Tracking down a weak spark issue?

[Guest]

Bike has started giving me issues starting - it will fire on full choke but run really rough, it'll die before it warms up then won't refire even with starting fluid. Checked the spark on cyl 1 and 4 and both have a really weak/inconsistent spark. Has anyone dealt with this before? I couldn't imagine both igniters would go back at once... help!!

[Cipher]

check primary and secondary coil resistance as per the manual

[Big T]

What bike are we talking about?
Have you cleaned your wiring harness and confirmed that you have 12 volts at the coil?

[cowboyup3371]

How much fuel is in the tank and are you getting any to the carbs? How long has it been sitting? When was the last time the carbs were cleaned?

[fastbysuzuki]

I couldn't imagine both igniters would go back at once... help!!

You have two igniters Or do you mean coils ? There is a good document to follow this is for a gs850

Testing The Ignition System.




Properly localizing a problem with the ignition is sometimes a bit confusing and the following below should of assistance:
Basic test, remove spark plugs. Fit them to the plug HT leads and ground them to the engine. Turn engine with starter and see if plugs spark. If any one spark plug does not spark swap it out. If the spark seems good on all 4 plugs, the ignition system is very likely in order. If spark is not present or very weak proceed with the following tests.
Remove the tank, left side cover, seat and signal generating unit (pickup) cover at bottom right of engine.
A good habit is to check the coils and igniter to see if they do not get very hot once the ignition is switched on, as this will most likely be the indication of a failed component of faulty connection or wire.
If the spark is weak but present, inspect the HT leads and plug caps. Suspect coil wires and spark plug caps, or voltage at the coils and thus the battery condition. It could also be due to coils with partially shorted windings, but do not jump on this cause immediately, and they may get hot.
Overheating coils with no spark may also be due to them getting a permanent full ground either from a faulty igniter or a grounded and pinched wire. Disconnect the coil plug connectors and proceed with tests.
Measure the battery voltage directly across the battery terminals. If lower than approximately 12.6V first charge battery fully before proceeding.
Next measure voltage over the coil connector plug, orange/white wire and the battery negative terminal. If lower than 12 Volt inspect the wiring for poor contacts and localise cause of voltage drop.
Again measure directly across the battery, but pull off the spark plug leads to prevent engine from firing and swing with starter. While starter is turning the voltage should stay at least above 11 Volt. Also swing the starter with the headlights on to see that the voltage does not drop significantly at the coils while the starter plus headlights load the battery, which could prove that even if your battery is fully charged, it cannot give full or sufficient current and is on its way out or your starter may be drawing excess current (usually unlikely if starter is spinning at full speed) and pulling the battery down. If it drops much lower, charge battery fully or have it load tested and replaced if faulty.
If all is well up to here you can assume your battery and the positive feed to your coils are in good order.
With the coil plug connectors disconnected, use an ohm meter and measure the resistance of both windings on each of the coils. Exact resistance measurements are not too important, but continuity of the windings close to the approximate resistance values given indicates that the coils are in good condition. It must be noted that it is possible for the coils to only show up a fault when at higher operating temperatures, but this does not happen frequently.
Ignition coil resistance:
Between the two HT plug caps of the same coil, secondary HT winding, approximately 30 - 35 K ohm
Between the orange/white and white on the first coil and orange/white and black/yellow on the second coil, primary winding, approximately 2-5 ohm. If this test is within limits you likely have two good coils.
Locate the igniter and disconnect the plug with the blue and green wires coming from the signal generator (pickup) at the right bottom of the engine. Test the resistance across these wires coming from the signal generator pickup coils, it should be approximately 250 - 360 ohm. If this is in order you have proved the pickups and the wires to be good.
The little back box or igniter is now tested as follows. With the ignition on, kill switch on, test for 12 Volt DC between the orange/white and the black/white wires in the plug going into the igniter. This proves that it is getting the correct voltage.
The next step is to prove whether the igniter is powering your coils. Remove all 4 spark plugs and connect the HT lead caps to a spark plug #1, #2, #3 and #4 which is grounded and located to enable you to see the spark. Ensure all the connector plugs are back in, except the one with the green and blue wires from the signal generator.
To simulate the small voltage generated by the pickup coil, prepare an ordinary 1.5V dry cell with two wires red for positive and black for negative. Connect the negative black wire from the dry cell to the blue wire on the connector plug going into the igniter. Switch on the ignition and kill switch to power the igniter and briefly touch the red wire from the dry cell positive to the green wire connector going into the igniter. You should see a spark on plugs #1 and #4 when you touch the wire and on #2 and #3 when you remove the wire. If this works your igniter is in a working condition.
One other check that is often overlooked. Run the bike at night with all lights off in a dark area and check that no sparks are jumping from the HT leads to the frame or tank. If so they may need replacing.
At this stage if all tests have passed you MUST get a spark at all the plugs when everything is reconnected and the engine is turned with the starter.
If a spark that was previously missing has mysteriously appeared, have a very good look at your wiring and connectors, as something may be making intermittent contact and corrected itself temporary when you moved the wires.
If there is a spark, but the engine will not fire, it could be due to ignition timing, valve timing or fuel problems. Ignition timing and valve timing problems are more likely on a bike that has not run yet after being disassembled and more unlikely to be the cause if the bike was not taken apart and was running before.
A quick test with a few drops of fuel directly into the cylinders before replacing the spark plugs and then trying to start will prove it to either the fuel system or ignition system.
If the engine then starts and runs for a few RPM's the ignition is correct and you need to look at the fuel and carburettor side.
If the engine does not fire, but occasionally gives one load pop through the carburetors or even exhaust, it may be igniting when the valves are open, the valve timing may be a problem, cam chain or swapped wires from pickup - plugs firing at wrong time.
Other reasons could be extremely low compression, too tight valve clearances, thus not closing fully (usually unlikely on all cylinders at the same time, but plausible), carburettor faulty or dirty, fuel line, filter or petcock faulty. Filter can cause an airlock if not positioned properly to allow free gravity feed.
Then finally the ignition timing must be set properly. At less than 1500 RPM connect a timing light to #2 or # 3 spark plug and check that the timing marks line up for 2-3 on F, then move to #1 or #4 spark plug and check that marks line up for 1-4 on F. Check the advance by pushing revs up to 2350 RPM and the timing marks should both line up on the 45 mark behind the signal generator mounting plate through the sight hole at the top. The three mounting screws can be loosened and the mounting plate can be moved slightly in the elongated holes to meet this.

