| 808OvalGreasemonkey |
Thu Oct 27, 2011 9:46 pm |
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Just finished installing my Chico built 2017. I have synched the carbs,and linkage,there is also a wideband afr gauge sensor in the collector.
The engine has dual 44IDF's,and a 1.5" A-1 sidewinder. The idle jets are 50's,the mains are reamed 140's,36 vents,airs are 200's.
8.5:1 compression,webcam 218,and 1.3 ratio rockers.
I have just began to tune this thing my main issues so far are
1. The idle afr does not remain constant. I am used to programmable EFI,and this is just a trip,sometimes it will be low 12's,sometimes mid13's,and sometimes even high 11's. At times it iwll be perfect and just remain a constant 12.9-13.5 and maintain a stable perfect idle ,but what is happening is this.
When driving,and then braking to a stop,the engine idle will drop and the afr will go lean to high 15's and stumble. Sometimes it will steady itself,but if I blip the throttle the idle will usually clean up and the afr will go back to 13's and be smooth.
Is this the float level? This happened with the previous engine as well,and the previous 44IDF's (the new engine also came with pre-jetted carbs)I thought it was a rich stumble,but now I can see it is a lean stumble . I cannot make any logical conclusion as to why this is. I thought maybe I needed a bigger idle jet?
2. My second issue is at cruise my AFR is high 11's-mid 12's and this is too rich IMO. On EFI cars I could run 15's-16's for economy,what can I do to improve this?
3. If you lightly tip in the throttle,there is a lean stumble,and I understand this can be cured with a bigger idle jet? It is very minor and if you drive normally,you don't feel it,but light acceleration,I can feel the hesitation.
Thanks in advance to the carb gurus. ! |
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| jfats808 |
Thu Oct 27, 2011 10:50 pm |
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| Increase the idle to 55 and main to 145. Retune mixture screws and drive. Note changes. Im pretty sure that is where you will have the best running performance. Im assuming your running 40 x 35 ported heads. |
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| 808OvalGreasemonkey |
Fri Oct 28, 2011 12:26 am |
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| Yes,I am running Mini D CNC ported heads. The engine is still being broken in,and up to 4500 rpm the afr is fine,but you think it will be a good idea to increase main jet size? I am mostly wondering about the stumble upon braking,and why it leans out. I wonder if this has to do with float level adjustment? Has anyone dealt with this? |
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| jfats808 |
Fri Oct 28, 2011 2:44 am |
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| 145 is what the formula is kicking out baseline for your 36 vents. You wont know if your current main is too small without dialing in the the idle hiccup first. Its stumbling because your still on the main progression circuit till it switches to idle and because the 50 is undersized while its transitioning. Bumping it up to a 55 should correct that problem, ensuring that your ignition settings, timing and valve lash is accurately set of course. Essentially your stepping down from EFI to carbs. EFI obviously is much more programmable and adjustable to attain target afr. Its going to take a lot more work to figure out what your engine runs best on performance wise and what is best AFR jetting. To find the comprimise between the two is up to you and what is acceptable inbetween. Ive figured out after lots of test driving what is acceptable performance driving for my drive style only just last year. A 65 idle drilled out between a 67 and 68. That has netted me 18mpg for city driving on my IDAs. You may find that you might drill out your 50s to 56 or 57 when all is said and done. I didnt build my 2276 for max economy, but finding a happy medium between best performance and best mpg is what I have attained and Im happy with that outcome. |
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| Slow 1200 |
Fri Oct 28, 2011 4:39 am |
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| how open are your butterflies at idle? you might be right on the progression drillings |
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