TOPIC:

My bike went from running great to running really rough at low rpms. I checked all fuel supply possibilities, poss vac leaks, filter. My last check was with a timing light. Well 1 n 4 looked real good then when it came to 2 n 3 it was very speratic. At high rpms ( above 3 grand) it runs fine but wants to die at lower rpms. I have a book for the 900-1000 kzs and I am wondering if the coil check is the same for my current bike. Any tips would be appreciated. Thanks in advance!!

Some good checks have already been made. But might not be a coil issue, so please bear with some questions.

First -- What is condition of the battery?

The battery is in good condition, as far as I can tell. The headlight is not affected by the brake light or any other additional load. Qs are great, anything to help me locate the problem!

Are these the original coils? Plug-wires? Plug-caps?

As related, My bike went from running great to running really rough at low rpms: Did this happen suddenly during a ride, or over some course of time?

Would install brand-new factory spec sparkplugs, and test run. If everything's fine, would quit reading and go riding.

Believe coil check method shown in book for the 900-1000 kzs is same as for current bike. However ohm rating of coils may differ. Would check and compare ohm measurements of both coils to determine whether 2/3 coil equates with 1/4 coil.

Coil may be okay, but not getting sufficient voltage, or not getting proper signal from igniter (could be poor wiring or loose connector somewhere).

Coil may be okay and getting sufficient voltage with proper signal from igniter, but with defective sparkplug caps or high tension wiring, or faulty connection between coil>plugwire or plugwire>cap or cap>plug.

Would visually check spark with plugs removed.

Would measure battery voltage between terminals at idle rpm (look for 12 volts), and at 3000-4000 rpm (look for 14-16volts).

Would measure voltage reaching coil primary winding on each coil (ignition switch ON) to determine extent of voltage drop between battery and coils.

Given the questionable results with 2/3 from checking with timing light, together with good performance above 3000 rpm but wanting to die at lower rpms, an ignition issue does seem to be a prime suspect.

Nevertheless, while the plugs are removed to view spark quality, would perform compression test (remembering to hold throttle wide open). If low psi, would assure valve clearances are to specs.

Remember -- The secondary high tension voltage runs in a loop from coil through both plugs back to coil. So any fault in either plug or either plugwire or either cap or any connection within the loop will likely cause firing problems in both cylinders involved. Therefore, the coil may be okay, with the issue being (a) somewhere else in the loop, or (b) in getting sufficient voltage or proper signal to the coil.

A fun test for plugwire leakage is to spray water over the plugwires and caps with engine running in a dark garage, and watch for sparks.

Not saying it can't happen, but would seen unusual to me for a coil to perform okay at higher rpm but not at lower rpm where everything else is the same.

Now after all that, cause of the problem may yet be a faulty coil as originally suspected. But that's better than first installing a new coil and then still having the same issue.

Good Luck!

Ok so here are a few pics of what I have! The coil with the upgraded wires, and the ign. Note the yellow wire leading to the 2-3 pickup and how it is exposed. I did put a know to be good coil, good wires and good heads on the wires setup on and the bike still has the same problem. HELP

Patton said:

Remember -- The secondary high tension voltage runs in a loop from coil through both plugs back to coil. So any fault in either plug or either plugwire or either cap or any connection within the loop will likely cause firing problems in both cylinders involved. Therefore, the coil may be okay, with the issue being (a) somewhere else in the loop, or (b) in getting sufficient voltage or proper signal to the coil.

This is a little confusing to me, please help!

I checked voltage at the battery with these results. Off 12.55, when the key is on, a steady drop when the bike is started good jump to 13-14 volts! Voltage at the coil with the key on is 11.51 volts and it is consistant between the two coils.

The effect I am having while I am riding is this, if I keep the rpms above 3000 its ok, when I start to accelerate the rpms drop and the bike bogs down terribly! During this bog period the bike moves very slowly and once it kicks in, usually without notice its back to golden and I need to hang on because it usually happens without warning.

I need to track this problem down because my bike is my current mode of transpo to work and I dont want to have to ride it in this condition for fear of it causing more problems. Please help!!

Voltage at the coil seems okay.

Am thinking no problem due only to yellow wire
exposure, because no obvious short appears.

Because the same problem continues on #2/3 after
testing with another known good coil, good wires
and good leads, am thinking any ignition fault
lies elsewhere besides in the #2/3 coil and
elsewhere besides within the #2/3 secondary
(high tension) loop.

The sporatic timing light test on #2/3 casts
suspicion toward the righthand side pick-up,
or possibly an intermittent short or frayed
internal wire somewhere between the
pick-up > igniter > coil.
Would double-check integrity of wiring
and connections in areas between
pick-up > igniter > coil.

Am thinking both the righthand side pick-up
and igniter are probably okay, because there're
both working fine over 3000 rpm. Could re-test
after installing another known good igniter.
But would first check the connectors
in wiring to and from the existing igniter,
making sure they are clean and tight.

But for the sporatic timing light test on #2/3,
would usually think "clogged carb pilot circuit"
where performance comes on strong after bogging
below 3000 rpm.

Do #2/3 plugs have a good quality spark when
viewed outside the cylinderhead?
What about compared to spark on #1/4 plugs?

Btw, did the problem present itself suddenly
or more gradually develop?

Good Luck!

Since you apparently don't have a manual, then you need to get religion and go HERE and download "The Bible"

Click on the link and your eyes will open wide in wondrous delight

Hey thanks everybody for your help! What I was suffering from was what I like to call over doin it! I encountered a problem and went for the heart of what I suspected. Problem being my checks were all comming back with fair results. What I didnt check, and what made itsself very obvious today was... the battery connection. Seems the connection on the positive terminal had come somewhat loose. Not so loose that I would not get any power, but loose enough that when I was riding, it would vibrate and cause weak power to all the units of the bike. Hence, my charging voltage check was fine (tested at the leads) My battery power was fine(tested at the terminals) and my coil voltage was fine (tested with the bike on, not running) None the less I have learned a very valuable lesson. That being that not all problems are complicated and tough, sometimes we must just take the time to check the basics! End result of tightening the leads? Bike is running like it has always, smooth, fast, and fun!! Thanks for all the help anyways everone, and Steel, thanks for thte link, very cool!!

jrjstuff wrote:

...Bike is running like it has always, smooth, fast, and fun!!..

Thanks for the report! Glad it's up and running!