full throttle clacking noise
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From: texas
full throttle clacking noise
what would cause a loud clacking noise coming from the engine in the following situation?; cruising down the freeway at 65 mph and then pushing the throttle all the way down to avoid getting run over by an 18 wheeler? bad valve? incorrect secondary vacuum advance? incorrect octane gas? wrong jets? some kind of carb setting? thanks.
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From: texas
69, 350 small block, 350/350, 4 speed, 770 street avenger carb., old skool torker intake, hooker longs, detonation??... so i finally get to buy a new motor and not not have have my wife hate me??
Team Owner
Joined: Jan 2006
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From: Crossville TN
I'm thinkin' the same thing as itsonlyairandfuel . Check your motor mounts.. chances are they are weak or "shot" and the engine is torquing when you go WOT. The fan will hit the shroud. The dead give-away would be "fresh" wear marks inside the shroud.
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From: texas
what exactly is detonation? Sorry to say, but i am new to the sbc. The car had a Holley 4778 double pumper w/ mech. sec. on it when i bought it, I replaced it with a street aveng. 770 w/ vac sec. I went to put the 4778 back on tonight to see it made a difference, but for the life of me i don't remember how the vacuum lines were hooked up to the 4778. the SA has a seperate port for the brake booster and also the headlights, wipers, etc. the 4778 has only 1 small accessory port. also i asked a guy thats about in his mid 70s about it today and he suggested that the rockers may need adjusted.?? <== causing the clacking noise at wot. also i was reading around that the metering blocks can become corroded and blocked when moisture gets in there. i definetly had moisture in there. also, what does running "lean" mean? not enough fuel/air? i really appreciate the help.
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Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
You have to run at least 93 octane fuel. Other causes can be lean A/F mix, improper timing, Improper advance curve, Crappy gas, Carbon buildup. Is this a new problem that started since the carb change. Might be as simple as using manifold vacumn instead of ported when you changed the carb. 350 350 HP is an 11 to 1 motor with iron heads. Detonation would be pretty common on that with the fuel available now. Downshift to 3rd before you kick it down at speed! Detonation will destroy your motor. Don't let it make the clacking sound!!!
Last edited by 63mako; Dec 20, 2007 at 01:48 AM.
Racer
Joined: Mar 2007
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From: Melbourne Florida
what would cause a loud clacking noise coming from the engine in the following situation?; cruising down the freeway at 65 mph and then pushing the throttle all the way down to avoid getting run over by an 18 wheeler? bad valve? incorrect secondary vacuum advance? incorrect octane gas? wrong jets? some kind of carb setting? thanks.
If you have detonation, run in 3rd gear at 25 mph and give it gas...or start off from a dead stop in 2nd gear...you should hear the same sound.
If not, you likely have another problem. One loud clacking noise can come from the exhaust pre-heater valve in the exhaust manifold (passenger side). Also possible, loose or damaged engine mounts allowing the motor to rock and have the exhaust pipes going through the frame to hit the frame. I'm assuming you know enough about cars to know if you're getting a carb backfire so I'd rule that out (that makes a loud clacking noise, but only one).
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From: texas
It's not one loud noise, but more like a continuous clacking of say a '91 chevy 6.7 liter diesel motor clacking noise. heard the same sound about 2 days before. I was at a stop, went to 1st, punched it, hit second, floored the throttle and there was the clacking sound. I'm not really impressed with this SA carb. Another thing is i have been trying to see which octane gas the car likes to run on. I've only recently gotten it to the point where i feel it is reliable enough to drive. Everytime i change octane, it pops through the exhaust for a a little while, then clears up. Which i know is scavenging in the collectors, etc... So from now on i'm sticking to 93 octane. But, i don't think this carb. is right for my car. it had a 4778 on it that the previous owner was running airplane fuel through it. i'm am wondering if any of this has anything to do with the fact that i replaced the fuel filter that had 1 inlet and 2 outlets; of which 1 goes back to the fuel tank. maybe the carb is getting too much fuel? man i don't know, i'm tired. merry christmas everybody.
Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
It's not one loud noise, but more like a continuous clacking of say a '91 chevy 6.7 liter diesel motor clacking noise. heard the same sound about 2 days before. I was at a stop, went to 1st, punched it, hit second, floored the throttle and there was the clacking sound. I'm not really impressed with this SA carb. Another thing is i have been trying to see which octane gas the car likes to run on. I've only recently gotten it to the point where i feel it is reliable enough to drive. Everytime i change octane, it pops through the exhaust for a a little while, then clears up. Which i know is scavenging in the collectors, etc... So from now on i'm sticking to 93 octane. But, i don't think this carb. is right for my car. it had a 4778 on it that the previous owner was running airplane fuel through it. i'm am wondering if any of this has anything to do with the fact that i replaced the fuel filter that had 1 inlet and 2 outlets; of which 1 goes back to the fuel tank. maybe the carb is getting too much fuel? man i don't know, i'm tired. merry christmas everybody.
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From: texas
how can i de-tune-it? i'm at a loss here! other than filling the tank with 93 octane and then pouring in some c (something) my buddy suggested from the race store.?? it has to be in the timing and carb. i replaced the dist. with a new mallory unilite, new sa carb (which i personally think is a p.o.s.) other than that, its heads? right?
Drifting
Joined: Sep 2007
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From: Wichita Kansas
how can i de-tune-it? i'm at a loss here! other than filling the tank with 93 octane and then pouring in some c (something) my buddy suggested from the race store.?? it has to be in the timing and carb. i replaced the dist. with a new mallory unilite, new sa carb (which i personally think is a p.o.s.) other than that, its heads? right?
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
dr:
THAT "clacking" noise is poor choice of descriptors ... that noise & condition you describe is more correctly referred to as pinging, spark rattling, detonation or pre-ignition (purists I know those are not all exactly same).
Correct for THAT pinging by either richening mixture or retarding ignition timing or combo of both.
Ultimately, it may need higher octane fuel or lowered compression or combo of both.
You can also alter effective compression by changing camshaft or degreeing existing cam. Retarding camshaft a few degrees will lower effective compression.
THAT "clacking" noise is poor choice of descriptors ... that noise & condition you describe is more correctly referred to as pinging, spark rattling, detonation or pre-ignition (purists I know those are not all exactly same).
Correct for THAT pinging by either richening mixture or retarding ignition timing or combo of both.
Ultimately, it may need higher octane fuel or lowered compression or combo of both.
You can also alter effective compression by changing camshaft or degreeing existing cam. Retarding camshaft a few degrees will lower effective compression.
Last edited by jackson; Dec 21, 2007 at 01:01 AM.
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From: texas
i keep reading about total timing, i don't have a dial back light. or understand the concept. like i said, i'm new to the sbc. i set the timing the old fashioned way> it runs ok. what's a good carb to buy? without all the plastic gears and crappy linkage?
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
dr:
read, read, read the timing & tuning papers here ... Lars & BarryK have some ... study until you do understand & know ... get a dialback light & know how to use it.
If I were you, I'd learn carb tune/ jet change before I'd just go buy another carb that'd probably need same too.
Maybe send your carb & distributor out to CF member lars for his expert freshening & tuning ... Lars has many satisfied customers.
read, read, read the timing & tuning papers here ... Lars & BarryK have some ... study until you do understand & know ... get a dialback light & know how to use it.
If I were you, I'd learn carb tune/ jet change before I'd just go buy another carb that'd probably need same too.
Maybe send your carb & distributor out to CF member lars for his expert freshening & tuning ... Lars has many satisfied customers.