Help! My GS won't hold an idle!

[SpiderMan]

Hi everyone!
When it's cold it doesn't have a problem. But after it warms up, everything goes downhill! If I try to let it just sit and idle, it will die. However, if I give it gas so it won't die, then it revs really high and takes a few seconds for it to come back down. It does the same thing as I'm riding it. Any help would be greatly appreciated! Thanks!!!

 

[CanadaDan]

Questions:

What RPM is it holding when it does idle?
Are the exhaust pipes REALLY hot?
What have you done recently (small things count here)?

 

[SpiderMan]

Okay,
It never does hold an idle.
They are fairly hot.
I have not done anything to it. (it has done this since I bought it! I have put a new airfilter in it and changed the oil.)
Thanks!

 

[anarki650]

First thing I'd do is check for air leaks, both on the intake boots from the airbox and the carb holders on the head. Are your pipes and intake stock or aftermarket? If aftermarket have the carbs been rejetted for the mods?

 

[TonUpSoldier]

Hi everyone!
When it's cold it doesn't have a problem. But after it warms up, everything goes downhill! If I try to let it just sit and idle, it will die. However, if I give it gas so it won't die, then it revs really high and takes a few seconds for it to come back down. It does the same thing as I'm riding it. Any help would be greatly appreciated! Thanks!!!

First off, what year and model GS are you talking about? There are different designs, 8 valve low oil pressure, roller bearing crank motors, and then the 16 valve high pressure plain bearing motors. I could go on about the differences, but essentially what you are describing are classic symptoms of an intake air leak. On ALL models of GS, there are, between the rubber intake boots that connect the carbs to the head, Viton (high temp, gas resistant rubber) orings that complete the seal between the intake boot and the aluminum head port. Over the years of constant heating and cooling, the rubber begins to deteriorate, and crack. Leaks form around the seal, allowing more air in than the bike should have to complete the delicate fuel/air mixture. This causes the bike to run lean. Running lean, besides your current problems, is BAD. It causes the valves to burn, and the cylinder temperature to rise to the point that catastrophic failure can result. Replacing these rings is necessary about every 15-20 years on the average, and the process is pretty easy. Simply remove the airbox and carbs, remove the boots, usually held in by two phillips head screws (you will want an impact driver for sure to aid in removing the screws) The boots will come off, and the orings are on most models, sitting in a recessed channel in the back of the boot. If they are flat, cracked, dry and brittle, replace them. They can be purchased through a member of the GSResources at www.cycleorings.com for EXTREMELY CHEAP. He also carries stainless allen head replacement bolts to replace the crappy phillips heads with, and i suggest you pic those up too. I think I paid less than 12 bucks for both products SHIPPED. BTW, if you should ever decide to break down and thoroughly clean your carbs, he also sells replacement carb oring kits for the various models of carbs they GSs use. Excellent resource, and even better value.

To test for an air leak around your boots, start the bike, and when the idle relaxes, (and obviously before it starts croaking) spray carb cleaner, starter fluid or something combustable around the joint of the boot and the head on all of them. One at a time. If the idle rises, or bogs (depending on what it is you use to spray) you have an air leak. Another thing to check also is the airbox. Over time the seal on them becomes a bit crappy. You can take it apart and use simple weather stripping around the seals to ensure that you are getting an adequate seal. There should only be TWO places on these airboxes that allow air. The snorkel (on the back of the air box) and the vent hose (usually coming out of the bottom of it) EVERYWHERE ELSE MUST have an adequate seal. Also you can use the same testing method once you have replaced your boot rings if the symptoms still persist on the airbox, and the airbox boots. If the airbox boots are bad, you can pick them up at www.BikeBandit.com.

Hope it helps.

Josh

 

[SpiderMan]

Great! Thank you for all of your help! I went to the Suzuki dealership today and ordered the carb boots with orings and new clamps, and airbox boots also with new clamps! Hopefully this will take care of it!
Thanks again!!!

 

[TonUpSoldier]

It will certainly help for sure. Again, after replacing those boots, I would still give a look at your airbox itself. I see by your sig line that we are talking about an 80 GS1000, in which case it will be fitted with BS3XSS ( i think 34s but maybe 32s) constant velocity type carburetors. These carbs rely on vaccum to actuate the slide, which more or less acts as a secondary valve, much like an old muscle car carburetor. Therefore, these carbs are EXTREMELY INTOLLERANT of ANY air leaks. If youve got leaks anywhere, you will go insane trying to dial them in. Another suggestion is to check your valve clearances. Your bike uses the FANTASTIC 8v roller bearing 1000 motor. A personal favorite of mine, and pretty much bullet proof. However, the valves need to be checked at 3000 mile intervals. The design uses a shim over bucket tappet system, and these motors are amazingly easy to work on. I can strip a top end and rebuild it and have it running in less than five hours. (yes, ive timed it...lol) If you havent checked them in a while, or dont know when the last time they were checked was, I would be happy to give you some guidance on doing so. As they wear, the valves in these motors tend to receed into the head, causing the clearance to become TIGHTER rather than looser. Eventually, your valves wont close all the way, and severe damage can occur, up to and including grenading the motor. We dont want that. You'll need simple tools to do the job, and once you've inventoried your existing shims, you'll need to order the sizes needed to get the clearances into spec. (.03-.08mm, yeah they're that intricate)

These motors will last forever. I am purchasing in the next month, an 83 GS1100GK, which uses the same 8v design ( I currently have a 77 750B, an 82 1100G, both are 8v designs, and a couple of 750 8v motors that im playing with, dropping 850 pistons and jugs on one. I also have a 16v 750 motor on my bench, thats been grenaded from lack of oil flow....personally, I dont like the 16v design, for this reason) The 1100GK i am purchasing has 128 THOUSAND miles on it (yeah a bike with that kind of mileage!!) and I am not worried about it in the least. With proper maintanence, they WILL LITTERALY run for ever.

 

[zixxerboy]

TonUp

You seam to know the GS line well. I have an 86 4 cylinder GS550 (TSCC). Is this just an 8 valve motor?

Any chance you'd have carbs for one? One of the two barrel carbs is causing me grief - been apart about three times and still can't get the cylinders on that side to fire up. Good spark and comp across all four.

Any help appreciated.

 

[TonUpSoldier]

That is actually i do believe the LAST official GS year. If im not mistaken the TSCC motors were all 16v motors, but I may be incorrect about that one. I dont know the 550s all that well, except that MOST of them (untill they became the 550ESs and GSX550s, tho they were never called GSX over here in the states) were 8v motors, and THOSE motors were considered the MOST reliable of the entire line. I do believe YOUR 550 uses the two carb for four cylinder design, of which I have never really gotten a close look at. I would suggest checking your valves first and foremost, and if it is indeed a 16v design, it will use tappet adjustment screws and locknuts, much like a Honda, which means you need no shims to adjust the valves. Unfortunately, the valves being in spec are integral to the bike drawing proper air/fuel mixture, and if they are out of spec, you may not be getting the mixture you need at the right time. You say the compression numbers are good, so its possible that the valves are ok, but i would check them anyway. From there, check for intake leaks. If none are found, and you have good spark, proper timing, and you are certain that the battery is ok ( i have had situations where it seemed i was getting good spark, and was having a similar problem, swapped the battery and all the sudden it was fine) then I would move back to the carb. Which two cylinders are not firing? are they paired off a coil or seperate coils? If one side of the carbs is working, and the other isnt, but they are exactly the same in settings, we will have to explore this situation further. I will see what i can dig up on this model, as I said im not terribly familiar with it.