390 Backfires
Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
Missing and stumbling can be signs of running rich, and edelbrock carbs are prone to running pig-rich on a Ford with the mechanical fuel pump. The carb does not like more than 5.5-6 PSI fuel supply, while the pump tends to output 7-8 PSI. This causes it to have fuel "leak" past the needle/seat assemblies, therefore run overly rich.
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Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
Missing and stumbling can be signs of running rich, and edelbrock carbs are prone to running pig-rich on a Ford with the mechanical fuel pump. The carb does not like more than 5.5-6 PSI fuel supply, while the pump tends to output 7-8 PSI. This causes it to have fuel "leak" past the needle/seat assemblies, therefore run overly rich.
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Joined: Jul 2011
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Missing
Junior User
Joined: Jul 2011
Posts: 80
Likes: 0
fe misses
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Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
I have done a number of things to the engine, since the initial post. Replaced timing chain with double roller. New glasspacks (blew out old muffler because of bad timing chain). Replaced old 2bbl intake with Performer RPM and Performer 600 cfm carb. Blocked off exhaust crossovers at head. Used right stuff to set intake manifold. No oil or vacuum leaks that I can find. Set timing @ 12 deg with total advance around 38 deg. Truck ran great initially, then started missing and stumbling while driving. Finally got around to a compression test. #1 - 135, #2 - 130, #3 - 125, #4 - 138, #5 - 128, #6 - 140, #7 - 130, #8 - 130. Any suggestions before I start tearing things apart again? Thanks.
Kurt
Kurt
Was your comp test wet or dry? doing a wet will tell if weak rings or burnt valve seats..
Also to test for bent push rod is roll them on a flat surface, Replace if bent more then 0.20th.
Orich
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Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
Try running a higher octane of gas. Does your motor have the harden valve seats ?
Was your comp test wet or dry? doing a wet will tell if weak rings or burnt valve seats..
Also to test for bent push rod is roll them on a flat surface, Replace if bent more then 0.20th.
Orich
Was your comp test wet or dry? doing a wet will tell if weak rings or burnt valve seats..
Also to test for bent push rod is roll them on a flat surface, Replace if bent more then 0.20th.
Orich
Kurt
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
If it's starting to cough & spite, backfire out the carb a little while you put your foot into like when passing or going up a grade, then it recovers when you let up on the gas pedal. Plus having low compression is a pretty good sign of valve troubles.
As long as your timing & points or other is set right like Pertronix unit is good plus getting enough voltage to the dizzy all engine grounds are good.
Then this leads to burnt valves.
But it should not have caused a no start issues like when you said it would not restart.
It sound like the Pertronix unit failed.
I ran the Pertronix lll unit fo a while and had no problems with it.
Send it back for testing & repair..
A oil wet test seals the rings and will bump up the comp. about 10 psi and any lost of compression over this is the valves not sealing from your regular engine specs.
Push rods can be turned while their still installed by bumping the engine over a little at a time with the coil wire out. And valve cover off right. Most of the time if bent out of specs to much the lifter will stop turning the start wiping the lobe out and you'll hear it clicking or tapping as there will be a lot more valve lash. Can't miss it.
orich
As long as your timing & points or other is set right like Pertronix unit is good plus getting enough voltage to the dizzy all engine grounds are good.
Then this leads to burnt valves.
But it should not have caused a no start issues like when you said it would not restart.
It sound like the Pertronix unit failed.
I ran the Pertronix lll unit fo a while and had no problems with it.
Send it back for testing & repair..
A oil wet test seals the rings and will bump up the comp. about 10 psi and any lost of compression over this is the valves not sealing from your regular engine specs.
Push rods can be turned while their still installed by bumping the engine over a little at a time with the coil wire out. And valve cover off right. Most of the time if bent out of specs to much the lifter will stop turning the start wiping the lobe out and you'll hear it clicking or tapping as there will be a lot more valve lash. Can't miss it.
orich
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Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
quick update
It's been awhile..... Good thing the truck isn't my daily driver. Removed intake, valvetrain and heads. The lifters, hydraulic, had faint visible wear lines, but nothing that I could feel. The cam, viewed through the lifter bores, looked good too. The engine had no sludge. The pistons are 30 over, so I may be at the limit of the block.
The heads are another matter. The intake valve stems had carbon deposits on the stems. Is this normal? I filled the combustion chambers with gasoline to see what leaks. The passenger side - no leaks. The driver's side - #5 & 6 intake valves leaked some, and the #7 exhaust valve leaked pretty good. I don't know if this is an accurate test, and it doesn't seem to jive with the compression test. The heads are C4AE-6090G.
So, I am still in the diagnostic phase and open to suggestions. Thanks.
The heads are another matter. The intake valve stems had carbon deposits on the stems. Is this normal? I filled the combustion chambers with gasoline to see what leaks. The passenger side - no leaks. The driver's side - #5 & 6 intake valves leaked some, and the #7 exhaust valve leaked pretty good. I don't know if this is an accurate test, and it doesn't seem to jive with the compression test. The heads are C4AE-6090G.
So, I am still in the diagnostic phase and open to suggestions. Thanks.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Bad exh. seats unleaded gas burns then out. you'll need harden seats install.
Mostly valve guilds to complete rebuilt of heads.
You have early heads like 64 tall port runners that don't match a 360 intake manifold or a even a edelbrock intake manifold.
A .030 not big deal with 352/360/390 BLOCKS most will go .060
Loose valve guilds can extra carbon up the valve stems.
Valve closes to the heat riser cross over ports burn the seat first
Orich
Mostly valve guilds to complete rebuilt of heads.
You have early heads like 64 tall port runners that don't match a 360 intake manifold or a even a edelbrock intake manifold.
A .030 not big deal with 352/360/390 BLOCKS most will go .060
Loose valve guilds can extra carbon up the valve stems.
Valve closes to the heat riser cross over ports burn the seat first
Orich
Thread Starter
|
Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
Bad exh. seats unleaded gas burns then out. you'll need harden seats install.
Mostly valve guilds to complete rebuilt of heads.
You have early heads like 64 tall port runners that don't match a 360 intake manifold or a even a edelbrock intake manifold.
A .030 not big deal with 352/360/390 BLOCKS most will go .060
Loose valve guilds can extra carbon up the valve stems.
Valve closes to the heat riser cross over ports burn the seat first
Orich
Mostly valve guilds to complete rebuilt of heads.
You have early heads like 64 tall port runners that don't match a 360 intake manifold or a even a edelbrock intake manifold.
A .030 not big deal with 352/360/390 BLOCKS most will go .060
Loose valve guilds can extra carbon up the valve stems.
Valve closes to the heat riser cross over ports burn the seat first
Orich
Are these heads worth the work that you mentioned? I don't see any visible cracks in the combustion chambers. Thanks Orich.