LD340 Can’t Get The Carb Base To Seal

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bradfields

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So, I have an LD340 and a 4611S AVS carburetor on my 71 340 Demon, I can’t seem to get the carb base to seal to the intake manifold, I’ve tried several gaskets (all the same shape / type as the one pictured) but still get a vacuum leak around the bottom of the carb when spraying carb cleaner around it. Do I need a different type of gasket? I’m stumped.
 
Maybe consider using the thicker insulating gasket that comes in the rebuild kits. I've got the same intake and carb and never had that problem. Also recommend hooking the PCV back up. A straight edge check of the carb and intake wouldn't hurt.
 
Blue glue. Lol. It never ceases.

I'd try a gasket that doesn't look 50 years old. Also, you give no background on just how it isn't sealing (or why you think it isn't) so it's hard to say.
 
Get the thick (over 1/4") insulating gasket with the plastic washers in each corner.
 
I would also recommend studs and not bolts to hold the carb down. Oh and get rid of that plastic fuel filter. A metal can type is the safe way to go.
 
gregcon said:
Blue glue. Lol. It never ceases.

I'd try a gasket that doesn't look 50 years old. Also, you give no background on just how it isn't sealing (or why you think it isn't) so it's hard to say.
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Trying to help the man out with what he has; that's all.
 
Thanks for the replies. It is an old gasket, it’s just what I had, I’ll check the carb base for flatness, I checked the intake but not the carb. I’ll also get a new gasket. The symptoms are, fast, rough idle, dies when idled down, using a vacuum hose as a nozzle and carb and choke cleaner spray, I have the leak isolated to the sides of the carb base, seems ok along the front and back.
 
bradfields said:
Thanks for the replies. It is an old gasket, it’s just what I had, I’ll check the carb base for flatness, I checked the intake but not the carb. I’ll also get a new gasket. The symptoms are, fast, rough idle, dies when idled down, using a vacuum hose as a nozzle and carb and choke cleaner spray, I have the leak isolated to the sides of the carb base, seems ok along the front and back.
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Use this one.

Edelbrock Heat Insulator Gaskets 9265
 
toolmanmike said:
I would also recommend studs and not bolts to hold the carb down. Oh and get rid of that plastic fuel filter. A metal can type is the safe way to go.
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Thanks for the heads up, I’ll get one of the metal type fuel filters.
 
i've been using a stacked up gasket then thin alum plate , and repeat a few times . this keeps the heat off the carb and seals well .
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Also- those bolt holes for the carb mounting.
Make sure they were never drilled or bolted thru to the intake plenum. I’ve love all my LD340s BUT one I had a terrible vac leak. Turned out one of the bolt holes were over tightened with too long of a bolt and cracked the bottom of the hole. When I bolted my TQ on it I had a leak I could discover with carb cleaner, heard it whistle but only found it with a flashlight from under the plenum and in a dark room. The hole was in the holes o was not using.
 
Syleng1 said:
Also- those bolt holes for the carb mounting.
Make sure they were never drilled or bolted thru to the intake plenum. I’ve love all my LD340s BUT one I had a terrible vac leak. Turned out one of the bolt holes were over tightened with too long of a bolt and cracked the bottom of the hole. When I bolted my TQ on it I had a leak I could discover with carb cleaner, heard it whistle but only found it with a flashlight from under the plenum and in a dark room. The hole was in the holes o was not using.
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Do you think thread sealant in the bolt hole would seal?
 
RammerJammer75 said:
Do you think thread sealant in the bolt hole would seal?
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Typically no- they would eventually suck thru. I ended up using Allen plugs. Like the kind used for set screws in Industrial pulleys. That and pipe dope- the white sealer for making up pipe joints.
 
bradfields said:
The symptoms are, fast, rough idle, dies when idled down,
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Why is your PCV port capped? per post #1,pic#1
This leads to the engine not getting enough idle-air bypass.
In compensation you have to increase the air going past the throttles. This puts them too far up the transfer slots, making it run both too fast and too rich. In compensation you close the mixture screws, and retard the timing.
Did you mean to do that?
 
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AJ/FormS said:
Why is your PCV port capped? per post #1,pic#1
This leads to the engine not getting enough idle-air bypass.
In compensation you have to increase the air going past the throttles. This puts them too far up the transfer slots, making it run both too fast and too rich. In compensation you close the mixture screws, and retard the timing.
Did you mean to do that?
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I’ve got the PVC hooked up to a fitting on the back of the manifold.
 
Syleng1 said:
Typically no- they would eventually suck thru. I ended up using Allen plugs. Like the kind used for set screws in Industrial pulleys. That and pipe dope- the white sealer for making up pipe joints.
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That's actually what I meant, use PTFE tape or dope on the carb stud/bolt. I didn't even think about using an allen plug. Fix it instead of trash it.
 
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