Loud air sucking noise on acceleration

[Asshat]

Originally Posted by 1966Step

I think you need to send that plumbing back to the carb base as you shouldn't experience any vacuum at idle which you said was the case. Vacuum should come on as the throttle is opened. Others can correct me if I'm wrong here.

Ok. I can put it back.

[Steeveedee]

The vacuum signal to the distributor won't be as strong if it comes from the PCV circuit, because that's meant to flow, not hold vacuum. Does the base of your carburetor have a plug where the line goes in 1966Step's picture? His appears to have a plug where your ported spark connector is installed.

I suppose that it is possible that a smaller carburetor bore could make more noise, but I'm not sure.

OK, after looking back to post #29, I see that there is a brass plug in the manifold vacuum port on the throttle plate your carburetor. Looks to be 1/8" pipe. You can get a brass piece that has 1/8" male pipe on one end and a 3/16" barb on the other end, and run a hose to your distributor. As you can see, they've been run both ways. That potentially may not work, depending on the gasket between the float body and the throttle plate. You can check that by removing the plug and see if you get a vacuum leak. Whether you have manifold vacuum or not at idle is a "tastes great/less filling" kind of thing, and just like beer, some people can get pretty worked up over it.

You could also use a steel line like 1966Step has, if you want to bend one up. That would take a different adapter fitting, but those are common.

[Asshat]

Originally Posted by Steeveedee

The vacuum signal to the distributor won't be as strong if it comes from the PCV circuit, because that's meant to flow, not hold vacuum. Does the base of your carburetor have a plug where the line goes in 1966Step's picture? His appears to have a plug where your ported spark connector is installed.

I suppose that it is possible that a smaller carburetor bore could make more noise, but I'm not sure.

OK, after looking back to post #29, I see that there is a brass plug in the manifold vacuum port on the throttle plate your carburetor. Looks to be 1/8" pipe. You can get a brass piece that has 1/8" male pipe on one end and a 3/16" barb on the other end, and run a hose to your distributor. As you can see, they've been run both ways. That potentially may not work, depending on the gasket between the float body and the throttle plate. You can check that by removing the plug and see if you get a vacuum leak. Whether you have manifold vacuum or not at idle is a "tastes great/less filling" kind of thing, and just like beer, some people can get pretty worked up over it.

You could also use a steel line like 1966Step has, if you want to bend one up. That would take a different adapter fitting, but those are common.

I did have that plumbed to the distributor a while back. I changed it because someone on here told me it was ok to run manifold vacuum to the distributor.
That was quite a while ago; I’ll change it back tomorrow and see how it runs.

[jayoldschool]

Also, I recall you saying you are using a paper filter. In the stock air cleaner, or an open element chrome one?

[Asshat]

Originally Posted by jayoldschool

Also, I recall you saying you are using a paper filter. In the stock air cleaner, or an open element chrome one?

In the stock filter housing, the one with the horn.

[geezer#99]

Originally Posted by Asshat

I did have that plumbed to the distributor a while back. I changed it because someone on here told me it was ok to run manifold vacuum to the distributor.
That was quite a while ago; I’ll change it back tomorrow and see how it runs.

When you took the hose off the carb what did you plug the port with?

[Asshat]

I have the distributor plumbed to the base of the carb, and was able to confirm the vacuum plate moves when blipping the throttle. So, at least I know it is now connected properly. Thanks for all the questions and suggestions. Haven’t driven it yet, hopefully tomorrow.

[1966Step]

Looks good! I need to locate the correct air filter assembly for my 292. Only recently discovered it's a '63 engine and when Shorty installed it 40 years ago he must have just used the assembly from the 230 that was swapped out. Back then, he told me he thought it was a '70 or '71 engine (came out of an old school bus sitting in his salvage yard) but I wasn't able to verify it easily with no Internet (we really had to work for information back then!).

[Asshat]

Got a better video... I think most of the noise is from the exhaust.

https://youtu.be/RgFKq_4KmSg

Really sluggish when going up the hill, just doesn’t have any pull.
Maybe the carb jets are too small?

[Steeveedee]

If there is a restriction in the exhaust it could hiss like that. It would for sure make the truck seem weak. This is actually easy to check. Hook a vacuum gauge to manifold vacuum and run the engine up to 2000 RPM, in neutral. You don't have to be on the road for this. If the vacuum at a steady engine speed starts dropping down, the exhaust is restricted. If so, it could be a collapsed inner layer (if the exhaust is double wall pipe) or a broken baffle in the muffler. Though with a broken baffle they usually rattle. If there is significant restriction in the exhaust you can pop a head gasket.

[Asshat]

Originally Posted by Steeveedee

If there is a restriction in the exhaust it could hiss like that. It would for sure make the truck seem weak. This is actually easy to check. Hook a vacuum gauge to manifold vacuum and run the engine up to 2000 RPM, in neutral. You don't have to be on the road for this. If the vacuum at a steady engine speed starts dropping down, the exhaust is restricted. If so, it could be a collapsed inner layer (if the exhaust is double wall pipe) or a broken baffle in the muffler. Though with a broken baffle they usually rattle. If there is significant restriction in the exhaust you can pop a head gasket.

