"77" WR250 Jetting ?

I'm looking to put a 38mm Mikuni on my 77 wr250 (because that is what I have) and was wondering a good starting point for jetting. Any help or recommendations would be very much appreciated.

Thanks, John

Here's what I am running on my 78 250CR with a 38mm Mikuni
250 CR Jetting
Needle 6DH3
Slide 2.0
Main. 390
Pilot. 35
I'm at about 900 ft above sea level
Bill

Thanks Bill. This bike is coming from two parts bikes I bought. The seller only had this carb (38 mikuni) that had a tag on it that said husky. I don't think this was the one on the bike because the rubber boots I have only fit a Bing. I'm going to take it apart and see what's in it sometime this weekend.
John

If swapping from Bing to Mikuni you'll probably need a newer manifold and carb to airbox boot. My 76 250WR came with the Bing on it and as I remember we had a bitch of a time getting it Jetted for the tight single track that we used to run here in the northeast. The Mikuni worked much better for those conditions on my 78 CR.
Bill

Yes this jetting thing is all new to me. I have lots to learn. I do need new rubber boots on both ends. I found one that will work on the airbox end at Lowes. It fits tight and will need to be cut down in length, but it should work fine.
John

I think the airbox boot that works is a Fernco
1059-22
Bill

That is correct, that's the one I got.
Thanks, John

I took mine apart and found:
main. 410
pilot. 45
slide. 2.0
needle. 6DH20
Not sure about that needle, the numbers are so dang small. The fella I got it from also had a 360 and I think this was the carb for that bike. I'm still up in the air about using this carb, I was originally going to get a 36mm Mikuni. I've even heard of people putting 34mm carbs on to get better low end?
John

Bill, if I could ask, what size needle jet are you using for that needle (6DH3)??
Thanks, John

Not sure, I haven't had apart in a few years. its probably what ever came with it in 78.

Carb specs for 78 250CR (38mm Mikuni) - may be of help:

Thank you Vinskord. Looking at that mine my be close. I might just put mine on with what it has and see how things go?
John