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Discussion Starter #1
Hey everyone, I recently bought my first bike (A 1980 Suzuki GS550L) and have been enjoying figuring it out, but something that worries me is, after a few minutes of riding, the idle jumps from a regular ~600 to a worrying ~2250.
Anyone have suggestions on what to check or do? I'm pretty handy with a wrench, but the bike didn't come with a manual or anything, and I've never worked on a bike before.
 

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Greatest Member Ever
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It's a pretty recent thing. been doing it for about a week.
I would start by checking for a vacuum leak. The rubber hoses on old bikes can develop cracks that become bigger as the engine heats up. Ride the bike until the problem occurs, then return to your home and spray the intake boots/vacuum lines with carb cleaner or wd-40 and see if the idle changes. If it does, the area that you sprayed is the culprit. Also check for cracks in the rubber boots that are between the carbs and airbox.
 

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Discussion Starter #6
Hey, just tried the wd-40 thing. Sprayed it on all four carb boots. All I accomplished with it is now my carb boots are covered in wd-40. Idle didn't change any. Maybe the carbs are dirty?
 

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No, what you accomplished was possibly ruling out one source of your problem. Personally I like to use carb cleaner for the task - seems to work better for me.

Vacuum leak would be at the top of my list, too, though it could be a lot of things. How old and beat are the carbs? Vacuum leaks can sometimes come from sloppy butterfly shafts in the carb itself. Dirty or poorly tuned/synced carbs can also do what you've described.
 

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Ghost in the machine
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I know this seems like a dumb question but it would be the simplest solution. you are not leaving the choke on are you?
It could also be a fuel delivery problem such as a dirty petcock/filter, fuel filter or fuel line. So that it doesn't supply enough fuel while running to maintain fuel level in all 4 bowls. This may cause those cylinders to "lean out" and increase rpms, the same way a lawn mower's rpms can often increase just as it is running out of gas.
 

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Discussion Starter #10
No question is dumb, friend! I made quite sure the choke was off. Fuel filter/petcock would be a good idea to check, but I'm not sure why they wouldn't be bothersome before the bike warmed up.
 

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Ghost in the machine
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It is possible it is not a "warm up" issue, but rather an issue of maintaining proper fuel level in all 4 bowls while under load for a prolonged period of time.
 

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Discussion Starter #12
Hey everyone, went out to my bike today to check a few things. I checked the boot clamps for the carbs, all very loose, so I tightened them down. The boots themselves appear nigh-on brand new. Made sure my petcock was set right and everything, checked that my choke shut off completely, as well as my throttle. Got it warmed up aanndd idled at 2250 again. So we know it isn't any of those things.
 

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Hey everyone, went out to my bike today to check a few things. I checked the boot clamps for the carbs, all very loose, so I tightened them down. The boots themselves appear nigh-on brand new. Made sure my petcock was set right and everything, checked that my choke shut off completely, as well as my throttle. Got it warmed up aanndd idled at 2250 again. So we know it isn't any of those things.

Well... I love a good challenge! I just reread every post in this thread, including the ones by cmonStart and Jag13 (both of whom are tops in my book when it comes to Motorcycle Diagnostics). But I have to ask... when you sprayed the carb boots, did you have the bike running at the time? Or did you shut it off, go inside and fetch the can and come out and spray it and then restart the bike? I realized that my posted suggestion could have been done wrong. I didn't make it clear to keep the bike running while spraying.

In your original post you stated the bike starts and idles around 600rpm... that's kinda low for an in-line 4. 900-1000 would be more like it. Then you said after a few minutes it suddenly jumps to 2250. Which is too high.

If you brought your bike into my shop, I would ask questions... Like I already did, did this happen all of a sudden? Then I would ask you to define "a couple of minutes"... are we talking 5, 10, 15, 20 minutes?? Is it consistent with the problem, or is it random as to how long it takes to do it? Lastly, I would test it out myself and experience it first hand. At that point, I would tell you about how much time it will take me to pinpoint your problem (not fix it, but pin point it). Then you have to decide if you want to spend that kind of money. Here in the forum, there is no money... we do this for free, but we do expect a reward... let us know if you find a solution.

That all said... I have an experiment that I would do if your bike was in my shop right now. Stone cold, I would start your bike. I would let it idle for just short of the time you say it starts to idle high. Or I would start it cold for like 20 -30 seconds... which ever is less. Then I would use my laser thermometer to read the temps of the header pipes. The reason I would do this is cuz you admitted that you recently purchased this bike and are new to motorcycles. There is the possibility that your bike is not firing on all 4 pistons all the time. You wouldn't know this cuz it has always run this way... but once it warms up, BooYAH!! It fires on all 4 and the idle is too high cuz the P.O. set it up high to sell it...


Here's what ya do... Start the bike when it's stone cold. no choke and do not rev it. Just start the bike, and then wait about 20-25 seconds and then shut the motor down. Next, simply feel the header pipes (carefully!!!) and see if there is a wide range of difference tween the 4 of em. If they are all the same temp then I just wasted our time... but if there is a noticeable difference, then we just found out a HUGE factor.

Try that... Lets see if we can narrow this down!!

Jack
 

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Ghost in the machine
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I wondered the same thing Jack. PO (or just some kid when it was parked) could have messed with the idle adjustment. You have more patience than I Sir. Best of luck.
 

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Discussion Starter #15
Alright, will definitely check header temps. Not firing on all four all the time would actually coincide with this beautiful electrical tape plug wire on the number 1 cyl. Looks like it's electrically fine, but I could be wrong. Both sides of the exhausts would sound different as well, wouldn't they? I'll answer the rest of your questions later today Jack, running a lil' late to class.
 

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Discussion Starter #16
Okay, so when I shot the boots, I ran in, got the oil, came out, started the bike, held the throttle open and let it rev til the idle went up (which, I was reading the tacho a little concervatively, it idles right where you say it should cold, and at about 2500/2600 warm.) Then I sprayed the boots. As far as estimated time to too much testosterone, it really depends on how quick I want the bike hot. The day I made this thread, I got it to do it in about 5 minutes of riding around a neighborhood... Swiftly. Legal speed, just quick acceleration. Yesterday it took about 10 minutes of much more casual riding.
 

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Discussion Starter #18 (Edited)
Hey Jack, did that test you suggeted. Couple of developments came from it: it started stone cold no choke for the first time ever, and cylinder 3 felt like it wasn't firing. After I singled out No. 3, I tried plucking the plugwire. It didn't change the idle at all, and it gave me a bunch of little tiny static shocks, that, I assume, were voltage attempting to set off a spark plug. Sounds like I've got a bad plug situation.
 

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Discussion Starter #20
Hey guys... doesn't seem to have helped much. we tried pulling the No. 2 and No. 3 plug wires while it idled, and they didn't do anything, even on new plugs. I'm stumped.
 
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