Car has a few passes now, enough to start trying to iron out tune. Have recording tach that shows stumble at 4600 RPM in first, then progress to 2nd gear. In second gear, curve is erratic and car breaks up. Finally into third gear, car still breaks up. Plugs look very rich but no black smoke. Fuel pressure and bowl levels are not issue, think it is jetting.

What are the under load symptons of rich/lean other than lean pop through carb and rich pop in exhaust? Timing is currently fixed at 33 with 12.7 domed pistons. Carb is 830 CFM annular discharge.

 

Sounds more like a coil or ignition box going bad to me.

 

just curious, what tach are you using that will replay full runs?
Thanks!

 

Autometer ultimate 2 tach

 

What is your fuel pressure at going down the track. Possible fuel delivery problem, but you have to have a gauge to see what it's doing exactly.

I had similar problems when my big pump took a dump on me. Once she started revving up with my temporary pump (Holley Red-all they sold in town and I was in the middle of a points race weekend) it would spit and sputter and carry on through the gears dropping me .3 in the 1/4. I installed a Holley Black pump spring in this Holley Red pump and that rasied my FP going down the track from 3psi to 7psi and it ran alot better.

Alot of guys were all saying lean condition, so I finally bought a FP gauge and mounted it under my cowl. Sure enough, as soon as the hammer dropped the psi went right down to 3psi, then as the bowls were running dry the pump could'nt keep up. Got my big pump back and steady 8.5psi the whole track, no more stumble/surging and got my .3 back.

 

Have fp gauge, 7.5 PSI during pass. Swapped carbs and trouble went away.

Current carb is 750 DP off red car. 82/89 jets. Problem w/830 may have come from PV plug used in secondary side.

Car went from 7.37 stumbling to 7.08 w/750 carb.

 

Have you had time to throw a PV and smaller jetting in 830 yet to see what that did if anything? Jetting seems about right, when I ran that same 830 on my 355 I think I was at 82/84 but i also had drilled out the front squirters too for more shot off the line and used PV in both metering blocks. If you've got it isolated down to the back metering block, maybe just pull it apart and clean it out really good first and see if that does anything. Float levels seem okay? Are you running jet extecsions? needle and seat not getting hung open with any little bits and peices of garbage? Seems if you picked up that much with the 750, maybe the 830 is indeed just running pig rich. try stepping down to 80/86 with PV plug once and see where that puts you. Just sounds weird you'd have to jet down with the bigger carb, I went from a 600, 650, 700, 750, and finally 830 the last year I ran my 355 and with every jump in carb size I had to jet up also.

 

The difference is the Annular boosters in the 830. Annular boosters develop a much stronger booster signal than Dog Leg Boosters ( and much better than straight leg ).

When switching from Dog Leg boosters to Annular boosters it is common to have to jet down 2 to 4 jet sizes.