Join Date: Dec 2000
Location: Clermont-Ferrand, France
I recently installed my new 409
(0.040" over 400).
Here are the current specifics:
AFR 210cc intake cylinder heads
Stahl raised port 1 3/4" primary headers
2 1/4" Borla exhaust
Demon 750 vacuum secondary
#72 jets in Primary's
#82 jets in Secondary's
50cc accel pump (was 30 cc)
Light Vacuum Spring
Carter Street/Strip Mechanical Fuel Pump
(8.5 psi), Hard line to pump, -6AN line to carb with Earl's sintered bronze filter.
Comp Cams Hyd. Roller 230/236 @ 0.050"
1.6 ratio roller rockers
13 inches of Mercury at Idle
Victor Junior intake with no spacer
10.3:1 compression ratio
Mallory Unilite Ignition with Accel Supercoil
(Electromotive ignition ordered 5 weeks ago!)
12 degrees advanced at idle
35 degrees total
NGK R5672A-9 plugs
6-inch rods, standard 3.75" stroke crank
Tremec TKO 5-speed, 3:08 rear end
02 sensor guage installed.
Here is the trouble I have been having:
The car started off very rich (78 primary, 86 secondary). I backed the jet sizes down to where they are now. The 02 guage still reads rich at part throttle and idle. (Idle set using max vacuum method). When full throttle is applied, it goes lean on the guage and stumbles for approximately 2 seconds. Eventually it clears out and goes back to rich if I keep the throttle down. I tried a #41 and a #28 squirter and could find no difference. I also tried several vacuum springs with no influence. I installed a 50cc accel pump and that seemed to help with the lean spot. It runs very well when the bog is not there and I have seen no black smoke. Now I am having a heck of a time getting it to cold start. I pulled a plug and it is completely black. They are fouled for sure.
My next idea is to replace the plugs (try a higher heat range) and keep reducing the jet sizes. The only thing that bothers me about continuing in this direction is that I am getting pretty far from the baseline that Demon set at the factory. Am I going the right direction?