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Old 12-14-2017, 06:09 PM   #1
chris mc bride
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carb question

Ok first I'm mechanical fuel injection guy. Haven't run a carb in 25 years. Well 20. I have 454 in 69 panel .Quadramess went bad after sitting for years , so I pulled edelbrock off old 383 sbc that had been sitting lot longer. Bolted it on and runs fine except 2 things. Has a surging issue mainly cold and thats choke issue,but also at low speeds. Rich or lean would cause it to surge some?
Truck still has old sagnaw 3 on the tree so surge shows big time with clutch instead of converter.
Second deal is secondary seems to open later than should.Figure vacuum maybe little lower with new cam xe268 comp cams. Any suggestions on where to start with another spring rate wise?

Hey for carb that set for 20 years and no rebuild its not doing bad,still blows tires off when matting it in first or second,just seems to hesitate pulling those big secondary flys open. Plus need to do away with hesitation for jap crap mad bubble bee punks. Always fun dusting them.
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Old 12-14-2017, 06:12 PM   #2
Coley
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Re: carb question

....surging?.....sounds like it might be a vacuum leak which is not uncommon when a carb is changed out.
I would go front to back and side to side everywhere to eliminate that possibility first.
Check every port, every hole, every bolt, every rubber vacuum line....including the power brake line, pcv, etc.

Coley
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Old 12-14-2017, 06:22 PM   #3
chris mc bride
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Re: carb question

Brake line sounds suspect since been having brakes coming and going,but have had leak and figure air got into system.Will check.Might be open and close deal with engine movement,although small.
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Old 12-14-2017, 06:53 PM   #4
Coley
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Re: carb question

2 things regarding the power brake vacuum:
1) make sure you don't have an 'open' port on the back of the carb that can be used on some carbs to run the power brakes.
(sometimes they are run off the intake manifold...and sometimes they are connected to the back of the carb)
2) To check if the power brake booster is leaking and part of the problem....simply, carefully clamp the vacuum hose to it with a set of vice grips.
(This same method of 'clamping' all the vacuum lines is actually a good, simple test of that line leaking)
....if your idle settles down then the problem can be within the booster...and I've had this happen to me before, so a booster change was due.

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Old 12-14-2017, 07:11 PM   #5
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Re: carb question

It does sound like vacuum leak. Another way to check is to spray carb cleaner on the base and linkage while it's running. If the engine speed changes, it's pulling air from somewhere at the carb. Don't catch yourself on fire.
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Old 12-14-2017, 08:46 PM   #6
chris mc bride
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Re: carb question

Yea have done carb cleaner trick few hundred times. Never had fire but can see where might happen. Brake booster could be issue since both acting stupid.Will see after bleeding lines.Carb cleaner has not shown any leaks yet,will try around lines tomorrow.Either its too cold out or I am getting old,yea its just cold.
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Old 12-14-2017, 09:47 PM   #7
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Re: carb question

Also check your accelerator pump. The Edelpukes have a rubber plunger on a plastic shaft. The rubber plunger part will deteriorate over time. Especially after sitting for awhile they tend to dry out and can get cracks. If ethanol fuel was sitting in it, the rubber part of the plunger will get gummed up. I believe there are plungers that are available that are tolerant to ethanol nowadays.

Gary
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Old 12-31-2017, 06:35 PM   #8
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Re: carb question

Surging....yes, I agree vac leak.I would ask a ? Is it a 1407, or 1411 carb? As far as lower vacumn.....I saw 16-17 inches on my 383(XE268 cam). If you are much lower than that, you may need to tune the ignition. I ran 34 total on my sb @2800-3000, + 10 on the vac can+ plugged to manifold vac source. You may find the BB to like around 36 total....just play. The vac can needs to be cut to 8 -10 degrees (at the crank). my thoughts are that you will be pretty close...(34-36 total@3000+ 8 or 10 on the can). Longhorn
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