problem with engine
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Elder User
Joined: Jul 2002
Posts: 526
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From: USA
problem with engine
just got my truck running the best it has run since i have owned it. well this past weekend it started running odd. it idles fine, but when i rev it, it starts to vibrate and seems like it doesnt have any power, i dont want to try to rev it hard for fear that i might break something. does anyone have any ideas? its a 460 with a new holley 4160 carb.
1977 F250 460
C6 Hedman Headers
Dual 40 series
edelbrock performer
holley 4160
msd 6a and blaster coil
1977 F250 460
C6 Hedman Headers
Dual 40 series
edelbrock performer
holley 4160
msd 6a and blaster coil
Moderator
Joined: Dec 2001
Posts: 22,436
Likes: 17
From: Louisville,Ky.
problem with engine
May have a piece of dirt in a main jet in the carb, causing a lean condition in an off idle situation.
Pull the spark plugs and see how they look. White? too lean.
Black? too rich. Oily? bad oil control.
Pull the spark plugs and see how they look. White? too lean.
Black? too rich. Oily? bad oil control.
Posting Guru
Joined: Jan 2000
Posts: 1,899
Likes: 1
From: Cullman Alabama
problem with engine
[updated:LAST EDITED ON 17-Oct-02 AT 01:30 PM (EST)]
Are you ready for some trouble-shooting tips?
Get a good timing light and check for some of the things that might have been changed before they replaced the Carb.
You are probably having more trouble with the Ignition setup that you are with that carb.
Put the light on, and watch as you increase the RPM. At first you should get a little jump of timing increase. Then it should settle out and be stable, then as the RPM goes up past 2000 you should see the Timing increase toward the Max. I dont know what the max is, but the timing should not be jumping around! You could have trouble in the Cap and wires. Plugs too, but it could also be in the Ign modules. The part on the fender and the pickup head in the Dist.
A burned valve can cause the Vacuam to jump around as well. So you have to do a compression test to make sure you have a good platform to do your troubleshooting. Get the engine warm for this test and have some extra plugs handy. I manage to break one or two duiring this exercize.
Is the Vacuam routing correct? The Dist Advance is supposed to be connected to the Reduced port. I think it's the port on the Passenger side of the Carb. Find a model that's working and copy it! Then make a map and keep it handy.
What was the problem that led to replacing the Carb?
That's an expensive carb! Is it new or rebuilt?
If you suspect a plugged jet, look at the plugs.
The jets feed the center cylinders on one head and the End cylinders on the other head. The jet feeds the center cylinders nearest the side of the carb.
So...If all the plugs are lean(not likely) your just not getting enough fuel.
If the plugs are good on the end cylinders and dry in the middle two cylinders, that's indicating a plugged jet. It dont matter which jet, you have to pull the top off the carb to clean them. That bowl should be perfectly clean! Make sure of that..Suck the stuff out with your hand vacuam.
In reality, a plugged jet should never occur in an existing system. Only in a system someone's broken open, and some dirt got in during the re-assembly.
I had one in a boat and the Fuel line was corroding, putting little grains of reddinsh looking sand in my carb. How that stuff got through the filter was a mystery, but it did.
So get into troublesooting mode and then let us know what's happening.
Are you ready for some trouble-shooting tips?Get a good timing light and check for some of the things that might have been changed before they replaced the Carb.
You are probably having more trouble with the Ignition setup that you are with that carb.
Put the light on, and watch as you increase the RPM. At first you should get a little jump of timing increase. Then it should settle out and be stable, then as the RPM goes up past 2000 you should see the Timing increase toward the Max. I dont know what the max is, but the timing should not be jumping around! You could have trouble in the Cap and wires. Plugs too, but it could also be in the Ign modules. The part on the fender and the pickup head in the Dist.
A burned valve can cause the Vacuam to jump around as well. So you have to do a compression test to make sure you have a good platform to do your troubleshooting. Get the engine warm for this test and have some extra plugs handy. I manage to break one or two duiring this exercize.
Is the Vacuam routing correct? The Dist Advance is supposed to be connected to the Reduced port. I think it's the port on the Passenger side of the Carb. Find a model that's working and copy it! Then make a map and keep it handy.
What was the problem that led to replacing the Carb?
That's an expensive carb! Is it new or rebuilt?
If you suspect a plugged jet, look at the plugs.
The jets feed the center cylinders on one head and the End cylinders on the other head. The jet feeds the center cylinders nearest the side of the carb.
So...If all the plugs are lean(not likely) your just not getting enough fuel.
If the plugs are good on the end cylinders and dry in the middle two cylinders, that's indicating a plugged jet. It dont matter which jet, you have to pull the top off the carb to clean them. That bowl should be perfectly clean! Make sure of that..Suck the stuff out with your hand vacuam.
In reality, a plugged jet should never occur in an existing system. Only in a system someone's broken open, and some dirt got in during the re-assembly.
I had one in a boat and the Fuel line was corroding, putting little grains of reddinsh looking sand in my carb. How that stuff got through the filter was a mystery, but it did.
So get into troublesooting mode and then let us know what's happening.