[Redman]

Good that you are looking at the sparks.

..... cyl 1 and 4 and both have a really weak/inconsistent spark. ......
..........................................

Spark Plug 1 & 4 are operated by the same coil (both at same time).
(plug 2&3 are operated by the other coil, both at the same time).
Cause of 1&4 being weak (while 2&3 are good) could be a weak/marginal coil for 1&4.
But I would first check the spark plug caps of 1 & 4. Each Should measure about 5k ohms. They do go much higher ohms with age and heat, and can go infinite resistance (open). Check those. They do twist off the wire. Cost about 4-5 bucks each.

>>>later note: When you say 1&4 are weak, I have assumed then that 2&3 are good, and we are looking for what could effect 1&4 only ......
but if the real situation is that 1&4 and 2&3 are weak, well then, that is different situation. THen I would first suspect low voltage at the coils, check that compared to battery voltyage. Other suspect is that battery is marginal, try charging the battery on a charger for some time.

.....
...........................................I couldn't imagine both igniters would go back at once... help!!

Please answer about "both igniters".

[Fjbj40]

Simplest and cheapest first.

Swap coils, see if problem follows or stays. If it changes plugs then problem is coil or caps, if not then problem is power feed to affected coil side. By doing it this way you are Killing 2 birds with one stone. And it's a fast painless way of the process of elimination.

Best of luck and report back!

[kevinl]

Apologies for the terrible first post in this thread. Bike is an '80 gs550 and it appears that I was referring to the coils as "ignitors" - I've also realized that when I was testing the spark I was attempting to ground the plugs on my engine which is painted. I grounded the plugs to a known good ground and I'm now seeing a good spark

Lesson from this if you're tracking down a similar issue: Confirm you're getting a good ground via voltmeter before testing spark

[Redman]

Good that you figured that out.

You still having this problem.....

................, it'll die before it warms up then won't refire even with starting fluid..................

?