Carb jet conundrum

[Spad]

Tearing apart the carbs on my XS400 the jet sizes are:
Main jet: 155
Jet, main: 135

According to all the replacement part catalogs the jetting should be:
Main jet: 160
Jet,main: 135

The bike was sold to me as a 1980, engine code 3F8(1980), but registered as a 1981...
Any thoughts on the non-stock jet sizes? Thanks,Spad

 

[xschris]

The jet on the front part of the carb is the pilot air jet. That should be 155. The main jet ( the one that is at the end of the needle jet ) should be 135. You also have a pilot jet that should be 42.5

 

[Spad]

Thanks xschris, the nomenclature can be confusing....All my pubs keep showing that pilot air jet (main jet) to be 160....This is a bike that the engine numbers don't match the frame number, so you can see why I am digging deep for a base point...The engine is a 1980 but the carb float bowls are from an 81....Some fun..Spad

 

[16VGTIDave]

Don't concern yourself with the Pilot Air Jet. It (almost) never needs changing.

Get the bike running, adjust idle mixture with pilot air screws and sync the carbs. Then ride it hard for 10 to 15 minutes to get it to full operating temp. Once warmed up, see how it pulls at full throttle above 7k RPM. If required, adjust the main jets for strongest pull.

Then repeat warmup and test full throttle 4k to 7k RPM for needle tuning, and adjust height of needle with clips or washers under clip depending on the needles you have.

Then repeat warmup and test full throttle from 2k to 4k for pilot jet. Get the closest pilot jet that performs well, or slightly rich. Adjust float height lower to lean cruising (pilot jet) mixture as required. Then adjust idle mixture and sync again.

The tuning process can't be done in any other order, and will probably take the better part of a day to accomplish, but it will be worth it.

 

[Spad]

16GTIDave,the bike was running when I bought it. I went thru the carbs and will change the jets as new ones are cheap. Used my Ultra-Sonic cleaner and they are looking good...Much appreciated on the tune-up you sent..Will follow that when I get it back to-gether...Thanks,Spad