I hope my experience diagnosing this tricky issue with my GSXR 600 helps someone else.
Diagnosing the Problem With My GSXR 600
After sitting for around six weeks my 2000 Suzuki GSXR 600 started to run crappy but in a way that was difficult to diagnose (for me anyway).
The bike was running a little rough at first, and I noticed a strange change in RPM as I came to a stop light. Throttle response was not very good, and when I revved it up while sitting there in neutral, it didn't want to wind out. Not knowing what the problem was, I let it sit for a couple more weeks, and then when I went to ride the next time it ran even worse. It didn't want to idle without me giving it gas, and it sounded like it was running only on three cylinders.
Beginning to Troubleshoot
The next step was to get out the factory manual and start to troubleshoot while my gut told me that it was a carb problem. As usual, the manual was leading me on a wild goose chase and had me thoroughly confused thinking that the problem could be anything from the CDI to the kickstand switch.
Anyway, I managed to keep the bike running for 30 seconds or so, and then I shut it down and felt each header to see if one or more of them was cold. It turned out that the number three tube was only warm while the others were hotter than hell. I then started the bike again, and while it was running, I pulled the number three plug wire, and yep, there was no change in the way the bike was running. I then rigged something up so that I could see how my plugs were sparking.
I got a faint white spark, not a fat blue one like they say you are supposed to have. I then made sure that fuel was getting to the carbs, which it was, and I also knew that the vacuum-actuated valve on the fuel tank that allows the fuel to flow was working correctly. I could also see that there was nothing wrong with the fuel filter nor was any of the ignition wiring damaged.
The manual states that if there is a weak spark or no spark at all, the problem could be with the signal generator or the CDI unit. So I tested the signal generator, and I could not get a valid reading. After smashing the crap out of my nice digital multimeter, I decided that I needed to take a break from the bike.
Searching the Internet
Another week went by, and during that break from bike repair, I started searching the internet for forum posts by people with similar problems. I did find a few things, but most people just leave you hanging after asking a question about the problem that they are having. Many never come back to tell you how they solved their problem. Another thing with forums is that the "helpful" folks seem to make comments more for upping the count on their comment counters and feeding their egos and less about actually providing useful information.
You see the same generalized tips thrown out there again and again and while not all of them are bad, some are really stupid. I think that I pretty much found everything that I could on all of the motorcycle forums out there and nothing really helped me. As a side note, I don't ask questions on forums because of the poor credibility of the people who log in to those things and the poor quality of the info that you usually get.
Testing the Signal Generator
Somewhere on the internet, I found a site that had something to do with my signal generator, and it got me thinking about it. Since by now my bike was running really bad and it was hard to keep running, I decided to bench test the signal generator. The person on the website did this also.
So by using a drill-press and mounting the sig. gen. securely, I was able to test this thing off of the motorcycle. Well, guess what? The 0.4 volt DC signal that you are supposed to get per the manual is wrong! The signal generator will actually put out approximately 0.4 volt AC (alternating current) signal. I wonder how many signal gens Suzuki sold because of this misinformation.
Anyway, the only thing that could ever go wrong with this thing is a broken wire and that's about it because all it is is a magnet that generates a signal when a metal tang flies by it.
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Experimenting With the Carburetors
As I said before, my gut instinct was that one or more of the carbs had a clogged jet. My next move was to tear apart the carburetors to see what was going on inside of them. Luck was not on my side during this whole ordeal, so naturally, I found nothing and my carbs were spotless. Nevertheless, I removed all of the jets, sprayed them all up and down with carb cleaner and blew them out with compressed air. With the carbs back in place, the bike ran the same (bad), but I noticed that it seemed to run a little better with the choke on, which still doesn't make sense to me.
I only had one other major issue with this motorcycle in the 11 years of owning it, and that was with one of the intakes, the rubber-coated things that the carbs mount to. Years ago, the bike was running crummy and had poor top-end power, so I took it to some shop that was recommended to me. $380 later it seemed to be running a little better but then soon started doing the same thing. Then I took it to my local Suzuki dealer (Southland Suzuki), and they had it for a couple of weeks and had done nothing, so I paid them $50 for something (I guess for pulling off some of the lines and leaving them hanging), and then I brought the bike home. I tore off the carbs and discovered that one or more of the intakes was loose thus allowing too much air into the mix and making the bike run like crap. I tightened them up, and it ran fine ever since.
Given that past experience, the intake manifolds (not sure if this is what they are actually called) were the next things to come off. These intakes have an o-ring on their bases, the end that mounts to the cylinder head. Anyway, it turns out that these o-rings don't seem to be anything that you can get outside of Suzuki, so I bought what the dealer had: two at $10 each. I then replaced the worst-looking o-rings and made sure that the bases of these intakes were nice and flat. To do this, I wet sanded them on a mirror (the flattest surface that I have) with 300 grit emery paper. You have to be careful not to take off too much because it doesn't take long to remove 0.002-0.005" and that's about all you can remove safely because the tolerances are pretty tight on these things (I could be wrong, but after taking measurements with calipers and doing some math it does seem so).
The bike was started, and it ran the same—still bad. I then thought that I missed something in the carbs—something was still clogging a pilot jet or something. Again the carbs came apart, and I thought that I had found the culprit. The number three carb's pilot jet looked not quite clear, so I sprayed carb cleaner through it and I stuck a very thin wire through it (ya I know they say not to do this) and then blew it out with air. I put the whole thing back together, and there was no change in how the bike ran other than this time right after running it I noticed fuel coming out of every port and tube connected to the carbs—really freaking weird!!!
This symptom of extreme flooding seemed crazy because I thought that the carbs were perfect; I mean I had the floats set as good as they could be at the time and there were no obstructions. Again I needed a rest from the bike.
Discovering the O-Ring Issue
Another week or so passed and I found something on the internet about mysterious carb flooding and then I realized what my problem was: the damn o-rings on the needle-valve seats inside of the bowls of each carb! The stupid thing was that when I was putting the carbs back together, I did notice that one or more of these needle-valve seats went into place a little too easily, but I ignored it for some dumb reason. It was too late, and the Suzuki dealer was closed, so I went over to True Value hardware and got some o-rings for 39 cents apiece that fit. I put everything back together, and the bike ran great.
These o-rings were not damaged nor were they alarmingly loose. They had most likely dried out a little from the bike sitting for several weeks and were just loose enough to allow too much fuel into the carbs thereby flooding the engine and keeping one cylinder from firing. Early on I did notice that a couple of the spark plugs were a little wet with fuel, but my lack of experience got me because I figured that there should be enough spark to fire things regardless. Initially, I guess the problem was just bad enough to make the bike run bad even though it did not seem to run richer than usual.
As time went on it just got worse and worse until the carbs would actually overflow with fuel. Gas was coming out of the vent tube, the tubes that go to and from the two solenoids mounted on the carbs, and of course, enough fuel dumped out of the ports on the carbs to fill the combustion chamber. I had to remove the spark plugs and crank the engine and push out the excess fuel. When this much fuel is inside of the combustion chamber, I'm sure that some of it worked its way down into the crankcase, so I changed the oil.
Lastly, I checked the float levels with a special gauge from Suzuki, adjusted the pilot screws to make sure that the idle was good (some idiots that worked on this bike years ago removed the pilot screw plugs and changed the factory settings), and then I synchronized the carbs. It's running as it should as of this writing.
I hope that this article helps someone else out there with a similar problem so that they are not ripped-off by some so-called mechanic and that they are not misled by all of the garbage spewed out by those Internet forum clowns.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
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