timing adjusted, now noise with acceleration
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Junior User
Joined: Nov 2004
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timing adjusted, now noise with acceleration
I just adjusted the timing on my truck- 1971 sport custom, f100, 360 with autolite 2100 2 B carb, 4 speed granny. Now the truck idles great but makes a noise when I accelerate. Sort of a low pitched rattling sound from the from the engine. Is this something I did?
I recently rebuilt the carb and the truck idled poorly. I had a hard time adjusting the idle fuel mixture screws, but finally i used a vacuum gauge hooked to the manifold and got it so that it was rock steady at 20.
I then adjusted the timing . I didn't use a timing light..i used the "bubba" method..advancing the timing until it started to sputter and then backed off a bit. I did have a vacuum gauge attached during this and when i finished it was rock steady at 20. I also was then able to lower the curb idle speed way down like i was supposed too...to 650 rpm. Anyway, now it idles great but makes this noise on acceleration. Is is something I did? Is there something else I need to do?
I recently rebuilt the carb and the truck idled poorly. I had a hard time adjusting the idle fuel mixture screws, but finally i used a vacuum gauge hooked to the manifold and got it so that it was rock steady at 20.
I then adjusted the timing . I didn't use a timing light..i used the "bubba" method..advancing the timing until it started to sputter and then backed off a bit. I did have a vacuum gauge attached during this and when i finished it was rock steady at 20. I also was then able to lower the curb idle speed way down like i was supposed too...to 650 rpm. Anyway, now it idles great but makes this noise on acceleration. Is is something I did? Is there something else I need to do?
Logistics Pro
Joined: Jun 2003
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That's "ping" or pre-ignition knock. It's not good for an engine to ping. Your timing is too high. I suggest you get a timing light and set it to spec.
With the vacuum advance line disconnected and plugged, set the base timing at 6-8 degrees. Readjust idle and check timing again. If the timing needs another adjustment, reset the idle.
To adjust the carb mixture, you will need the vacuum gauge hooked up to manifold vacuum. With the engine off turn each mixture screw in until it bottoms and then turn each out 1 1/2 turns. This is a good place to start.
Each screw adjustment must closely reflect the other.
Start the engine. Going about 1/2 turn at a time, adjust each mixture screw in and out, while keeping an eye on the vac. gauge until the vacuum reaches a maximum steady point.
This will get you as close as possible without a smog sniffer.
With the vacuum advance line disconnected and plugged, set the base timing at 6-8 degrees. Readjust idle and check timing again. If the timing needs another adjustment, reset the idle.
To adjust the carb mixture, you will need the vacuum gauge hooked up to manifold vacuum. With the engine off turn each mixture screw in until it bottoms and then turn each out 1 1/2 turns. This is a good place to start.
Each screw adjustment must closely reflect the other.
Start the engine. Going about 1/2 turn at a time, adjust each mixture screw in and out, while keeping an eye on the vac. gauge until the vacuum reaches a maximum steady point.
This will get you as close as possible without a smog sniffer.
Postmaster
Joined: Apr 2002
Posts: 3,613
Likes: 6
From: Coal country
If it sounds like marbles rolling around in a can, that is pinging, or detonation.
It is caused by over-advanced timing, mixture too lean, or too low grade fuel for the compression ratio of the engine. Since you have a 360, compression is definitely not a problem.
I would back your timing off a few degrees at a time, until it disappears, but by no more than 4 degrees.
If that doesn't fix it, I would increase the idle mixture a bit. You will probably have to increase the idle speed at the idle screw just a bit as well.
One important point to check: is your distributor vacuum hose connected to ported or manifld vacuum? It is supposed to be connected to ported, not manifold vacuum. If you made your adjustments with the hose connected to manifold, then you definitely have over advanced timing.
It is caused by over-advanced timing, mixture too lean, or too low grade fuel for the compression ratio of the engine. Since you have a 360, compression is definitely not a problem.
I would back your timing off a few degrees at a time, until it disappears, but by no more than 4 degrees.
If that doesn't fix it, I would increase the idle mixture a bit. You will probably have to increase the idle speed at the idle screw just a bit as well.
One important point to check: is your distributor vacuum hose connected to ported or manifld vacuum? It is supposed to be connected to ported, not manifold vacuum. If you made your adjustments with the hose connected to manifold, then you definitely have over advanced timing.
Junior User
Joined: Jul 2006
Posts: 53
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From: Swift Current, Sask
I have the exact same problem with my 390. My timing is set to 4 degrees and still when I accelerate on the highway it pings. If anything my mixture is too rich and I tries octane boost and it seemed to improve it a little, could premium be the answer?
Logistics Pro
Joined: Jun 2003
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On my 390 I have my vacuum diaphram on my distributor plugged and my initial timing set at 16 degrees with a total advance of about 38 degrees. It has been like that for 20 years. I have an Edelbrock manifold and an AFB carb. My truck has never pinged. It has been 105 degrees lately and even in traffic my truck does not ping. It doesn't ping when I mash on it either.
Junior User
Joined: Jul 2006
Posts: 53
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From: Swift Current, Sask
OK, I put in premium with octane boost, changed the cap and rotor today and it got a little better again but still noticable. It only seems to do it if I'm doing around 60mph and floor it.
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Junior User
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Thanks You Guys !!!!
Today I went and bought the cheapest timing light I could find and then followed the advice from you all.
I set the timing to 6 BDTC and then sped up the idle a little bit to get to 650 RPM. Man o man what a difference!!! The trucks runs beautifully...such a smooth,quiet idle that you have to check to see if its still running a stop light. Great acceleration with no pinging. At a stop light i floored it and then blew past some guy in a late 90s chevy..heehee you should've seen the look on his face! Didn't think the old girl had it in her.
Anyway, thanks a lot. I should've come here first instead of losing all that time with the truck beforehand....
andrew
Today I went and bought the cheapest timing light I could find and then followed the advice from you all.
I set the timing to 6 BDTC and then sped up the idle a little bit to get to 650 RPM. Man o man what a difference!!! The trucks runs beautifully...such a smooth,quiet idle that you have to check to see if its still running a stop light. Great acceleration with no pinging. At a stop light i floored it and then blew past some guy in a late 90s chevy..heehee you should've seen the look on his face! Didn't think the old girl had it in her.
Anyway, thanks a lot. I should've come here first instead of losing all that time with the truck beforehand....
andrew
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