Mixture Adjustment With Semi Heavy Cam - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 3 (permalink) Old Dec 31st, 02, 09:30 PM Thread Starter
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Join Date: Nov 2002
Location: Aiea, Hawaii
Posts: 571
My valves don't seem to need adjustment after putting a fresh rocker in to replace the one that flew the coop on 8. But I'm having a real problem being satisfied with the mixture adjustment since I'm getting a loping idle. I was kind of satisfied setting the idle up to tune mixture but blew it going back to real idle to try to fine tune. I'm between 9 and 10 for vacume at idle. Comp cams .513 lift with 306 duration. Holley carb and fuel pump. Is it OK to do a vacume gauge mixture adjustment at a higher than normal idle?
OH yah. I'd never concider the valve cover long handle screw downs a dress up item. Sure makes it nice finding a problem.

[This message has been edited by Snatchin'gears (edited 01-01-2003).]
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post #2 of 3 (permalink) Old Jan 1st, 03, 06:40 AM
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Join Date: May 2001
Location: Ashby,MN, USA
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i always try to get as much vacuum at idle as possible, no matter how big the cam.
i do this by setting a base idle of around 900 or so, then tweaking the mixture screws until i get the most vacuum, as well as a higher idle reading. then i back the idle down to 900 again, then play with the mixture screws some more. keep doing this until it doesn't increase vacuum anymore by playing with the screws. remember, tho, that everytime you change the timing, you might need to do this all over again. but it really isn't that hard, and can be rather enjoyable once you get a good idle and crisp throttle response.
that being said, with big cams you aren't gonna be able to get 20" of vacuum at idle- it just aint gonna happen. my engine gets about 16 at idle, which seems pretty good just by looking at the specs of my gm HOT hydraulic roller cam- .525 lift, 219 intake duration, 228 exhaust duration @.050 lift. it has a slight lope at my 800 rpm idle, but not too bad.

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1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
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post #3 of 3 (permalink) Old Jan 1st, 03, 09:52 AM Thread Starter
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Just got the car a couple of weeks ago. So I'll have to dig out the old combo dwell/tach and whatever else meter. The non standard tach must be off for getting my idle rpms 2-3 hundred. At least I think maybe so. I'm worried about leaning it out too much even though I was playing like it's a firecracker on the hwy last night. I would be smart to tune the old 650 holley all around instead of just playing with the mixture. Maybe the old Offenhauser intake is adding to making things trying. I looked at the exhaust gas temp gauges on the internet and might as well whimper thinking about getting one of those expensive tricks for mixture. Most small airplanes are 24 volt but I'd sure love to find a plane engine parting out so I could get the exhaust temp gasses gauge. Next would be finding a big carb I could put plane mixture controls in. Maybe I'm still foggy after new years eve night with these dreamings.
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