Carb base vacuum leak (1 Viewer)

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Jul 11, 2020
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So, I have what I think is a vacuum leak between the Weber carb, and one of the adaptor plates that mount it onto the intake. The intake is new to me (the previous one had crack at the front that was jb welded back together), and I had it machined flat, and installed a new remflex gasket, as well as new carb gaskets from red line.
After having the typical symptoms that you'd get from an intake vacuum leak (loss of power under a load, and the smell of a lean mixture), I checked again today to make sure the carb hold down nuts were all tight, and found that two of them were a little loose. I put locktite on them when I installed them, but suspect it wasn't strong enough.
After all this narrative to paint a picture, my question is, could it be possible the adaptor plate(s) is/are warped? I've read stories where depending on the year of manufacturing, they were made in some not so quality places, with less quality control. If so (which I'll pull back apart you check later), can they be machined flat? Thanks for reading my long, but hopefully descriptive, post.
 

klinetime574

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I would verify you actually have a vacuum leak by spraying some carb or brake cleaner around the base of the carburetor (At the adapter plates). If the idle increases then you have a leak.

Weber’s can be tricky to tune. I had best results when running a fuel pressure regulator and making small adjustments with the idle set at 500rpm. Once I had it smooth at 500, I ramped it up to 800 or so (set higher than with stock carb to offset A/C idle load).

HTH
 
Joined
Jul 11, 2020
Messages
48
Location
Pacific Northwest
I would verify you actually have a vacuum leak by spraying some carb or brake cleaner around the base of the carburetor (At the adapter plates). If the idle increases then you have a leak.

Weber’s can be tricky to tune. I had best results when running a fuel pressure regulator and making small adjustments with the idle set at 500rpm. Once I had it smooth at 500, I ramped it up to 800 or so (set higher than with stock carb to offset A/C idle load).

HTH
Thanks, I'll give it another go with the co-owne cleaner. I've got the Weber set for baseline adjustments, as per their instruction. Can you have the idle screws (I have a 38, with two of them) too far out and still have it feel like it's lean? It would seem to me it would be rich all three time.
 

klinetime574

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It has been a while since I tuned a Weber carburetor. I would follow the instructions and make sure that you are running a fuel pressure regulator. I remember my instructions saying 3psi max. Depending on your location it might need a jet change for fine tuning.
 

MoaByte

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Moab
 
Those adapters can be a real pain. They often expand and contract or warp at different rates then the manifold and carb base giving intermittent problems. I've had a progressive Webber on my Toy pickup for 15 years. There have been brief periods where it has been trouble free, but I can't remember when. It always starts and runs and usually don't take long to remedy, if even for a day or two.
 

lcolon

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Oct 14, 2007
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East Bay, SF, CA
 
 
Have you plugged in a vacuum gauge and measured the overall level? That should give you an indication if you have a bug leak or not. +1 on spraying around with carb cleaner. If that does not work you could build yourself a cheap smoke machine and check for leaks.
 
Joined
Jul 11, 2020
Messages
48
Location
Pacific Northwest
Have you plugged in a vacuum gauge and measured the overall level? That should give you an indication if you have a bug leak or not. +1 on spraying around with carb cleaner. If that does not work you could build yourself a cheap smoke machine and check for leaks.
I have, but it's been a while and don't remember the outcome. I have some plans to look at things, but have to wait for the storm front that blew in last night to be done, hopefully this weekend. It sucks not having an indoor area to work.
 

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