Grr - I hate small petrol engines! (Johnson 4hp 2-stroke)

[prv]

My outboard motor saga continues.

After I put it back together over the winter, the engine tended to run ok in neutral but then die about ten or fifteen seconds after putting it into gear. A week ago I had a go at adjusting the slow speed needle valve, according to the instructions commonly found online, without much effect. I decided to order the carburettor rebuild kit and have another go at that.

This weekend I duly dismantled and rebuilt the carb, replacing the float and its valve and adjusting the float height (15mm) as described in an old PBO cutting. The carb was of course still nice and clean after my winter efforts. At that point I didn't know what all the small rings and seals in the kit were for, assuming maybe the kit spanned different models of carb, so I didn't replace the packing or O-rings in the fuel tap or needle valve, nor did I discover the rubber "bladder" that acts as a tiny pump at the end of the tap. I'm probably going to replace these bits tonight, but I doubt there was anything wrong with them anyway.

Running in the tank at home, all seemed fine and I congratulated myself on finally having a working engine. We're off to the West Country in a couple of weeks, so I thought a proper test run was probably a good idea, so I took it down to the boat and blew up the dinghy. I buzzed around for about ten or fifteen minutes, mostly at full throttle. Then I throttled back to have a look at some of the wrecks up past the Northam Bridge, and the engine promptly died. What's more, I couldn't restart it, even after about half an hour (tied to a buoy) of trying. Actually, I did get it to start once or twice, but it died as soon as I put it into gear. There was plenty of fresh fuel in the tank, the vent was open (and no hissing when I opened the cap, so it wasn't blocked), the spark plugs are new, the carb is clean. I was trying every possible combination of choke and throttle setting.

Eventually I gave up and rowed back (against the tide! Foolish mistake to have headed upriver, but I wanted to see the bits I can't get to with a mast). Once tied up alongside Ariam, I had another go with the engine and it started reasonably easily and seemed to run well. I tweaked the slow speed a bit at this point; can't remember if that was before or after starting it. Then, imagining (unrealistically) that this tweak might have fixed it, I went off for another run, this time against the tide. I went all the way down to Ocean Village mostly at full throttle, went in and out of their basin at low speed (wanted to wave to my mate who has a flat overlooking it ), then back up to Kemp's. Since slow speed seemed like a potential problem, I circumnavigated the pontoons at little more than tickover. Just as I was completing this circuit, the engine died again - although possibly this was due to lack of fuel after all the buzzing about at max chat. You can't see the bottom of the fuel tank through the cap, but certainly it was low, so I topped it up and started again reasonably easily. Then it quickly cut out again, at low speed. I restarted and banged it straight to full throttle, which worked, and I buzzed around for a few more minutes. Then the same performance as I'd had above the bridge - I slowed down from full speed to slow, the engine died, and it couldn't be restarted. In the end I rowed back to the boat, lifted the dinghy out, and took the engine home. When I tilted it forwards during this process, a lot of petrol flooded out of the front of the engine, but maybe that's just what you get for tipping a carb up by 70 or 80 degrees? In the tank at home (to wash the salt out), the engine started somewhat reluctantly and then ran ok, including in gear.

This has been a long post, but I'm at a loss as to why the engine keeps dying, and especially why it then can't be restarted for about half an hour, so I wanted to mention everything in case it's significant.

To recap, the fuel is new, as are the spark plugs (and I checked the gaps). Compression is good, and the same in both cylinders. So my suspicion is focussed on the carburettor, which is scrupulously clean but might be misadjusted somehow. The float and associated valve are new, and the float's height (when pressing the valve closed) has been checked. I did see a reference to checking the other end of the float's travel, but surely it would bottom out on the chamber first and I don't understand why it would matter anyway; I haven't done this one. The slow speed needle has been adjusted according to instructions. I screwed the high speed jet / nozzle / vertical-bar-with-holes-in into position fairly firmly at one point, but I don't think it was hard enough to have damaged anything. I haven't poked anything into nozzles and jets, I used spray carb cleaner in my original winter dismantling session.

