I just wanted to share some information with you - The last Jets I ordered were sized up 1 size.  The standard size jets for GS850’s are 40 for the pilot jets and 115 for the mains.

I replaced the pilot jets from 40 to 42.5 and initially left the stock 115’s.  The bike still was not running correctly.  So then I changed the mains 115 to 117.5.

The bike now runs fine, with the fuel adjustment screw in the middle of the range at 2 and 1/2 turns out.

I think I was able to correct the pilot range of the carb system by increasing the main jet size is because the Mikuni CV carbs on the GS850G are really a bit of a bastard design!

When the carbs are disassembled, this can immediately be seen as the orifice leading to the pilot jet has been blocked at factory with a rubber plug.  The pilot jet is actually fed through the main jet via small internal orifice below the main jet next to the needle jets.  What a crazy set-up! But it was designed that way - if one leaves the rubber plugs out of the pilot orifices, the mixture is far too rich and the engine will not run very poorly indeed.

So, assuming the internal passages of the carbs are patent, one can enrich the mixture either by using larger pilot jets, larger mains - or both.

The problem with my bike - and many vintage bikes is that the carb systems develop air leaks - perhaps around the intake manifold boots, accelerator shafts, air filter box, etc.

I tried chasing these leaks for a while - even replacing the accelerator shaft seals ( a big job! ) and still I had some leaks.  So, in the end, I decided to take a lazy boy’s approach and cure the lean mixture by simply increasing the size of the jets - of course, I won’t get quite as good a “gas mileage” and I will increase the air pollution slightly as well but I just could not face chasing the air leaks any longer!

I’m sharing the information about the carbs on the GS850 as there are many old Suzuki’s out there with this weirdly designed Mikuni carburettor -

Among others, I believe the GS650’s, and the GS1000 have the same bloody Mikuni’s!!  And most of these older bikes can benefit greatly by re-jetting, even though no modifications were made to the air intake systems or exhaust systems but simply to correct for the insidious air/vacuum leaks which can develop over time - perhaps this knowledge - properly disseminated - would have a spin-off of some business promotion.

Well - I just thought this might be of some interest to you and to others who are experiencing similar carb troubles.

Suzuki GS850G jets