390 backfire through carb
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New User
Joined: Jun 2005
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390 backfire through carb
OK Guys. My 390 has less than 10,000 miles on it. This is a recurring problem that is driving me crazy. First, I have a metallic ting sound on the passenger side. Does it mostly on start-up. Most importantly, If I romp on the gas, I get a loud pop from under the hood. Sounds like a back fire or cough from the carb. Occasionally, with the engine in drive, I get a miss at irregular intervals. This is what I have done so far. New 4160 carb. New coil, wires and rotor. Timing at 10btdc. New distributor. Idle in drive is @700rpm. Any thoughts / suggestions? Engine is stock btw. Intake manifold not sealed? Head gasket bad? I am at your mercy.
Elder User
Joined: Jan 2004
Posts: 867
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From: Eastern Pa
Does the carb have the anti power valve blow out protection? If not one backfire could waste the power valve. Check for any vacuum leaks. Use some choke spray around all sealing surfaces, vacuum hoses and plugs etc. If the idle goes up when your doing it you've fouind a leak. Recheck your timing throuigh the acceleration range to see if its really wacked, it could indicate a timing chain problem.
Junior User
Joined: Feb 2006
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Retard timing and increase by ear. ie, retard time, drive and
throttle the engine, increase advance until no ping,
then retard 1-3 degrees advance.
You may have other problems with this engine that need addressing.
Thx, Rog.
throttle the engine, increase advance until no ping,
then retard 1-3 degrees advance.
You may have other problems with this engine that need addressing.
Thx, Rog.
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Fleet Mechanic
Joined: Nov 2004
Posts: 1,857
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From: Northern CA
Engine could be running too lean. Ping usually happens when timing is too far advanced. 10 deg BTDC should be ok. On the sides of the carb are 2 small screws. (one on each side) Turn screws, one at a time, clockwise until engine begins to sputter. Then back out the screw about 1/2 turn or so until the idling smooths out. Both should be backed out about the same amount. Then reset idle. If under hard deceleration you get backfire, it still may be too lean.
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Junior User
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bryyce62,
hey is the motorcraft 2V carb worth keeping, it runs good on my 3602V4SPD.
It hesitates a bit/fair cold ingnition bahavior.
From what i understand the Holley 2800 (500 cfm) works better. Given the formula CID X RPM / 3450, at 360X4000/3450=417CFM.
This engine wont see more than
4500/5000 RPM. It runs good, has an RV cam,
(dont know the grind), not balanced for high RPM. (above 5000).
Would like more towing power.
Thx, see my new thread, Motorcraft-vs-Holley 2800 (500 CFM).
Rog, jarmeister@msn.com.
hey is the motorcraft 2V carb worth keeping, it runs good on my 3602V4SPD.
It hesitates a bit/fair cold ingnition bahavior.
From what i understand the Holley 2800 (500 cfm) works better. Given the formula CID X RPM / 3450, at 360X4000/3450=417CFM.
This engine wont see more than
4500/5000 RPM. It runs good, has an RV cam,
(dont know the grind), not balanced for high RPM. (above 5000).
Would like more towing power.
Thx, see my new thread, Motorcraft-vs-Holley 2800 (500 CFM).
Rog, jarmeister@msn.com.
Fleet Owner
Joined: Sep 2005
Posts: 28,609
Likes: 18
From: Lake Tahoe, Nevada
Could be a tight intake valve, vacuum leak (lean condition,) timing overadvanced, spark plug too hot (heat range,) but most likely a combination of two or more of the above.
If this has been going on since the rebuild, you might do well to check all you valve clearances.
If this has been going on since the rebuild, you might do well to check all you valve clearances.
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New User
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Thanks guys, I'll start checking everything you all pointed out. I noticed that it pops from the carb if I am at low speeds or at a dead stop and mash the pedal like I'm trying to roast the tires. It hasn't missed since I put the new coil on it. How do I check to see if my valves are too tight or for bent push rods. If I find a bent rod, what length do I go with since the engine is still relatively new?
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Originally Posted by jarmeister
bryyce62,
hey is the motorcraft 2V carb worth keeping, it runs good on my 3602V4SPD.
It hesitates a bit/fair cold ingnition bahavior.
From what i understand the Holley 2800 (500 cfm) works better. Given the formula CID X RPM / 3450, at 360X4000/3450=417CFM.
This engine wont see more than
4500/5000 RPM. It runs good, has an RV cam,
(dont know the grind), not balanced for high RPM. (above 5000).
Would like more towing power.
Thx, see my new thread, Motorcraft-vs-Holley 2800 (500 CFM).
Rog, jarmeister@msn.com.
hey is the motorcraft 2V carb worth keeping, it runs good on my 3602V4SPD.
It hesitates a bit/fair cold ingnition bahavior.
From what i understand the Holley 2800 (500 cfm) works better. Given the formula CID X RPM / 3450, at 360X4000/3450=417CFM.
This engine wont see more than
4500/5000 RPM. It runs good, has an RV cam,
(dont know the grind), not balanced for high RPM. (above 5000).
Would like more towing power.
Thx, see my new thread, Motorcraft-vs-Holley 2800 (500 CFM).
Rog, jarmeister@msn.com.
A 500 CFM 2 barrel is a preformance carb and never worked well for me on my 360s. A 500CFM 2 barrel is a 2300 series carb.
Fleet Owner
Joined: Sep 2005
Posts: 28,609
Likes: 18
From: Lake Tahoe, Nevada
Originally Posted by albcasummit
How do I check to see if my valves are too tight or for bent push rods. If I find a bent rod, what length do I go with since the engine is still relatively new?
If you need pushrods (which I doubt,) go to whoever put the engine together.
I don't know if there is a valve clearance spec for your engine. But you should be able to feel a little play with each piston at the top of it's compression stroke.