Another Secondary Main Jet Question


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Hi there...

I'm the person putting the CB1000C carbs on a 1980 CB750F. While I did get the bike started and running, I had some bad o-rings that were causing fuel to leak, so I decided to tear them apart and refresh/rebuild them.

When rebuilding the CB1000 carbs should I jet them with the 110 secondaries that were installed or should I jet them with what the CB750 calls for, 100 or 102 secondaries? Also, the CB750F is currently fitted with a 1980s era Kerker 4 into 1 exhaust if that makes a difference.
Use the 110s first, the carbs are bigger than what comes on a 750. Being CVs they will likely only open part way due to the dropoff in flow from the 1000 to the 750 and you may not need secondary much anyway. CVs tend to do that and why all the DOHC carbs seem to run well on various motors, the bigger carbs simply don't open up as much on the smaller motors.

If the Kerker is the one that has the very fine holes in baffle and it has a true megaphone end, then you can cut off the first 3-4 inches or so before the sealing plate of the baffle extension that extends deep into the collector and run with zero fiberglass in it to get an awesome sound that flows virtually as well as an open header but the noise is very controllable to not get tickets. My favorite small tube header and one that really works well. So well I repaired mine when the bottom two tubes got crunched from lunching on curbs. Run like that on an engine with good compression you get a very noticeable hit of mid range torque the stock engine does not have at all. Packing the back end with fiberglass will kill that, the fine holes with no glass act like the header is open, it allows the bell of the megaphone to really work like designed to. The later design early Kerker meg has a short small OD tube welded into the end of baffle, remove that one too. It allows the full length of the meg to be felt by the waves going through baffle.
amc49 you're the person that I wanted to hear from, thanks for the info and your time taken to answer my question.

The old school Kerker is of the true megaphone type. I actually have two baffles, but I forget which is which, it was a long time ago when I purchased the other one. I think one is longer and the other that is installed currently is the shorter of the two. I will have to get it apart and have a look. Currently it's probably rusted up inside. All fiberglass was removed 35 years ago... It did sound sweet back in the day.
The comp baffles are shorter and typically like a much bigger core too and too loud, thinking 2 1/4" or so, the OEM street baffle is like 1 1/2"-1 3/4ish" ID. Been awhile.