1979 BS38 Carb jetting

[big_ang]

I started to rebuild my carbs last night. I'm going to run the stock exhaust and pod filters.

The carbs have 125 main jets (stock should be 135), and the pilot is the correct 27.5.

125 seems really small to me, and it doesn't look like they were drilled out larger.
Any reason why somebody would go smaller on the mains?

I'm going to start with 30 pilot, 140 main, and needle clip raised one step to slot #2 (lowering the needle).

Rebuilding the carbs are the last thing I need to do to start this engine for the first time.
Once it's running, I'll rebuild my calipers and see how she rides!

 

[DogBunny]

If you are sure it's a 1979 carb set, then your proposed jetting sounds right on to me.

 

[grizld1]

Re. the small mains, I can think of a few reasons for the change. One: PO filled the holes with whatever was on hand. Two: plugs looked dark due to oil fouling or poor ignition, and PO thought he could lighten 'em up by fooling with the MJ's. Three: PO was half blind or blind drunk and misread the numbers on the jets. Four: vacuum carbs compensate somewhat for changes in altitude, but the compensation isn't 100%. The bike may have been jetted for very high altitude. If that was the case, though, I wouldn't expect to see MJ's reduced by 4 steps; looks a little extreme to me. Five: Bozo the PO may have been using those cute little cone filters that block the bypass air jets and make the mixture fatter than Billy Bob's prize sow.

It might be tempting to try to figure out why PO or his minions screwed up, but it's best not to go there: looking for logic in craziness can drive you crazy too.