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overthinker extraordinar
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650 Posts
Discussion Starter #1
Hey folks,
I am currently working on dialing in my 85 2.8l. I put a new motor with crower cam and a weber 38dgas on it. It still is not quite right. I am trying to understand what each jet does so that I can make educated guesses on what to do.

Idle jets - pretty self explanatory. Mixes air/fuel ratio for the engine when it is at idle. These do not come into play at higher rpms. So I have read.

Air corrector jets. I am guessing here. I think these jets determine how much air will be mixed with the fuel. A smaller jet will give a leaner mix, a larger jet will give a richer mix.

Main jets, again I am guessing. The main jets determine how much mixture the carb can draw into the engine. The larger jet allows more mixture, and thus a richer burn, smaller is also leaner.

I am not certain this is right. Can anyone who knows carbs educate this poor old soul???

Thanks in advance.
mark
 

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overthinker extraordinar
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650 Posts
Discussion Starter #2
I just leaned up my carb. I replaced all 6 jets to one size down. Now she runs awesome. I mean AWESOME!!!!!

I had her at about 600rpm and you could almost balance an egg on her. :D
 

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overthinker extraordinar
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650 Posts
Discussion Starter #3
A couple of tings. On my carb, I was adjusting the idle fuel mixture. I turned it almost all the way in until I had any affect. Then about 1/8 turn more and it bottomed out and died. I assumed, and correctly I believe, that the jets were too rich. I put leaner jets in and they worked well. I may order one step leaner yet and try them.
 

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4 Year Intermediate Tech
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your on the right track
 

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A couple of tings. On my carb, I was adjusting the idle fuel mixture. I turned it almost all the way in until I had any affect. Then about 1/8 turn more and it bottomed out and died. I assumed, and correctly I believe, that the jets were too rich. I put leaner jets in and they worked well. I may order one step leaner yet and try them.

I hope this link will help you out. http://www.redlineweber.com/html/Tech/38_dgas_tunning.htm It has helped Me out a bunch.
 

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Early Member
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3,113 Posts
I always used a vacuum gauge. Tuning by ear is good to a point, if your hearing is not screwed up by listening to loud music. When using a vacuum gauge, the gauge will indicate where your engine is set best. And the sound will be good. Also make sure you have no vacuum leaks.
 

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overthinker extraordinar
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650 Posts
Discussion Starter #7
I always used a vacuum gauge. Tuning by ear is good to a point, if your hearing is not screwed up by listening to loud music. When using a vacuum gauge, the gauge will indicate where your engine is set best. And the sound will be good. Also make sure you have no vacuum leaks.
I have not heard of or seen this method. I'll look into it.

Set it to highest vacuum? Is that the goal?
 
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