Reduced power, 80's Johnson 90 V4

[Jungleboat]

Hi, just wondering if anyone has a solid clue or two...

Background - Engine usually runs fine, though a few times has lost a pot due to loose connections between pack and cylinder coil (it has a coil per pot). Replaced all 4 of those wires with new.

Lately power has reduced again, same low power but I don't notice the vibration that occured when she lost one pot before. With engine cover off, all 4 seemed to be sparking OK, and all (now) have the correct Champion plug and correct gap.

It's a 21ft deep V cabin boat, usually does 32mph WOT, has dropped to 21mph (GPS). Beyond a certain point, more throttle just makes a deeper engine note, presumably air intake, but no extra oomph.

It's not loss of compression, because every now and then she'll surge forward, before settling back down into a miserable drone. Does that for approximately 3 seconds, and extremely intermittent. Might happen, might not.

So fuel starvation, right?

Then the starter relay went. While the local mechanic was fixing that asked if he could service the carbs, which he did. Next day tested it, ran fine, full power.

Today we went to move the boat ready for the tide tomorrow morning, first trip since the test drive - low power again!

I can't believe the carbs have clogged again already, without being used.

So I'm presuming this is electrical?

I should add that I'm on Borneo, ohm meters, compression gauges and such are not available, just a local guy with a box of spanners and a local new boat dealer who can get Johnson parts (eventually).

It's not the fuel breather vent, because 1. it was open and 2. I forgot once and noticed because it had sucked the plastic tank concave...

Talking of fuel, it was the same fuel when slow, when fast and when slow again, so not stale fuel.

At this stage I'm guessing the power pack (what exactly does the power pack do, anyway? Some little black box thing?) or corroded wiring somewhere?

Or could it be fuel again?

What happens if you get water in the carbs? Would that block it somehow - or just throw non-igniting water through the engine? I ask because the tank and its breather vent are exposed to the rain. It's quite possible a few drops have worked their way in there, if the vent were left open.

(Yes, I know I should get a water separator, it doesn't seem to have one, just some sight-glass thing and a squeezy pump)


Any ideas?

A couple of points which I presume are irrelevent but I'll mention them anyway -

I usually leave the positive battery terminal disconnected, to prevent any chance of fire when the boat is unattended. When setting off it's just twisted back on by hand. This has never been a problem but today the starter motor was totally dead until the battery was twisted and fiddled with a lot - including pulling it out of its mounting to check the other connection. There's a whole bunch of wires under there that got pulled and moved around.

It was deffo making contact, no corrosion on the terminal or anything, but after some twisting around it suddenly came to life and turned the engine over. I find it unlikely there was a bad connection on that battery, so just wondering if I nudged some other wire somewhere?

Would, or could such a wire, away from the engine, cause such low power?

The other thing is the first new relay (solenoid) the guy fitted didn't work, he had to go get another one. Again, could it be it did work but had a bad battery connection or some other wire? Then it was clicking but not turning the motor, the replacement worked OK, though today it wasn't even clicking, until I just kept on twisting the terminal connector.

I'm presuming the battery connection and starter relay are nothing to do with the low power, but thought I'd mention them anyway :redface:



JB

 

[j_k_bisson]

Re: Reduced power, 80's Johnson 90 V4

Check the startor coil up under the flywheel. Where the wires come out of it there is two black coil's. They tend to leak black goo and it is a sign that the startor is going. If you had lost you tack, it would be a sign that your retifier is going. If it is your startor you will want to fix it ASAP as using it will lead to the retifier burning out.

So just check up under the flywheel for any signs of black goo leaking out from the startor on to the block. If it is. It is probably your problem.

 

[Jungleboat]

Re: Reduced power, 80's Johnson 90 V4

Kool, I'd have never have looked up/under there.

I'll check it out tomorrow for black goo (the boat is parked on the river)

"If you had lost your tack" I'm afraid I have no idea what that means? Tachometer cable? A lost track, sparking out?

