That makes sense markt. My measurements were done with a tape measure and eyeball, could have easily been off a mm or 2.

And I was kind of thinking similiar things about the pilot circuit, but I'm unsure how to go about addressing it.  Will it just get worse if I go away from the 60 pilot?  Currently I can turn it out the full 3 turns, and idle keeps increasing.  But it does seem to help this issue if I leave it rich, at 1.5 turns.  Yes the condition is when just initially tipping into the throttle.  

I'm kind of leaning back towards the rt2mx top end, but i need to have a bit of knowledge on the pipes.  I know the piston to head clearance is .065 or so on that setup with normal gaskets.  At 2.5mm timing it never pinged.  Ran awesome with the rt2mx pipe, good torque overall, and a wicked powerband.  With the rt1mx pipe it's a turd down low, then comes on at higher rpm and scares the $#it out of ya.  So the pipe really needs to be right imo.

Didn't you say you have an RT2 carb in some of your other posts? No matter what it is...  I believe the RT1MX had a 1.5 slide cutaway and the RT2 had a 2.5.  What are you running?  Higher cutaway definitely leans out the off idle transition.  If you can make sure you have a 1.5 slide, it might make the difference and cure the problem

Well, that may clue us in.

cliff

It's 2.5 cut away.

The rt3 has a 3.0 cut away, had 2 of them to verify that.  The 1970 rt1m calls for the 1.5, a different jet needle, and a 280 main jet.  Im using 1971 rt1mx specs, which specify a 2.5 cut away.  Perhaps I should get the components for the 1970 calibration all-together?  I'm still running rich on top, even with genuine 310 mikuni main.  It was a cold day that I initially tested it..

The needle and needle jet were richer on the RT1b-MX with the 2.5 slide. 

Not sure what carb components you have assembled into a possible facsimile of the original MX carb and it really doesn't matter.  The engine needs what it needs.  If you have the 34 RT1b MX carb size, 60 pilot jet, P-0 needle jet (of the same series), 6DH2 needle, 310 main, and either an original MX air box or one that flows the same (with foam filter that is not restricted by the wrong oil or too much oil), jetting should be close.

If it's not right... too rich at full throttle could just need a 300 main...  (it could be that in a race, the engine would be pushed hard and needs the 310 when it gets hot.)  Detonation at throttle opening is a likely indicator of it going lean under those conditions so the fix would be adjustments so it doesn't go lean under those conditions. 

If you are using a different needle or needle jet than specified, one or both of those could be the answer?  And/or different needle/needle jet might work fine with adjustments to other calibrations like the cutaway (to possibly correct lean at initial throttle opening) and main (to correct rich at sustained full throttle)

Carb components are a system that work together...  and the engine needs what it needs.

Yeah I'm running the 71 setup. 60 pilot, 310 main, p-0 needle jet, 6dh2 needle, 3rd clip, 2.5 cutaway. Runs very happy otherwise, initially started with p-4 and p-2 needle jets. They were too rich for sure. Feel rather confident with it. I'm gonna do some measurements on the squish band, and go from there. It definitely doesn't touch .080" solder right now. I have a feeling it's pretty loose. After that's taken care of I'll get a 1.5 cutaway, and an assortment of main jets. Oh and I'm not running an air box. I've got a uni filter clamped onto the stock intake tube, essentially where the air box was. I doubt I can find a stock rt1mx airbox, and I feel like the stock rt1b airbox is restrictive. But now I expose the air charge to the varying atmosphere, so maybe I should look into making an airbox?

Well, I'm winning now lol. Figured out setting squish wasn't possible using the rt1mx head. The piston is .040 over. I pulled the base gasket, and checked it again. Still nothing, except for the very edge, which was at about .020" clearance. The head needs to be machined to accept the larger piston. So.. I took a look at my rt2mx head... I didn't realize how close they were, except the rt2mx head has already been machined for a bigger piston. So I put a base gasket on, and bolted it down. I've got roughly .060" squish band now. Just got back from a ride, adrenaline still pumping! Thing hauls ass now, and it even seems smoother somehow? I dunno how the math works out, but I'd gladly buy high octane fuel for it now!

The pinging/pre ignition sound is still there, I hear it mostly lower rpm, but as we discussed it is off-idle, in the 1/16 to 1/8 throttle range.  I'll be getting the 1.5 cutaway ordered.  As for the main jet, it just cleaned out better than it ever has, and if anything I'm gonna try jetting up some more now.  Good times, I'll have to get someone to record me riding this beast a little bit.