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| Carter BBD whistle https://slantsix.org/forum/viewtopic.php?t=42878 |
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| Author: | ESP47 [ Mon Dec 13, 2010 2:41 pm ] |
| Post subject: | Carter BBD whistle |
I bought a new vehicle with a 2bbl super six and I'm in the process of tuning it up. When I got it, the mixture screws on the Carter BBD were only turned out 1 turn a piece. I put a vac gauge on it and it was reading about 17. I played with the mixture screws for a bit and now I'm reading just above 20 on the gauge and I'm 3 1/2 turns out on the mixture screws. I started to notice a faint whistle that sounds like it's coming from the throat of the carb. I decided to do some vacuum leak tests on the manifold and carb and didn't detect anything. I did notice that the whistle would do some strange things. Like sometimes it would increase a bit as I increased idle rpm. Sometimes it would go away when I'd lower the idle to 500rpm or so. It never really consistantly did the same thing when I played with the idle. You'd think it's a vacuum leak but is it really possible to be holding steady at 20hg and still have a noticeable leak like that? |
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| Author: | THOR [ Mon Dec 13, 2010 4:01 pm ] |
| Post subject: | |
Sure is! I had a 1920 do that. The port on the base for manifold vacuum to the choke pod leaked. Made a tea kettle-ish noise. I would check the hose for the choke pod, and verify that the pod is actually pulling the choke off when running. ~RDE~ |
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| Author: | Capt Jim [ Mon Dec 02, 2013 6:07 pm ] |
| Post subject: | My Carter BBD whistles too |
I can't figure out where exactly it's coming from, but I have a very good idea. I've double checked all the vacuum tubes and they are secure, even the choke works fine. I think the noise is coming from the Throttle body. Maybe the air escaping past one of the disks is creating the whistle? Anyway, I've rebuilt the carb twice now and it still whistles. Runs like a champ, but whistles when idles. I wouldn't care that it whistled if it wasn't so loud and embarrassing. I know this post is really old, but maybe someone has had the same problem and figured out how to stop it? Help! |
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| Author: | nzpete [ Mon Dec 02, 2013 10:01 pm ] |
| Post subject: | |
Try listening around with a length of hose, one end at your ear, and the other moving it around until you hear the source |
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| Author: | Capt Jim [ Tue Dec 03, 2013 7:43 am ] |
| Post subject: | Excellent Idea! |
NZPete, That is an AWESOME IDEA! I've been shoving my head and ears into the engine this whole time and because of all the engine noise, it's next to impossible to tell where sounds are coming from. I'll let you know how it goes. I won't be able to get to it until maybe this weekend though. Thanks again! Jim |
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| Author: | oldskoolracer [ Tue Dec 03, 2013 9:54 am ] |
| Post subject: | |
Mine whistles too, both BBDs Ive had on it now whistle, run and idle fine but yea they whistle. Also pulling 19" of vac at idle, no vac leaks that I can find either lol. Are you hearing it without the air cleaner on? Does it go away with the cleaner on or if you just barely place your hand over the choke horn? I only hear mine when the air cleaner is off or the lid is off... |
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| Author: | Capt Jim [ Tue Dec 03, 2013 6:57 pm ] |
| Post subject: | |
Mine whistles pretty loud. sounds like a tea kettle. and it whistles at idle only. And only sometimes, but most of the time. Usually when it decides it's going to whistle, I can stop it by increasing the RPM, but when I let go of the gas and the engine slows down to idle, it starts whistling again. Oh, and it whistles with, or without the air cleaner on. If I put my hand over the choke horn, it does tend to go away, but I've got to practically smother it. I can't wait to try NZPete's trick to see if I can hear exactly where it's coming from. |
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| Author: | Aggressive Ted [ Wed Dec 04, 2013 12:52 pm ] |
| Post subject: | |
It is just whistling around the throttle plates/blades at high vacuum levels. 20" is good vacuum! When you crack the throttle plates/blades open the vacuum drops and the whistling stops. |
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| Author: | 64ragtop [ Thu Dec 05, 2013 6:42 pm ] |
| Post subject: | |
Isn't it possible that the whistle is from the throttle shafts having worn the throttle body, and those holes need new bushings?? Seems like if the whistle is from the throttle plates the only cure is to open the throttle slightly. That would raise the idle speed and lower the manifold vacuum. I've seen articles about carb rebuilding that mention re-bushing those worn bores. Of course, as always, I might be wrong. BC |
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| Author: | Capt Jim [ Thu Dec 05, 2013 7:54 pm ] |
| Post subject: | |
I haven't done anything with it yet, but I do know that the plates do not completely seal the throttle body shut. I've rebuilt the carb twice and as much as I tried and adjusted the plates before tightening them, I can still see some light through it. I figured this was normal, but it might also be what's causing the whistle as it's a pretty tight space for air to try and get through and I can only imagine the plate vibrating pretty good from the air passing through it. 64ragtop, I'm not sure where the bushings would fit unless I bored something out. Everything is solid (no current bushings) and everything is very tight minus the slivers of air gaps past the plates. We'll figure this out! |
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| Author: | oldskoolracer [ Fri Dec 06, 2013 10:19 am ] |
| Post subject: | |
No the bushings wont change it, yes it is normal, and it is just the air passing around the throttle blades at idle. Not really anything that can be done about it. The bushing get pressed in were the throttle shaft passes through the throttle body after the holes have been drilled out. They will cause a whistle if they are really bad because it will cause a vac leak. If it runs good, has good vacuum, and good driveability just leave it and ignore it 
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