engine and drivetrain odd sound from engine- down on power

[vintage_car]

driving down the interstate and the engine began to make a loud sound when applying the throttle. cruising is okay. It is a difficult sound to describe. Sort of sounds like an exhaust leak right at the block, but it isn't t the exhaust. it is more around the carb. I pulled the air filter and when you blip the throttle you hear it loudly through the carb. Almost has the sound of one of those big exhaust mufflers that are very loud. I checked around the intake and don't see anything. Pulled the valve cover and nothing looks suspicious. There is some noticeable power loss. ideas?

[DavidLMM]

Spark plug backed out? I've had it happen more than once on a Honda.

David

[vintage_car]

I'll give it a look.

[vintage_car]

plugs are all snug.

here is a video of the noise I experience.

http://www.youtube.com/watch?v=ifb4KiZ2c2I

[Tbone]

headgasket blown between 1&2 or 3&4? It's happened to me. Do a compression check

[Chamonix72]

headgasket blown between 1&2 or 3&4? It's happened to me. Do a compression check

Yeah, kinda sounds like a blown head gasket.

[TKMad]

Could also be a valve that is too tight or has burned a little.

[c.d.iesel]

adjust the valves COLD 0.006"

and COMPRESSION TEST

leave the spark plugs out of the hot motor,

with pressure (12-16 psi) held in the radiator, let sit

for 1 - 2 hours, return and crank over motor

and watch for any coolent pumping out of

the spark plug holes

WHAT COLOR IS THE COOLENT?

what color is the motor oil?

any abbynormal exhaust smoke?

[Scott Sislane]

wow, love that '48 chevy! very cool...

[vintage_car]

Thanks on the 48 compliment. It's a fun project and coming along.

Checked oil and antifreeze before heading to work both look clean. I'll do compression test/valve adjustment this weekend. I thought a compression test was to be done on a warm engine? Does it matter in this case?

[c.d.iesel]

compression test good COLD because that is the

actual condition of the motor when your actually

starting a motor COLD

a re-test HOT is also good back up test

either way you need more than 135 psi

in all cylinders

[vintage_car]

remove all plugs before the compression test or one at a time, and replacing them as I go?

[Chris_B]

Pull all of the plugs before the test- you want maximum RPM when testing, so reducing the compression in the cylinders not being tested helps.

[vintage_car]

Blown headgasket between 2 and 3. Cyl 1 and 4 had 155psi. So my question is where is the piece that was between cyl 2 and 3 that caused the problem.

[Guest Anonymous]

a crack in the exhaust manifold or broken air injector if it has a reactor system. Both make that sound. Check for leaks