470 whistle

[2fishy4u]

Hello guys, back with a new issue. I got twin mercruiser 470 3.7lx with quadrajet carbs. Port engine has a super light wistle that started coming from the carb, so I took one of my old carbs in and had it rebuilt. After installing, the thing whistles now about as loud as a horn.... There is no vacuum hoses or nothing. So any clue why I am getting the whistle. Barely in the old one and full on intense with the rebuild......I took the rebuild back to the shop, he installed it on a engine there and it worked perfect. So its something on my end. Any ideas what I am looking for?

 

[gm280]

First, are you absolutely positive the whistle is coming from the carb? If you place you hand over the opening, does the whistle stop? Can you swap it out with another carb and the whistle stop? :noidea:

 

[GA_Boater]

The question is the whistle caused by blowing or sucking? This sounds like it could be an intake leak.

Mix up some dish washer liquid and water in a spray bottle and spray around the running motor looking for bubbles - Blowing leak.

Use an unlit propane torch and direct the nozzle around the running motor, if it speeds up - Sucking leak.

 

[Bondo]

Ayuh,.... Was the manifold Cleaned,..?? New gasket,..??

Sounds like an intake manifold leak,....

Try GA's propane torch trick, or a can of carb cleaner sprayed 'round the intake's gaskets,...

 

[2fishy4u]

Thanks guys, the whistle is almost nonexistent with the old carb. I can hear it but the wife does not. But with the rebuilt a deaf person could hear it a 100 yards away. It sounds like its coming directly from the carb, at least carb side. Covering the carb in any way does nothing to change the sound. I will give what GA said and see what is going on. I am going to assume intake as it is definitely that side.