GS650 carbs still have factory mixture screw covers intact - keep it that way?

[sacruickshank]

The mixture screw inserts on my recently acquired '83 GS650 are still intact from the factory, a first after ~20 rescue projects of vintage carb'd bikes.

Most mixture screws regulate fuel and are on the lower half of carbs adjacent to the float bowls. If I understand correctly, ones positioned on the top of the carb regulate air rather than fuel.

Hypothetically, since they do not have fuel flowing through them they are probably not clogged and I can leave the screws and inserts intact when ultrasonically cleaning the carbs.

Does that sound correct or should I drill them out anyway and remove the mixture screws when cleaning the carbs? I expect the mixture screw's oring is probably dried out, which leans towards a "clean them out" approach.

Caveat - I have not yet opened up the carbs to see the general condition after 20 years in a shed, i.e. are they fully varnished from sitting fuel or still clean after being drained?

PXL_20211129_212205227.jpg

[Nessism]

Fuel/air emulsion travels the pilot passage. There is no way to properly clean the carbs without removing the pilot screws. You also can't properly update the various O-rings throughout the carbs without unganging them. The carb rebuild tutorial linked in my signature will provide a guide.

[phydeauxmutt]

Just because the covers are there does not mean that the factory put them there. Some of the 'better' rebuild kits actually have covers you can put back on.

As to whether to remove them? It has been said on this forum many, MANY times: any shortcuts you take are merely another chance to do the job over, and (maybe) do it right.

One last thought: the carbs were set lean from the factory and ran poorly because of that. Chances are that partially-clogged passages are not letting it run any richer. Add in the fact that today's liquid that passes for 'gasoline' has fewer BTUs per gallon, you need a slightly richer mixture. The best way to do that is to clean the carbs thoroughly (according to the tutorial that Nessism mentioned) and turn the mixture screws out about three full turns from lightly seated to get the bike going, then turn them in slowly until it runs the best. Might end up 2 to 2 1/2 turns out, but start with 3.

[sacruickshank]

Got it. Thanks all.