Correct Rpm At Idle And Choke Adjustment On 240Z

[jalexquijano]

Finally i managed to replace the Far 311 Race Cam with the following smoother cam manufactured by Schneider:

 

http://schneidercams.com/274FL6.aspx

 

I also changed the springs, .175 lash pads, retainers and rocker arms (the full kit). In addition to this my carbs were recently remanufactured by Z therapy in order to avoid any issues. I plan on installing an AC system so using a cam that went from 4500 to 8500 wouldnt work.

 

Anyway, i just tested the car yesterday, and have a couple of queries on its performance:

 

1. The choke cable when pulled only reaches 1,500 RPM at idle. Is this okay or should it be adjusted to 3,000 RPM when pulled? With the Far 311 Race Cam i managed to pull it reaching 3,000 RPM. The mechanic says it should be kept until 1,500 RPM.

 

2. He set the RPM to 800 at idle to avoid high gas consumption. Should i raise it to 1,000 RPM using the fast idle screw?

 

I really appreciate anyone´s feedback on this crucial issues.

 

Jorge

[240260280z]

800 rpm is purrrrfect for a nice idle

The choke is used primarily to add more fuel to a cold motor because so much of the fuel vapour condenses in a cold engine and can not burn. The way Nissan designed the choke linkage, it does increase the idle ~ 200rpm.

Since you are in Panama, you do not need to ever use your choke as the engine is always warm. I would not worry about it.

[240260280z]

btw did you want to sell your cam?

[jalexquijano]

When are you coming to Panama? How much can you offer?

 

Should i leave the choke adjustment as the mechanic set it?

[240260280z]

Sure, don't worry about the choke. Just make sure that when the lever is pushed to off that the jets are all the way up.

A friend of mine is building a BRE tribute car so I just told him about your cam. He may be interested. I'll send an offer when I hear back from him. If you could email me pictures that would be great: philip@atlanticz.ca

Thanks!

[jalexquijano]

800 rpm is purrrrfect for a nice idle

The choke is used primarily to add more fuel to a cold motor because so much of the fuel vapour condenses in a cold engine and can not burn. The way Nissan designed the choke linkage, it does increase the idle ~ 200rpm.

Since you are in Panama, you do not need to ever use your choke as the engine is always warm. I would not worry about it.

I will also need you to guide me on the parts i need to install the AC System. I already purchased the Vintage Air Gen II Mini evaporator and Sanden 508 compressor. I am now looking for the bracket to install the compressor on the 4 bolts found on the driver´s side of the 240z. Should i also get a Fan Shroud for the Champio 3 row radiator my car has?

[jalexquijano]

800 rpm is purrrrfect for a nice idle

The choke is used primarily to add more fuel to a cold motor because so much of the fuel vapour condenses in a cold engine and can not burn. The way Nissan designed the choke linkage, it does increase the idle ~ 200rpm.

Since you are in Panama, you do not need to ever use your choke as the engine is always warm. I would not worry about it.

Yesterday  my car was stumbling when accelerating from a stop sign in first gear (back and forth shaking when releasing the accelerator pedal). I had to readjust the carbs, dial the idle mixture knob to 3.5 turns and raise the RPM on each of the carbs to 1,000 RPM. Is 3.5 turns  okay for recently remanufactured carbs by Ztherapy? They advise that the starting point is 2.5 turns.

 

Could this be due to a bad timing issue and i need to advance the timing or the electric fuel pump is not pushing enough fuel? I just installed a Carter P60504 which is really silent and has the following specs:

 

Free Flow Rate:30 gph

Maximum Pressure (psi):4 psi

 

Please let me know if i am going the correct direction.

Edited March 16, 2015 by jalexquijano

[Stanley]

If raising the idle and richening the mix made it run better, doesn't sound like it's the fuel pump. Sounds like it needed more gas and the F.P. is providing it.

 

Hot weather and high altitude (Hot summer day in Denver) needs a leaner mix; cold plus low altitude (couple weeks ago at sea level on the East Coast) needs richer mix. There's a table for that in the FSM. But a non-stock engine might need more gas, if it moves more air. In that case it might be better to change or modify the needles instead of richening the mix. Otherwise the mix that works best when going WOT from 70 mph to 90 might be too rich at idle and for ordinary driving around town.   

 

Maybe the mix where it runs the best at all rpm without fouling the plugs is OK.

 

Does higher compression engine need a richer mix? Wondering about that one. Seems like it would need leaner mix but I'm guessing.

Edited March 16, 2015 by Stanley

[jalexquijano]

Okay. Thanks for the advice. I thought it could be the Carter Fuel Pump due to the fact that when the engine was turned off, it only filled 3/4 of the clear fuel filter. The camshaft my car is carrying right now is a Schneider 274-F which goes from 1850-6000 RPM which was swapped last week. Sincé the swap i am noticing that whenever i turn the engine off i can hear a small whistle. Is this normal?

[HuD 91gt]

Whistle sounds like a vacuum leak.  Weren't you having vacuum issues previously?

[HuD 91gt]

Sorry to interrupt this thread, but its on the same topic.

 

The Just SU's DVD states 12-1400 is what you should be going for with the choke on.   I noticed my Z when starting cold with the choke on it idles quite low, but once it warms up it idles high (2000RPM+).  I think I need to adjust the choke linkage to lessen the opening of the butterfly, but when should this 12-1400RPM happen?  As soon as the car is running, or once it has stabilized and "warmed up"?

 

For example.  Once I get the car running with the choke, i'll reduce the amount of choke and get it to idle around 1000-1200rpm. I'll get out of the car and close the garage door.  By the time I get back to the vehicle it's back up at 2000rpm.

Edited March 17, 2015 by HuD 91gt

[Mark Maras]

 1200-1400, engine cold, full choke. I always adjusted my c-cables so that the lever, on the console, wouldn't quite bottom out in the slide, in the off position. The idea is to ensure the chokes are all the way off by giving them a bit of a push. Only a couple of times in a bitter cold spell did I have any starting difficulties.

The chokes on SUs just deliver more fuel. As the engine warms, the fuel starts to burn more efficiently raising the RPMs.