Very strange/annoying whistle. - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-26-2007, 10:56 PM Thread Starter
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Very strange/annoying whistle.

MC2100, HEI, split header. This started very softly this morning, but got progressively worse.

I started getting a very high pitched whistle from around the carb itself. This was very slight only at idle, but within only a few minutes grew to a very loud scretching whistle at idle and under even load. If I put the engine under heavy load, the noise goes away.

It sounds like an air type whistle. I've checked the carb/gaskets for vacuum leaks with no luck. There is no loss of performance. I tore down the MC2100 and cleaned/blew out all passages and reassembled. No luck.

I started to second guess myself and began pulling belts off to try and eliminate a bad bearing in something. No change.

The noise is very high pitched. As I said, it goes away under load, but comes right back as soon as I lift off the accelerator. The pitch is fairly constant, but does seem to rise some when down shifting.

It seems to me that it has to be air either leaking out, or in somewhere... but I can't figure out where to look next.

Any ideas? It's so loud right now, no one wants to wheel around me... it's giving them (and me) headaches.

Is this the only hammer you've got?
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post #2 of (permalink) Old 05-27-2007, 07:43 AM
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High frequencies are difficult for our ears to get a directional fix on, but with a stethoscope you should be able to locate the source. Take a piece of 1/4" or 3/8" plastic tube a couple of feet long. Stice one end in your ear. Move the other around the engine compartment until you zero in on the source. Or build an electronic stethoscope.

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post #3 of (permalink) Old 05-27-2007, 07:50 AM
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don't over look Pullies. I hd one go south and sounded like a damn blow pop.

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post #4 of (permalink) Old 05-27-2007, 07:59 AM
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So this is without any air cleaner, hat, or intake tube?

Mine only makes a flushing sound (10mpg... undetectable to the ear, but noticeable in the wallet )... but have ridden in YJ/TJs with aftermarket air cleaners that sounded like turbos spooling up!

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post #5 of (permalink) Old 05-27-2007, 09:00 AM
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Start disconnecting vacuum hoses one at a time ‘til you find the one making the noise.

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post #6 of (permalink) Old 05-27-2007, 09:57 AM
 
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Check you private for a quick answer...
I'm going to hang out here and see how long (if ever) it takes for the right answer to pop up...
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post #7 of (permalink) Old 05-27-2007, 10:09 AM Thread Starter
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Update: I have taken all of the drive belts off, no change. I have removed all of the vacuum lines, no change. I disassembled the choke housing, no change. I am going to try JYG's advice here in a little bit. Keep coming with the ideas though. Thanks

Is this the only hammer you've got?
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post #8 of (permalink) Old 05-27-2007, 10:25 AM
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Next step is starter fluid or WD40 around the base of the carb, where the carb mates to the base and throttle shafts.

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post #9 of (permalink) Old 05-27-2007, 10:50 PM
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My vote is vacuum leak.
How are your brakes? Is it harder to stop? If so, your booster is leaking.

A quick way to find the leak is to take a pair of pliers and start pinching hoses.

Next, check the intake manifold. See if you have any loose bolts. It could also be a crack in the intake...that is hard to find.

And don't forget the heat riser....on the underside of the intake is a plate....it has an electric heater in it....I had that gasket leak one time.

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post #10 of (permalink) Old 05-28-2007, 07:47 PM
 
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I vote for intake /exhaust leak at the head.
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