Originally Posted by leejoy
it's a mess right now. the initial timing "for today" is about 35deg BTDC at idle (no vacuum advance) don't know total timing yet because I am still tuning it and selecting which MSD springs I should use on the centrifugal weights. Help................
You need to get the base timing down to around 14 to 18 degrees before trying to figure your mechanical advance. Then proceed as all the others have said on the idle slot and secondary throttle plate adjustments. Drill the primaries as a last resort.
Personally, on a 2 mix screw carb, I prefer to drill as apposed to opening up the secondaries. The front of the carb will be richer and the secondary side will be fairly lean drawing in the extra air without the added fuel from 2 add'l screws.
On a 4 screw carb, its easier to open the secondaries some and then compensate on all 4 corners.
My son's 400 did the same thing, cept we had a Qjet on it. I ended up drilling a 5/32 hole in each primary butterfly and it cured the idle mix problem right up, but its a permanent modification too, short of changing out the primary blades if you drill too big.
How big is
A "big cam" and wanting good idle @700 in gear may not be possible, as we found out. We ended up with 700 in gear but in park it jumped to 1200 and would not shut off. We ended up putting an idle solonoid on it to get it to settle down when we shut the key off.