ORIGINAL: kdheath
It might be worth asking over at SSW about the K&B Sportsters. I think some one out West has been running either the 20 or 28. A Ro-Jett it ain't, but given plenty of castor oil and a low pitch prop like a 9-4 or so, it might make a pretty decent sport motor.
You're right, the 25 is not called a BigMig.
The K&B Sportster can be modified to a venturi and NVA by buying the venturi and nva for the Fox 25BB. It drops right in. To slow it down if you want to a piece of 1/4 inch tubing lightly flared and secured by the nva will work extremely well. Do not try for a 4/2/4 run as it wont do it. Use fuel similar to a Fox 35 i.e. 25/29% oil and 10% nitro.
For the Norvel 25 the Norvel 15 nva fits and makes this a good runner. Not a stunt run but fast and consistant..
Hope that this info is useful.
Dennis