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Engine running lean
#1
I'm slowly working my way through my 429 cobra jet (had about 6 months). Noticed from the previous MOT (from UK though not needed it seemed prudent when buying the car) that there is a note saying that the car should be running richer than it is. Haven't pulled a plug yet to see but wondered what the readings are actually saying about the state of tune? The carb is not the original Rochester, it's a standard replacement holley 750cfm 3310 and I have no idea, short of pulling the carb apart, as to what jets etc are in it.

Would anyone know what the readings might be expected to be for a presumed healthy 429 CJ (done 52K miles) and, if mine are too far adrift, what things I should do, and in what sequence, to the car to address them?

Cheers

[Image: 20190713-181004.jpg]
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#2
Assuming the emissions was tested at idle, then it is as easy as adjusting the idle mixture.

https://www.dragzine.com/news/how-to-pro...rburetors/

Beyond that I would read the plugs.

If it is lean across the running range, you'll probably want to take the jets up 2 sizes in the primary from their current size and read the plugs after running it to see if you need to go further.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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#3
https://www.holley.com/products/fuel_sys...ts/0-3310C

That is what it would have likely come with from the factory

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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#4
(07-13-2019, 02:44 PM)Jeff73Mach1 Wrote: Assuming the emissions was tested at idle, then it is as easy as adjusting the idle mixture.

https://www.dragzine.com/news/how-to-pro...rburetors/

Beyond that I would read the plugs.

If it is lean across the running range, you'll probably want to take the jets up 2 sizes in the primary from their current size and read the plugs after running it to see if you need to go further.

Thanks Jeff. Yes I presume it was at idle so sounds sensible to start there. That certainly looks like my carb. Best have a read with holleys links and get a service kit with different sized jets etc
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#5
How does the engine run? How do the spark plugs look? I wouldn't just start changing jets without more diagnosis.

Has the carburetor been thoroughly cleaned recently? Did it set on the shelf or engine for a long time without being used? You may want to take it apart and make sure it is clean, especially all of the ports, and put new gaskets, accelerator pump, and enrichment valve in it.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#6
(07-14-2019, 08:09 AM)Don C Wrote: How does the engine run? How do the spark plugs look? I wouldn't just start changing jets without more diagnosis.

Has the carburetor been thoroughly cleaned recently? Did it set on the shelf or engine for a long time without being used? You may want to take it apart and make sure it is clean, especially all of the ports, and put new gaskets, accelerator pump, and enrichment valve in it.

Cheers Don. The car seems to run OK when warmed up and I think it pulls well enough (though I wouldn't know for sure how savage the acceleration should be - its c6 auto) though it struggles on start up. The manual choke does operate but actually achieves nothing (don't know the reason why not) as I have to feather the throttle until the engine is warmed up for it to idle without cutting out. No idea, as yet, as to the timing or carb settings etc.

I got the car from a dealer who had it stored for 3 years and only ran it occasionally. I guess maybe the carb needs an overhaul, despite having covered maybe 200 miles in 3 years, as it's stood for so long. The engine always fires up readily, it's just the warming up that's the problem. A rebuild it is only like 30 bucks so that's a no brainer.
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#7
From my post and submitted by Hemikiller.
http://brucerichards.com/tuning.htm
May help with your "problems" too
Geoff.

I learn something new every day!
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#8
I think you need the choke side of the carb set up properly. It sounds like the choke idle needs to be increased.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
  Reply
#9
I would also verify that the choke butterfly actually closes when the choke knob is pulled out.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#10
Thanks again guys. I'll check out the choke function for sure and certainly go through the carb tuning link as well as the holley one.
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