The need to wait before restarting makes me (now) think about overheating - but wouldn't that just seize up the engine? It turns over freely after these stops, even if it doesn't fire. There is water being sprayed out of the telltale when running, though not the solid jet you see out of bigger (25hp etc) motors. I guess that's ok. I haven't checked the impeller as that had supposedly been done shortly before I bought it.

I'm getting really frustrated with this thing - chasing a problem I can't see or identify - and I've decided I hate carburettors . I'd be willing to pay someone to magically make it better, but I don't know anywhere that works on small outboards (actually I know one, but he declined the job as he's too busy), and because it's so intermittent I worry that a workshop would run it in a tank for a bit and say "can't find anything wrong". I would really like to have it reliably working before we set off in two weeks for places like Salcombe where it's a long way to town.

I guess this post is looking for three things...

1) suggestions of what the problem is, or at least steps towards identifying it
2) recommendation of someone who can just fix it for me
3) general venting of spleen towards things with carburettors

Pete

 

[Ruffles]

I don't have your make of outboard but I think the general problem with small 4 stroke outboards is that they are too efficient. They have a tiny jet which is not ideal when your fuel is coming from a can.

My guess is that there's dirt somewhere. Strip it down enough times and it will start working! Usually I need to clean the jet a couple of times and run it for a good hour at the beginning of the season.

Does the engine get used a lot? Mine becomes quite reliable as Summer moves into Autumn.

 

[Giblets]

Use the Johnson as an anchor and buy my nice Seagull 40 Plus!

 

[lw395]

Many years ago, a friend of mine had a moped like that, the problem turned out to be the coil.
What does the rest of the ignition consist of on this engine?
A failing electronic ignition module might do what you see.
Alternatively an old-style points condenser can do the same.
Or breaking down insulation anywhere in the circuit.
Including the LT generator coil, which might do something odd as it heats up?
Or the sensor coil which controls the timing?
Suppressor in the plug cap?

Crankcase oil seals can do some odd things too...

Is it a simple piston port 2T or does it have a reed valve/disc valve etc?

Other engines that have defied diagnosis for a while include having the air cleaner mis-assembled to block air flow and an exhaust clogged by rust flakes.

 

[RichardS]

I can feel your pain. Outboards are so frustrating.

It doesn't help but when we used to charter a boat each year, the charter company usually had a selection of Mercury and Johnson 4HP / 5HP. After a few years of experience with both we learned to check what was on the charter boat when we arrived and if it was a Johnson I used to get the company to swap it for a Mercury. For some reason, the Johnsons just seemed more temperatmental.

Trying to be helpful, run the engine with the top removed but carry with you a small bottle of petrol (old pill bottle or similar). When the engine stalls and won't start just splash a bit of the petrol directly into the air intake and try to start it. If it runs for a few seconds then it's a good indication that it's a fuel problem rather than a HT or LT problem. I've used the trick a few times with engines over the years and it really does help identify the problem area, if not the actual problem.

Good luck

Richard

 

[johnphilip]

Back in the day we bought and hated a Johnson 4 two stroke. Cost a lot in ineffective repairs and lost holiday days apart from wasting time on my own efforts.
The cure, a Mariner 4. ( Still a 2 stroke in those days) Should have cut losses sooner. The Mariner not only started with total reliability but was much more effective at pushing our 19' Prelude. I had bought the Johnson thinking twin cylinder would run more smoothly. No, the Mariner won again.

 

[VicS]

What is the model number?
Quote that and at least we know which variation you are talking about.

have yu checked the sparks.. Esp when it wont start. Should jump best part of 1 cm if its CD ignition Not quite so much of its points

If its points ignition have you checked cleaned adjusted them and looked at condition of coils etc etc

Stop button Ok /


Lots of useful info at http://forums.iboats.com/forum/engine-repair-and-maintenance/engine-frequently-asked-questions-faq esp on cleaning and adjusting carb, setting points


AFAIK none of the 4 hp 2 stroke Johnsons have a cooling water telltale. The don't pee like larger engines but you should see some droplets or a fine mist/ spray from the exhaust back pressure relief ports.