So this rectifier, coil thingy, could explain the low power?

And if so it would affect all 4 cylinders, hence no power but not lumpy?

Must admit I'm a little confused over spark plugs, in that I'd have thought a spark is a spark is a spark, hence detonation - but I presume a weak spark somehow produces a weak detonation, sorta thing?


But anyway, thanks for the heads up regarding under the flywheel. I presume there's some sort of magneto under there. I have a vague knowledge of engines but didn't realize there's a separate coil





JB

 

[j_k_bisson]

Re: Reduced power, 80's Johnson 90 V4

"Tach" means the tachometer guage. Meaning not working. No feed pulse(voltage on sending wire)

The Stator produces the elecricity for the spark.

The retifier regulates the voltage of the electricity. AC to CD voltage. And supplis the pulse fr the tachometer.

The coils increases the electricity to make the spark happen.

The spark plug causes the spark.

There could be a number of things that cause the power loss. Any one of the components listed and more!

Best to check fuel, spark, and compression every time when trying to figure out what is wrong.

I was assuming that fuel was ok, But a fuel separator would help alot to keep the carbs clean.

These motors are known to have stator issues that would still let the motor run but at loss of power. The carbs can also cause this. As can a scored cylinder (due to faulty VRO pump).

I would check up under the fly wheel and all electrical connections. A cheap (no cost) and easyfix. Next I would check the compression (cost of a compression tester-harbour freight). and Last I would start playing with the fuel system.

The electrical system error I stated earlier (stator leaking) is very noticable.

 

[Jungleboat]

Re: Reduced power, 80's Johnson 90 V4

Thanks!

My basic understanding of electrical systems, gleaned from motorcycles years ago, goes something like 'Magneto is a magnet around copper coils to produce electricity, which it 'timed' via a spring-loaded gappy thing called "points", which goes to a coil for higher voltage, then to the spark plug'.

And on multi-cylinder engines there's a distributor in there somewhere, presumably after the coil - or before it. Dunno.

So I was surprised this thing had 4 coils, let along discovering it has 5 of em...



I presume if replacing the stator I should replace the rectifier at the same time - or are such things expensive?

For now it's staying firmly on the river but if I can get this thing reliable it will be used a few miles out to sea again, so I'm willing to replace all the electrical bits, if I can get hold of the parts.

I'd love to get a manual for this thing too but I don't know the exact model. I'll start another thread for that...


Thanks again!


JB

 

[emdsapmgr]

Re: Reduced power, 80's Johnson 90 V4

Your miss could be that one of the two lower plugwires is grounding out when the cowling is installed. (you said it fired OK with the cowling off.) Not unusual for older wires to short out against the lower cowling latches. When shipped from the factory, the wires are held away from the block and any other metal ground by rubber-coated wire holders. Over time, the wires holders may not be properly positioned and the wires can break down-short to ground on the two large rear cowling latches. If you have an inductive timing light, that may show you the condition of the spark on each plugwire. If you find a spark issue, you may be able to swap any of the spark plug coils to see if the problem moves. Also, many of these early 80's engines used twin power packs. They, too, can be swapped for testing purposes.

 

[Jungleboat]

Re: Reduced power, 80's Johnson 90 V4

This thing only has the one power pack. I don't think it's the original though, as while bolted on tight with 2 bolts it clearly doesn't line up with the original fitting.

I've been swamped with work lately (advertising writer) and the weather hasn't been helpful, so at present no further forward with it.

That the cowling is causing a problem does seem likely, as it's a real pig to get back on. In truth I often just use 2 latches insteal of all three!

Will try and check it out, cheers



JB

 

[emdsapmgr]

Re: Reduced power, 80's Johnson 90 V4

Please post the model number of your engine. Let's make sure we are talking about the correct ignition system. Always possible you have the wrong power pack if it does not match up with the mounting holes.