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johnny2013
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Joined: September 30, 2013
Posts: 128
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 Posted: Sun Jul 05, 2015 3:07 am Post subject: fuel mixture |
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which setup would result in a richer fuel mixture at idle: (carburetor is a brazil 30 pic s) a size 60 idle jet with volume control screw set at 1.5 turns out, OR a size 50 idle jet with volume control screw set at 2.5 to 3.5 turns out. both set at 800 rpm idle. (btw the car doesnt run on the size 50 idle jet, will run when hot but not very smooth unless i turn out the volume control screw 1-1.5 extra turns)
engine is 1200cc, main jet 115, air jet 110.
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1971 orange beetle, 1200 engine, with weber 40 idf!!, 1971 beige beetle,1200, ALL STOCK,
both undergoing slow restoration. |
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Aussiebug
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Joined: June 03, 2002
Posts: 2162
Location: Adelaide Australia
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| Posted: Sun Jul 05, 2015 3:24 am Post subject: |
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The engine runs both at idle and up to roughly 2500 rpm on the idle jet, gradually handing over to the main jet. Your main jet is quite small, even for a 1200, so it needs the larger idle jet to ensure it does not go over- lean off idle and at lower speeds, or to stall as the engine revs drop back to idle.
If you had a slightly larger main jet - 117.5 or so, it would probably run ok on the 50 idle with a volume screw adjustment. But with a larger main jet you would probably need a larger air correction jet to stop the mixture going over rich at higher speeds. The air correction jet has little effect at idle but effects the mixture at medium to higher air flows through the carb.
All jets interact with each other, so changes in one usually need a change in another to keep everything in balance.
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johnny2013
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Joined: September 30, 2013
Posts: 128
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| Posted: Sun Jul 05, 2015 3:39 am Post subject: |
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| Aussiebug wrote: |
| Your main jet is quite small, even for a 1200 |
i used to run a 122 main jet, and a 55 idle. the spark plugs were dead black, so i lowered the main jet size to 117.5, still black. then finally to 115, the plugs looked OK after much testing. unfortunately, i misplaced that 55 idle jet while cleaning, i looked for another 55 size but they didnt have any at the stores... leaving me no choice but to either use a 50 or 60 size while im looking for a 55 jet. the size 50 never really ran smooth even with the 122 main.
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1971 orange beetle, 1200 engine, with weber 40 idf!!, 1971 beige beetle,1200, ALL STOCK,
both undergoing slow restoration. |
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Multi69s
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Joined: January 24, 2006
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Location: Lefty, CA
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johnny2013
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Joined: September 30, 2013
Posts: 128
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| Posted: Sun Jul 05, 2015 7:05 pm Post subject: |
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| Multi69s wrote: |
| If the 60 is running good at 1-1/2 turns keep it. If you have to turn out the mixture screw more then 2 turns, you have the wrong size jet. |
my only problem is that it runs too rich at lower speeds with the size 60 idle jet. i also noticed little flames coming out of the exhaust when i rev the car (was it called afterfire?)
i cant find a size 55 idle jet as of the moment so i have to either stick with the too rich 60 jet or the too lean 50 idle. i really prefer using the size 50 idle jet. so my question is, if i use the 60 idle jet with the volume control screw at 1.5 turns, would it be richer,leaner, or as lean as a size 50 idle jet with the volume control screw out 2.5-3 turns?
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1971 orange beetle, 1200 engine, with weber 40 idf!!, 1971 beige beetle,1200, ALL STOCK,
both undergoing slow restoration. |
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[email protected]
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Joined: August 03, 2002
Posts: 12785
Location: Salt Lake City, Utah
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| Posted: Sun Jul 05, 2015 7:55 pm Post subject: |
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changing idle jet sizes by even 5 is a 20% change in fuel flow, far too drastic a change. 10 is unfathomable.
Make changes in increments of 2 or so. If a 55 is too rich, it's very common for a 50 to be too lean. Duh. 20% reduction? Try a 52 or 53.
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johnny2013
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Posts: 128
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| Posted: Sun Jul 05, 2015 8:28 pm Post subject: |
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| [email protected] wrote: |
changing idle jet sizes by even 5 is a 20% change in fuel flow, far too drastic a change. 10 is unfathomable.
Make changes in increments of 2 or so. If a 55 is too rich, it's very common for a 50 to be too lean. Duh. 20% reduction? Try a 52 or 53. |
well a 55 isnt too rich for my bug. its just that i misplaced my 55 idle jet and cant find any 55 in stock at the local store... and if im having quite a hard time finding a 55 idle jet, how much more for a 52 or 53? haha
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1971 orange beetle, 1200 engine, with weber 40 idf!!, 1971 beige beetle,1200, ALL STOCK,
both undergoing slow restoration. |
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johnny2013
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Posts: 128
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| Posted: Sun Jul 05, 2015 8:42 pm Post subject: |
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surprisingly though, with the size 60 idle jet, i know that the car isnt lacking power at low to medium speeds. but she just feels heavy. with the smaller size 50 jet the car feels lighter, and still has the same power. just few idle problems...
maybe the size 60 idle jet is giving too much fuel at low speeds therefore flooding the engine a bit? then the size 50 idle would give less fuel so the engine wont flood making it easier to burn the mixture. then the size 55 (which i dont have access to right now) would be a compromise of the two, giving power at low speeds and smoother idle operation.
anyway, back to my unanswered question. i really want to know which would give a richer fuel mixture: 60 idle jet, volume control screw at 1.5 turns. or 50 idle jet, volume control screw at 2.5-3 full turns out? if more details are necessary, then: main jet 115, air 110, (desired) idle speed 800RPM, timing: 10 degrees btdc, and solex 30 pic s carb
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1971 orange beetle, 1200 engine, with weber 40 idf!!, 1971 beige beetle,1200, ALL STOCK,
both undergoing slow restoration. |
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mukluk
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Joined: October 18, 2012
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Location: Clyde, TX
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| Posted: Mon Jul 06, 2015 12:26 am Post subject: |
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| johnny2013 wrote: |
| anyway, back to my unanswered question. i really want to know which would give a richer fuel mixture: 60 idle jet, volume control screw at 1.5 turns. or 50 idle jet, volume control screw at 2.5-3 full turns out? |
If you want the definitive answer, you're going to need a wideband tuner or an exhaust analyser.
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johnny2013
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Joined: September 30, 2013
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| Posted: Mon Jul 06, 2015 4:51 am Post subject: |
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| mukluk wrote: |
| johnny2013 wrote: |
| anyway, back to my unanswered question. i really want to know which would give a richer fuel mixture: 60 idle jet, volume control screw at 1.5 turns. or 50 idle jet, volume control screw at 2.5-3 full turns out? |
If you want the definitive answer, you're going to need a wideband tuner or an exhaust analyser. |
unfortunately, i also dont have access to an exhaust analyser... and i dont think i would have any other use for it, so it might just be a waste.
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1971 orange beetle, 1200 engine, with weber 40 idf!!, 1971 beige beetle,1200, ALL STOCK,
both undergoing slow restoration. |
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