Help! I am baffled by intermittant miss , I need XPERTS
Here goes, Bought me a new car off RJ,, a few months ago. Made it to the finals @ the Superchevy its first race! Problem started then & its still here.
Some backround.
Car is back halved monza running a 4:10 w TH 350 w 8 inch conv. Tires are MT 29.5x13.5
358 sbc with Brodix trac 1 , msd 6al , msd billet dist, 4150 holley 750 mech 2nd.
After Dyno tuning (ran great) brought to track. First 3 runs same et, ran great. run # 4 started to break down after 5800 in 2nd to 3rd shift, lost .2 et run # 5 same thing, looked over everything nothing obviouse, last run ran fine, back to original et.
Brought back to Dyno, changed cap, rotor, SP wires(all msd stuff) New Proform 750 carb. Ran both carbs, ran like a beast, all the way to redine in 3rd no problem. Hot day too.
Went to track
3 runs dead nuts. 4th run again with the pop pop pop @ the top of 2nd. this time with the pro form which was jetted rich. sounded like a lean pop, but I know it was rich. Some spectators who knew the car said it sounded like ignition.
I turned up Fuel pressure to 7 from 6 , ran fine next 2 runs then It started again, I raised my dial & shifted early, made many rounds, some great , some broke down. Last 2 runs were perfect & I ran to redline.
Went back & borrowed a msd & coil off a pal. Rewired all the wiring to ignition, grounded to the battery, soldered all connections. Replaced the autolite racing plugs. prior owner had them gapped @ .25 I opened to .40
1st run fine. 2nd run slight break up, 3rd run breakin up again, swapped coil. run #4 run OK.
Regrouped. Put in new msd mag trigger, & swapped a mallory digital 6 al, in place of the MSD just to see. Run # 1 started to break down again @ same place top of 2nd, this time on 1st run not 3rd, so not heated up. all 4 runs the same.
The one thing I did notice was my fuel pressure guage was fluctuating slightly when I reved the engine without load seemed to move (down when reved, but not by much) I may just be paranoid, but I didnt remember any movement prior.
Also when I picked up car from Dyno I noticed the fuel cap wasnt on correctly.
Could this be a fuel vent issue?
Why would it run fine @ the dyno & not on the track(attitude of the car? front end lift @ speed?)
I am stumpped, any ideas will be appreciated.