Knock/Detonation under acceleration
Thread Starter
Intermediate
Joined: Nov 2013
Posts: 30
Likes: 0
From: East Meadow NY
Knock/Detonation under acceleration
Hello fine folks of the forum. My 1969 Roadster has had a knocking sound under acceleration since I got it a couple months ago. I also had a nice "tick" under driver side valve cover. I brought it to my mechanic and he resolved the tick by making some adjustments. Engine runs swimmingly now.
I still have that knock under acceleration and he's attributing it to carbon buildup. He had mentioned an engine lube that gets poured directly into the carburetor when the engine is hot, and we let it sit for 6 hours, then run the car to "blow" the carbon out. What are your thoughts on this and anything else I should mention to him to try? He seems to know his stuff and I do trust him, I know he doesn't nor has he owned a corvette (he's a Ford Mustang guy). Just looking for the surest way to fix this. Car seems to have a loss of about 50 hp at this point so I'm really hoping we can get that carbon buildup out of there and I can regain some hp back.
Thanks for reading and thanks in advance for any input.
I still have that knock under acceleration and he's attributing it to carbon buildup. He had mentioned an engine lube that gets poured directly into the carburetor when the engine is hot, and we let it sit for 6 hours, then run the car to "blow" the carbon out. What are your thoughts on this and anything else I should mention to him to try? He seems to know his stuff and I do trust him, I know he doesn't nor has he owned a corvette (he's a Ford Mustang guy). Just looking for the surest way to fix this. Car seems to have a loss of about 50 hp at this point so I'm really hoping we can get that carbon buildup out of there and I can regain some hp back.
Thanks for reading and thanks in advance for any input.
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
Back in the old days, we would simply set the idle up a little and SLOWLY pour a little water into the carb. You have to keep the engine running by bumping the throttle lever but that would make the black sooty mess really roll out of the tail pipes. It doesn't take much water to do the trick. Probably no more than a bathroom size Dixie cup would be enough. Just keep revving the engine a little as you do it so it won't die.
These days, carbon buildup is not as much of an issue as before with changes in gas and such. Taking the car out and driving is a little harder than usual should clean it out.
Have you checked the plugs, points, and timing? Have you checked for vacuum leaks that would lean out the mixture and contribute to spark knock?
I am assuming that you are running the gasoline recommended for the car.
There is troubleshooting to do...
These days, carbon buildup is not as much of an issue as before with changes in gas and such. Taking the car out and driving is a little harder than usual should clean it out.
Have you checked the plugs, points, and timing? Have you checked for vacuum leaks that would lean out the mixture and contribute to spark knock?
I am assuming that you are running the gasoline recommended for the car.
There is troubleshooting to do...
Thread Starter
Intermediate
Joined: Nov 2013
Posts: 30
Likes: 0
From: East Meadow NY
Sorry guys... it's 350/350 with 11:1 compression I believe. The car was just tuned up and the timing was adjusted and is a little retarded to compensate for the car dieseling after shut down.
I'm using 93 octane since I've had the car and just added a lead additive and an octane boost with my past fill up. I've been using only Mobile in the car so far. I only drove the car briefly after that and will look to put some mileage on it in the next week.
After the tuneup and timing adjustment, the car idles so much better than it did and the knock is only on acceleration.
I'm using 93 octane since I've had the car and just added a lead additive and an octane boost with my past fill up. I've been using only Mobile in the car so far. I only drove the car briefly after that and will look to put some mileage on it in the next week.
After the tuneup and timing adjustment, the car idles so much better than it did and the knock is only on acceleration.
Le Mans Master
Joined: Oct 2010
Posts: 6,937
Likes: 848
From: melbourne florida
2023 C3 of the Year Finalist - Modified
your mechanic was suggesting " sea foam" its popular with ford guys they seem to have good luck with it. as stated a little water will break some of the carbon up and either may help a little.
im thinking water injection with a little methanol mixed in may be the ticket in some cases. especially if gasoline gets any worse.
im thinking water injection with a little methanol mixed in may be the ticket in some cases. especially if gasoline gets any worse.
Drifting
Joined: Oct 2005
Posts: 1,615
Likes: 150
From: Forth Worth TX
Still not enough info on the timing.
What is idle timing with vacuum advance disconnected?
What is full mechanical advance timing and at what rpm does it reach its peak?
What vacuum advance can are you running?
If and only if your timing happens to be perfect, you may be having a carb/vacuum leak issue. But you really need to get the timing perfect before troubleshooting all over the place.
What is idle timing with vacuum advance disconnected?
What is full mechanical advance timing and at what rpm does it reach its peak?
What vacuum advance can are you running?
If and only if your timing happens to be perfect, you may be having a carb/vacuum leak issue. But you really need to get the timing perfect before troubleshooting all over the place.
Last edited by Revi; Jun 24, 2014 at 02:03 PM.
Thread Starter
Intermediate
Joined: Nov 2013
Posts: 30
Likes: 0
From: East Meadow NY
Still not enough info on the timing.
What is idle timing with vacuum advance disconnected?
What is full mechanical advance timing and at what rpm does it reach its peak?
What vacuum advance can are you running?
If and only if your timing happens to be perfect, you may be having a carb/vacuum leak issue. But you really need to get the timing perfect before troubleshooting all over the place.
What is idle timing with vacuum advance disconnected?
What is full mechanical advance timing and at what rpm does it reach its peak?
What vacuum advance can are you running?
If and only if your timing happens to be perfect, you may be having a carb/vacuum leak issue. But you really need to get the timing perfect before troubleshooting all over the place.
