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Old 10-06-2019, 03:55 PM   #1
adileo
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Default Uncharted waters

RHi guys

39 dual eldebrocks. Helmet built by bubba 11a. Carbs rebuilt by Charlie (the best btw) prob about 3 years ago. Running lil rough at idle. Here’s my uncharted waters.

I’ve never used a vacuum gauge. Did a lil utubeing. I disconnected vacuum from manifold and connected the gauge to it . Put my finger over hose going to distro.
Gauge read 10.

So couple questions:
1 - am I connecting this properly?
2 - 10 seem low and based on YouTube idle mixture may be needed?
3 - if idle mixture is needed how do I do (w dual carbs)?

As always thanks in advance
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1939 Deluxe coupe
1952 F1
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Old 10-14-2019, 09:04 AM   #2
Bored&Stroked
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Default Re: Uncharted waters

Since you have 2 carbs, there are a couple things to note. If the car will idle (even rough), then you first want to balance the flows on each.

On a brand new setup, I loosen the idle speed screws on both carbs and make sure the throttle plates are fully closed, then I put the linkage on the carbs - usually with the "arms that attach to the throttle shafts" at about the 10 o-clock position. The arms should be parallel. Tighten the linkage arms to the shafts and make sure the linkage works from closed to fully open throttle. The arm angles should be mirrored - between fully closed to fully opened (angles the same on either side of 12 oclock). Parallel arms are key!

Before you start the engine, gently close off all four idle mixture screws, then turn them back out about 1.5 to 2 turns - this is a good starting point. Turn in the idle speed screw on one carb enough to get the throttle plates open a bit. Adjust as necessary when you first start the engine - to a good higher speed idle condition.

With Engine Running at a Higher Idle Speed: I then use what is called a UniSyn carb sync tool. You should only be using ONE idle speed screw on one of the carbs - the other carb needs to be synchronized to flow the same air as the first one (back the idle screw out on the second carb - it should not be touching). The UniSyn tool is used to get them both in sync (the red plastic bead should be at the same height when you move the UniSyn from one carb to the other). The carburetor vacuum being pulled (air flow) raises the red plastic bead - same height on both carbs - this means the same flow. You may need to adjust the round air-disc to get the red bead to the middle of the sight tube - do this on the first carb, before you attempt to sync them.

https://www.amazon.com/Uni-Syn-Carbu.../dp/B073RPZKBX

You'll loosen the threaded linkage that connects the two carbs - threading the rod in/out to synchronize the flow on both. Basically, you're getting the red plastic level on the second carb to match the first (as the first one has its idle speed screw in use). You'll see it fluttering around a bit - that is normal - but it should be at the same basic level when you move the UniSyn back/forth between the carbs.

Now that you have the throttle position air-flows equal - then starting with either carb, you'll set the idle mixture screws (two in each carb base).

With the engine running and while keeping your hands out of moving parts! . . . turn an idle screw in and listen to the engine: It will start to stumble when the screw is too far in (too little fuel) -- back the screw back out until the engine speed picks back up and it runs the smoothest. Do the same for the other three screws . . . in until the engine slows/stumbles, then back out until it smooths back out.

Once you've synced the carbs and set the idle mixture screws, you can adjust the overall speed of the engine with the idle speed screw on one carb.

Use the UniSyn again - the air flow should be the same on both carbs. If not, then adjust the linkage and then do the idle mixture screws once again.

It takes a few times of doing this to get the overall procedure working in your mind - it will become second nature after a few times.

Good luck!

Last edited by Bored&Stroked; 10-14-2019 at 10:01 AM.
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Old 10-14-2019, 09:19 AM   #3
outlaw
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Default Re: Uncharted waters

Quote:
Originally Posted by Bored&Stroked View Post
Since you have 2 carbs, there are a couple things to note. If the car will idle (even rough), then you first want to balance the flows on each.

On a brand new setup, I loosen the idle speed screws on both carbs and make sure the throttle plates are fully closed, then I put the linkage on the carbs - usually with the "arms that attach to the throttle shafts" at about the 10 o-clock position. The arms should be parallel. Tighten the linkage arms to the shafts and make sure the linkage works from closed to fully open throttle. The arm angles should be mirrored - between fully closed to fully opened (angles the same on either side of 12 oclock). Parallel arms are key!

Before you start the engine, gently close off all four idle mixture screws, then turn them back out about 1.5 to 2 turns - this is a good starting point. Turn in the idle speed screw on one carb enough to get the throttle plates open a bit. Adjust as necessary when you first start the engine - to a good higher speed idle condition.

With Engine Running at a Higher Idle Speed: I then use what is called a UniSyn carb sync tool. You should only be using ONE idle speed screw on one of the carbs - the other carb needs to be synchronized to flow the same air as the first one (back the idle screw out on the second carb - it should not be touching). The UniSyn tool is used to get them both in sync (the rod plastic bead should be at the same height when you move the UniSyn from one carb to the other).

https://www.amazon.com/Uni-Syn-Carbu.../dp/B073RPZKBX

You'll loosen the threaded linkage that connects the two carbs - threading the rod in/out to synchronize the flow on both. Basically, you're getting the red plastic level on the second carb to match the first (as the first one has its idle speed screw in use). You'll see it fluttering around a bit - that is normal - but it should be at the same basic level when you move the UniSyn back/forth between the carbs.

Now that you have the throttle position air-flows equal - then starting with either carb, you'll set the idle mixture screws (two in each carb base).

With the engine running and while keeping your hands out of moving parts! . . . turn an idle screw in and listen to the engine: It will start to stumble when the screw is too far in (too little fuel) -- back the screw back out until the engine speed picks back up and it runs the smoothest. Do the same for the other three screws . . . in until the engine slows/stumbles, then back out until it smooths back out.

Once you've synced the carbs and set the idle mixture screws, you can adjust the overall speed of the engine with the idle speed screw on one carb.

Use the UniSyn again - the air flow should be the same on both carbs. If not, then adjust the linkage and then do the idle mixture screws once again.

It takes a few times of doing this to get the overall procedure working in your mind - it will become second nature after a few times.

Good luck!
Dale, thanks for the explanation. It is a good reminder for those of us who haven't done this for a while. Bill
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Old 10-14-2019, 09:30 AM   #4
Ol' Ron
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Default Re: Uncharted waters

when you start working on a problem tuning an engine. I like to make sure the mechanical areas of the engine is working properly. This can be done with a compression test of all cylinders. If all cylinders are with in 5 lbs of each other, your good to go. If one or more cylinders have more than this, it may have an affect on the tune, making you think it's the problem. Good luck.
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Old 10-14-2019, 11:34 AM   #5
solidaxle
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Default Re: Uncharted waters

What Ron said first. 10 on the vacuum gauge is low, check for a leak. There's youtube for how to on that also. Make sure your gauge is working properly.
I was having issues with my 8ba until I found a cracked intake.
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Old 10-14-2019, 02:49 PM   #6
adileo
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Default Re: Uncharted waters

As always great advise! Thank you!!!!
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