No resistance

I have been having one heck of a time with my idle. At 2000 rpms It will purr all day blip it it will sky rocket to 4000 rpm and hang there then slowly settle down. Now before any body says yes my carbs are cleaned to the edge of there life. Slide bores polished so much that you can read news print with them. The slide easily pass the clunk test. Enrichment jets passed the 10 foot squirt test. New shaft seals, installed properly. New o-rings on pilot screws, set at 3 out. Floats set at 17 mm dry, right at the top of bowl screw wet. Plug chops are a hot coco color rather a coffee and cream color. So I know it probably not the carbs. The kicker is some days it will purr like a mountain lion. Then you have THOSE DAYS that it wont idle, hesitates, acts like I am taking off in third gear. I am NOT having FUN!
Well today, it was one of THOSE DAYS . So I decided to look elsewhere. I started the bike and tried the spit slap test, (come on, you never spit on your finger and slap the headers. If it sizzles its running, if not, it is dead). Well #1 and #4 are dead at idle. Rev it a little they come to life. #2 and #3 passed the spit slap test. So i unplugged the primary to the #1 and #3 coil while it was running, nothing changed it was still running bad. Plugged it back in and unplugged the other coil it went dead. :idea: took the offending coil off checked the resistance, primary 2.5 ohms on the money. The secondary's --- nothing, open circuit. But it runs at speed! Hooked the coil up, started the bike it is idling bad. Took the # 1 wire off and hooked a spare plug up, started the bike, it is idling bad. Little to no spark. Revved the engine, I got better spark though it was more orange than blue. So my theory is that the coil has an open secondary but is allowing a spark to jump it at speed. But at idle not enough juice to jump it and the plug gap. Don't get me wrong it runs fine at speed, but it makes it interesting when you have to come to a stop and you have to play with the throttle while using the front break. I know this post was a little long winded, but I see so many other riders on this post with there bikes running same as mine I just had to throw it out there. Any and all comments (good or bad) are very welcome.

 

can you swap the coils around and see if the problem follows or stays?
sounds like you have done the hard part of troubleshooting but just need a little advice to confirm it

 

No need the secondary has a short. My question is can a spark jump that gap at speed and run fine, but can't jump that gap while at idle?

 

uhhh - i'm assuming you mean the secondary is an open circuit?

do you have an analog or digital ohm-meter? an analog could look like an open circuit even when it's not. although, i'm pretty sure a spark plug would measure as an open circuit, too. could be it's not a true open circuit, but a circuit with a huge amount of resistance. that would, i think, cause the coil to not work until it's getting plenty of juice from high revs.

 

I am using a digital set at 10k ohms and it is showing absolutely no resistance. The other coil shows 11k ohms on the same setting. That one is within spec.

 

Try taking off the spark plug boot. It has a 5k ohm resister built into it test the coil with out the boot on it. Then test the boot for 4k to 5k ohm resistance. The Haynes manual says nothing about this. They just say to test for 11k ohms with the boots on.(secondaries)
James

 

No. The Haynes resistance is with the boots off... but you're right that they don't say anything about taking them off, so a lot of people wonder why their coils read too high in resistance.

However, Razz's description of the good coil reading 11K when the meter is set to the 10K range sounds a bit odd. Most non-auto-ranging meters will show open when you go beyond their range. Does the bad coil still read open on the 100K range?

In answer to your main question: yes, you could have a break somewhere (probably in a wire or where the wire connects to the coil) that the spark is jumping at higher RPMs. Since a new coil is in order anyway, you could try the coil surgery technique (search that to see posts on how to replace wires) and see what the resistance is of the coil itself with the wires removed. You might be able to salvage the coil with new wires.

 

thanks SQLGuy I didn't know that.. they show the test done with the boots on in the diagram so i just figured...
thanks,
James

 

Stop the presses. Yesterday on the way home from my sons football game, (we won 49-20) the bike barely got me home. So it was having one of THOSE days really bad. I done a plug chop. All was OK put all but #4 plug back in, started the bike, I was getting spark.killed the bike but left the ignition on. Put the plug and wire back on. Went to hit the start button, click, click, click. What in the @$#%&,,,, Dead battery? Put volt meter on, only 11 volts. Out comes my trusty digital battery charger and I put it on charge. 4 hours later I started the bike and it ran fine, idles at 1500 steady. But the coil is still bad though because it does not have any resistance at all on the secondary's. Could it be just the wires or do you all think it really is the coil?
Also, how do you take of the plug boots, or are the removable?

 

The plug boots are replaceable. Counter clock wize like unscrewing a nut.

 

Yes, it could be just the wire. The open could be in the coil itself or in the plug wire. Why they made a coil with the plug wires built in is beyond me. A couple of guys here have managed to change the plug wire. I don't have time to look for the thread now though.

Good luck,
Mike