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 I have a 2000 T-Cat I run on the asphalt. I have 40mm TMX Boswell carbs, V-Force 2's, with D&D trail pipes into a MBRP canister, no porting, stock compression, with stock cat pistons, and stock ignition with a 2 degree key. When we had it on the dyno we used 360 mains. I only made a few runs on the asphalt with it so far, but my EGT's were getting hot quick, mid 1200's before 1000'  and climbing quickly, i changed my jetting, but it was still hot, I ended up with 480 mains and EGT's still in the mid 12's at 1000'. I didn't have bigger jets, and we have had rain outs so im done for the year. My question is with the Boswells how much bigger on the mains would I have to go. If they flow more air, how much bigger should I go on the mains. Obviously I have to add more fuel, but is there a "rule of thumb" with these carbs as far as adding more fuel, compared to stock 38mm flat slides?  Thank you.

Your problem may not be the main jet but rather a jet tube(needle jet)that is to small to flow enough fuel to get to your desired air fuel ratio,if you continue to install larger and larger main jets and the temps stay the same then i would have to conclude that there is not enough fuel coming up the jet tube.Changing the jet tube or remachining the I.D. is some options.we have used some boswell prepaired carbs before and if they are done right you should actually have to jet down due to the better input signal running past the main jet tube.Hope this has helped you out. Todd Guthrie Dyna-Tek Performance.

 Ok, thank you that makes sence. I will look into it this winter pull the carbs apart and get it ready for the tar. Thank you again.

Q; Do your modded TMX's have removable needle jets? OEM Mikuni TMX's are fixed cast in place needle jet. Some shops bored out the fixed needle jet and machined the TMX to accept a brass slip in needle jet.

 Just a thought,

  You may want to look over your pipe stinger size and the size and construction of the MBRP silencer. You may have a backpressure issue.

  Check for proper float bowl venting and vent routing.

 Thanks for the info. Im pretty sure the needle jets are fixed. What shop can machine these out? I paid a couple hundred too much for these and I hate to dump any more money in them. I wanted tried and true round barrel carbs, but the sales pitch was good on these carbs. thanks again.

What shop can machine these out?

 The CRANK SHOP offered this feature many years ago.