Help!!! big power loss under load
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Help!!! big power loss under load
Hello,
I have a '78 F250 4X4 with the C6. My engine caught on fire a couple months ago, so I got a new carb from national carberator, and new distributer/cap/rotor/wires from NAPA. After I got it put back together, I developed a nasty rod knock and dropped in a 400 CID rebuilt block. So now almost everything under the hood is new, but my truck does not run that well. When ever I step on the gas when I am on a hill, it sputters and has even stalled out. It tends to want to give small back fires when I step on the gas. The funny thing is that when it is in park it runs great. Any ideas?
I was thinking maybe my carb was under-jetted, I had a 351M engine before, the jets in it are 57s, im at 5000 ft elevation,
The distributer does advance the timing when I suck on the air line,
I have gone through 2 cans of choke cleaner looking for air leaks and found none,
Brand new spark plugs,
I was thinking it may be a fuel line or filter, but I dont understand why that would give me problems at low RPM (but I am not sure. Is there any other filters besides the one on the carb)?
Thanks in advance for any help!!!
Jon
I have a '78 F250 4X4 with the C6. My engine caught on fire a couple months ago, so I got a new carb from national carberator, and new distributer/cap/rotor/wires from NAPA. After I got it put back together, I developed a nasty rod knock and dropped in a 400 CID rebuilt block. So now almost everything under the hood is new, but my truck does not run that well. When ever I step on the gas when I am on a hill, it sputters and has even stalled out. It tends to want to give small back fires when I step on the gas. The funny thing is that when it is in park it runs great. Any ideas?
I was thinking maybe my carb was under-jetted, I had a 351M engine before, the jets in it are 57s, im at 5000 ft elevation,
The distributer does advance the timing when I suck on the air line,
I have gone through 2 cans of choke cleaner looking for air leaks and found none,
Brand new spark plugs,
I was thinking it may be a fuel line or filter, but I dont understand why that would give me problems at low RPM (but I am not sure. Is there any other filters besides the one on the carb)?
Thanks in advance for any help!!!
Jon
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Joined: Jul 2001
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From: Warrenton, VA
From what's been described, it really sounds like the timing is off. I would verify timing. Also, what about the possibility of having a couple plug wires cross. If you 1 on each bank crossed, it can still idle smooth and run ok while not under load, but it would be running on 6 instead of 8-I have seen that before.
Check the accel. pump on the carb, proper fuel volume, fuel filter, and I would definately tune the carb for the bigger engine. But I'd get ya a nice 4-bbl carb, unless you've already got one.
Let me know how it turns out
Check the accel. pump on the carb, proper fuel volume, fuel filter, and I would definately tune the carb for the bigger engine. But I'd get ya a nice 4-bbl carb, unless you've already got one.
Let me know how it turns out
Last edited by WrenchHead84; Feb 1, 2006 at 07:18 PM.
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dont know about the fuel filters but i got the fireing order
1-3-7-2-6-5-4-8
dizzy spins CCW
#1 is the one twords the front of the rear clip on the cap.
1-3-7-2-6-5-4-8
dizzy spins CCW
#1 is the one twords the front of the rear clip on the cap.
Last edited by 76 F-150 390FE; Feb 1, 2006 at 08:14 PM.
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Is this engine a hi-miler with a worn out timing chain and gears ?
Is the distributor worn out ?
There is only the one filter in the line at the carb.
The pickup tube in the fuel tank however has a special material that can clog from debris in the tank.
Is the distributor worn out ?
There is only the one filter in the line at the carb.
The pickup tube in the fuel tank however has a special material that can clog from debris in the tank.
Last edited by Mil1ion; Feb 1, 2006 at 09:50 PM.
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The engine is a rebuild, less then 200 miles on the timing chain and gears. The distributer is also a recent reman. I have factory dual tanks, and I get the same problem with both tanks, so I doubt it is the material in the tank.
If I was having fuel delivery issues, wouldn't that show up at high RPMs more then low RPMs?
If I was having fuel delivery issues, wouldn't that show up at high RPMs more then low RPMs?
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Fleet Owner
Joined: Sep 2005
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From: Lake Tahoe, Nevada
If it's backfiring through the carb, it can also indicate a lean condition. Backfire through the exhaust can be a rich condition. Either one can be agrevated by incorrect timing or incorrect firing order.
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