backfire/popping out of velocity stacks

[tdiddy]

first time car has ran in 15 years... new after market fuel pump, new fule lines.. gave cylinders a squrt of maverics.. runing heavy sea foam mixed fuel...not running the air filter right now. started nice runs rough and with a lot of backfires and theres this backfire'ish thing happening out of two of the velocity stacks

sitting for 15 years, needs a valve adjustment no?? can that cause the popping??.. i'd like to let it idle for a while to burn of the 15 YO junk and get good fuel and oil running thorough the system... but do i run the risk of hurting something.. valves????

car is 70 911 t

thanks

[Hoss3.0]

Timing is likely out of whack. Try tweaking the distributor slightly to see if it helps. Did you change the cap, rotor and points? Make sure the plugs are good and in the right firing order. I do believe that a valve adjust would help what you are describing. Good luck, it sounds like you're having fun. I enjoy my car more everytime I drive it. I just passed the one year mark of ownership.

[Zeke]

See my post on your other thread.

[A Quiet Boom]

Popping is usually too lean, this could be vacuum leaks from old gaskets or clogged idle circuits/jets. It can also be from too much advance at idle, check to make sure the dizzy mechanical and vacuum advance mechanisms aren't stuck. Did you put some lightweight oil on the felt under the rotor? Easy way to check for vacuum leaks is by spraying carb cleaner on suspect areas with the engine running, if the rpms drop you've found a leak. Acetylene also works for this.

[Nitrometano]

is carbureted or fuel injected?

[tdiddy]

zenith carbs it a 70' T

[Nitrometano]

I dont know nothing about the zenith carbs, but in my case I have webers carbs. When I feel the backfire & popping out of velocity stacks there are 2 individual problems:

First, the back fire is caused by over rich mitxure in one or more cylinders You need to lean it buy the mixture screw. Also a clogged idle jet can cause it. You know if is the idle jet because if you ran the car at more than 3,000 RPM you will notice no back fire. But is running less than 3,000 RPM, the backfire will beging. Just take out the idle jet and clean it with carburetor cleaner.

Second, the popping out the velocity stacks are caused by very lean condition on one or more cylinders. You need to rich it.

To get the proper mixture adjustment, you need to lean out the mixture screw in one carb until the screw are closet complety, then unscrew until you get or heard the engine acelerating and then you will notice that the engine will not accelerate any more. Close back the mixture screw until the engine drops and the take it out until the engine RPM rise. Then stop the screw there and follow to the next carb. That setting is the proper mixture for that cylinder.

Remember, I have never done this into a zenith, this are the procedure that I use in my webers. If the configuration are the same between both carbs (weber & zenith) it will works.