Vacuum Squeal?

[Droff]

I've got a 350 with an Edelbrock 1405 carb. I haven't had any noticeable problems with the truck starting or running but it has been sitting for about 6 months until I started her up yesterday. Previously, I had noticed a sharp squeal when getting on the throttle, this is just sitting in the driveway, pushing on the throttle. Yesterday, it was a bit worse. Very loud squeal, actually sounds like a belt slipping, and only at initial quick throttle.
I think I have a vacuum issue due to where it sounds like it is coming from but not able to test the theory yet. I'm going to pick up some starter fluid and see if I can find out for sure if I have a vacuum leak. I've tried to find pics of the back of the carb so I can make sure what connections I have but not having a lot of luck. The pic is the back of my carb.
The large port on top looks like it is for the power brake booster connection (which I have going to the intake). I can't find what the port underneath it is, it looks like an air hose fitting on maybe an adapter plate? Just wanting to make sure what vacuum lines need either connected or blocked off.
Any help?

[Troy Sr]

That Quick Connect fitting is there so that if you hook up an air hose to it it acts like a super charger and puts more air in. The problem with it is you need a long hose or an air compressor in the bed!!!!

[demian5]

Originally Posted by Troy Sr

That Quick Connect fitting is there so that if you hook up an air hose to it it acts like a super charger and puts more air in. The problem with it is you need a long hose or an air compressor in the bed!!!!

Dude I was thinking it was so you could vacuum the truck while as a car show...

[RodnRudy]

Those fittings are quick disconnect fittings for an air hose. Some one used them to plug the holes and put plastic caps on the ends. The lower one looks like the cap on the end has come off since the coloration is lighter on the end of it. Find a rubber cap that fits over the end and your squealing should go away. Auto parts stores have a selection of those vacuum caps in various sizes in the help section of the store.

[Droff]

Garage monkeys I suppose.
I'll look for more of a correct plug for these. Hopefully, that'll resolve it.
Is there a standard size for these?

(The other suggestions for more power and a shop vac option are interesting though)

[Wrenchbender Ret]

They are either 1/4 or 3/8 nat. pipe thread.

[RodnRudy]

1/4"NPT, take one with you in your search.

[Jcfcamaro]

Had the same carb on a 72 k10 blazer. It made the same sound with no vacuum leaks. That's why I'm a Holley guy now I hated that sound. It was just like a loose belt making noise but they were tight also.

[Steeveedee]

That's low on the throttle body, so it is for your vacuum advance. You don't hear it at idle because it isn't truly open for business until the throttle plates are opened to uncover the vacuum port.

[Droff]

Originally Posted by Steeveedee

That's low on the throttle body, so it is for your vacuum advance. You don't hear it at idle because it isn't truly open for business until the throttle plates are opened to uncover the vacuum port.

My vacuum advance is routed to a port on the front of the carb. Have not really checked it out yet.

[Steeveedee]

Originally Posted by Droff

My vacuum advance is routed to a port on the front of the carb. Have not really checked it out yet.

OK, could be a live port. Easy to check. Do you feel suction on that nipple when the truck is at idle?

[Droff]

Yep, that port has pretty good suction at idle. When the vac advance is removed, idle changes, but it's not horrible.
I put my finger over the bottom quick disconnect and there was no suction and no change in the squealing issue. I need to check my manifold connection where I connected the brake booster. This is about the only recent difference, but the squeal was there before I did it.

[Stocker]

Originally Posted by Droff

I've got a 350 with an Edelbrock 1405 carb. I haven't had any noticeable problems with the truck starting or running but it has been sitting for about 6 months until I started her up yesterday. Previously, I had noticed a sharp squeal when getting on the throttle, this is just sitting in the driveway, pushing on the throttle. Yesterday, it was a bit worse. Very loud squeal, actually sounds like a belt slipping, and only at initial quick throttle.

Unless you're positive it's vacuum, it might actually be a belt problem. Mine recently sounded just like your description (in the driveway, pushing on the throttle) and I figured it was a belt, but the adjustments felt fine to me. I snugged up the alternator belt just a tad and the squealing went away.

[Droff]

I'll check the belts again, nothing wrong with making sure. I removed the quick disconnect fittings and the top one, the one with the zip tie in the pic, smelled like gas. Should there be fuel on the threads?
I know it's in the carb, but it is a vacuum line, just wanted to make sure.
Thanks.

[geezer#99]

If there is fuel on the threads it means your carb is flooding.

[hamjet]

touch a bar of soap on the belts while its squealing, [ watch fingers] if loose belts it will stop squealing.

[Richard2112]

If you have a belt squealing you can put soap on it to find out if that's the one but the squealing will return sooner than later. If it's a belt squealing, check for fit, belt to v-groove on the pully. Some aftermarket pullys do not match well. The chrome ones will often generate quite a squeal until you scuff up the finish inside the v-groove.

[Stocker]

Originally Posted by hamjet

touch a bar of soap on the belts while its squealing, [ watch fingers] if loose belts it will stop squealing.

I have been doing exactly that, and giving the same advice, for a lot of years. With the squeal I recently had (post #13 above) the soap test failed me, for the first time ever.

[Droff]

I adjusted the idle mixture screws a little, not sure how close they are to where they need to be, but it may have helped the squeal to a small extent. Or I could be hearing things.

I'll try the soap test but still leaning toward the belts being okay. I'll keep this updated.
Thanks.

[Boog]

You can remove the belts for test purposes for just a few minutes to eliminate them as a cause. I was about to suggest tweaking the mixture screws but see you have already.