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Discussion Starter · #1 ·
Hey Guys,

I know my bike isn't an SRAD and I'm technically in the wrong forum, but I believe my issues are somewhat universal. My problem seems pretty wacky and I'm hoping you guys come come up good again with some helpful advice/hints/tips.

Some brief history. The bike ran badly when I bought it a few months ago, seeming to suffer from lean running symptoms. I did a complete service (oil, filter, spark plugs, valve clearances, etc) and a carb strip and clean. I also opened the carb pilot screws to 2.5 turns out. The bike is now back on the road and running a lot better than before. However, it still seems to have a lean condition, a conclusion I arrived at by the bikes poor idling (revs rise fast and fall slowly, erractic idling) and an off-throttle surging.

A couple of nights ago I attempted to balance the carbs and see what affect that had on the bikes running. I get the first 2 of the 3 carb balancing screws done and I'm in the process of balancing up the final screw when the bike engine just screams to the limit. I turn it off as fast as possible and wind down the throttle idle screw a few turns before firing the engine up again. It still screamed, and before I could turn the engine off there was a huge backfire in the pipe..!! This only happened after I had been fiddling around for a good 45 minutes, the engine was not running solidly during this time, but on and off as I was making adjustments. Also, on a run last Saturday, I had been riding solidly for about an hour when I came to pull into a carpark for a coffee. The revs started to rise as I rolled to a stop, so I just shut the bike down. It restarted and ran fine 15 minutes later when I came back to it. I have down a few shorter shake-down rides prior to my longer run, and they didn't have the revs problem.

I am wondering if heat build up is having an affect on some component(s) in the system, such as coils or plug wires..?? But, I would have though that heat would make things run badly and make the bike stutter, rather than making the bike behave like I just gave it a 50 shot of nitrous..!!

I'm not ruling the carbs out either, as they are the one component that can supply so much extra juice to make the engine rev so high, but what would make them run fine for so long before going crazy..!!

I did notice the rear coil making a faint clicking noise whilst I was during the balancing. I now wonder if I have a faulty coil , which was causing the erractic idling, and also the sudden increase in revs. Does this make sense..??

I did a static bench test on the rear coil, which I've read from other posts isn't a guarantee things are fine on the road. Both the +ve to -ve terminal and cap-to-cap tests revealed near perfect resistance figures. Didn't test the front as it's a total bear to get to.

Sorry for the long post. Any help is VERY appreciated.

Dave.
 

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i'd check the throttle cables/linkages for binding first.....it doesn't take much to cause the motor's revs to shoot up in neutral.

also, it's possible that when your revs shot way up, the bike was actually running correctly....and all the other times, it wasn't. having set your idle to be 'correct' when the bike was misfiring, would mean that when the bike began running correctly, the idle would shoot up. of course, this is assuming you've got some sort of ignition problem....

with your stock exhaust, you can't really hear if the bike is misfiring (although you should be able to feel the power loss). if you had an aftermarket pipe, the bike would sound 'sick'.

coils should not make any discernible noise. the 'clicking' you heard, if it did in fact come from the coils, could be electricity arcing from a crack in the coil to the frame (or any other ground), and yes, that would cause the bike to misfire.


if you can, try swapping in a known good set of coils and see how it goes.
 

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When John was syncing my TB's, he took off the vacum caps, and then started it before he put the sync tool on. The vacum leak caused the engine to rev up immdiately.

So, I'm wondering if maybe you have a vacum leak somewhere, or one of your sync tubes fell off while you were doing it, or something like that.

Did you try to start it again since you attempted to sync it? Check all the caps, maybe one is missing or cracked?
 

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Discussion Starter · #4 ·
also, it's possible that when your revs shot way up, the bike was actually running correctly....and all the other times, it wasn't.
<font size="2" face="Verdana, Arial">After each adjustment I blipped the throttle a couple of times to make sure there was no lingering effect from the slight pressure needed to turn the adjustment screw. I also used this to check I had free play in the throttle cables. I do think you could be onto something with the bike going nuts as the adjustments make it run better. The bike seems to run great once rolling, just the idle is a complete dog.

Did you try to start it again since you attempted to sync it? Check all the caps, maybe one is missing or cracked?
<font size="2" face="Verdana, Arial">I haven't started it since, I'm very nervous in case it goes crazy again. I will back the idle screw off all of the way and gradually screw it in until it's enough for the engine to start and idle.

Thanks for the input guys, I'm kinda stumped and any opinions give me something to work on. I don't want to replace components unncessarily, but I'm really wondering about new plug wires to start with. Maybe coils after that. But I don't want to go this route if it's the carbs that are causing me grief.

Dave.
 

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Mine did the same exact thing. I had a clogged slow jet in 3 and my carbs needed sinced. So me and my cousin cleaned the carbs up good and sinced them and it is fine. I would def check the vacuum hose though cause mine did the same thing when I was sincing my carbs and we found it to be a vacuum to the sinc fell off.
good luck!
 

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Discussion Starter · #6 ·
Restarted the bike without any of the crazy high revving problems from when I turned it off last, but now it won't idle without the choke at at least the halfway position.

I did suspect either the coils or plug wires, but now I'm thinking it's the carbs. I've already cleaned them, but I don't think I have much choice but to rip them apart again and pay closer attention to every nook and cranny.
 

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Make sure you set the float bowl too...

John
 

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Discussion Starter · #8 ·
I set the float heights to 15mm (as close as I could measure to the specified 14.7mm) when I did the original rebuild of the carbs.

Oh well, I know what I'll be doing this weekend....
 

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Sounds like you need to resync your carbs, but readjust your idle mixture screw first to get the bike to idle....been there done that, lemme tell you!
 

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Discussion Starter · #10 ·
I have just been struck by a possible lightning bolt of inpsiration....maybe.

Because my problems only seem to happen when the bike has been running for a while and is hot, I automatically suspected thermal breakdown of some kind, primarily coild and/or plug wires.

However, now I'm wondering if the heat is having an effect on the petcock. Could I be onto something, or am I just grasping at straws.

I know I should run a pingel instead of the OEM petcock, so maybe I'll just be nice to the wife and get the OK to spend more money on the bike.

Dave....
 

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I think the vacume leak is the most likely with the syptoms you're describing.It lets air in after the carbs which will make the bike rev,it only does it once it gets hot because it leans out heaps and won't run when it's colder.That could be why you've got to have the choke on for it to run now.
just my opinion but this is where i'd start
 
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