Compression in a 2 stroke outboard?

When you said earlier Fuel - Fresh mix 50:1 was the fuel itself fresh (or just the mix with the oil)?

I spent a couple of hours in the river in Dartmouth once wrestling with an outboard that wouldn't start.

After doing all the obvious (plug, spark, carb clean etc.) I borrowed some 'new' fuel from my neighbour and was delighted when it fired up on the second pull.

Old petrol can give problems.
 
I wouldnt use wire on the transfer ports in the carb except as a last resort. If there are varnish / gum deposits blocking the fine holes ( very common on old 2 strokes) best answer is an ultrasonic bath / carb cleaner solvent
 
I wouldnt use wire on the transfer ports in the carb except as a last resort.
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True, but I had too with one a while back that had got some water in it and then dried out. Looked clear but it took a wire through it to clear it.

I did say a soft copper wire as that wont damage the jet
 
Using your electric drill method, are you SURE you are trying to start the engine in the correct direction of rotation?
Normally a 2 stroke will start in either direction, but reed valve units tend to run in only one direction?
I've had this same problem years ago with model aircraft 2 strokes, using an electric hand held starter. The engine wouldn't go until I rveresed the polarity of the starter and then it burst into life straight away!
Worth checking??
 
The drill direct on the nut will be turning it the right way providing the drill is not in reverse !


The ignition timing would be way out if attempting to start it backwards. hevens knows where the saprk would occur That would probably stuff its chances of starting

Why are reed valves sensitive to direction of rotation?

Any chance that the flywheel key is sheared and the timing IS way out as a result of the flywheel having slipped ??
 
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VicS said:
One of the items in the link I gave earlier gives the procedure for adjusting the mixture needles
You do have to get running first of course but it should run with the needles in their basic settings.

If the carb is in need of further cleaning I would expect it to run by fiddling with the choke ... It is an ordinary strangler type BTW.

Compressed air may not get the jets clean. It may be necessary to poke something through which will not damage them. I use soft copper wire but I have seen nylon monofilament fishing line suggested.
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I agree, but if the jets are getting blocked, you need to deal with that before you can get the rotten thing to run properly. I would suggest there is value in fitting an inline fuel filter close to the carb with new hose between the filter and the carb.
 
I would suggest there is value in fitting an inline fuel filter close to the carb with new hose between the filter and the carb.
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AFAIK a 1974 4hp Johnson has a remote tank and therefore has a fuel pump with an integral filter.
Just leaves a short length of hose to the carb to be replaced perhaps. Not normally any trouble though except in countries where there is a high ethanol content in the fuel. Then ethanol resistant hose has to be used in place of the original.
 
I can confirm that following early failed attempts to get it going, I went to a garage and filled a 5 litre can with petrol. So yes, the fresh mix was with petrol only hours old (from the garage).

I've checked the drive key a number of times because I've read they can be sheared and troublesome, so I know that's OK.

I'm turning the engine over in the same direction as the hand pull turns it, which incidentally drives the prop forwards in the wheelie bin...

The remote fuel tank I also purchased from a boat jumble, but I cleaned it out before use. The pick up in the tank has a strainer, as does the fuel pump. Both are clear, unblocked and clean. No sign of any contamination in the float chamber so the fuel hoses aren't suspect.

I think I'll thoroughly strip the carb down and check / clean out all the holes, jets and ports. I believe there's a rubber washer round the main jet that can cause trouble too, so I'll see about replacing that.

If that still doesn't do it, I'm beginning to think that I may have to fork out for 2 replacement coils at £30 each. Ouch! Didn't want to do that except as a last resort, but I'm fast approaching it..
 
VicS said:
Try the trick I mentioned earlier. Spray some fuel mix directly into the carb throat using a trigger spray bottle. It should fire and run briefly if its only the cab that's at fault. If it really wont then it's time to look at some of the other suggestions.
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Thanks Vic, I saw that on the link you gave earlier, which I've read through extensively by the way but came to our very own forum for help because it still wouldn't go!

I can't spray fuel directly into the carb because the inlet is only about 3/4" away from the front body so I can't get to it. However I had noticed fuel dripping out of the inlet when I was trying to start it (the engine was tilting forwards a bit so the inlet was pointing downhill slightly) so it was obvious there was fuel getting through. I figured spraying even more in really would flood it!
 