The muffler and pipes are all new. I guess it’s possible.

[ACK]

Have you used a length of hose held to your ear to try and track down the source of the sound? If you haven't, it is easy, accurate, and cheap. Even if it can't be pin pointed, at least you'll have the general area where that noise is being generated in under 5 minutes.

[geezer#99]

Nice sounding vacuum leak you got there!

[Steeveedee]

Originally Posted by Asshat

The muffler and pipes are all new. I guess it’s possible.

OK, I remember you mentioned that you might take it to the muffler shop. If you did, and reported that here, I missed it. I highly doubt that you have a restricted exhaust, if all the parts are new and that noise hasn't changed.

What is the part number on the carburetor? It sounds to me (now that I know that the exhaust is unrestricted) that it's starving for fuel, but not enough to cause it to buck or stall, like a clogged filter or bad fuel pump would cause it to act. I recall that it is a rebuilt carburetor? Sometimes rebuilt carburetors aren't calibrated like they should be. I'm strongly averse to blaming carburetors, because they are not usually the problem on these vehicles. 99% of the time it was ignition causing the problem, but I'm not hearing any misfire in the video.

[Asshat]

Originally Posted by Steeveedee

OK, I remember you mentioned that you might take it to the muffler shop. If you did, and reported that here, I missed it. I highly doubt that you have a restricted exhaust, if all the parts are new and that noise hasn't changed.

What is the part number on the carburetor? It sounds to me (now that I know that the exhaust is unrestricted) that it's starving for fuel, but not enough to cause it to buck or stall, like a clogged filter or bad fuel pump would cause it to act. I recall that it is a rebuilt carburetor? Sometimes rebuilt carburetors aren't calibrated like they should be. I'm strongly averse to blaming carburetors, because they are not usually the problem on these vehicles. 99% of the time it was ignition causing the problem, but I'm not hearing any misfire in the video.

I did not get the new exhaust yet.

Carb: https://www.rockauto.com/en/moreinfo...=1324336&jsn=1

[Asshat]

Originally Posted by ACK

Have you used a length of hose held to your ear to try and track down the source of the sound? If you haven't, it is easy, accurate, and cheap. Even if it can't be pin pointed, at least you'll have the general area where that noise is being generated in under 5 minutes.

I will try this tomorrow.

I wonder if my valve adjsutment could be that far off to make it run crappy? A compression check should indicate this, correct?

[Asshat]

Originally Posted by geezer#99

Nice sounding vacuum leak you got there!

The only place I could have a vacuum leak is at the intake manifold or carb base, correct?

[geezer#99]

Or on the carb or pcv hose.

[Asshat]

I just noticed, it looks like the carb is leaking a little, maybe this is related?

[Asshat]

Vacuum leak test with smoke.
https://youtu.be/3zgQtaGpPoc

I think it’s the carb.

EDIT: replaced the gaskets on the carb and started it up. Idles great, sounds good. However, I did see that the exhaust is leaking pretty bad right at the pipe going into the exhaust manifold. Pretty sure that’s the majority of the loudness, but it still could have a vacuum leak. I’ll have to get the exhaust remedied then I can go from there.

[Asshat]

You guys were right - exhaust restriction. I took the exhaust off, since it was leaking really bad at the manifold. I forgot I had welded a small baffle in place when I was running a straight exhaust with no muffler. I removed that section and started it up and it sounded a lot better. Taking it for a drive tomorrow to see how it runs.

Here’s a video... it’s in the garage and cold, so a bit of hesitation; it gets better when it warms up.

https://youtu.be/J0wPm4wNPGQ

[cwcarpenter98]

Oh yeah, that's sounding a lot better. Methinks you found the problem

[Asshat]

I hope so!

I also picked up a header pipe, so eventually, hoping to take it to a muffler shop and have a complete exhaust installed. This pipe i picked up is 2-1/2”... the one I have on the truck is 2”. Not sure if I will see a difference in performance when I get the 2-1/2” exhaust installed. Then again, I’ve been thinking about getting some 292 312 exhaust headers, like the two piece ones on the Langdon website.

[AcampoDave]

I'm mostly a sb V/8 guy but I seem to recall that some 292's came with an exhaust manifold that had a 2.5 outlet. Be cool to fine one of those and then you'd be set for 2.5 inch pipe without the restriction at the outlet.

[Asshat]

Originally Posted by AcampoDave

I'm mostly a sb V/8 guy but I seem to recall that some 292's came with an exhaust manifold that had a 2.5 outlet. Be cool to fine one of those and then you'd be set for 2.5 inch pipe without the restriction at the outlet.

Pretty sure mine is 2.5”, it is the 3-bolt clamp.
The header pipe end I found on eBay is 2.5”.