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Engine Idle AFR

tsaarts

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Hello.

I m having issues with setting the carb. I have 600 vacuum secondaries holley. Engine is 400 cid and the cam has 218/224 duration at 50 lift. With vacuum gauge i have about 12 inch of vacuum at 750 rpm idle. Timing is about 15 degrees at idle. I bought wideband for further tuning for cruise/wot etc. What i found is that the engine idles with best vacuum at 13,0 to 1 AFR ratio. It seems to be a bit rich and is smelly. Is it normal with this spec engine or is there any other reason why engine likes this rich idle?
 

tsaarts

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Are you using air fuel ratio or Lamda?
I m using Innovate wideband kit and gauge shows me air fuel ratio 13.0 at idle with highest possible vacuum.
Not using gauge to show me lamda number, if that is what you meant.
 

Steve340

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It is I wasn't sure from your post.
The AFR reading at idle can be anywhere from 13.5 to 14.5 or even leaner.
It is not an exact science but as lean as possible at idle and cruise
If it is a Holley carb set the primary main jet/cruise mixture first because this will influence all the other settings.
 

Adam

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Imo you need a bigger carb on a 400 😁, but anyway make sure your secondary spring is keeping the secondaries closed at idle; make sure your power valve is not ruptured; make sure the needle and seat is closing when full, otherwise you will have internal leakage no matter what you do. Also, it is possible your fuel pump is over powering the needle/seat. I had a new Carter mechanical pump on a small block that put out 11 psi at idle. I thought it was the Holley carb and rebuilt it twice with no improvement. I swapped on a new demon carb and still had the same problem. Finally I tested the fuel pressure... duh. after I installed a regulator to keep the pressure down everything was great.
 
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