tune up
since I installed the 3" exhaust I am having a skip at idle . It seems to smooth out above 2000 rpm and the pipes are black and sooty . Holley #3310 vacuum secondaries with #72 jets front and rear . Vacuum advance distributor with 24* advance and 5* at the crank .
Cam:
Comp x-treme energy .500 lift , 292* dur., 244*[email protected]".
Ran strong before 3" exhaust . It's just at idle , sounds like crap. Sputter, I guess . Yes 29* total timing . Thanks guys and keep up the comments .
The only thing adding an exhaust should have done at idle/off idle is reduce exhasut reversion. Should show as slightly higher manifold vacuum.
What else may have happened - includeing old fuel - mentioned by lilifontery - who knows.
Wet above the throttles suggests fuel bowls are too high. Check that first. First thing on carb is always float level.
Next. Issue is only below 2000 rpm, so the main jets are irrelevant. Same with the maximum advance.
As far as tuning.
292 adv duration in 383 would definately like more initial timing.
Distributor starting point for a curve
I'm going to say 17-19 initial and not to start advancing until 800 rpm would be good start. More adv with less compression and stock heads, etc.
Since you've already drilled the throttle plates, that's fine, just roll with it. It should let you set the primary thottles so only .020 to .040 of the transition slot shows beneath the blade at idle. If you measure while the carb is off, and write down the turns of the idle speed screw from just touching until the blade opens to each of those, it makes tuning easier.
If its too lean and dies as you accelerate from slow speed 25 - 35 , 1/2 throttle or less, then stick some wires down the primary idle air bleeds until its rich enough.
Once you have the low speed in gear worked out - Then work on cruise timing and fueling - or work on WOT top gear timing and fueling. Don't try to do both at the same time. its just not clear whether you go to the drag strip alot or not.
Like crackedback said, don't go wide open throttle until the mechanical advance is readjusted so the total timing is in a safe zone for WOT testing.
The last illustration in this link has the guidelines from Direct Connection for both highway cruise & 'max'. ['Max' is in quotes because Chrysler distributors rarely stop advancing before 3000 rpm. As long as they only add roughly a degree every 1000 rpm above that's generally a good thing.]
How To Limit and Adjust Chrysler Vacuum Advance Cans
Holley jetting as sold for most aftermarket carbs is shown on this list:
https://documents.holley.com/techlibrary_carb_numerical_listing.pdf
3310-3 (and newer) will be probably be in ballpark around 70 - 74 PMJs and 76 - 80 SMJ.
PS. IMO that cam/motor is only borderline for having a significant advantage going true 4 corner idle adjustment. Its most useful when vacuum at idle is low. Bet that engine will hot idle with 10"Hg once more intial timing is used.
