So, I have a '90 B2200. I recently swapped on a 32/36 Weber, it had a vacuum leak from the intake. I assume, that I got that cleared with some gasket shellac, and sanding down the adapter plate to be flush. However the carb still whistles, like a busted tea kettle. It also infrequently, does not want to idle. This seems to all lead back to a vacuum leak, however I cannot seem to find one.

Anyone got any ideas of common places of vacuum leaks, that I may be looking over?

 

Normally I would let these thread go to the Mazda Truck team here on this forum because there advise and recommendation are top notch but in this case I will toss in a thought.
WEBER's are not the only carburetor that get to whistling... LOL. The usual cure is to loosen the throttle plate butterflies and reposition them properly or at least better? Holley 0-1850's were notorious for being a whistler. Also even some "original" CARTERs.

 

Hmm alright. I did not think of repositioning the butterflys, I think I may do that if the whistling persists. I have also noticed while having a look over, that one of the nuts that I had tightened, seems to have been shook loose and fell off. Thus causing what I thought caused it, but alas no after a shake down run, it started to it all over again despite every bolt being tight as all hell.

 

Did you spray some starting fluid, or choke cleaner, etc.......around the intake where the adapter plate is bolted to it?

This will let you know if the adapter plate is still leaking or not........OR......if the screws that attach the two adapter plates together, are "lifting" the lower adapter plate off of the intake manifold surface......and therefore causing a vacuum leak that will DEFINITELY WHISTLE!!!! How do I know this? I have had this happen before!! The fix was to double the gasket BETWEEN the two adapter plates.

If you spray some choke cleaner (or the like) around the adapter plates, and the idle changes speed (up or down) then you've got a vacuum leak there. If the screws attaching the adapter plates together are too long, they will bottom out on the intake manifold and effectively RAISE the lower adapter plate OFF of the intake manifold sealing surface, creating the vacuum leak and the whistling noise.

IF this is your scenario, then if you remove the Weber AND the adapter plates, you will see 4 telltale signs on the top of the intake manifold surface, where the 4 adapter plate screws, "dug into" the flat surface of the intake manifold where the carb mounts.......like this......

 

Here are the 4 screw locations (circled in red) that can "raise" the lower adapter plate off of the intake manifold sealing surface, IF they are too long, OR if the recessed hole that they are located in......is machined too deep.....effectively lowering the screws down to the point that they go completely through the lower adapter plate, and contact the intake manifold surface........

 

Yep. Looks like one of the screws marred the adapter plate.

 

Yep! But that is where one of the carburetor studs was tightened down too much......and probably lifted the upper adapter plate to create a vacuum leak.

While you have it torn down that far, go ahead and remove the lower adapter plate to check below where the 4 cap screws (already removed in your photo) thread into, to make sure those weren't contacting the intake manifold also.......and creating a vacuum leak also.

Good job finding the vacuum leak! As soon as I read in your thread here, that your carb was whistling......I knew you had a vacuum leak at the adapter plate(s)!

 

I checked that when I had both adapter plates off, no marring there. However I have noticed what exactly caused my vacuum leak. Apparently those four bolts on the first plate backed out, and we're causing the adapter plate to the intake to not be seated properly thus the whistle and leak.

 

I use a small amount (1 drop) of red Loctite on each of those screws......AND on the carburetor studs where they screw into the upper adapter plate.....that way, they stay put.

 

Ah, good thinking. I did the same but with green loctite. I suspect in 5 years time Ill be kicking myself over that decision but thanks for the help.