Topic: 74 CB750 Suddenly Rich on 2&3 After Cleaning

[Wingnut74]

74 CB750 suddenly rich after cleaning out idle air passages only on 2 and 3 after cleaning out air passages to the emulsion tube/main (105s) and idle passages/jets.  All 4 were perfect color before - only went cleaning because air idle screws did nothing and still barely do anything.  What's weird is that at idle all 4 are still OK, but 2&3 will be super sooty after a ride where I am at 3-4.5k rpm a lot doing back roads 30-50 mph.  Since idle seemed OK I was thinking I had to have messed up the main emulsion tube/ports. But do  you think the Mains would be kicking in much at that kind of riding? Per Hondamans's book if you accidentally make the emulsion tube ports too big it will run rich from pushing up too much into the mains, so followed his recommendation to drop 2&3 from 2nd notch from bottom to middle notch to lean them out, but wondering if this a Main problem or an Idle/Pilot circuit probelm? Any thoughts appreciated

[calj737]

Depending upon your RPM range, even at 30-50mph you can be hitting the main jets. But since it's both 2&3 I'd suspect an ignition issue. That's something you can double-check in the garage before replacing your plugs and doing a new plug chop.

I'd also encourage a Clear Tube check for fuel level on all four.