I just reviewed Engine Masters episode. It's the Street Demon that has to be removed to change jets. Good news!

i am in Minnesota.     I am thinking that the lowering is what I am going to try and the 64/69 sounds like a good starting point.  Wish me luck as I am learning in area never had to be in..  Thanks for your in put.

Melly, if you're at/near sea level, I would go down 4 sizes on both primary and secondary jets. According to Summit, the 600 cfm uses 68 primary/73 secondary. Their 500 cfm carburetor uses 62 primary/68 secondary. Going down four sizes will give you 64/69. What I can't remember is if the Summit has to be removed to change jets. I could be thinking of the Street Demon.

What altitude do you live at?  I am just lowering my jets two sizes in my stock 1273, but I live at Denver altitude.  

Ralph

at this point i tend to agree.  But I already have the 600 to deal with.  Thanks! Have ordered jets will have to figure it out.  Hoping to here from someone that's delt with this problem for more insight, as I am not a carb. person.

You're not the first who has said the Summit 600 cfm runs rich. You will have to re-jet. For a basically stock engine, the Summit 500 cfm might have been the better choice.

Anyone out there used a Summit MO8600VS - 600 CFM carb on their 292 or 312 y- block?  I purchased this and appeared to maybe too much for me set up   I have a pretty basic set 292 with a 57 dizzy, pterionic II, Runs and Idel's good but at WOT stumbles. Pull plugs all show black running to rich.  So, thinking I should go to lower jets.  Looking for some direction.  Not a Carb. guy.