Carb tuning

[76bonanza]

I have heard to use a vaccum guage to tune your carb now this guage I assume will just plug into the full vac port on carb?
Were can I get a guage like that?

Thanks

[bpmcgee]

Any auto parts store would have it.

And you're right -- full vacuum from the carb or the intake.

Brian

[PHOENIX]

Get this one here:
Mityvac #4000
http://www.harborfreight.com/cpi/cta...temnumber=2068


$53.99 (cheapest I have found it)
Sears wants $70 for the same one.
Make sure you get the #4000, its metal, the plastic ones are not as nice.

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Test vacuum motors, control valves, vacuum sources and almost any part or system that requires sealing, pressure, or vacuums to operate. Exclusive Silverline(TM) pump features precision die case metal construction, fluid resistant valves, vacuum gauge graduated in inches and millimeters.
Pumps 1 cubic inch per stroke. Includes accessories for tune-up, and reservoir jar with adapters for brake bleeding. Complete with detailed instructions and durable molded storage case.
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[PHOENIX]

I also recomend getting one or two of these

"CARBURETOR ADJSTING TOOL"
They can be found in the isle at any checker or autozone. They run anywhere from $5 to $20 each. I bought (2) and they were about $6 each. The long shaft is flexable to get around parts and work between vacuum lines. They come with different bits for different carbs. I recommend getting two of them because you can hook one to each mixture screw and keep good track of each turn. When you have to take the tool off and on to go back and forth its not as easy to keep track or the turns and its a hassle.
Save your self the headache and get two of them.

[76bonanza]

Now that I have a guage what are the steps for tuning the mixture screws with the vac guage?

[Newt408]

turn your idle mixture screws 1/8 turn each until you have your highest vaccum.

[PHOENIX]

Setting Carburetor Air Fuel Mixture

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Step 1: Get the vehicle up to operating temperature.
Do not set the mixture if the vehicle is cold, if needed do step 5
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Step 2: With the vehicle off turn the mixture screws all the way in.
Dont tighten them a lot though, you could do damage
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Step 3: Back both mixture screws out 1-1/2 turns.
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Step 4: Have your vacuum gauge hooked to full manifold vacuum.
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Step 5: Start the truck and set the desired idle speed (700-800 rpm)
If the truck will not run try backing out the mixture screws another 1/2 to 1 turn
This is also a good time to check the timing, a timing light with tachometer is helpful.
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Step 6: Back out the right mixture screw 1/4 turn, then back out the left mixture screw 1/4 turn (keep them even)
The vacuum should rise
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Step 7: Reset your desired idle speed
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Continue steps 6 & 7 until you reach the highest vacuum (a good range is 18-22)
You will get to a point were the vacuum stops rising.
Once you turn the mixture screws 1/4 turn and there is no vacuum change you know you are at the highest vacuum setting.
Turn the mixture screws back the 1/4 turn to were they were the highest.
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Notes to remember:
Always keep the mixture screws even, if you turn 1 screw a 1/4 turn, turn the other screw 1/4 turn.
Adjust your mixture screws in small adjustments, 1/8 or 1/4 turns, 1/2 turns and full turns are not recommended.
Keep setting your idle speed after every mixture screw adjustment and check you vacuum gauge reading.
Once you have the highest vacuum and desired idle speed your are ready to go.
For emissions you may want to turn the mixture screws back in another 1/8 to 1/4 turn.
I have used this method a few times now and it has always worked great and I have passed emissions with no problem.
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[MylilBowTie]

First set your timing to where you want it. Then set you idle rpm, if you have an after-market ignition curve make sure it idles below where is starts the curve. I use the port on the back of the intake (modulator line) of the source of vacuum its a little lower but for me its steadier. Once all that is done now its ready to adjust the IMS. Counter Clockwise (richer) Clockwise (leaner). When the engine is warm turn one IMS all the way in and lightly seat it. Then start turning it in small amounts ccw. During that you also need to watch the tach to keep the idle rpm the same. When you have the highest vacuum then turn it cw 1/2 turn. Then do the other IMS the same way. If its an Edelbrock the air filter should be on when tuning it. With it off it will be leaner with the air flow it can get without the filter.

This is off the top of my head so it might need a little help.

[76bonanza]

Can I hook the guage up to where the brake boster is just pull it off. Or should I hook it up to the carb were the tranny vaccum is hooked?

[MylilBowTie]

Where the tranny vacuum is hooked is fine and the right port on the carb is fine. I just prefer the rear intake port.

[79BIG10]

Here's the best site I've seen on vacuum readings. http://www.centuryperformance.com/vacuum.asp

[76bonanza]

First let me say thanks for all your help just a few more questions.

I set my timing just now to what I think is 12 deg advance my tab has a long line at zero then small lines then a long line no number I asume they go by 2 and the long line is 10. Does twelve sound right? no knock or anything at twelve. I set my idle to 700 i think just have crappy tach but seems right. I will do the vacum tommorow does it sound ok so far?

Also can you over tighten your dist? I made it pretty tight but could have gone tighter?

one more thing with the vaccum advance disconected when I rev the motor my advance line still advances is this right? And how can I check my vaccum advance to see if it is working?

Thanks you guys are most kind. I have listened to my idiot friends for to long I Think I trust you guys.

[79BIG10]

I'm not sure on the advancement but look here for more great articles on our trucks. http://www.73-87.com/7387garage/garage_drivetrain.htm

[76bonanza]

I have a holley with a accelerator pump it looks to be adjustable?

How do you adjust it.

The previous owner was not to keen on setting anything as everything was jacked up.

[NeCrOmAnCeR]

The timing advancing when you rev the engine is normal. This is the centrifugal (mechanical) advance operating. (weights in the dizzy) You only need to tighten the dizzy up enuf so it won't rotate when you try to turn it. If you overtighten it obvious damage to the mounting hardware will occur, and it can make it nearly impossible to loosen up next time. I replied to your other post about the accel. pump question.