This past weekend I replaced a broken base plate on my carb and ever since I get this noticable high pitched whistle sound coming from the primary side. Changing the throttle blade angle makes the sound go away. I inserted some home made throttle shaft bushings made from teflon sheet and there are zero external vacuum leaks.
Unless the donor part was the EXACT same part, it could have minor differences that are causing the noise issue. Teflon inserts do NOT keep the shaft centered in the bore, so may cause issues there as well. Some Holley carburetors used that deal, but the shafts were undersized and machined for that type of insert. I would install bronze bushings using the correct method, Greg Gessler has the bushing install kits here: http://quadrajetparts.com/rochester...-for-516-carburetor-throttle-shaft-p-286.html There have been a few folks advocating on the Forums to use a standard 3/8 drill bit and drill press to bore the baseplate for new bushings, this is a BAD idea as it does NOT keep the drill bit centered in the bore or keep it from going out of round during the drilling operation and making the hole too large/off center. In other words a half-ars method recommended by folks who certainly have little if any experience at this deal, and are better off keeping their day job and staying off the Forums, at least when it comes to giving advice in an area that they really know little to nothing about. Considering how many throttle bodies Ive had sent here that were ruined using that method, its just a good idea to do it once and do it right, rather than risk the possibility of destroying a part that is difficult and in some cases impossible to replace. Anyhow, the factory tolerance on the primary shaft was pretty loose for my liking right to start with. Ive measured brand new NOS q-jets at .008-.010 side play on the primary shaft right out of the box. This allows some unfiltered air to enter the engine and within 50,000 miles or so most throttle bodies are worn out past .015, Ive seen some twice that number. The installation of bronze bushings, done correctly is a permanent repair for that issue and will set the side play at less than .001, and should be part of every complete/correct rebuild done on a q-jet carburetor.IMHO.Cliff
Cliff wont say it, but I will... he sells an idiot proof self guiding drill bit and application specific shaft bushings in a kit that is WAY cheaper than finding another core to replace a wrecked baseplate. The tool is well designed, and I've used mine at least a dozen times with perfect results. Don't even bother to consider any other way......just saying. http://www.cliffshighperformance.com/bushings.html
check for sharp edges on all openings and gasket material in the airflow I have stopped whistles from time to time by smoothing edges.
The gasket used or wrong gasket between the main body/airhorn can also cause a "whistling" noise, ran into this a few times where the air coming in between the airhorn and main body enters a small entrance hole on it's way to the void(s) in the casting leading to the baseplate. Didn't think that information applied here, but it can produce a high pitch whistling sound with some applications.....Clif
Is it possible the sound could be coming from using throttle plates from another base plate I had? They had different numbers stamped on them but to my eyeballs looked exactly the same.
Unlikely if they were centered, indexed and completely sealed off the bores evenly when closed. It's common to see them bent, which caused uneven airflow when they are open at idle, which may contribute to some additional noise.....Cliff
I had a plywood carb spacer that caused a whistle because it had collapsed a little on one corner. A hard phenolic spacer solved the problem. Also, those thick 1/4" Q-jet gaskets MUST have the hard plastic buttons on each corner for the bolts or studs. Discard any that don't.
So that when tightening they do not allow the gasket to be compressed more from corner to corner. Think of them as a limiter.
