I have a 350 in a 56 Chev I purchased and I cannot get rid of a random light throttle pinging. 2nd gear is always when it pings, ??? and to add to the issue when it is manually in 2nd gear (TH400 Auto) it is much more frequent than if it is in Drive. Can the Modulator have anything to do with these symptoms? (No loss of Tranny Fluid) I have the base timing backed down to only 5 degrees and though that helped it a bit it did not cure it. I do not have any info on compression, cam, etc. so I realize I am not helping much with the info I am providing. The modulator function when manually in 2nd gear makes me think there might be an issue there, but I am not a Automatic Tech. Any thoughts or tips would be greatly appreciated! Fedman
NOTHING to do with the transmission. I'd experiment with the vacuum advance. The vacuum can be connected to ported, non-ported (ports above or below the throttle blades), even no vacuum advance (what I normally do). I'd also modify (light springs, different weights) the mechanical advance to be all in by 1600/1800 rpm. That will get rid of that possibility. Is the trans. vacuum pulled off of a full time port. Should be in the manifold, not the carburetor. Mike
I have changed Vacuum Cans, installed an adjustable one. I have tried both ported and non-ported, and even no vacuum advance. I have messed with the spring combo on the mechanical advance. The Trans Vacuum is hooked to the rear of the base of the front carb (2 Edelbocks) rear Carb is the primary unit. It is Random, does not do it all the time, worse when cold, no chokes on Carbs Thanks for the input!
I also ran water down the carb while running it in case I was getting Carbon Hot Spots, Made no difference at all.
Doesn't sound like pinging then. 5 deg. initial, no vac. advance, heavy springs..Still pinging..when cold? Have you checked TDC? As an experiment, when the tank gets low, throw in a couple of gallons of race fuel.
No, I have not checked TDC. I was going to take engine out and go through it so I know what I have. We are selling our House now and are going to be building a new one. I was hoping that I could sort this out before I put the Car in storage. Again thanks for the input.
Thanks for all the replies, I should have posted this much earlier and let the great resource of the HAMB steer me in the right direction. BOBKATRODS was on the right trail with it being lean. Like I said I did not build this Engine so it is kind of a mystery as far as parts and workmanship go, I tightened the carb studs but then I put a wrench on the intake manifold bolts..... 1/2 to 3/4 of a turn on all of them and that appears to be the culprit. It will need the intake gaskets replaced but I was able to add back timing and no more ping. Thanks again for all the replies and suggestions, it is truly appreciated! Brian
Yes, would it not be great if everyone came back to "finish" the thread, so many times you are just left wondering. Not only that, but it helps the next HAMBer that runs into the same issue.
Hello, I am also in BJR's camp about the use of premium gas. It might be as simple as changing to a higher octane level, plus gas additives if necessary. Our 2nd El Camino was loaded with the factory emissions crap and the gas crisis was in full swing. Trying to be thrifty at the time, we used regular gas. Sometimes, our 350 SBC ran well and then the low rpm throttle at acceleration made the pinging sound. A lot of our neighbors had the same issue with those new 350 SBC motors. The local expert, Chevy mechanic was stumped even after a full on timing/tune up and parts replacements. His thing was the emissions crap from the factory did a number on our motors. He even tried an octane booster, but the cheap gas still kept pinging. Jnaki We solved the problem with not one grade of gas up, but all the way to the top gas available with the highest octane rating. We kept filling the tank until all of the cheap/low octane gas was gone. The cost was much higher, but the pinging sound and the continuous running after the ignition was turned off was also gone... We have been premium gas users on all of our vehicles ever since, even though we could use regular. The costs are negligible, for a few cents difference. Moot point...Since we are a big chain grocery store gas points members, we get $.20 off of every gallon anyway...
My 86 c10 with a 305 always had a light throttle ping no matter timing on 87 or 89 octane. Its fine on 93 or ethanol free 89. Never thought about the intake gaskets. My motor has 193k and that is a real possibility
I had a similar thing happen a couple of years ago. The car started missing on one cylinder at low throttle all the time. Then it started leaving a little anti-freeze puddle on the floor every morning. I thought I blew a head gasket after a hard run, thinking it must have been leaking anti-freeze into the cylinder too, because the plug was washed clean. Then I noticed it was leaking out of the back of the intake manifold and running down around the back of the head and dripping off by the dip stick. So, I checked the intake bolts and they were loose! I tightened them up 1/2 to 3/4 turns and it stopped! I thought sure I was going to have to pull the heads and fix it, but I didn't. Still running good today!
I am glad it was an easy fix for you! The type of Engine I am sure makes a Big difference in how the Intake Gasket see's the Weight and Load of the intake. I had a 56 Buick 322" Nailhead that used Solid Steel Shim Style Gaskets and the torque would not changed at all after a fresh install. The S.B. Chev with "angle" between the intake and the cylinder head seems to pull the intake across the gasket as you tighten it, if that make sense in how I an trying to explain it. When we ran our Dragster, again a S.B.Chev with the 6-71 Super Charger, the Weight of Blower coupled with the pull of the drive belt would compress the new gaskets a surprising amount! Multiple Re-Torques were required before the Gasket took a set. I chased my tail on this for more than I care to admit, only to learn a lesson I had learned many times before already. Is this not what makes our Hobby so "Enjoyable" ?
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