Ok you have confirmed that it is a remote tank. I thought it was but was not 100% sure. "British" models are sometimes different to those listed on the American websites

Prime the carb with the fuel line bulb gently just until you feel it is full.. Be careful not to force any more in by squeezing harder.

Then disconnect the fuel line.

OK it cannot now flood, but it should run for several minutes on a bowl full
Try with and without choke.

I find I have to pull mine choked until it fires, then I push the choke back in but turn the idle mixture adjust to max richness. One more pull and it goes. As it warms up I turn the mixture control to its normal setting. Just my own technique which saves trying to set the choke half way.

It should not leak fuel out of the front of the carb if its only slightly tilted. Some models have a "shallow water" device that tilts them a bit for use in shallow water .

Check the float and its needle valve. The valve should close and shut off the fuel when the top of the float is parallel with the top part of the carb

Don't rush out and waste good money on coils if the spark is good.
I know a CD ignition will produce sparks that will jump 7/16" but the points type wont do that. I reckon you should get 1/4" though.
 
"However I had noticed fuel dripping out of the inlet when I was trying to start it "

That should not happen, and means it is badly flooded. It sounds like the float is not shutting the incoming fuel off. I don't know that particular carburettor, but it is worth checking that needle valve operated by the float is seating correctly and shutting off the fuel. It's usually quite easy to put them together slightly out of alignment, stopping them from working properly. The float chamber then floods completely. Having fuel trickling out of the inlet sounds like this is what is happening.
 
I don't know that particular carburettor
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Here you are then. All its innermost secrets revealed. SEE HERE

Replacement float needle valve, if it comes to that, will almost certainly come with a little clip which fits on the needle and hooks onto the float arm.
 
Trundlebug said:
If that still doesn't do it, I'm beginning to think that I may have to fork out for 2 replacement coils at £30 each. Ouch! Didn't want to do that except as a last resort, but I'm fast approaching it..
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Pointless until you know that coils are the problem.

Everything you have said so far suggests fuel issues including the fact that is did once fire up. So there must have been a spark and in any case you can check for that in the usual way.

If you fuel up as Vic suggests, then you need to test systematically. Its more likely that the fuelling is too weak than too strong - being strong will normally fire up but run badly whereas a weak mixture from, for example, an air leak might never fire. So in your position I would first try to start with max choke and reasonable throttle - enough to take it just above the idle jet level. If that doesnt work then take off a bit of choke and try again. If none of these work, then take out the plugs, heat them up with a blowlamp, put them back and try with little choke and lots of throttle.

If you manage to get it running again, then leave the choke alone and try to open the throttle a little bit at a time. If the engine starts to die as the throttle is open, then the main jet mixture is too weak.
 
just bought one of these a few hrs ago for spares,if you give up on yours may be interested,but have three of these and lot of problems stem from old fuel gumming up the carb but if fuel coming out when tilted you need new float needle and jet ,these engines were meant to run when slightly tilted in shallow water,have you changed your condensers?
 
Johnson OB

I would imagine that an o/b of this age will have old fashioned magneto type ignition. All the ignition c0omponents are under the flywheel. This is removed with a puller. The coils will be mounted under the flywheel and 2 sets of points will be operated by a cam on the shaft. The cleanliness and gap of the points can be critical.
If you can find a o/b wrecker he may be able to supply components for CD ignition as fitted to later motors.Here you have 2 coils under the flywheel an electronics pack attached to the back of the engine and 2 coils also attached to the back of the engine each having a lead to the spark plugs.
The CDI (capacitive discharge ignition) delivers a lot more powerful spark especially at cranking speed. Later model manuals will give all the details.
Anyway the original ignition should work fine. If I remember correctly the points should open as the magnet in the flywheel passes the coil. So make sure the points correspond to the correct coil. (not likely to be wrong). And won't give any spark.
Does the magnet in the flywheel feel strong? A weak magnet will give poor spark. Sorry I can't give any definitive check. But it should grab a big spanner very convincingly. The magnet of course is on the inside of the flywheel rim.

Wet plugs after trying to start an engine is usually as sign of bad ignition. Dry plugs a sign of bad fuel/carb supply.
In my experience these carburettors will usually work with choke and plenty of revs. Dirty channels gives bad idling but start with lots of throttle and choke OK. Yes I always use a bit of stainless steel wire from 7X19 thin wire. Just be gentle. good luck olewill
 
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