Dunno about this float height adjustment. Usually when inverted the float/ arm is parallel with the joint face. I hope you did not alter it much.


Check/change that bladder!

What plugs have you fitted ? What gap have you set them at?


If all else fails post your query on the iboats forum ........ but quote the full model details.

Marineengine.com forums also v. good ........ and work better than iboats sad recent upgrade ( you thought ybw forums have trouble with upgrades ??). Many of the same people on both.

 

[Bobc]

I have recently felt your pain, so completely sympathise.

In fact, the one piece of advice that I can offer...is to not take any advice about outboards from me.

 

[prv]

What is the model number?

J4REEA. Sorry, should have said.

have yu checked the sparks.. Esp when it wont start. Should jump best part of 1 cm if its CD ignition Not quite so much of its points

I haven't - I'd convinced myself that it was the carburettor, but I will certainly look now.

How exactly do I do that check? I know about touching the plug on the block and looking for a spark between the plug terminals, but talking about jumping 1cm suggests something else?

Stop button Ok /

I think so, yes.

AFAIK none of the 4 hp 2 stroke Johnsons have a cooling water telltale. The don't pee like larger engines but you should see some droplets or a fine mist/ spray from the exhaust back pressure relief ports.

Two holes underneath the power head, just aft of the leg? Yep, a mix of spray and drops from there.

Dunno about this float height adjustment. Usually when inverted the float/ arm is parallel with the joint face. I hope you did not alter it much.

Mentioned in several instructions I've found, both online and the PBO overhaul article. You are directed to hold the carb upside down so that the float is supported by the closed valve, and measure the height of the top surface of the float above the joint face. There is a special Johnson/Evinrude tool (just a plastic template really) to give the proper distance, but the PBO article also states the dimension as 15mm, and I measured it with a vernier. It results in the float being more or less parallel to the joint, yes.

What plugs have you fitted ? What gap have you set them at?

Champion QL86C. Can't remember the gap, but it will have been from either the PBO article or an online manual.

Pete

 

[prv]

It doesn't help but when we used to charter a boat each year, the charter company usually had a selection of Mercury and Johnson 4HP / 5HP. After a few years of experience with both we learned to check what was on the charter boat when we arrived and if it was a Johnson I used to get the company to swap it for a Mercury. For some reason, the Johnsons just seemed more temperatmental.

Mm. I also have a 2hp Suzuki, which has been absolutely reliable. Much easier to work on, too - time and again on the Johnson things have just been gratuitously difficult due to poor design, part A mounted in front of the screws for part B when there was no need to, etc.

However, the 2hp has felt very underpowered at times, so I really want to persevere for the extra power.

Pete

 

[VicS]

QL86C are the correct plugs. They should be gapped at 0.030"

In idea from lakey's website for an improvised spark tester:

Its a modern CD ignition so no problems with points or condensers and coil unlikely to be any trouble ( old ones could deteriorate). Ignition module could be at fault. Hope not as thats £many to replace. Do a spark test . To check the system needs a meter with peak reading ( expensive Fluke) or a DVA adapter, ( It is possible to make a DVA adapter easily enough)

See http://issuu.com/cdielectronics/docs/practical_ouboard_ignition_troubles for CDI electronics troubleshooting guide.

I'd put a small wager on the bladder being holed!
but do you also have a remote tank and facility to connect it?

 

[prv]

I'd put a small wager on the bladder being holed!
but do you also have a remote tank and facility to connect it?

I don't have a remote tank, but I suppose for testing purposes I could jerry-rig a hose direct to the square fuel pump.

