thinking of trying a smaller 36 to 38mm mikuni and was wondering if anyone has experimented with a smaller carb. my hsr42 has not impressed me with throttle response from off idle to wot. I have an egt guage and have ran it very rich to very lean with borderline too lean being a little snappier than running rich. I tried every sensible combination of jets and nothing really grabs my fancy with this carb. The one thing I just had done was the heads and that did improve the mid range and top end a fair amount and the throttle response is a bit more crisp but not as snappy as I want it to be. A couple years ago everone was telling me to run a 600cfm carb on my v6 airboat so I did and it did work but it had this same sluggish response. I stuck my neck on the chopping block and purchased a 500cfm carb and the diffenence was night and day. the 500cfm carb had superb throttle response and pulled hard to wot. I was thinking the same may apply in this situation. the only downfall I can think of is the smaller carbs dont have an accelerator pump which may be an issue with jammning the throttle from idle. thanks for any replies.

Did you buy the full kit or just a 42mm carb amd stick it on? Asking because I know the bps kit comes with the black death intake or at least I think they do? Anyways maybe you should try a performance intake unless you have one

You can't bolt the carb up without an intake adapter of some sort, you cant just buy a carb by itself and just put it place

Are you running a performance exhaust?

I bought the kit right from mud buddy and it had the older style carb adapter which I upgraded to the black death and had it ported with the headwork. I definitely had a fairly significant improvement with the porting and head work. I am totally satisfied with the porting and head work that was done. I have made 2 performance exhausts and the current one has 1.5" pipes that run into a 12.5 degree y pipe and a 6" 1.75 pipe that runs into a supertraqpp which I ended up putting in various numbers of discs and ended up with 16 discs as the best overall performance. I just wonder if that 42mm carb shines on motors cranking a minumum of 55 to 60hp as it has always felt a bit lazy on my motor other than the midrange. I've tried all 3 different needles at almost all the various positions along with main jet and pilot jet changes. The main place this carb shines is starting and idle. I just think there is a better carb out there for stock and mildly modded engines. I currently have the k&n filter with about a 5" velocity stack consisting of 2" pvc pipe which made a very noticeable difference at all off idle throttle positions. I may be totally out in left feild with this idea but I have felt an incorrectly sized carb several times and this feels like that same condition. I was just hoping someone had tried various sized carbs so as to possibly save me some $ with another of my crazy ass experiments. According to the holley website I determined that a 61 cubic inch engine (993cc) at 85% volumetric efficiency will suck in about 68cfm at 4000rpm, 77cfm at 4500rpm, and 85cfm at 5000rpm which if my calculations are correct according to their carb sizing graph the 42mm which flows a max of 213cfm is way too large a venturi for the aformentioned cfms. The velocity of air through that big venturi is probably fairly slow thus creating a sluggish situation in the engine. I found that a 34mm mikuni will flow around 114.7cfm and a 38mm carb will flow about 129cfm which would be way closer to the air my motor will ingest. I have read that engines perform best with the smallest carb they can get away with as it keeps the port velocities high and stuffs the chambers with air/fuel mixture much more effectively. I know their are exceptions and that is why I thought some of you guys may be able to throw some real life experience my way. thanks.

Cody at setxperformancevwill know this stuff or BoatDr.

I hear ya, I'll have to contact them. thx

Are you by any chance running a cdi motor