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Troubleshooting uneven exhaust on 81 GS450

  • Thread starter Thread starter sicnarf442
  • Start date Start date
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sicnarf442

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Newbie here. Just started working on a GS450S w/ 17,000 mi that came from a clueless previous owner. When he sold it to me ($300) he told me before he stopped riding it, it only fired on the right cylinder, and he had to use the choke to keep it running.

I cleaned the carbs. (I know: newbie mistake. have since bought o-ring kit from Bob Barr and intend to rebuild). Using a small funnel to bypass the gas tank and petcock, and a piece of electrical tape to seal the vacuum line to petcock I was able to start the bike immediately. This is what I saw:

At idle, left exhaust was cold, right exhaust perfect.
at higher rpm left cylinder started firing and produced hot acrid smelling smoke. Not blue like burning oil, if anything black.

Now left cylinder always fires and always produces hot acrid smoke.

Sometimes idle wanders: will climb to 2000-3000 and then slowly come back down to 1000 RPM (left cylinder always firing).

Final bit of info. left exhaust is significantly more corroded at outlet than right, so what ever is going on has been going on for a while.

Here is what I have done to trouble shoot:
1) compression test on just-run engine: LHS 120 psi, RHS 130 psi. Left cylinder not doing as well as right but seems to be within the service limit (100 psi, 28 psi allowable difference between cylinders). This would seem to rule out valve issues?
2) looked at plugs: both show fuzzy black soot, probably from all the idling. Not sure there is any news here. Gap correct on both and both produce strong spark, visible in daylight, when out of the bike.
3)sprayed wd 40 around boots and air intake while idling. No change in rpm, so I am guessing problem is not related to air leaks (did order Boot o-rings from Bob as well, plan to install those as well).

So I am going to rebuild the carb for real this time, however, before I do that I would like some feedback if likely cause of problem is with the carbs, and in particular what part of the carbs? Pilot jet, since this is an idle problem? Float level? Also am I correct that the air screw is sealed on these carbs. Should I drill it out? Is it possible that the only problem is a too-rich mixture at idle on the left cylinder? Should I order new float needle and valve? The looked to be in very good shape when I cleaned the carb. What is a good source for carb parts (gaskets etc.) if I need parts in addition to the o-rings I got from Bob?

Thanks,

Francis Stefani
 
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Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr. sicnarf442,

I'm going to say "E", "All the above". Valve adjustment, carb cleaning, idle mixture screws adjustment, float height adjustment, vacuum synchronization, air intake repair, new fluids, new filters, new fork seals, rebuild the brake calipers, service the charging system, etc, etc, etc. Take what the PO tells you with a grain of salt and just do all the proper maintenance up front. Then you know it's done right and you will have a good baseline for further troubleshooting, if necessary. There's a carb rebuild "how to" on my little website that is specifically for the 450 carbs.

Anyway, let me dump a TON if information on you and share some GS lovin'. :D

I just stopped by to welcome you to the forum in my own, special way.
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If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....
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Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. Now let me roll out the welcome mat for you...

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Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike! :D

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff
 
Welcome to the forums!

Do what BassCliff says, it will help 100% :D

Sounds to me like it may be valves, but I could be wrong.

As I understand it, if you're not firing right on one side, it can do ugly things to your valves, and running too lean for too long can burn them out too.
 
Thanks, Pete and BassCliff,

By valve adjustment, you mean adjust tappets, not plunge into doing a valve job (at least not just yet based on the compression results)?

I've read your primer on how to rebuild the GS450 carbs. The part that worry's me the most is drilling out the air adjust screw. I assume that has to be done?

I'll keep you posted.

Thanks,

Francis Stefani

BTW, changed fluids and found stripped nuts on oil filter cover, as predicted by this forum. Also had to replace shot R/R with Honda R/R, also as predicted by this forum. Figured I would spare everyone the predictable stuff. I'll post photos next time.
 
Hi,

sicnarf442 said:
By valve adjustment, you mean adjust tappets, not plunge into doing a valve job (at least not just yet based on the compression results)?
Click to expand...

Yes, adjusting the valve clearances (tappets) is regular, required maintenance every 4000 miles or so. I was not speaking of a "valve job".

I've read your primer on how to rebuild the GS450 carbs. The part that worry's me the most is drilling out the air adjust screw. I assume that has to be done?
Click to expand...

You're actually NOT drilling out the screws. You only want to take out the cap that is covering the "idle mixture screws". They are not really "air screws" because they vary the amount of fuel in the idle circuit, not air.

Usually you can pull out the caps by screwing in a wood screw a couple of turns so that it gets a bite. Then pull out the screw, cap and all. Be very careful not to damage the screw beneath.


Thank you for your indulgence,

BassCliff
 
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Hi,

Rising idle is usually indicative of an air leak. You could be leaking at the intake boots without any visual signs of a leak. Spraying various petrochemicals at the boots searching for leaks is not a good test. After replacing the intake boots and O-rings we'll know more. It's possible that you are a little lean in the idle circuit. That can be adjusted once the idle mixture screw caps are out of the way.

Thank you for your indulgence,

BassCliff
 
BassCliff knows what he's talkin' about for sure :D

The other potential intake issue is if your airbox is not sealed or is missing the air filter, or possibly even if the air filter isn't oiled, although I don't know that that would have such a drastic effect.
 
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