However, a hole in the bladder would be excellent news - it's a definite visible fault rather than a subtle misadjustment, and I have a spare from the rebuild kit sitting on the bench

Pete

 

[Binman]

I had to take my carb to be checked and they cleaned it 3 times in a ultra sonic tank, before the problem was solved in my case it was bogging down when trying to rev, on my Suziki 3.5 DT two stroke, it was the gapping of the spark plugs, it said 28-31 thou, I opened them up to the max and hey presto. Could possibly be electrical but doubt it, but undo what you can clean and tighten, best of luck, I have just fitted a new spring to the Suziki recoil starter it's worse than before, it's a good thing it starts with one pull from the hooked top plate.

 

[prv]

OK, a brief update...

Sadly no sign of damage to the bladder. I put the new one in anyway.

Replaced the seals on the fuel tap, and the packing on the slow speed needle, though I doubt either was really needed. Blew and sucked through the bladder-pump arrangement to check as far as possible that the tiny valves in it were working.

Checked the float height again, as described above.

Dismantled the high speed jet assembly again. Gave it a blast of carb cleaner just in case though it all looked pretty clean. No visible damage etc. I also blew carb cleaner through the low speed side while it was out, since I hadn't done that during the initial clean.

Took the plugs out. Looked ok I think, though as should be quite clear by now I'm no expert on engines, especially small petrol ones! If anything perhaps slightly dirty / oily but I'm not sure what's normal. Noted Vic's figure of 0.03" above; unfortunately my feeler gauge is metric and can't reproduce that exactly. It's 0.762mm (tenth of a bullet ) - with my gauge I can do 0.75 or 0.8. The existing gap was slightly larger than 0.8mm; I reset it to be in between 0.75 and 0.8, closer to the former, so as near as I can manage to Vic's 0.03".

By this time it had got a bit late to be running noisy two-strokes under the neighbours' back windows, so I'm going to have to wait till tomorrow to see if it's made any difference. Of course, given that last time it got me all the way to Ocean Village and back, that's a lot of running in the dustbin before I can say it's any better...

Pete

 

[VicS]

OK, a brief update...

Sadly no sign of damage to the bladder. I put the new one in anyway.

Replaced the seals on the fuel tap, and the packing on the slow speed needle, though I doubt either was really needed. Blew and sucked through the bladder-pump arrangement to check as far as possible that the tiny valves in it were working.

Checked the float height again, as described above.

Dismantled the high speed jet assembly again. Gave it a blast of carb cleaner just in case though it all looked pretty clean. No visible damage etc. I also blew carb cleaner through the low speed side while it was out, since I hadn't done that during the initial clean.

Took the plugs out. Looked ok I think, though as should be quite clear by now I'm no expert on engines, especially small petrol ones! If anything perhaps slightly dirty / oily but I'm not sure what's normal. Noted Vic's figure of 0.03" above; unfortunately my feeler gauge is metric and can't reproduce that exactly. It's 0.762mm (tenth of a bullet ) - with my gauge I can do 0.75 or 0.8. The existing gap was slightly larger than 0.8mm; I reset it to be in between 0.75 and 0.8, closer to the former, so as near as I can manage to Vic's 0.03".

By this time it had got a bit late to be running noisy two-strokes under the neighbours' back windows, so I'm going to have to wait till tomorrow to see if it's made any difference. Of course, given that last time it got me all the way to Ocean Village and back, that's a lot of running in the dustbin before I can say it's any better...

Pete

I thought the symptoms matched those of a perforated bladder .... obviously not this time.

Plug gaps not that critical ... until late 1980s all OMC plug gaps were 0.040" but were revised to 0.030" across the board. (To improve plug life I beleive) If you'd asked what the gap should be in mm I would have said 0.7 to 0.8 mm.

You mention the square fuel pump. Any chance that this is pumping air into the fuel system. Id expect it to be connected to a remote tank connector which has a valve in it which should be closed when the remote tank is not connected.

IIRC the fuel tap operated by turning the choke knob just opens/ shuts off the fuel supply from the internal tank. That appear to be working correctly?


Did you check the float operated needle valve. Does it close and shut off the flow properly or is it letting by, causing flooding, or was there a new one in the carb kit

Is the tiny spring clip linking the needle to the float arm installed or is it missing and allowing the needle valve to stick shut.

