When I had my engine dyno'd the exhaust pipe sniffer registered an AF mixture of 12.8 which the tuner said was perfect. However, when you stand behind my '70 440/512 c.i., 4-speed A833 'Cuda with the engine running at idle it's like being tear gassed by the toxic exhaust fumes. Otherwise, I have no complaints about how the engine/carb run. The engine starts and idles fine, accelerates great with no bogging, doesn't stall, etc. While I can take a carb apart and rebuild it and adjust the idle, idle jets, and float bowell level, any further carb tunning (jetting), booster, squitter and acclerator pump adjustment is beyond me. Can any of you expert carb tuners please tell me what aspect of my carb is resulting in the toxic exhaust fumes and what I can do to fix the issue (jet changes, etc)? The carb is a Quick Fuel Super Street series 880 CFM with vacum secondaries. The primary and secondary jets are 80 and 86 respectively. The booster size is 160. The hi speed air bleed is 28 and the idle air bleed is 70.
The engine is a bored .030 over 440 block that has been line bored, and decked to 0 quench. I'm running a 440 Source 512 stroker crank and rods with custom Diamond pistons. The cam is a "Bullet" custom hydraulic roller grind with 234 intake and 241 exhaust duration at .050. Gross valve lift is .552, intake on exhaust. Lob separation is 108. Hot vavle lash is .000 intake and exhaust. The engine has ProMaxx aluminum heads with 1 7/8" TTI headers. The intake manifold is an aluminum single plane Holley Dominator. The ignition has been converted to electronic and I'm running 36 degrees timming all out and I can't remember for sure, but between 12-16 degrees at idle. Idle is set at about 900 RPM. My engine builder told me my compression was about 9.75 to 1. I run 93 octane unleaded fuel. I checked the plugs and they look normal, charcoal gray. Not fuel or oil fouled.
Every engine will be different but I found my engine runs best around those same numbers. The 14.7 "ideal" I only have at idle but changes with the quality of fuel I use. Fuel quality will also likely be different where you live also. Here we have 87 (Regular), 89 (Mid-Grade), 91 (Premium) and 94 (Super Premium) but it all contains ethanol
Do you have a A/F ratio gauge?
No I don't have an AF gauge. I live in Utah and our fuel does have ethanol, although I will occasionally run 100 octane non ethanol when my station has it and I feel like I can afford it. :'( :bigmoney: :bigmoney:
You could try 1/16-1/8 turn in on your idle mixture screws on the metering block and see if that helps but without the gauge you can't see what's happening?
12.8 at what rpm as it will change depending on what circuit is being used at the time? I saw your post on FB as well. You can also try the Holley page for help as well, their are a lot of knowledgable carb "gurus" there.
https://www.facebook.com/groups/1376996543069027
Thank you. I will check that out.