Ignition on two strokes

[baiwan]

Do spark plugs light twice in a stroke of each piston?
There are 2 magnets on flywheel for the timing base at 180 degrees and two or four sensors at 90 degrees in a four cyl engine.
This shows one magnet passes sensor twice per 1 rpm - 1 stroke and spark plug fires twice or there is a counter in power pack and fires every second time.

 

[R.Johnson]

Re: Ignition on two strokes

The Johnson-Evirude engines Do not have a double, or what is called a waste spark ignition. Although I believe the early 4 stroke twins did have.

 

[jonesg]

Re: Ignition on two strokes

older 2 strokes used points to trigger one spark per.
new ignitions use electronics and timing base trigger,
mine is optical , the timing wheel having cutouts where the light flashes thru.

double sparking can occur and is a fault, you can see it if you put a timing light on a cylinder plug wire and it lights up twice on the timing wheel.
Its all in the manual.

 

[baiwan]

Re: Ignition on two strokes

What could cause this fault? And what's the result?

 

[jonesg]

Re: Ignition on two strokes

depends which engine, on optical ignitions the early 150 and 175 HP engines did not have the tension washer on top of the sensor encoder wheel. This washer is necessary to keep the encoder locked in place. If it is not on the engine, you'd see erratic firing of the cylinders.

lack of RF shields behind coils on mine can cause power packs to go nuts too, theres other causes I'm sure.

 

[baiwan]

Re: Ignition on two strokes

depends which engine, on optical ignitions the early 150 and 175 HP engines did not have the tension washer on top of the sensor encoder wheel. This washer is necessary to keep the encoder locked in place. If it is not on the engine, you'd see erratic firing of the cylinders.

lack of RF shields behind coils on mine can cause power packs to go nuts too, theres other causes I'm sure.

Mine is magneto ignition. I have faulty charging probably stator and double reading on the tacho which I thing gives me the trouble?

 

[wilde1j]

Re: Ignition on two strokes

Has the tach always read double? If so, the pulses/rev on the back of the tachometer may not be set correctly. The tach reading high does not mean the plugs are sparking twice per flywheel rotation! Also, the tach itself may be faulty. Check with a known good tach to be sure.

 

[F_R]

Re: Ignition on two strokes

Has the tach always read double? If so, the pulses/rev on the back of the tachometer may not be set correctly. The tach reading high does not mean the plugs are sparking twice per flywheel rotation! Also, the tach itself may be faulty. Check with a known good tach to be sure.

It would help to know what you are working on. But just general information, one magnet and one sensor can fire two cylinders. It can do that because the magnet has a north and south pole, generating a positive or negative pulse as it passes the sensor. A negative pulse fires one SCR in the power pack and a positive pulse fires the other one.

None of this has a darn thing to do with a tachometer. The tach counts the AC pulses from the alternator. The ignition system has nothing to do with the tach. The tach has to be programmed to count the AC pulses according to how many the alternator produces per rev.

 

[jonesg]

Re: Ignition on two strokes

Baiwan,

the best approach is list your engine, hp, yr and model number, then the symptoms.

 

[baiwan]

Re: Ignition on two strokes

I have tried this and didn't get much.
I have bad ignition, no charging and double reading on tacho and spark plug wires, measured by three different types of external tacho, to compare with mine.
Electronic on spark plug wires - show double, mine shows double, while light and mechanical on fly wheel show normal.
When I throttle without moving time base engine accelerates smoother, then when I move time base stuttering increases.
Timing done by timing light - 28 deg, as it says in the manuals.
I blame the stator. It could be the source of both troubles.
Next week I'll test more thoroughly, the boat is away from where I live.
I didn't realize I was wasting your time.
Apologies.

 

[tx1961whaler]

Re: Ignition on two strokes

It's not that; you have not posted which engine model you are working on so people are confused.
I think that you are referring to a 1982 Johnson 90 HP from this previous thread ?
http://forums.iboats.com/showthread.php?t=316419

Were the stator and rectifier replaced?

 

[baiwan]

Re: Ignition on two strokes

I am waiting for delivery of stator, the rectifier is o.k. I'll make a bench test on the regulator and test run without if faulty.
I have a rectifier test solution.

 

[baiwan]

Re: Ignition on two strokes

Stator coils are ok, now.
Checked with a new rectifier, regulator working, checked by DVA on running engine.
Double reading on tach remains and double fire on all four cyllinders.
I have used the same tacho on two and three cyllinder engines, just switching to 2 and 3. Now the switch is on 4.
I've got this engine used and it didn't work well when I bought it.
Now I intend to change power packs.
Timer base is good after bench test.