Mikuni for a "77" WR250

Ok, I hope this makes sense. I'm working on a 77 WR250 and I'm looking to put a 38mm Mikuni on it. I know it came with a Bing, but the Mikuni is what I have. When I try to install it, it seems to be to long, meaning it actually sticks into the air box by about 10mm. There's enough room to put the rubber boot on, but the fact that it actually sticks into the air box doesn't seem correct (I've never seen a carb fit like that). It's like the Mikuni is to wide to fit Between the reed cage and the air box. I do have both styles of reed cages (slip on boot and the bolt on flange) but I end up with the same results.
So to anyone who installed a Mikuni on the older 70's bikes is this normal??

Thank you all for your time and knowledge, John.

No not normal. You probably are using the longer reed block manifold housing. Husky had the longer early style and a shorter one (about 8-10mm shorter). Also what is the overall length of your Mikuni carb?

Marty

My Mikuni is 116mm in length. I was surfing around on the interweb and noticed some of the older Mikuni's had a shorter width intake bell (if that makes sense, my terminology is terrible). My intake bell on the Mikuni is around 30mm. Not sure if that's the problem or not?

John

Yes, you need the shorter version 38mm mikuni and the large air intake bell. Off the top of my head the airbell diameter should be about 65mm.

Marty

Thanks Marty. Also you mentioned a shorter reed block manifold? Do you know what years this was on or even a part # by chance?

John

FYI - the rear bell can be trimmed:

AAhh, I wondered if I could do that. The one pictured on the right looks exactly like mine. I think I may give that a try.
Thanks Vinskord.

John

Curious - if the rear of the carb intrudes +/- 10mm into the airbox, but doesn't interfere with the filter or anything else, is it really necessary to trim the rear of the carb? Does it hit the central mounting stud?

No, it doesn't hit anything. Actually, I still have enough room to get the rubber boot on because the bell is so big. It just didn't seem right to me. With it protruding into the air box it doesn't seem like a very smooth air flow. I don't know if that is a big concern or not? In the automotive world you're always looking for the smoothest flow as possible. At first, I thought I could fill that area with a big O ring (it's like a small pipe inside a big pipe with a 4mm gap around it). I did find some O rings that would work. Not sure what to do really?

John