Adjusting carb (continued) - Page 2 - Off-Road Forums & Discussion Groups
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post #11 of (permalink) Old 06-29-2002, 12:08 PM
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Re: Adjusting carb (continued)

I have a simular question w/a Edelbrock carb. Is this a good place to jump in?
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post #12 of (permalink) Old 06-29-2002, 02:48 PM Thread Starter
 
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Re: Adjusting carb (continued)

might as well, we will probably both learn something.
ok, i'll recheck it with vacuum advance hooked up.

I forgot to mention, I read that you don't want the idle screw to far in, otherwise you bypass some kind of idle circuit or something?
I'll first turn the idle down and see how it works.
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post #13 of (permalink) Old 06-29-2002, 08:18 PM
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Re: Adjusting carb (continued)

Joey..I'm not sure how contemporary carbs do it ..but .... (yeah ..one of those "back in my day" type thingies)

If you look into the bore and open the butterfly you should see two (one per barrel) little slots that span above and below the butterfly when it's closed. You should also see where the other side of the mixture screws are (one in eachy barrel). This provides the air and the fuel to idle. If you have the butterfly opened too far ..you have basically rendered the idle circuit useless. Sometimes with a 4 barrel carb ...you can turn the screws all the way in or out and it doesn't change anything ..that's why I mentioned secondary throttle bore alignment. It's rare ..but as you can see it too would bypass the idle circuit.

The technique LEVE gave you is a varient of the "lean drop" carb setup. In the pre-unleaded engines (GM 73-74 and I say this because that was the last time I ran into it) you were instructed to achieve the highest idle speed using the mixture adjustment screw ..you then had a spec to adjust the idle to (850 let's say) ..you would then turn in the mixture screw until you achieved the other spec (let's say 750) ..that's why is was called a "lean drop" adjustment. All of this was on the sticker under the hood. These engines were prone to after-running. They even incorporated idle solenoids that held the throttle open for idle ....and slammed it shut when you cut the ignition.
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post #14 of (permalink) Old 06-29-2002, 09:16 PM Thread Starter
 
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Re: Adjusting carb (continued)

Ok I redid it as leve suggested.
This time I went from 1600 as a base, and it made it a bit easier as it didn't try to die.
I'm about 2 full turns out, as 1 1/2 seems where it stopped.
It gets really confusing when I get to down to near all the way in, my rpm isn't consistent, and lkes to move up and down..and it can be really hard to see if that 1/2 or 1/4 of a turn even made much difference
I've set the drive idle about about 900, but my idle in park is extremely high.
On vacuum, my guage reads at 15 in drive, and 25 hg in park.
I tried using the vacuum gauge too, but when I got the highest reading, it didn't run all that great and it dieseled like crazy.
25 hg is also out of the range of normal engine readings according to the article I've read, and leve posted.
Its supposed to be anywhere from 17-22 hg.
I'll go out and drive it around, and see how she runs.

You all have been very informative, and I'm hoping this works out well.

The only other thing I could see wrong is possibly the timing.
I asked a while ago on the board, and will replied with 4 degrees.
I don't think I told him what tranny I have, and I don't know if that matters.
Does it?I couldn't find anything about the timing at all.
Thanks again
Joey
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post #15 of (permalink) Old 06-29-2002, 09:23 PM Thread Starter
 
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Re: Adjusting carb (continued)

ok it seems to work fine, other than the fact that my idle speed is much to high.

I do still have a problem though, which is that since I started screwing with everything, my jeep takes a lot to crank over.
Sometimes a lot of cranking and a lot of gas, and sometimes it just decides to do it..
Most of the time it feels as if it doesn't have enough power
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post #16 of (permalink) Old 06-29-2002, 09:59 PM
 
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Re: Adjusting carb (continued)

Joey
If your Vacume reading is going up as you accelerate you are hooked to PORTED vacume NOT MANIFOLD vacume ...to have 19 hg vacume at Idle you must be hooked to a MANIFOLD Source NOT ported.POrted vacume won't kick in till around 1000 RPM and will rise above that ...manifold vacume will Idle around 17 to 19 hg at Idle and drop as you accelerate when you let off the gas manifold vacume will jump to appx. 25 hg and ported will drop to 0 hg at idle.
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post #17 of (permalink) Old 06-29-2002, 10:08 PM
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Re: Adjusting carb (continued)

No idle or carb adjustment is going to make any real difference in your down the road power.

Answer me this Joey....what is the lowest smooth idle that you can get in Park?

At that idle ...what happens when you put it in drive?

Keep in mind you may have a dead (or at least wounded) cylinder or two ...so you may still have other "issues" that make this task defy resolution.

Feel free to advance your timing a degree or two (three or four) and see what happens.

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post #18 of (permalink) Old 06-29-2002, 10:21 PM Thread Starter
 
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Re: Adjusting carb (continued)

it is hooked straight to my manifold :shrugs:
I couldn't find anything on my carb which didn't act real funny when adjusting things.
It does increase as rpms rise.
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