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Ignition as it relates to the 4 cycles

  • Thread starter Thread starter GS1000G Shopper
  • Start date Start date
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GS1000G Shopper

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I'm working on installing a Microsquirt controller on my red GS1000G. I'm having issues getting it started, so while I'm waiting for the gurus on that forum to help, I thought I'd post here for help from our ignition gurus :). I'm trying to figure out when a spark should fire for each cylinder. I know the setup is a wasted spark (fires on compression and exhaust for the paired cylinders) one due to the two coils for four cylinders.

The engine is of course a 4 cylinder 4 stroke:
Intake
Compression
Power
Exhaust

The firing order is 1-2-4-3.

The stock 1981 GS1000 uses two pickup coils on the right side of the engine that are triggered by a single tooth piece that is on the crankshaft end. The tooth changes from 17 degrees Before Top Dead Center (BTDC) at less than 1500 RPM to 37 degrees BTDC over 2350 RPM (shop manual specs). The pickups have three wires- one to each coil, and a common ground wire. These wires go to the ignitor box, which controls the coils.

From what I can deduce, as the tooth lines up with the rear coil (1-4), this is 17 degrees BTDC for those pistons. 180 degrees of crank rotation later, and the tooth lines up with the front (2-3) coil.

My question:
Is #1's power stroke #4's intake stroke and vice-versa? Based on the cam lobes and from what I've read about wasted spark, I think this is the correct answer.

I'll throw a wrench in here in that I have segreated the pickup coil wiring for the Microsquirt so each coil is independent, but the physical movement of the engine is the same. I have not yet figured out via the software to allow my 4 cylinder engine to run as two 2 cylinder engines, so I'm researching how the original system operates. The MS has two ignition inputs and two outputs. I have wired the 1-4 pickup coil as one input, and the 2-3 coil as the other. The outputs are the same, output 1 is 1-4, and 2 is 2-3.

My "twin trigger" setup is supposed to work with 4 cylinder 4 stroke wasted spark ignitions, but I do not have something set up correctly.

Thanks for any advice, education, or info.
 
GS1000G Shopper said:
The engine is of course a 4 cylinder 4 stroke:
Intake
Compression
Power
Exhaust

My question:
Is #1's power stroke #4's intake stroke and vice-versa? Based on the cam lobes and from what I've read about wasted spark, I think this is the correct answer.

I have not yet figured out via the software to allow my 4 cylinder engine to run as two 2 cylinder engines, so I'm researching how the original system operates. T
Click to expand...
I don't know if this is what you are looking for, but when #1 cylinders plug is firing before TDC, #4's cylinder is firing on it's exhaust stroke.
 
Think about it this way; 1 and 4 are at TDC at same time- if 1 is just about to fire (power stroke), then 4 has just about finished its exhaust stroke. As 1 piston heads down on its power stroke, #4 piston is on it's intake stoke . one revolution of crankshaft later, the situation is reversed- i.e. 4 is about to fire and 1 is finishing its exhaust stoke. remember that crankshaft makes two revolutions for one revolution of camshaft(s).
 
Last edited:
All of the above answers seem to be correct, and they seem to not disagree with what you originally said, so I'm not sure what your confusion is.

Like just about any four-stroke engine, the spark will fire just before TDC. Because it is before TDC, it is technically still on the compression stroke.
When #1 is on compression, #4 is on exhaust, so the wasted spark in #4 will happen at the end of exhaust, just before intake.

Of course, 180 degrees of crankshaft rotation later, the same thing happens for #2 and #3.

If your engine is not starting, you might want to use a timing light to make sure you don't have your inputs swapped.

.
 
Perhaps the ambiguity that you are wrestling with can be deduced from the diagrams..... :o

Beyond the obvious firing order and cycles of a 4 stroke, an interesting tidbit is that it is the rear igniter pickup that always fires the 1-4 coil and it is the front igniter pickup that always fires the 2-3 coil regardless.

I probably figured this out by inspection of my 1100.

On a 2 cylinder is like 1/2 of a 4 cylinder in that the rear fires cylinder 1 and the back fires cylinder 2.
 
posplayr said:
I did this a while back

http://www.thegsresources.com/_forum/showthread.php?t=168652&highlight=firing+order



Yes that is clear from the first figure.

I see there was little interest in the original posts or just a general consensus that the figures were correct, so they should answer your question.
Click to expand...

Thanks. I did "firing order" as a title search before posting and read about a half dozen threads. Obviously, that was not one of them, but your diagram was what I was looking for. :o
 
I've learned ambiguity is SOP for anything Mega/Microsquirt. I look up how to wire a dual ignition, and the instructions are for a different firmware version than what I have, or a different board (hardware). The Microsquirt is basically the same hardware as a Megasquirt 2, but there are differences, notably in driving coils.

Then there is the software. I use Tuner Studio, and recently found a relevant page that listed an older SW- Megatune.

If I use the latest firmware for my V3 (hardware) Microsquirt, it does not recognize the ignition input, so I used what is known as MS2 Extra.

It's certainly a maze and a learning process. Once I get it figured out, I should have a decent end result. I'm thinking I can make the process simpler by using the OEM pickup coil as-is for a fuel-only setup.
 
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