NGK BP6ES spark plug burn color OK?

[jalexquijano]

Do both of the idle mixture knobs need to be set up equally? ie 3 turns clockwise on the front carb and 3 turns clockwise on the rear carb or could i set 3 turns clockwise on the front and 3.5 on the rear carb striving to get a brownish tan color burn in all 6 spark plugs?

[240260280z]

You can have different turns on the jets due to mechanical differences, wear and user error.

Getting all plugs to the same colour is a good goal.

Also lifting the piston in the back carb with your finger and idling on the front 3 cylinders then doing the same and running on the rear 3 cylinders is a good balance check. We call it the equally shitty test.

[bartsscooterservice]

Did you use the right gaskets between the carbs and the manifold ?

 

Set the stationairy idle with the idle screws ( not the fast idle one ).

[siteunseen]

Also lifting the piston in the back carb with your finger and idling on the front 3 cylinders then doing the same and running on the rear 3 cylinders is a good balance check. We call it the equally shitty test.

I spit coffee on my screen when I read that. 

[jalexquijano]

First of all, both of these carbs were fully remanufactured from scratch by Bruce Palmer at Ztherapy so they do not have any type of wear. I did this piston lifting test on the rear carb, if i lift it too much, the engine shuts down. If i do the same in the front carb, the engine slows down but does not shut off. I drove the car last night at 3 turns clockwise each of the idle mixture knobs with Brand new bp6es spark plugs at .35 mm gap. The car lacked power as it tend to stumble when accelerating under 3,000 RPM. I closed the gap to .31 mm each and richen the mixture of the rear carb to 3.5 turns and it has more power.

 

Any clues of what could be wrong? as background of my car it has a Shneider 274F cam with  crank and rods from a L26, special oversized 84mm flat top black coated pistons from D.L. Potter Engineering with E88 Head. Recent rebuilt 5 speed transmission from 280Z with new Center Force 1 clutch with stainless steel clutch hose.

[240260280z]

I did this piston lifting test on the rear carb, if i lift it too much, the engine shuts down.

This means you need more fuel to the front carb. give the front carb 1/2 turn more fuel and retry.

If i do the same in the front carb, the engine slows down but does not shut off.

This carb has enough fuel. You may have to reduce.

Be sure to balance air after each adjustment using unisyn or flow gauge. The engine should be able to run on 3 cylinders when fuel and air is balanced.

Repeat the test at 3000rpm then balance air then adjust fuel so that the rpms drop the same amount when you finger a carb.

Edited May 27, 2015 by Blue

[jalexquijano]

Thanks Blue.

 

Will i need to get a Timing light gun to adjust the time also as follows:

 

12 BTDC at 950 RPM IDLE

 

36 BTDC at 2,800 RPM

 

I really appreciate your assistance on this.

[Diseazd]

Spark plug gap should be .035 inches not .35mm

[240260280z]

Glad to help. I am now in Fiji.... one day I will be back in Panama!

[jalexquijano]

Glad to help. I am now in Fiji.... one day I will be back in Panama!

 

I hope so!! Mechanics here in Panama only know how to change parts and not diagnose anything. I will need your technical advice to complete my Project.

[Stanley]

Tuning the SU's is not that bad. The various methods all work if you do it right. If you download the FSM, or Blue's method, or the one from the other link,  print it out so it's sitting on the fender while you do it first time. Need the uni-sen or synchrometer. It's almost fun. Just setting both at 2 1/2 turns down only works if the engine's perfectly stock, float bowl settings are perfect, your temperature and altitude are happen to be correct for that setting, and you're lucky. Even if 2 1/2 turns is correct for both carbs, you still need to balance them.

[jalexquijano]

Well i finally managed to tune both front and rear carbs at a Little less than 3 and a half turns. I am using Automatic Transmission Fluid as damper oil. However, i am getting a hesitation and stumbling if i drive the car at slow speed between 1st and 2nd gear or if the car passes through a bumpy Street at slow speed. Could i have the ignition time wrong? I read that if the time is not set properly with a timing light you could present this problem.