the clutch is engaged. One possibilty with the poor compression is that the piston rings are gummed up. I have once got an old engine going after pouring some WD 40 down the plug hole, turning it over a few times, leaving it to soak for a bit then tipping it out.

 

[VicS]

Re: Johnson 2hp outboard - won\'t start-compression?

I have been checking for details of the ignition system. It apperars that up to 1985 it was a coil and points system. There is no 2hp listed for 1986 and in 1987 a 2.5hp appeared with electronic ignition. So coil and points it is. (But if you tell us the model nuber, not the serial number, we can confirm the year) So check the points as well as the plug. Failure of the condenser is a possibility, you could appear to have a decent spark but not good enough.

Have you checked the carb. It could have a blocked jet. Also check that fuel is actually getting into the carb. Recently when I resurrected an old outboard to lend to a friend I found the inlet needle valve had stuck shut. When I got it back the carb was in a terrible state as water had got in somehow but good clean sorted it out.

The low compression is the biggest worry though. It might be that you could seal things up a bit and get it to start by injecting a little light oil ( the 2t oil or Redex I'm not so sure about WD40 though) into the cylinder and having another try.

Take the head off as a last resort only. It may not now be easy to get spares. Generally repair shops won't look at anything that old.

 

[aitchw]

Re: Johnson 2hp outboard - won\'t start-compression?

It's not uncommon for small engines to lose timing as a result of the magneto head slipping round the shaft when the engine comes to a stalled halt through fouling. There is a key locating it on the shaft which deforms (starts to cut through). It happens a lot on mowers. It's at least a cheap thing to replace.

 

[Norman_E]

Re: Johnson 2hp outboard - won\'t start-compression?

The reason I used WD 40 was that it was to hand, but it is actually quite a good choice if the problem is that "varnish" has gummed up the rings, as it seems to dissolve the gum.

 

[JimMcMillan]

Re: Johnson 2hp outboard - won\'t start-compression?

Hi,
No compression, most probable reason is siezed piston rings. Reason why your man says start again,it is almost impossible to remove cylinder head/cylinder to expose piston without breaking cylinder head bolts/studs.Alloy head,alloy studs, salt water,no go..

Jim

 

[jkim1]

Re: Johnson 2hp outboard - won\'t start-compression?

Have the same problem be careful not to break the cylinder head bolts. The gasket blows between the head and the water passages. It will run ok until you stop it and then never start. There should be a fair bit of pressure if you stick your thumb over the spark plug hole. The spark can be tested at the same time by pulling the start cord. Cylinder head gaskets are a rip off about 7 pound each. best of luck.

 

[PaulR]

Re: Johnson 2hp outboard - won\'t start-compression?

thanks all for the above-have checked spark between plug and cylinder and looks good - have also cleaned points just in case- am now trying leave redex to soak for a few days and then will try again - will let you know if I succeed - thanks again

 

[KieronRyan]

Re: Johnson 2hp outboard - won\'t start-compression?

I have a JWL-20 (1965) 3 hp and I find if you clean the carburettor you'll probably get a result.
Clean means take apart and wash in petrol/thinners.

The timing on a JW can't slip as it's fixed. If you have a spark that's fine.

screw in the low speed needle (gently!!) it's only brass and Au ! give it a spin, no choak.
The needle wears at the tip and the mixture goes all rich and floods. The tip should be a smooth cone shape.

While you've got the carb off take the next thing off it's the reed valve block and gently remove the reeds and use wet and dry to dress the seats of the Ali block that they sit on. Refit the valves the otherway round. Let me know...

Kieron