Well If I told you, I'd have about three forum members all telling me how terribly wrong I am. and I'm getting really tired of that.
I left enough clues in my post that in less than two minutes it could be cured.
But, I can almost guarantee you that, if you set the timing to less than 12 degrees, she will stink out the tailpipes so bad that you'll never run it in the garage again.
The cure for that is Idle-Air bypass.
Your 650DP is not likely to have a setting for this, and the gurus here might suggest cracking the Secondaries You can try it if you want but in 30 years of tuning, that has never worked for me.
I'll tell you what I do, and you can decide for yourself.
Here's what I would do.
I would take the carb off, flip it over, and with the curb-idle screw, set the transfer slot exposure to appear square, then make them a little taller than wide. AFTER THIS, do not touch the Speed screw. see below.
Next I would flip it right side up and set the mixture screws to 7/8ths Turn out. Next, I would shut the Secondaries up tight, but not sticking.
After that, you might have to reset your pump arms and so on.
I would plumb the VA to a PORTED vacuum source.
Ok bolt her back on, start her up. If the Idle speed is too high, RETARD the stinking timing. Warm her up, then reset the Fuel levels as may be required.
Next, adjust the mixture screws for smoothest idle. If this does not end up at 3/4 turn then the transfer slot is not quite right. If the mixture screws tell you she wants less Idle fuel, then take out a quarter turn from the Curb-Idle screw; and so on.
If the Idle speed is still too fast, RETARD the Idle-Timing some more.
If the exhaust stings your nostrils and burns your eyes, the engine wants some bypass air. I get by it by drilling one tiny hole in each Primary throttle blade. I put the hole on the front side, between the discharge ports and about .250 back from the edge. As to the size, I can't be sure. I know that .125 " will be way too big, and .0625 will be too small. My guess will be from 5/64ths to 6/64ths.
If you drill too big the idle speed will desynchronize from the transfer slot and you will not get a decent idle speed, nor a decent quality; so start on the small side. Chamfer the holes, both sides.
The purpose of these holes is to let you close the throttle back into the sweetspot of the ratio of Transfer fuel to mixture fuel, AT IDLE, in order to get a good throttle tip-in reaction and resulting in a good driveaway experience.
Do not be afraid to retard the idle timing. Your engine does not care about Idle timing, except to use it as a jumping off point to hit your stall-timing. But YOU can modify that in a better way.
Don't forget that if your Power Timing was perfect before you started making these changes, it won't be anymore, so, you are gunna have to fix it.
Yeah so, as you may have noticed, somewhere along the line, I lost it. I went from; what I would do, to what I think you should do. Sorry about that, but I'm not reWriting it; you'll figure it out.
And Like I originally said;
If I had to guess.
I mean;
1) yur cam timing could be off,
2) yur pistons could be tight,
3) yur valve lash could be tight,
4) the engine might not be operating at the best temperature,
5) the carb might not be delivering liquid fuel. and
6) If the Va is on full-time manifold vacuum, yur on yur own.
7) and so on.
