How does timing get so far off?
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From: Cleveland, WI USA
How does timing get so far off?
I have a 71 460 in my 78 F150 and have had starting problems since day 1. I've replaced everything in the starting system but never messed with timing. I had it set to 12 deg BTDC and it ran great. I also have an insulated alum. heat shield to protect the starter from the exhaust heat.
When it wouldn't start yesterday (engine was hot) I decided to pull the coil wire and see if it was the timing causing the hard starts. It turned over like crazy, so I checked the timing. it was at 26 deg BTDC! I set it back to 12 BTDC and it starts great now but it did backfire when I started it.
Any idea how the timing can get that far off? Could my mechanical advance be screwed up and can it be fixed/adjusted?
Any thoughts would be greatly appreciated.
Kevin K.
When it wouldn't start yesterday (engine was hot) I decided to pull the coil wire and see if it was the timing causing the hard starts. It turned over like crazy, so I checked the timing. it was at 26 deg BTDC! I set it back to 12 BTDC and it starts great now but it did backfire when I started it.
Any idea how the timing can get that far off? Could my mechanical advance be screwed up and can it be fixed/adjusted?
Any thoughts would be greatly appreciated.
Kevin K.
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Joined: Sep 1999
Posts: 2,297
Likes: 1
From: Indiana
Originally Posted by kjkozak2
I have a 71 460 in my 78 F150 and have had starting problems since day 1. I've replaced everything in the starting system but never messed with timing. I had it set to 12 deg BTDC and it ran great. I also have an insulated alum. heat shield to protect the starter from the exhaust heat.
When it wouldn't start yesterday (engine was hot) I decided to pull the coil wire and see if it was the timing causing the hard starts. It turned over like crazy, so I checked the timing. it was at 26 deg BTDC! I set it back to 12 BTDC and it starts great now but it did backfire when I started it.
Any idea how the timing can get that far off? Could my mechanical advance be screwed up and can it be fixed/adjusted?
Any thoughts would be greatly appreciated.
Kevin K.
When it wouldn't start yesterday (engine was hot) I decided to pull the coil wire and see if it was the timing causing the hard starts. It turned over like crazy, so I checked the timing. it was at 26 deg BTDC! I set it back to 12 BTDC and it starts great now but it did backfire when I started it.
Any idea how the timing can get that far off? Could my mechanical advance be screwed up and can it be fixed/adjusted?
Any thoughts would be greatly appreciated.
Kevin K.
Do you have your vacuum advance hooked to full vacuum or part throttle vacuum?
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From: Cleveland, WI USA
I don't remember. I hooked it up according to advice I got in this forum over a year ago. I'm pretty sure it comes out of the carb (Holley 750) on the pass. side near the front. Does that tell you anything?
I did disconnect the VA and plug the tube when I checked the timing.
Thanks!
Kevin K.
I did disconnect the VA and plug the tube when I checked the timing.
Thanks!
Kevin K.
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From: Indiana
If you checked the timing with the vacuum hose unhooked, you had set your base timing @ 12 degree's.
Then if the hose is hooked up to a full vacuum port, that will advance the timing immediately. If you re-checked the timing and did not remove the vacuum hose, this would account for the increased timing reading.
I am not sure if your port your hooked to, is full or part throttle vacuum. If you have a vacuum gauge check it to see which it is.
Always check your base timing at the recommended rpm and with the vacuum advance hose unhooked and plugged. With the rpm's low, your mechanical advance won't come in either.
Then if the hose is hooked up to a full vacuum port, that will advance the timing immediately. If you re-checked the timing and did not remove the vacuum hose, this would account for the increased timing reading.
I am not sure if your port your hooked to, is full or part throttle vacuum. If you have a vacuum gauge check it to see which it is.
Always check your base timing at the recommended rpm and with the vacuum advance hose unhooked and plugged. With the rpm's low, your mechanical advance won't come in either.
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From: Cleveland, WI USA
SuperDave,
I have a vacuum guage and I'll check the vacuum hook up tonight. Just so I'm clear, full throttle vac will only go up at full throttle and part throttle vac will gradually go up as throttle increases, correct?
greenhighboy,
That doesn't sound good. I'll have to check that tonight, too. I suppose it would help if I knew what the stator was. Is that the spoked thingy under the rotor?
Thanks guys!
Kevin K.
I have a vacuum guage and I'll check the vacuum hook up tonight. Just so I'm clear, full throttle vac will only go up at full throttle and part throttle vac will gradually go up as throttle increases, correct?
greenhighboy,
That doesn't sound good. I'll have to check that tonight, too. I suppose it would help if I knew what the stator was. Is that the spoked thingy under the rotor?
Thanks guys!
Kevin K.
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From: Union, Washington
If your vacuum source is the ported vacuum fitting on the right side of the carb in the metering block between the float bowl and the carb body. Then it should be zero at idle and show manifold vacuum above idle speed.
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From: Indiana
Yes, you want it to be on the part throttle port, where Bear mentioned. A 0 vacuum reading, idling at the vacuum port.
A full vacuum port delivers full vacuum even at idle, which will pull the vacuum advance, to advance the timing right off the bat.
The stator is the star wheel thats on the distributor shaft under the rotor on the electronic ignition systems. That is what trips the pickup in the distibutor to allow the ignition to fire.
A full vacuum port delivers full vacuum even at idle, which will pull the vacuum advance, to advance the timing right off the bat.
The stator is the star wheel thats on the distributor shaft under the rotor on the electronic ignition systems. That is what trips the pickup in the distibutor to allow the ignition to fire.
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