Kawasaki Ninja ZX Forum banner
1 - 15 of 15 Posts

·
Registered
Joined
·
50 Posts
Discussion Starter · #1 ·
Hi all. I just bought a 2000 zx7r which only has a couple thousand miles on it and is completely stock, but is running a little rough and occasionally doesn’t want to start. (sometimes when hot, sometimes when cold) The previous owner put in a new battery and cleaned the carbs. Says he took them all apart but I couldn’t say for certain how good of a job he did. He’s an automotive service technician so I would think he had some idea what he was doing, but who knows.

Here's what I did so far:

I synched the carbs and have the mixture screws all set at 2 turns out. I put in new NGK CR9E plugs. When cranking I see either a thin blue spark or a yellow spark at all plugs. The spark will jump across a 7mm gap but is definitely yellow during that test.

The coil primary resistance is 3.8 on both coils, the specs are 2.3 – 3.5 ohms. The coil secondary resistance is 14.66 K on both coils, spec is 12 – 18K ohms. The battery voltage is 12.99 with the ignition off, spec is 12.6 V or more. Charging output is 15.25 @ 4000 rpm, spec is 14.2 – 14.8 @ 4000 (I tested this by connecting a voltmeter to the neg and pos battery terminals while holding the throttle at 4k, not sure if that is the correct way to test charging output.)

Here is what I'm wondering:

Are the coils enough out of spec to be causing the weak spark, and is that enough to cause the described problem? Do the symptoms point to something else?

Don’t know if this has anything to do with anything, but if I spray a little water from a squirt bottle onto the individual header pipes, the water will sizzle off the number one header but stays on the other three and slowly evaporates off (was trying to see if it was firing an all 4).

Any help would be appreciated, thanks.
 

·
Premium Member
Joined
·
13,222 Posts
Check the voltage regulator and see if you can get someone to swap you a couple of known good coils. The fact that the primary resistance is too high and so is the charging output tells me the regulator may have gone bad and put too much juice into the coils, possibly toasting them in the process.
 

·
Registered
Joined
·
50 Posts
Discussion Starter · #3 ·
Thanks for the suggestion. Unfortunately, the voltage regulator is part of the alternator on the 7, I don’t know that there is any way that I could check it myself. Will have to remove the alternator and take it to the dealership for testing.
 

·
Premium Member
Joined
·
13,222 Posts
Still might be cheaper than getting new coils and toasting them too. Once you know the alt/reg is good to go, you can try some different coils to see if that fixes the problem.
 

·
Registered
Joined
·
9,979 Posts
Whoa! :headscratch Don't you think it odd that in your commentary OP you state the bike only has a few thousand miles on it AND the previous owner COMPLETELY disassembled the carbs, yet you're going about troubleshooting as though there's something already wrong with the electrical. Wouldn't it make more sense to concentrate on items the 'automotive service technician' PO may have fouled up when he took them all apart? :dunno

I'd be going over the carbs with a fine tooth comb, like I did for a newb's Ninja 750R, who's PO was also an automotive mechanic. What a fouled up mess those turned out to be. I spent five hours repairing and replacing. Parts were misplaced, jets were WAAAAY over jetted for sea-level, let alone 5,000 AMSL, and some of the key components to the pilot air screws were lost. The guy was a total numb nuts!
 

·
Registered
Joined
·
50 Posts
Discussion Starter · #6 ·
That’s true hammerhead, though I hate to have to drain the coolant, and replace the o-ring on the alternator and the o-ring on the water pump pipe, and take the alternator down to be tested if I wasn’t fairly certain it was causing problems. But if the charging output being .45 over spec is enough reason to believe there is a problem with the voltage regulator, then I’ll need to do it regardless.

Nope e1 ZX9r, I didn’t think it was odd. He told me he disassembled and cleaned the carbs but did not synch them. I already considered that he could have done a poor job with the carbs (which I indicated in the post), but while I had everything apart to synch the carbs, it was pretty easy to replace the plugs and check the spark while I was there. At that point I noticed the weak spark, so I began testing for reasons why the spark might be weak and posting this question as to whether a fat blue spark is truly needed. I don’t know how the carbs could make the coils or the charging voltage test out of spec . I saw no point in further fiddling with the carbs while something else could be wrong that could make it difficult or impossible to tell if the carbs were right. If a number of people respond saying something like “that coil and charging voltage is normal for that bike” or “any spark is enough, doesn’t need to be fat and blue”, then I would go back to the carbs. That’s the reason for the post and why it’s titled “how important is the fat blue spark”.

I don’t think it’s odd that a 12 year old bike that has been driven fewer than 2600 miles might need to have the carbs cleaned. It also seems quite possible that the PO rebuilt the carbs because it was running rough while the problem may have been something else, like weak spark.
 

·
Registered
Joined
·
9,979 Posts
I apologize. It was rude of me to not answer the question. I'm sitting back down with my popcorn.

