240Z, 260Z, 280Z Performance / Technical Discussions related to performance motor enhancements, upgrades.

Not getting a steady idle with new cam and carbs

Old 03-22-2015, 02:39 PM
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Not getting a steady idle with new cam and carbs

Recently installed a Shneider 274F, changed the timing belt, adjusted the time, and installed SU Carburetors fully rebuilt by Ztherapy. I decided that 1000 RPM as idle was my target but if i get stucked in a traffic jam or leave the engine on for more than 10 minutes, the idle starts to lower to 900 or 800 rpm. If i turn the lights on it lowers more from 900RPM. How can i install an AC System in this car if the idle is not stable?

Am i missing something here? My car has a 60 amp Bosch Alternator for 280zx and pertronix ignitor.

I even removed the EGR system from the car cancelling the Throttle Opener Valve and Servo Diaphgram.

Anyone???
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Old 03-22-2015, 04:54 PM
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The A/C systems I've seen for the Z cars have a separate actuator that opens the throttle a bit when the compressor is running. That will keep your idle up.
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Old 04-01-2015, 07:59 AM
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Originally Posted by beg3yrs View Post
The A/C systems I've seen for the Z cars have a separate actuator that opens the throttle a bit when the compressor is running. That will keep your idle up.
Do you have a picture of this actuator?
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Old 04-01-2015, 10:36 AM
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You're in luck. Found this in my archives.

The FSM calls it the F.I.C.D. for Fast Idle Control Device. It is used to increase the idle when the A/C compressor is actuated. There's a reasonable discussion of it in the Air Conditioning section of the FSM.

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Old 04-30-2015, 09:01 AM
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Originally Posted by beg3yrs View Post
You're in luck. Found this in my archives.

The FSM calls it the F.I.C.D. for Fast Idle Control Device. It is used to increase the idle when the A/C compressor is actuated. There's a reasonable discussion of it in the Air Conditioning section of the FSM.

That pod on the left is known as the anti backfire valve. It opens the carbs a little when you are decelerating to keep raw fuel from igniting in the exhaust. Since your new cam may be producing higher vacuum it might be holding the carbs open a little. It is adjustable.
The ac fast idle is probably not on your car if it wasn't AC equipped originally. All 240Z cars were shipped to the US without AC. It was installed by the dealers. You can use an electronic fast idle and wire it into the system control. Example http://www.ebay.com/itm/1973-76-GS-G...st-Idle-Switch .
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Old 04-30-2015, 09:46 AM
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Originally Posted by theramz View Post
That pod on the left is known as the anti backfire valve. It opens the carbs a little when you are decelerating to keep raw fuel from igniting in the exhaust. Since your new cam may be producing higher vacuum it might be holding the carbs open a little. It is adjustable.
The ac fast idle is probably not on your car if it wasn't AC equipped originally. All 240Z cars were shipped to the US without AC. It was installed by the dealers. You can use an electronic fast idle and wire it into the system control. Example http://www.ebay.com/itm/1973-76-GS-G...st-Idle-Switch .
Doh! I must be getting old. I now recall reading about that when trying to figure out my own carb setup. Thanks for the correction.
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Old 04-30-2015, 09:54 AM
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Rough Idle!!! Really annoying!!!

I have a disgusting Rough Idle problem with my 1972 240z.


The car Idle is set up at 950 rpm (Shneider 274 F Cam, Pertronix ignitor and ignition coil, remanufactured SU carbs from Ztherapy and stock exhaust). If i leave the car in the parking after warmed up for more tan 10 minutes, the rpm starts to go lower from 950 to 850 and rises back to 1000 Rpm, the same at traffic jams? Arent these cars suppose to keep its idle as smooth as possible in 950 RPM? Could i have a leak somewhere?? I did a compression check and all valves are okay! Will i need to raise the car in an elevator to see if there is a leak somewhere in the exhaust or manifold? Already did the carb cleaner test around all the hoses and did not notice any change.


Please advise all the possible vacuum leaks i must need to check!
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Old 06-09-2015, 10:30 AM
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Back and Forth jumpy / Hopping acceleration at 1st and 2nd gear!!

My 1972 240z with dual SU carburetors recently remanufactured by Ztherapy and Schneider 274F cam with new valve springs, rocker arms and lashpads is presenting a jumpy hesitation at 1st and 2nd gear.

The sympton is described as follows:

First i get the car warmed up for 5 minutes. Start going in reverse to take it out of the parkway. Slide to gear N° 1 with the clutch stepped, reléase the clutch and start accelerating normally. The car starts to shake back and forth. To avoid this you need to step on the gas fully for it to pickup or very softly. Another scenario where this is shown is the following:

Passing through a slightly broken road at 1st gear or after a Street bump or accelerating on 1st gear and suddenly releasing the gas pedal.


My mechanic says Carburetor cars normally do this Kind of hesitation at low rpms. I dont believe it! My car had a Far 311 Race cam previously installed and this jumpy hesitation was not present.

THe car has a recently installed Carter P60504 Fuel pump:



http://www.ebay.com/...b7fab24&vxp=mtr



which is measuring 3psi. Should i install the previously Airtex 8012S electric fuel pump which advertises as 5 to 9 psi? Could this be fuel starvation issue?
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Old 06-10-2015, 07:49 AM
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Originally Posted by theramz View Post
That pod on the left is known as the anti backfire valve. It opens the carbs a little when you are decelerating to keep raw fuel from igniting in the exhaust. Since your new cam may be producing higher vacuum it might be holding the carbs open a little. It is adjustable.
The ac fast idle is probably not on your car if it wasn't AC equipped originally. All 240Z cars were shipped to the US without AC. It was installed by the dealers. You can use an electronic fast idle and wire it into the system control. Example http://www.ebay.com/itm/1973-76-GS-G...st-Idle-Switch .
Sorry, but i did clean out all that emission anti backfire valves that were placed on top of the balance tube! THis is a picture of how it is right now!
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