I have been noticing my slant popping a lot more than usual, what normally causes this? Iit doesn't happen on acceleration, mostly when on idle and rolling down hills when the gas is backed off.

This is a combination of a few things and usually happens on manual tranny cars. Typically the engine is running at higher rpm and in the mains on the carb, when you suddenly slap the throttle plates shut with a load on the drivetrain, you get lots of less fuel for the mix (idle circuit is like a squirt gun compared to the "hose" of the main circuit), you have high vaccuum due the plate position and the load on the engine...which causes a lean out and "shooting ducks"...sometimes the advance/timing doesn't reel back in quickly under those conditions as well and can cause this to happen occasionally.

In the early days they added a dash pot to the carb to apply some gradual pressure to the carb throttle lever so the plates close slowly over a few seconds and it doesn't just 'lean out'. The "band aide" used by most hot rodders is to just richen up the idle and transition circuits to blanket this out...this is not the best solution as a fair bit of extra fuel can cause quicker wear to your cylinder walls by washing the oil off the walls and rings...If not corrected the popping/'detonation' can do some not so nice things to your cylinders/pistons/plugs/valves/rods/bearings.

You can check the condition by looking at a vacc. gauge and your O2 sensor if your car is so equipped for power tuning...If not, you'll have to look at your plugs to see if they are clean when this occurs, if so you are most definately lean.


-D.Idiot

Thanks for the info,
I have regraphed the elec dissy and put in springs from big slant six fan, would this have caused the popping? Unfortunately I've lost the original springs so I cant swap to check. Currently I have a green and black spring in the dissy and narrowed the slot to 0.360. I also ain't running vacuum advance, would it be necessary with the engle kv1 cam? I have connected a hose but it didn't seem to make much difference.

If the springs are too light the weights can bounce, but that doesn't sound like the problem here since you are running all mech and probably not using the lightest springs in the kit.


If this is on a Hyperpak intake...time for some carb mods to keep one of 3 circuits happy for daily driving....if you do have a clutch...engage it before letting off the go pedal to coast....if it still pops I might suspect carb mix or carbon deposits at this point before going to carb mods.

-D.idiot

I see I will mock around with the carb, jets and idle mixtures. When you say carbon deposits are you talking about in the combustion chamber, on the valves?