 

·
Premium Member
Joined
·
13,222 Posts
That’s true hammerhead, though I hate to have to drain the coolant, and replace the o-ring on the alternator and the o-ring on the water pump pipe, and take the alternator down to be tested if I wasn’t fairly certain it was causing problems. But if the charging output being .45 over spec is enough reason to believe there is a problem with the voltage regulator, then I’ll need to do it regardless.

Nope e1 ZX9r, I didn’t think it was odd. He told me he disassembled and cleaned the carbs but did not synch them. I already considered that he could have done a poor job with the carbs (which I indicated in the post), but while I had everything apart to synch the carbs, it was pretty easy to replace the plugs and check the spark while I was there. At that point I noticed the weak spark, so I began testing for reasons why the spark might be weak and posting this question as to whether a fat blue spark is truly needed. I don’t know how the carbs could make the coils or the charging voltage test out of spec . I saw no point in further fiddling with the carbs while something else could be wrong that could make it difficult or impossible to tell if the carbs were right. If a number of people respond saying something like “that coil and charging voltage is normal for that bike” or “any spark is enough, doesn’t need to be fat and blue”, then I would go back to the carbs. That’s the reason for the post and why it’s titled “how important is the fat blue spark”.

I don’t think it’s odd that a 12 year old bike that has been driven fewer than 2600 miles might need to have the carbs cleaned. It also seems quite possible that the PO rebuilt the carbs because it was running rough while the problem may have been something else, like weak spark.
I don't know if a half-amp of overcharge says it's bad, but since you get zero warranty on electrical parts, I would check before I started replacing stuff wholesale. Seems like there should be a way to check out the regulator without removing the alternator
 

·
Registered
Joined
·
50 Posts
Discussion Starter · #9 ·
I don't know if a half-amp of overcharge says it's bad, but since you get zero warranty on electrical parts, I would check before I started replacing stuff wholesale. Seems like there should be a way to check out the regulator without removing the alternator
I’ve been searching but haven’t found a way to test it yet, still looking. It would be a bummer to replace the coils and then have them go bad too because the voltage regulator was going bad. Also still hoping to hear from anyone about whether the spark or the coils and charging being slightly out of spec is actually something to be concerned about.

I apologize. It was rude of me to not answer the question. I'm sitting back down with my popcorn.
I didn’t think it was rude of you to not answer the question and do believe it’s quite possible that the PO didn’t get the carbs back together right or possibly even actually cleaned right. But I don’t want to tear into them before I know if there are other issues to deal with first (or instead of).
 

·
Registered
Joined
·
517 Posts
I believe a nice blue spark is neccessary as I have heard a weak, yellow spark may not even fire under compression. Regardless, you should have a nice blue spark if everything in the ignition system is working properly.
 

·
Registered
Joined
·
1,761 Posts
fat blue spark in ambient air is unlikely to begin with, not impossible. every spark plug ive ever tested has never given me that without being under pressure. at my old job we had a chamber tester that would simulate the increased pressure of a cylinder under pressure. then i would see a nice fat blue spark
 

·
Registered
Joined
·
50 Posts
Discussion Starter · #13 ·
fat blue spark in ambient air is unlikely to begin with, not impossible. every spark plug ive ever tested has never given me that without being under pressure. at my old job we had a chamber tester that would simulate the increased pressure of a cylinder under pressure. then i would see a nice fat blue spark
That's interesting. Makes it seem a bit odd that the manual suggests the need for a fat blue spark if you aren't going to get one in regular "home mechanic" testing situations. Though maybe the Haynes manual is using language from the shop manual, where it might be possible to test in that way.

I talked to a friend of mine who works at an independent auto shop, and he indicated that when testing, they just look for "spark" and don't qualify it any further than that.

If what you say is correct, then the spark should be a non-issue and all will likely be well when I get the carbs sorted out.
 

·
Registered
Joined
·
1,761 Posts
id agree with your friend on just looking for spark... decreased air pressure decreases the resistance across an air gap where increased pressure increases the resistance... a fat blue spark means a much more powerful current in order to create a spark. the same reason on airplanes that have turbos, the magnetos (mechanically powered ignition units) are pressurized for higher altitudes so they dont arch themselves out
 

·
Registered
Joined
·
50 Posts
Discussion Starter · #15 ·
Got the carbs sorted and back on the bike. Did the airbox mod while I was there and put in smaller mains. Found that the PO had reused the old o-rings on the float valve seats, which look like they were put in dry as they were stretched out of position. He also had the different sized mains in the wrong order. It starts up easily now and runs very nice with all header tubes heating up as close to the same as I can tell with my primitive meathods. so I expect the yellow spark wasn't causing any problems and "fat blue" is either not necessary or not visible under these conditions.
 
1 - 15 of 15 Posts
Top