1974 Mag 250 jetting

I recently purchased a '74 Mag. It came with an aftermarket expansion chamber (I beleive it is the type sold by Vintage Husky. I plan to run a Mikuni carb with it and would like to know if anyone is able to recommend ballpark jetting. It will be used at sea level. I have both 34 and 36mm Mikunis. Given the size and shape of the pipe I beleive a 36 will probably be more appropriate. Thanks/cheers Francis

My Mag has a ProForm pipe , Boysen reeds , and an Mzb electronic ignition . I live in an area that averages about 1200 feet above sea level . I went with a 36mm Mikuni . 270 main jet ( Everybody tells me that is way too small but the bike loves it and the plug looks perfect .) , 30 pilot jet , 2.5 slide , I forget the needle numbers but it is a common one with the clip set in the second groove from the top . I run Maxima Super M oil at 40:1 with a mixture of 50% 93 octane pump gas and 50% VP 110 racing fuel . At sea level you will most certainly have to go richer on the jets . Hopefully this will give you an idea of where to start . An " expert " told me to go with a 380 main and 50 pilot . The bike slobbered all over itself . Many jets and $$ later I ended up with the combo mentioned . The bike is used in the age classes at AHRMA MX events and isn't out-motored by anything I've come up against including period big bores . It has gotten this fat old man a number of holeshots . Just wish I was a better rider !

Your question falls right in place with a concern I also have about my Mag clone. Am new to this forum, but been around these vintage bikes since they were new. Still remember my older brother and I purchasing new 75' 250 and 360 GP bikes new. Of course we all know they needed the Mikuni's at that point too. My suggestion would be to certainly go with a 36 on your bike. Do you know what has been done to the motor? None of these bikes is stock. And from what I've read before when I was part of the HuskyClub organization, the reed intake Mags take a quite different approach to jetting. What I can do is give you Craig's recommended jetting specs (saved my Husky Club newsletters even though he cancelled my membership)for the OEM Bing to where you could contact Sudco for their "spot-on" conversion to a Mikuni. Also, on this note, my bike has the updated porting/piston modification change which Husqvarna Racing adopted very early on in this model's racing career. I'm running a NOS Motoplat with the timing being close. Also, my bike has new Boyeson reeds and a Vintage Iron pipe. Don't know if the timing is as much of an issue as my carburation. Anyway, I had decided to go with a modern carb. Made contact with someone who put together a new Keihin 38mm which is ported close to what a Yamaha YZ from that era would have. Just been able to refocus back on this bike to where I have been able to run it around the streets near my house. Even with a 10T countershaft sprocket, I'm finding I have to really slip the clutch to get anything going well, but when it gets going, the front wheel is high into the air only using half throttle for the first three gears. Am using a race gas mix that I found works well on my KTM 380 and can pretty much eliminate timing. Do you have to really slip the clutches on these series of bikes for them to do anything??? Or am i just suffering from having too big of a carb? Sorry for getting a bit off track to the original comments.
Pat

Thanks guys I will let you know how it goes!! My mag has the same afffliction as yours. The nut on the top of the seat doesn't perform nearly as well as the rest of the bike