vacuum tuning/carb mixture
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vacuum tuning/carb mixture
okay guys- last post for the day, i promise.
(can you tell i did a lot of work on the truck over the weekend?)
i vacuum-tuned my timing and carb mixture for maximum vacuum pressure. it holds at about 22, with a steady needle. (and man oh man, does it ever run better!)
my question- if the engine is cold, and i use the manual choke to get it started- i can pull out on the highway, and let it idle along in first gear...(with the choke still on). when i drop the hammer, without touching the clutch- the 360 will leave a long streak of hot rubber.
however, if i try it when the engine warms up, without the choke on, all i get is a quick chirp from the tires. does this mean i'm running too lean a mixture?
thanks,
sam
(can you tell i did a lot of work on the truck over the weekend?)
i vacuum-tuned my timing and carb mixture for maximum vacuum pressure. it holds at about 22, with a steady needle. (and man oh man, does it ever run better!)
my question- if the engine is cold, and i use the manual choke to get it started- i can pull out on the highway, and let it idle along in first gear...(with the choke still on). when i drop the hammer, without touching the clutch- the 360 will leave a long streak of hot rubber.
however, if i try it when the engine warms up, without the choke on, all i get is a quick chirp from the tires. does this mean i'm running too lean a mixture?
thanks,
sam
Senior User
Joined: Jun 2000
Posts: 168
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From: Stratton
vacuum tuning/carb mixture
I also have a 360 w/manual choke. Can you describe please how you did this tuning. I am real interested because my motor is close to running great and just can't get that final 5% dialed in.
Cargo Master
Joined: Jul 2000
Posts: 2,281
Likes: 18
From: Northern California
vacuum tuning/carb mixture
I'd clean the plugs and warm it up, then take it out and make a run then shut the engine off without letting it idle down. then take a reading of the plugs and see if it's running too lean. When you vac tuned the engine, I assume you mean for idle and a different carb circuit kicks in for off idle and that maybe too lean.
You might want to get a kit that has different jets and different acc pumps and if it's a vac sec try different springs to get the secondaries to kick in at different speeds. When the engine is cold, the air/fuel mix is colder and the exhaust crossover hasn't heated up the intake yet, that alone can make a noticeable difference. You might consider cooling down the intake and carb with exhaust crossover blockoffs and plastic 1" spacer under the carb and maybe a carb bowl heat plate that goes under the carb and float bowl to keep the fuel cooler. I've read where a cooler intake charge can increase power by 7~10%
Another idea is to use an O2 sensor in the exhaust to read the O2 at different times, for example you might be lean at one time and rich at another and an O2 sensor really helps to read the exhaust, cost is about $25 + install and you can use a simple digital multimeter to read the output.
You might want to get a kit that has different jets and different acc pumps and if it's a vac sec try different springs to get the secondaries to kick in at different speeds. When the engine is cold, the air/fuel mix is colder and the exhaust crossover hasn't heated up the intake yet, that alone can make a noticeable difference. You might consider cooling down the intake and carb with exhaust crossover blockoffs and plastic 1" spacer under the carb and maybe a carb bowl heat plate that goes under the carb and float bowl to keep the fuel cooler. I've read where a cooler intake charge can increase power by 7~10%
Another idea is to use an O2 sensor in the exhaust to read the O2 at different times, for example you might be lean at one time and rich at another and an O2 sensor really helps to read the exhaust, cost is about $25 + install and you can use a simple digital multimeter to read the output.
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Joined: Sep 2000
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vacuum tuning/carb mixture
thanks karljay-
it's the stock ford 2-barrel...i don't know much about jetting, but i'll try to do a little research. i rebuilt the carb a couple of years back, (with an autozone kit) but that's all i've ever done to it, other than toying with the mixture screws.
here's the link for the vacuum tuning-
http://www.public.iastate.edu/~wish/Tech/Tuneup/tune.html
it's the stock ford 2-barrel...i don't know much about jetting, but i'll try to do a little research. i rebuilt the carb a couple of years back, (with an autozone kit) but that's all i've ever done to it, other than toying with the mixture screws.
here's the link for the vacuum tuning-
http://www.public.iastate.edu/~wish/Tech/Tuneup/tune.html
