I have a set of bike carbs with 38mm chokes, will they be suitable to fit to a ST170 engine or would I be better with bigger chokes
Thanks
Ian

I have 38mm ZX6 carbs on my 2.0 Blacktop and they work well. What size are the inlet ports on the ST?

I'd be surprised if the carbs would limit power if the engine is standard.

Stu

Thanks for the reply Stu, the inlets on the st are oval, about 40mm x 47mm
Ian

I think from memory that is quite a bit bigger than the Blacktop, so might not be ideal.

[Edited on 26/9/17 by SJ]

Hi Ian. Although not exactly comparable my 3SGE engine was making 170hp on 36mm choked Mikuni Solexes. Oval port 56 x 35mm.
The engine now makes substantially more power on 42mm GSXR throttle bodies so the chokes were the limiting factor in this case although the inlet manifold may have been a factor too.
As already stated, if its a standard engine and you are not looking for the last hp then 38mm chokes should be fine.
If you are chasing the last bit of oomph ( or may in the future ) then sell them and get some bigger ones.
Driveability might suffer though. "Bigger than strictly necessary" butterflies can be a bit "on-off" at low openings. I fitted a larger cable quadrant on mine and offset it to give a "rising rate" action. See pic below.
The spindle axis is between the four grey screw heads. The change of cable angle is allowed for by the rose joint. I would recommend this even with the 38mm carbs.
Are you using the ST170 manifold to respace the carbs?
Whichever way you go I've got lots of lots of Mikuni jets if that will help. I'm not far away.

Thanks Spyder may take you up on some help with the jets if I stick with what I've got. I was going to try and make my own inlet manifold, I cut the plate out and drilled the holes for the studs yesterday, will put that little project on hold until I've decided whether to spend £500 with bogg brothers for an ally manifold and a set of 41mm R1 carbs....

I made my own manifold. Here it is all jigged up ready for welding. I cut the mounting flange from a standard manifold.
The runners were shaped at the end by basically driving wedges between two semi circular bungs ( a socket cut in half) to give the oval section.
The other ends were machined to help retention of the mounting rubbers.

I didn't go for anything so elegant! I just bolted the ZX6R carb rubbers to a piece of 5mm ali plate cut to shape. Works great and cost abut a tenner.

My carbs are respaced to match the zetec though.