PROBLEM: Found and Solved!

[Demon 408]

The only reason I'm posting this thread is to hopefully help out a fellow FABO in the future. Here goes...

Problem:
I just got my Demon running with the new 408 and I have a popping in the exhaust on deceleration and light throttle. If I try to adjust the idle below 1100 RPM it gets worse. I also noticed it got worse when I disconnected the vacuum advance to check timing.

I have a FBO A688 Mopar Ignition with vacuum advance and 18 degrees initial and 35 degrees total. Plugs are Autolite 65. Carb is a Pro Systems Holley 4150, Jets are 78 primary and 88 secondary and the throttle plates have holes drilled in them. LD-340 intake. 308 heads with 9.9:1 compression. Camshaft is a Hydraulic Roller (Cam Motion); Duration Intake/Exhaust is 242/248; Lift Intake/Exhaust 570/562; Lobe Separation 110; Centerline (Installed) 105.5. TTI headers and full X-pipe exhaust. I’m running a mechanical Carter Super Fuel Pump with 3/8” line from tank to carb with no fuel regulator of fuel gauge.

Engine was broken in on the dyno and did not show any signs of popping on deceleration. But I used the dyno ignition box (MSD 6) with the FBO distributor with no vacuum advance and a cheap set of Summit Racing headers and the dyno electric fuel pump (6 PSI).

Can you guess what the problem is?



Solution:
Floats were adjust on dyno with 6 PSI electric fuel pump, but I'm using a mechanical Carter Super pump (7-8 PSI) on the car. I knew the problem had to be related to something that was different between Dyno and the as installed in car equipment. Sure enough, I adjusted the carb floats down, readjusted the idle curcuit and it runs and idles like a rapped Ape!
:munky2:

 

[pettybludart]

Glad to see you got the problem solved!8)I also have my 408 raped ape running now.The torque at lower RPM,s is incredible.Keep us updated on your engines performance.:cheers:

 

[Demon 408]

Glad to see you got the problem solved!8)I also have my 408 raped ape running now.The torque at lower RPM,s is incredible.Keep us updated on your engines performance.:cheers:

Will do. This is my first 408 and man does this thing pull down low, this will be a great street car! Only have about 10 miles on it, still need to install sound deadner, carpet and rear seat. Very noisy right now but fast as hell!

 

[pettybludart]

I hear ya on the lowerend,mine has a Coan 4500 stall behind it in my little 66 Dart(2700lbs) which only has tops 5 miles on it.I just picked up a roll(4x20ft)for $40 at the swapmeet/show last weekend.

 

[Demon 408]

Your shift light is defintately good idea. Need to hide one up by my sun visor so I can keep my eyes on the road. Mines a 4 speed and the gear chages come at you very quickly. No doubt with that stall on your converter you'll be seeing daylight under the front tires.

 

[pettybludart]

Yup,will definetly see air under the front tires.My 73 Dart Sport 340 4 speed I had the 340 stroked to a 372(360 crank) and only ran a best of 12.82@108mph,I should,ve been down in the low 12,s at that mph,but running a 4 speed has it,s dissadvantages.The 73 is now going back to just a street car,so no more pounding it.

 

[pettybludart]

Oh and if your gonna go to the track for some time runs,a quick easy weight transfer trick is to just pull your front swaybar pins.You,d be surprised at how much this helps with weight transfer.