early vs. late first gen GS750 carb differences?

[Guest]

I just bought a 1979 GS750E that came with a spare rack of carbs tucked away in a box. They appear to be off an earlier model; one of the ones where the choke is on the side of the carbs instead of a pull cable below the gauges. Are there any other differences or benefits to using one set of carbs over the other? They both look really good and seem to have been rebuilt, or at least internally cleaned, recently.

[Nessism]

Both choke methods work fine. Personally, I'd stay with the cable type choke. Regardless, I suggest you do a full rebuild, take inventory of the jets, compare to the service manual, and replace the old O-rings. Never trust old carbs.

[gearheadE30]

yeah, definitely. I've got an O-ring kit on the way and a few brand new jets and needles in one of the spare parts boxes. I just didn't know if the carbs were changed jetting-wise or had different needles or diameters or anything that would mean I should rebuild one set over the other.

[Coady]

Stick with the ones that came with your bike and don't mix parts up between the two sets of carbs - there were diifferences between years. Following is an excerpt I found a while ago but can't find the link to anymore:

The GS750B came with a # 100 main jet, 0-6 needle, 5F21-3 jet needle, and # 15 pilot jet. The GS750C (1978) and GS750N (1979) carburetors were changed to a #102.5 main jet, 0-4 needle, 5DL36-2 jet needle and #15 pilot jet.

What that all means is that the GS750N is leaner at the small throttle openings usually encountered in EPA emissions test modes. The dual-taper 5DL36-2 jet needle is initially leaner, secondarily richer to smooth the transition from idle to off idle, (or from small, steady-state carb openings at low speeds to gentle acceleration, as encountered in traffic). The float level was also lowered between the GS750B and GS750N, from 26mm to 24mm.