Have you checked the filter in the outlet plumbing from the internal fuel tank?


Did you pry out the plug on the top of the carb to access the slow running passages below it. There should be replacement plug in the carb kit

Pity Lakesailor got himself suspended He is pretty clued up on these 4 hp OMC engines


Sorry no logic in the order of the suggestions above ... just the order in which I thought of them.

 

[mawm]

I have a Johnson 4hp that had the same problem. The outboard shop eventually found a small split in a bit of rubber something in the carb. Sorry I can't be more specific than that.

 

[prv]

You mention the square fuel pump. Any chance that this is pumping air into the fuel system. Id expect it to be connected to a remote tank connector which has a valve in it which should be closed when the remote tank is not connected.

That's right. The remote connector has a valve which seems to be working. When running in the bin with the front cowling removed, I've been plugging the hose with a screwdriver bit.

IIRC the fuel tap operated by turning the choke knob just opens/ shuts off the fuel supply from the internal tank. That appear to be working correctly?

Yes, I tried blowing/sucking through that and it opens and closes as expected. I dismantled it and changed the O rings last night since they were in the kit, but the old ones looked perfectly fine.

Did you check the float operated needle valve. Does it close and shut off the flow properly or is it letting by, causing flooding, or was there a new one in the carb kit

I don't know how I would check it. But the old one looked ok when I originally rebuilt it - the PBO overhaul instructions said to look carefully for a groove worn in the rubber, which there wasn't. It's now been replaced anyway - that's mostly what I bought the carb kit for, as the same instructions said that if it was worn it would give "no end of trouble", and that description seemed to fit!

Is the tiny spring clip linking the needle to the float arm installed or is it missing and allowing the needle valve to stick shut.

It's present and working.

Have you checked the filter in the outlet plumbing from the internal fuel tank?

Checked during the winter. And the hose from it pisses fuel everywhere each time I take the carb off

Did you pry out the plug on the top of the carb to access the slow running passages below it. There should be replacement plug in the carb kit

I didn't take the plug out, though there is indeed a replacement in the kit. I gave the slow running side a good dose of carb cleaner through the hole where the needle valve goes, though, and saw it come out the holes in the carb barrel.

Thanks for the suggestions

Pete

 

[prv]

I have a Johnson 4hp that had the same problem. The outboard shop eventually found a small split in a bit of rubber something in the carb. Sorry I can't be more specific than that.

That'll be the bladder that Vic suggested. Sadly mine was fine.

Pete

 

[lw395]

........Champion QL86C. Can't remember the gap, but it will have been from either the PBO article or an online manual.

Pete

I have never rated Champion plugs, particularly for 2 strokes.
Is there an NGK, or second best, Denso?

And go with the gap stated by the plug manufacturer, not the engine maker.
The required gap is a function of the electrode dimensions, which varies from one type of plug to another.

 

[VicS]

OMC recommended that only Champion plugs should be used.

There is problem with " equivalents" offered often being resistor suppressed . The Champion Q series plus are inductively suppressed and were I believe specially developed for the OMC CD ignition system.

However there is no problem IMO with using other plugs provided they are not resistor plugs. There is no direct NGK equivalent of QL86C but QL77JC4 were at one time listed as alternatives to QL86C. The NGK equivalent of these is BZ7HS-10 ( The Z series being inductively suppressed)

Unsuppressed B7HS-10 would be OK. The -10 part of the number can be ignored as it only indicates that they are supplied gapped at 1.0mm and they will have to be re-gapped anyway.


QL86C are a little hotter than QL77JC4 (and NGK "7" heat range plugs). This maybe the reason they are now the only plugs on the OMC recommended list.

At this stage it would be a mistake IMO to complicate matters by messing about with different plug makes, different electrode designs and gaps. That is something that can be done when the engine is operating correctly to optimise performance.

FWIW my 6 hp Evinrude, similar but larger cc capacity, to the OP's 4hp is using the original Champion QL77J4 plugs with which it was supplied in 1984 . I do have a spare set (of NGK B7HS) in the toolkit.