Valve Lash or Timing???
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Joined: Apr 2008
Posts: 91
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From: Stockton California
Valve Lash or Timing???
OK, so I just installed them long tube headers we were all talking about and I set my valve lash about 2 weeks before hand, along with my timing (36 degrees).
Today I changed wires, plugs and belts.
Went out to burn some fuel and noticed upon deceleration after WOT, or damn near it anyways, my exhaust makes some really loud popping noises (and not the ones I'm used to hearing).
On top of that, when I got home I let it idle for a minute or two to check for clattering of my valves. When I shut her off the engine diesels and spits out some exhaust from the carb
I am wondering as to what is causing this... Is it bad valve lash? Timing?
Thanks in advance for the help.
Today I changed wires, plugs and belts.
Went out to burn some fuel and noticed upon deceleration after WOT, or damn near it anyways, my exhaust makes some really loud popping noises (and not the ones I'm used to hearing).
On top of that, when I got home I let it idle for a minute or two to check for clattering of my valves. When I shut her off the engine diesels and spits out some exhaust from the carb
I am wondering as to what is causing this... Is it bad valve lash? Timing?
Thanks in advance for the help.
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
A few ideas.
New headers often require rejetting and adjustment of the idle mixture. The headers allow more air through the engine and if you don't compensate with more fuel, you go lean. Popping on decel is a sign of a lean condition. Adjusting your mixture will likely solve this, but I would further investigate the need for re-jetting.
This week I learned that retarded ign. timing will cause dieseling. While trying to get my timing set up on my initial start after rebuild, I found that that dieseling got less and less as I bumped up the advance. I also got backfiring in the carb while retarded.
Good luck.
New headers often require rejetting and adjustment of the idle mixture. The headers allow more air through the engine and if you don't compensate with more fuel, you go lean. Popping on decel is a sign of a lean condition. Adjusting your mixture will likely solve this, but I would further investigate the need for re-jetting.
This week I learned that retarded ign. timing will cause dieseling. While trying to get my timing set up on my initial start after rebuild, I found that that dieseling got less and less as I bumped up the advance. I also got backfiring in the carb while retarded.
Good luck.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Your problem sounds like a classic case of not using full manifold vacuum to the vacuum advance canister on the distributor. You do have vacuum advance, right?
Another thing that can cause popping on deceleration is spark plugs too short for the heads. If you have heads (Vortecs as an example, or aftermarket), they may require a threaded 3/4 inch reach plug. If the plug is the older short reach, there will be a problem during high vacuum conditions such as deceleration.
IMO, I'm less sanguine about the header and mixture explanation - just tune your idle mixture adjustment screws for maximum vacuum and you'll be good.
Thread Starter
Advanced
Joined: Apr 2008
Posts: 91
Likes: 0
From: Stockton California
Your problem sounds like a classic case of not using full manifold vacuum to the vacuum advance canister on the distributor. You do have vacuum advance, right?
Another thing that can cause popping on deceleration is spark plugs too short for the heads. If you have heads (Vortecs as an example, or aftermarket), they may require a threaded 3/4 inch reach plug. If the plug is the older short reach, there will be a problem during high vacuum conditions such as deceleration.
IMO, I'm less sanguine about the header and mixture explanation - just tune your idle mixture adjustment screws for maximum vacuum and you'll be good.
And how do I go about that???
Sorry, scared of carburetors.