Drifting
Joined: Oct 2005
Posts: 1,615
Likes: 150
From: Forth Worth TX
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Thread Starter
Intermediate
Joined: Nov 2013
Posts: 30
Likes: 0
From: East Meadow NY
Thanks again Revi - I can cut the sh#t out of crown molding, frame a house and build an exchange server from scratch - but when it comes to cars, I'm pretty much useless. lol
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
I agree with Casey Jones. Run a trickle of water down the carb while revving it. The motor must be hot!!!
It's rare that carbon will build up enough to cause problems but it does happen.
Back to the timing issue. If you have a good hotrod shop around, they'll usually have a machine to set the advance curve up on your distributor.
But backing off the timing 2 or 3 degrees may solve the problem or a good tank of gas
It's rare that carbon will build up enough to cause problems but it does happen.
Back to the timing issue. If you have a good hotrod shop around, they'll usually have a machine to set the advance curve up on your distributor.
But backing off the timing 2 or 3 degrees may solve the problem or a good tank of gas
Burning Brakes
Joined: May 2014
Posts: 1,094
Likes: 16
From: Los Angeles California
Yeah sounds like sea foam to me. I used it on my moms, dads, brothers and wifes cars no problem but you don't just pour it in you spray it in or pour lightly. A bunch of smoke will come out of tail pipe you hop on freeway for til smoke dies down (10 min) and head back home a lot of guys in smog class did it to clean up emissions #'s the older fellas said water is better like steam cleaning youor engine always wanted to try it but seafoam seemed safe. And I had a problem with my car dieseling or backfiring and all I did was change from 87 cheap gas to 91 octane from top 3 gas stations made the difference.
Racer
Joined: Feb 2002
Posts: 378
Likes: 19
Altering the vacuum advance curve may solve the problem to the point that you could return the initial advance to as spec, which I guess is something like 10-12 degrees btdc. The problem is that no-one owns a Sun distribuator machine or they own one and don't know how to use it. When I had my motor rebuild for my daily driver, I used Robert Davis at 901-412-4414. Unforntunately he's in TN. But, he may be able to set up your distr.
Another thing to keep in mind is that if your valve stem seals are shot, allowing oil to get sucked into the combustion chambers, that will aggravate the carbon build-up problem leading to detonation problems. As such, have the mechanic pull the plugs to check for the presence of oil in the cylinders, especially #7 and 8.
Another thing to keep in mind is that if your valve stem seals are shot, allowing oil to get sucked into the combustion chambers, that will aggravate the carbon build-up problem leading to detonation problems. As such, have the mechanic pull the plugs to check for the presence of oil in the cylinders, especially #7 and 8.
Le Mans Master
Joined: Oct 2010
Posts: 6,937
Likes: 848
From: melbourne florida
2023 C3 of the Year Finalist - Modified
http://www.nelsonspecialties.com/nel..._draft_001.htm
nelson has been in business for decades , builds systems for NASCAR.and an electrical genius. if anyone can set up your distributor he is the guy.
nelson has been in business for decades , builds systems for NASCAR.and an electrical genius. if anyone can set up your distributor he is the guy.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
SeaFoam can help clear out carbon problems in the combustion chamber (if that's really the problem). Best way to use a can is to fill up your gas tank, then pour 1/2 of the can of SeaFoam into the tank.
With the engine warmed up fully and idling (make sure the exhaust pipes are NOT aimed at anything meaningful [ie, light colored garage door
], pull the hose off the dizzy advance can and stick it down to the bottom of the remaining 1/2 can of SeaFoam. Rev engine to 2K rpm (or so) and let it suck that stuff into the intake. Billows of white smoke....interspersed with lots of black, sooty carbon bits...will shoot out the exhaust. Essentially, what it does is steam-clean the combustion chambers with the water/solvent in the SeaFoam and the heat/impact of combustion.
I use it about once a year in my cars (new and old) and it seems to work as intended. The local police garage crew swears by it. I know lots of folks say that it's "snake oil". But, somehow, I doubt that any of them have actually used it.
With the engine warmed up fully and idling (make sure the exhaust pipes are NOT aimed at anything meaningful [ie, light colored garage door
], pull the hose off the dizzy advance can and stick it down to the bottom of the remaining 1/2 can of SeaFoam. Rev engine to 2K rpm (or so) and let it suck that stuff into the intake. Billows of white smoke....interspersed with lots of black, sooty carbon bits...will shoot out the exhaust. Essentially, what it does is steam-clean the combustion chambers with the water/solvent in the SeaFoam and the heat/impact of combustion.I use it about once a year in my cars (new and old) and it seems to work as intended. The local police garage crew swears by it. I know lots of folks say that it's "snake oil". But, somehow, I doubt that any of them have actually used it.
Racer
Joined: Feb 2002
Posts: 378
Likes: 19
I've notice the Lars just posted about tach drive distr problems, he should also be able to help out with setting up your ignition curve, if after getting your combustion chambers, tops of the pistons cleaned up as 7T1vette posted, and there is still a pinging/detonation problem.
Limping across the line
Joined: Oct 2002
Posts: 5,299
Likes: 109
From: Peoria Az
Another tip since you're running such high compression for todays fuel. Drop you spark plug heat range down by 1 or 2.
My Olds 455 with used to ping a bit with AC45's in it I've dropped down to AC43's and the ping and dieseling was eliminated with no loss of performance
My Olds 455 with used to ping a bit with AC45's in it I've dropped down to AC43's and the ping and dieseling was eliminated with no loss of performance