1972 Datsun 240z Original Camshaft and Hitachi SU Carb stock needles

[LeonV]

Sounds like a vacuum leak/tuning issue.

[madkaw]

Those cam specs look like my Schneider Cam stage 2 -which should idle like normal-not 1100 rpm.

[jalexquijano]

Took the car again back to my mechanical engineer. Tested the car and it seems to accelerate fine. The problem is in the deceleration. When coming to a stop sign, slowing to make a u turn or traffic light the car tends to lower the revolutions from 1,100 to 600 tends to stall but immediately goes back to 1,100 RPM. THis is not normal, something is wrong here. After a couple of tests the needle now reads empty on the tank and the car is now shutting down completely even though there is still fuel present in the fuel filter (mine is a glass fuel filter which can show any impurity in the line). The engineer did tuned up the car and changed all the spark plugs in front of me.

Do you guys think i can solve this issue by myself or should i take the car back to him again? We are thinking on replacing this Far 311 race came with the Original Stock cam so i can get a smooth idle and use my car as a daily driver. THe spark plugs are getting dark in traffic jams due to the race cam.

I want to solve the stalling and irregular RPM drop when decelerating first and then swap the cam. Can anyone advise me on how to tackle this problem?

[LeonV]

Check your brake booster.

[djwarner]

The original throttle linkage had a dash pot that limited how fast the throttle would close. The control valve for the dash pot is located on the balance tube above the forward carburetor. Your pictures show the control valve with tubing connecting the inlet to the outlet.

Perhaps some of the more experienced users here can do a better job of describing how and when it originally worked. It is not uncommon for the dash pots to be MIA.

[siteunseen]

I think LeonV hit the nail head. https://www.google.com/webhp?sourceid=chrome-instant&rlz=1C1BOFA_enUS494US494&ion=1&espv=2&ie=UTF-8#q=testing%20a%20brake%20booster

But Mr Warner makes a good catch also, inlet and outlet hoses reversed.

Here's a picture of mine for reference.

Edited October 19, 2014 by siteunseen

[jalexquijano]

Just checked and I dont see any signs of rust or impurities in the glass filter. I even checked all the spark plugs and they are burning well. I also sprayed carburetor clear to all the hoses end in the car in order to check any vacuum leak with the car parked on idle and the RPM did not change. Do you think i should also adjust the mixture idle Wheel underneath each of both SU CARBS? The problem is when i reléase the gas pedal i.e. if i speed up real hard on 1st gear and then reléase the pedal the RPM drops to 500 and tends to stall but pick up back again to 1,100RPM. Should i play with the idle mixture wheels underneath each of both carbs? maybe give it a Little bit more counterclockwise?

Im really fed up with this situation!

[jalexquijano]

Check your brake booster.

Leon,

OKAY. Yesterday i removed the air filter, caburetor domes, inner springs and sprayed carb cleaner to both of the 3 screw SU carburetors. I refilled both carburetors with 3 in one motor oil and retightened each and every screw in the air filter and carb domes. Finally i did moved each of the idle mixture nuts a Little bit counterclockwise. Result: The car is maintaning its RPM when decelerating or stopping at an intersection.

Could this have been the problem??

[LeonV]

Leon,

OKAY. Yesterday i removed the air filter, caburetor domes, inner springs and sprayed carb cleaner to both of the 3 screw SU carburetors. I refilled both carburetors with 3 in one motor oil and retightened each and every screw in the air filter and carb domes. Finally i did moved each of the idle mixture nuts a Little bit counterclockwise. Result: The car is maintaning its RPM when decelerating or stopping at an intersection.

Could this have been the problem??

It sure could have been.