Keihin CR carbs 31s or 33s?

[80GS1000]

What about a 2V GS1000 engine with a 1085 or 1100 cc overbore and hot aftermarket cams? Would RS34 or RS36 be the better choice for street and roadrace style trackday duty?

[GregT]

What about a 2V GS1000 engine with a 1085 or 1100 cc overbore and hot aftermarket cams? Would RS34 or RS36 be the better choice for street and roadrace style trackday duty?

Here the bike would be built to our pre '82 regs which specify period carbs.,..So my experience has been with Keihin CR's.
31's produce a very sweet running GS1000. 33's and above generally produce a curve with a huge bump at about 5500RPM.
Our race GS1000 is a wheelie monster at 5500...

[wyly]

What about a 2V GS1000 engine with a 1085 or 1100 cc overbore and hot aftermarket cams? Would RS34 or RS36 be the better choice for street and roadrace style trackday duty?

The supplier for my carbs recommends the RS36 for the GS1000-1150, I'm no expert but that appears to be the consensus with every GS expert I've asked. The 36 is ideal for street/road performance and offering greater usable midrange.

A RS38 is for people who live in the upper end of RPM range, racers and those with a wish to lose their license.

[wyly]

Looking at a photo of the Mikuni RS36 I see each of the carbs has an atmospheric pressure vent to the float bowl. Do those atmospheric vents eliminate the need for a vacuum line from the petcock for fuel flow?

If that's true I'd like to replace my oem petcock with a Pingel for better fuel flow.

[80GS1000]

Looking at a photo of the Mikuni RS36 I see each of the carbs has an atmospheric pressure vent to the float bowl. Do those atmospheric vents eliminate the need for a vacuum line from the petcock for fuel flow?

If that's true I'd like to replace my oem petcock with a Pingel for better fuel flow.

I use a Pingel fuel valve with my RS34s. No vacuum line is required. If I could do it again I'd go with the RS36.