I know there are better pictures somewhere out there, but for those who may want to see the difference between a stock 250cc piston and the BB 351cc piston and bore right now, here's my contribution.

250 piston still has the rings on it so it looks a little bigger than it really is. Bill also checked gaps and installed the rings on the new piston so there's one little step that won't need doing.

I am very lucky to be in the local area with The Man himself so was able to do drop off and pick up right at his shop. He's 1st class and has lots of knowledge. We even reversed the Marcelino cam mod (ACR portion) on his shop press since that mod won't work on a big bore so well.

It'll take a few days to get the full assembly done since the amount of work done in my garage is inversely proportional to how chilly it feels out there to me, which right now is cold.

 

Thanks Kansas,
That second pic really does it!
Is your #132 main jet Kaw (Keihin) or DJ?

 

Wow, the second picture tells it all. I have never seen a picture like that before, only the one's with the piston's side by side. Have fun!

 

My #132 is a stock CVK number (Keihin). May actually be too large. A #130 might work better. The only other jet I had handy was a #128 but Bill's rule of thumb was two up on the main and one up on the pilot for the conversion. My main for 250cc was #125 so the #130 may be best. We'll see as things progress. The #132 will do initially.

I think most folks are already aware of the BB rules of thumb from your build up thread that was posted not so long ago and other posts on jetting but that's one of those things that is worth repeating from time to time.

 

you have a dirty, dirty piston.....

 

You shoulda seen it before I scraped off the top layer of carbon crud...

 

I'm thinking you need to take a look at your jetting...

 

That's nothing...

 

Thanks. I'm trying to study other folks 351 jetting to help me nail mine down quicker once I'm able to get back on the steed. I have the 128DJ in, about equal to Keihin 138, and I'm pretty sure its rich. I've seen threads of guys running the 132 DJ on the 250 and I don't see how they do it. I don't want my new piston looking like my old one.

From the jet comparison chart:

Keihin DJ
142.5 132
137.5 128
132.5 124
130 122
125 118
117.5 112 (stock jetting)

 

mine is similar, likes having a 120 dj for the main jet with my fmf q4 on it