Engine "Fluttering"?

[colnago]

I'm still breaking in my 352 rebuild, but it just started an unexpected noise the other day. The best way to describe it is as a rapid fluttering, more pronounced when warm. Kind of like the baseball card in your bicycle spokes (c'mon, we all did it, trying to sound like a motorcycle), but not hard enough to be a tap. It seems to increase with engine RPM, and more on the driver side than on the passenger.

Looking on the net, a lot of people say a fluttering sound could be an exhaust leak. I checked the nuts from the manifold to the exhaust pipe. They seemed to be snug, but not "gorilla tight." I snugged them up some more, but couldn't tell if anything changed. I haven't checked the heads to exhaust manifold yet.

Another possibility mentioned was bad spark plugs, but these were new with the rebuild. It's kinda doubtful, but possible, I suppose. I did upgrade to Duraspark ignition.

So, do either of these sound likely? Is there anything else I should check?

Joseph

[DuckRyder]

Might be worth checking the plugs for tightness...

I assume it is definitely coming from the engine itself and not down stream exhaust like a Y pipe or muffler?

[Ohiotinkerer]

Might be a long shot but it happened to me once - got a new spark plug that wasn't sealing where the ceramic meets the metal base and it made a strange noise........

[Manny]

Might be worth checking the plugs for tightness...

I assume it is definitely coming from the engine itself and not down stream exhaust like a Y pipe or muffler?

Yep had one dang near blow out of the bronco don't ask how it was loose.

[colnago]

Well, it wasn't a plug. They were all snug. I didn't have the time to check all of the bolts for the exhaust manifold; hopefully I can do that tomorrow.

Joseph

[fastEdsel]

Did you use your previous 2 barrel carb? My guess is that your carb has an internal vacuum leak where only 1/2 your engine gets fuel at certain speeds hence the flutter. Been there, done that. And depending on the age of your carb a new carb kit can usually fix it.

[Ren]

Maybe a small piece of something caught in the fan blade or shroud?
And I can't believe you bothered rebuilding a 352.
Surprised you didn't hear a "fluttering" sound when all that money flew out of yer wallet for the rebuild.

Good luck, though. And I do enjoy reading your posts as I often learn something.

[Manny]

Well, it wasn't a plug. They were all snug. I didn't have the time to check all of the bolts for the exhaust manifold; hopefully I can do that tomorrow.

Joseph

Hope fully you find something simple!!

[colnago]

Did you use your previous 2 barrel carb? My guess is that your carb has an internal vacuum leak where only 1/2 your engine gets fuel at certain speeds hence the flutter. Been there, done that. And depending on the age of your carb a new carb kit can usually fix it.

I did use the previous 4BBL Edelbrock carb. I was thinking it needed a rebuild anyway, just cuz the rebuild is nice 'n shiny, and the carb isn't.

Maybe a small piece of something caught in the fan blade or shroud?
And I can't believe you bothered rebuilding a 352. Surprised you didn't hear a "fluttering" sound when all that money flew out of yer wallet for the rebuild.

Actually, it's bored over 0.030, so it's really a 357! Now I have one on my hip (Smith & Wesson), and one in the driveway (Ford)! I kept it a 352, just to see people's expressions when I say "352;" they want it so hard to be a 351! As far as the money leaving my wallet, that was more of a "whoosh!" My wife and I had a really good policy on that; don't ask me no questions, and I'll tell you no lies.

Joseph