1940 carb whistle? Any ideas?

Griffon

Griffon

Member
I have a Holley 1940 on my 73' 258 that has a "turbo like" sounding whistle at mid rpm's, it is silent before and after but whistles pretty good in the middle. The truck has only a pcv valve for smog, k&n 7" filter and no hose to charcoal cannister. I've tried spraying water to find an intake leak but pretty sure there isn't one. If I choke off the air w/my hand it goes away. Any ideas?
 
Internal vacuum leak caused by gasket failure, loose fastener or a cracked/warped main body. If you have a vacuum gauge, you could take some manifold readings at idle, cruise under load, and wide open throttle under load for corroboration. You're most likely looking at pulling the carb down for disassembly and inspection.
 
Thanks for the suggestions. I just had it rebuilt by one of the best carb guys in san diego. He suggested it was the pcv valve. It runs great through the entire range. Last resort is pull the carb back off, maybe I just don't want to face reality....
 
Well, I won't rule the pcv out as a possibility from all these miles away, but I think it is an unlikely source. Its easy enough to check though. How about the vacuum line to your brake booster and the booster itself? Plug off the line and see if the whistle goes bye bye.
 
I have a 196, in my 800. It had a 152 in it, with a 1904 mixer. I upgraded to a holey/weber 32/34 from stovebolt, rejetted it, and it runs like a top.
You will need to get a gasket kit if you get it from stovebolt, found some issues with trash in mine, from setting I imagine, and to do the jets you'll need t anyway. On a 258, you May not need to rejet, not sure.
But I was so glad I did it, and I am not a carb guy so it was easy to change the jets and rebuild.
Now I see there is a 36/36 that a few have suggested for a 196, so I May try that if I find a cheap one, one day.
Right now I am changing out a carb on my sii so fuel problems of another kind still haunt me.
 
I've had six holers with 1 bbl carbs whistle. Ford 144 and 170 and dodge 225 slant six. Usually at a bit of rpm like 2000 and a small throttle opening. More throttle and it stops. Just an idiosyncrasy of the beast. Could hardly hear it with the air cleaner on.
Any way you could take a video with sound and post it? Is it possible it is not the carb?
 
That's exactly what it does. The highflow aircleaner does almost nothing to muffle it. It runs really good too, so maybe it's something I'll have to live with. Thanks for the replies-
 
The leave it alone treatment sounds like the right one to me.
The air cleaners I had were the oem ones and went a fair distance in muffling the whistle.
 
I had a simular problem, not really a problem but I felt like there was some type of air starving since the engine seemed not to respond as well when I put the square weber filter box on the 196. So I went to advance or autozone and got one of those edelbrock trainagle type filter assm. Fabbed up a plate to match the football Holley weber air horn, and whistle went and got more pop. I guess it needed more air, and I think it looks sweet. Since I dont off road with that Scout it seems to be fine. I did loose one before I got the right jets via a backfire that scorched the filter material, but got a replacement and corrected the jet and now she runs like never before.
 
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