Timing - runs like junk!
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From: Buffalo
Timing - runs like junk!
Just finished a complete tune-up on this 302 and it's definitely driving better (before, in 3rd gear it had little to no acceleration), but it still feels like it's lacking some power so I want to check the timing.
In the past, I've marked the balancer (in this case at 8 degrees as per emissions decal), plugged the vacuum line and start the engine and proceed to time as usual. In this case, I did all of that and when I started the engine it ran like absolute junk and at such a low RPM, I don't even know how it stayed running. So I shut it down and tried again, same thing, except this time it wouldn't stay running. I put the vacuum line back on and tried to start it but now it won't start. Acting like it's flooded. I let it sit for ten minutes or so, went back, tried to start it and finally got it running. Had to feather the gas to keep it running and finally it ran on it's own.
So what the heck happened with the vacuum line capped off? Why were the RPMs so low? And could have really been running that rich with the line capped off that it flooded the engine? How do I proceed, do I advance the timing with the advance hooked up, then disconnect it?
In the past, I've marked the balancer (in this case at 8 degrees as per emissions decal), plugged the vacuum line and start the engine and proceed to time as usual. In this case, I did all of that and when I started the engine it ran like absolute junk and at such a low RPM, I don't even know how it stayed running. So I shut it down and tried again, same thing, except this time it wouldn't stay running. I put the vacuum line back on and tried to start it but now it won't start. Acting like it's flooded. I let it sit for ten minutes or so, went back, tried to start it and finally got it running. Had to feather the gas to keep it running and finally it ran on it's own.
So what the heck happened with the vacuum line capped off? Why were the RPMs so low? And could have really been running that rich with the line capped off that it flooded the engine? How do I proceed, do I advance the timing with the advance hooked up, then disconnect it?
pedant
Joined: Jan 2008
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From: EXTREME southwest CT
Read the emissions/ ignition timing tag on the radiator support or under the hood.
With the engine warmed up to operating temperature...
1) Remove and cap the vacuum line.
2) Set the curb idle speed to whatever the call out is for your vehicle, ie 650 rpm in gear if automatic or 700 in neutral if manual ( check YOUR sticker!)
3) THEN adjust ignition timing to what you need (mind that if you have a performance cam & carb you may not be able to reach stock specs)
4) Reattach the vacuum line and *reset* curb idle speed.
With the engine warmed up to operating temperature...
1) Remove and cap the vacuum line.
2) Set the curb idle speed to whatever the call out is for your vehicle, ie 650 rpm in gear if automatic or 700 in neutral if manual ( check YOUR sticker!)
3) THEN adjust ignition timing to what you need (mind that if you have a performance cam & carb you may not be able to reach stock specs)
4) Reattach the vacuum line and *reset* curb idle speed.
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From: Buffalo
The "running like **** with vacuum advance line plugged" is boggling me because it seems to be running just fine with it connected.
Laughing Gas
Joined: Apr 2013
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Sounds like you have full manifold vacuum to your distributor vacuum advance at idle and your idle speed is tuned accordingly.
When you disconnect the vacuum advance your timing retards (to base timing) and your idle speed drops too low to continue running.
Increase your idle speed a couple hundred RPM then disconnect the vacuum advance. It should then continue to run so you can set your base timing.
Then, once you've set the base timing, reconnect the vac advance and back the idle speed down.
When you disconnect the vacuum advance your timing retards (to base timing) and your idle speed drops too low to continue running.
Increase your idle speed a couple hundred RPM then disconnect the vacuum advance. It should then continue to run so you can set your base timing.
Then, once you've set the base timing, reconnect the vac advance and back the idle speed down.
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From: Buffalo
Ok, this makes sense- but shouldn't I get the correct vacuum routing from a timed vacuum port? Come to think of it, it is full manifold vacuum because the vacuum line is coming right off the port on the back of the intake manifold. I'm thinking technically this is not factory (it was this way when I got the truck). I've always been under the impression that the advance gets its vacuum from a port just above the throttle plates or a ported vacuum switch which can change between ported and manifold vacuum.
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Cargo Master
Joined: Aug 2007
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From: New Zealand
I would apply vacuum to the vacuum advance can, using a pump or your mouth (with the engine off), & see if there is a leak.
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From: Buffalo
You could also have a leak at the vacuum advance diaphram itself, (again, maybe with the idle rpm & idle mixture adjusted to suit)......so when you unhook & plug the vacuum line, your idle drops to the point of stalling.
I would apply vacuum to the vacuum advance can, using a pump or your mouth (with the engine off), & see if there is a leak.
I would apply vacuum to the vacuum advance can, using a pump or your mouth (with the engine off), & see if there is a leak.
Is the idle mixture adjusted using the two screws on the front of the carb at the bottom near the throttle plates?
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From: Buffalo
Balancer is original. I suppose this could have happened but how could I tell if it did? it begs the question why was the distributor vacuum source switched to manifold vacuum in the first place.
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
Bring the engine up to TDC#1 using an indicator.
Look to see that the balancer indicates 0.
Many Fords used manifold vacuum and a restriction (VREST) for timing advance.
Often there was a thermal vacuum valve on the water neck so if the engine started to overheat, full manifold vacuum would be applied increasing the idle speed, thus the fan and water pump would offer more cooling if sitting in a traffic jam or at a light.
Look to see that the balancer indicates 0.
Many Fords used manifold vacuum and a restriction (VREST) for timing advance.
Often there was a thermal vacuum valve on the water neck so if the engine started to overheat, full manifold vacuum would be applied increasing the idle speed, thus the fan and water pump would offer more cooling if sitting in a traffic jam or at a light.
Thread Starter
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From: Buffalo
Bring the engine up to TDC#1 using an indicator.
Look to see that the balancer indicates 0.
Many Fords used manifold vacuum and a restriction (VREST) for timing advance.
Often there was a thermal vacuum valve on the water neck so if the engine started to overheat, full manifold vacuum would be applied increasing the idle speed, thus the fan and water pump would offer more cooling if sitting in a traffic jam or at a light.
Look to see that the balancer indicates 0.
Many Fords used manifold vacuum and a restriction (VREST) for timing advance.
Often there was a thermal vacuum valve on the water neck so if the engine started to overheat, full manifold vacuum would be applied increasing the idle speed, thus the fan and water pump would offer more cooling if sitting in a traffic jam or at a light.
The last thing I need to get sorted out is this confounded hiss when I'm accelerating. It's driving me nuts!
I'm fairly certain my booster is leaking but I don't know if that would be causing it. I let the truck sit for about 3 minutes and pulled the check valve off and no release of vacuum.
I want to thank everyone for all the help!
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