gs550l carb problem

[Anonymous]

The #3 spark plug fouls with carbon. The bike will idle fine at start up for about 3 minutes, then begins to backfire. The other three cylinders are fine. When I ride the bike on the highway, it runs flawlessly. I swapped plugs, no change. I swapped the diaphrams between carbs, no change. I have cleaned the carbs and synchronized them. The idle air screw is sealed, and have not adjusted it. Should I open the air screw and adjust it? Any ideas would be a great help. Thanks

MSal9999

[Anonymous]

If you didn't remove the idle air screw then you didn't fully clean the carbs. Every jet and rubber piece needs to come off the carb bodies, then dip all the metal parts in cleaner and reassemble. See the carb clean up series elsewhere on this site for details.

[Dink]

Yes you do need to unseal your idle air screws, fully strip and re-clean your carbs. Re-assemble and reset them up .
There are no shortcuts.
Dink

[KEITH KRAUSE]

I agree with the others about a complete cleaning.
Don't re-adjust a factory sealed mixture/air screw.(what year/model?) If the screw was never moved, it shouldn't be the problem. Don't compensate for a possible rich mixture by adjusting the screw.
Do the easier thing first. Check the lead/cap/coil connections to that plug first. Clean/replace anything you find that looks like a poor connection. Check that plug's gap. If this doesn't help, then check/clean the carb further. Use compressed air and cleaner. Check the float height too. Check for a loose jet or incorrect jet size if you're not the original owner.
Any fuel spills from that carb? Do you get a good plug read at higher speeds but a rich/fouled read at lower/idle speeds?