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Troubleshooting uneven exhaust on 81 GS450
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
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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