Jet sizes???

I have a modified, 'streetfightered' 1993 VFR750 that I have just had jetted. It's all cool to cut down the stock exhaust for the 'fighter look - until the bike runs like crap....

The bike had 130 mains in it, and the jet kit was a UMI kit supplied with DynoJet needles and jets, 120's and 124's IIRC. The mechanic installed the larger of the jet options, the 124's but the jetting has not really changed much, the bike still burbles at steady throttle and pops a bit on overrun, although it is reduced.

Are the DJ main jets sized differently from the OEM jets? I guess I'm just surprised that they'd be smaller and not larger unless they are actually different scales.

Anyone with experience with this? I'm likely to experiment with fattening up the clip settings a bit (which is easy with the carbs on the bike), just wondering if I need to pull the carbs and readdress the mains as well...(?)

Thanks,

 

Main jets are the metering device for 3/4 to wide open. Is this where your runnablity problem is? You may need to shim a needle or something similar.

 

WOT a bit was flat on the bike (in the midrange) after I hacked the pipe, didn't pull so well up top either and ran a bit hot which led me to believe that it was lean. The needles won't need to be shimmed as they are new DJ needles and have clips for adjustment. I intended to play with them to try and fatten up the part throttle and eliminate the burbling, but unless the mains are correct that's just going to cause worse problems; hence looking for feedback on main jet sizes and whether the DynoJet sizing was the same scale or different from the Keihin jet sizing....

 

I see what you're saying now. Do you have a jet cleaner to do comparisons with, or may a set of small bits?

 

I don't have a set of jet bits, but a friend does. I was hoping to find out if the DJ jets were scaled differently before I just go putting my 130s back in or drilling out the DJ ones. My inderstanding is it's not just size but also the taper to the passage that may be different.