Stalling problems with Hitachi SU Carbs on a 1972 Datsun 240z

[jalexquijano]

Just filled the carbs on my 1972 Datsun 240z with Engine Oil 10w30 as damper oil. However, while keeping the car parked with the engine running it tends to lower the rpm from 1,100 rpm to 500 - 600 rpm. Eventually if i decide to turn the lights on and actívate the turn signal light the car tends to stall and shuts down.

This car has the following modifications:

New Datsun L24 motor with crank and rods from a L26, special oversized 84mm flat top black coated pistons from D.L. Potter Engineering with E88 Head and Far 311 New Race Cam.

2 original SU Hitachi round top carburetors rebuilt with race needle.

I already used a synchronizer to sync both of the Hitachi carburetors. Another thing i did noticed is that the first three spark plugs are turning black

Another weird thing i noticed is that after filling the gas tank to half, i had to wait to 20 seconds for the car to start. It has an electric fuel pump.

Shall i consider buying a pair of fully refurbished Hitachi carbs from Palltech or Z therapy?

Edited April 17, 2014 by jalexquijano

[SteveJ]

Check the voltage from the positive side of the coil to ground while having someone turn on the lights, etc. I imagine your voltage is dropping too low. It should be around 9 VDC. How old is the battery?

Another weird thing i noticed is that after filling the gas tank to half, i had to wait to 20 seconds for the car to start. It has an electric fuel pump.

I think Captain Obvious had some good write-ups on checking the float bowls. If those run dry, you have to crank the car to get enough fuel back into them.