vacuum advice
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Cross-Country
Joined: Jan 2019
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Likes: 5
vacuum advice
Ok folks. Need some help. my vaccum gauge is a steady 10. I have checked and found no leaks. I have checked the timing and it is set correctly. I even advanced the distributor based on advice on another thread. Any advice on where else to go with this?
Thanks
Thanks
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Cross-Country
Joined: Jan 2019
Posts: 54
Likes: 5
Don't know cam. No tach so not sure of rpms. I guess about 1500-2000
I believe the mix is right. I have gone back and forth between lean and rich and think it is correct.
I do think it can take more advance. But it cranks up the rpms
I believe the mix is right. I have gone back and forth between lean and rich and think it is correct.
I do think it can take more advance. But it cranks up the rpms
Lead Driver
Joined: Oct 2018
Posts: 7,894
Likes: 2,372
Any idle over 900 is pretty fast. but it's not that important.
If advancing the timing ups the rpm it's upping your vacuum too. just set your idle speed back. you need to check your timing with a dial back. but you can also advance it a little at a time until it kicks the starter or pings under load if you don't have one. the more advance the better right up until it causes problems.
If it idles lumpy like it has a performance am you'll never get a high vacuum reading.
If advancing the timing ups the rpm it's upping your vacuum too. just set your idle speed back. you need to check your timing with a dial back. but you can also advance it a little at a time until it kicks the starter or pings under load if you don't have one. the more advance the better right up until it causes problems.
If it idles lumpy like it has a performance am you'll never get a high vacuum reading.
Laughing Gas
Joined: Feb 2011
Posts: 996
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Do you have power brakes? At 10" of vacuum I can't imagine you'd have have any boost. Was it always like this or did you just buy the truck? Any history on a rebuilt engine? Be double sure you block or pinch off all vacuum lines to accessories including the brake booster.
.
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Lead Driver
Joined: Jul 2017
Posts: 9,606
Likes: 1,175
From: San Jose, CA
Have you tried your gauge on another known-good engine? Just to verify it's working properly.
And what is your altitude, since that effects the final results as well.
Advancing the timing almost always increases the idle rpm. Just as retarding the timing lowers it.
You don't set your idle with ignition timing however, you set it with the idle speed screw and idle mixture screws. The "tune-up" process is a dance. A little of this, a little more of that, then back and forth.
Advance the timing for whatever reason, set the idle speed screw back until you're where you want to be. Then you have to re-tweak the two idle/air mixture screws to get the smoothest or highest idle, then you dial back the speed screw some more.
You keep doing all that until you get it all where you want it. Don't let it dictate to you. Within certain parameters, you dictate to it.
Why are you checking vacuum? Having troubles?
What has been done to the engine, if anything? Did you perchance change the front timing cover, harmonic damper, or timing pointer at any point? Since Ford had so many different combinations, changing any of those parts means you have to re-verify the timing marks line up with the pointer at the proper time.
Paul
And what is your altitude, since that effects the final results as well.
Advancing the timing almost always increases the idle rpm. Just as retarding the timing lowers it.
You don't set your idle with ignition timing however, you set it with the idle speed screw and idle mixture screws. The "tune-up" process is a dance. A little of this, a little more of that, then back and forth.
Advance the timing for whatever reason, set the idle speed screw back until you're where you want to be. Then you have to re-tweak the two idle/air mixture screws to get the smoothest or highest idle, then you dial back the speed screw some more.
You keep doing all that until you get it all where you want it. Don't let it dictate to you. Within certain parameters, you dictate to it.
Why are you checking vacuum? Having troubles?
What has been done to the engine, if anything? Did you perchance change the front timing cover, harmonic damper, or timing pointer at any point? Since Ford had so many different combinations, changing any of those parts means you have to re-verify the timing marks line up with the pointer at the proper time.
Paul
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Cross-Country
Joined: Jan 2019
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Thanks for all the help. I did advance the distributor more and reduced the idle. It still has RPMs a little high, but lower than above. Where i used to not be able to put it in gear until it hit temperature, it runs right after it turns over now. Also has good power when i hit the gas. So i have no idea what is going on. still reading 10, but everything that i think with low vacuum reading like that isnt happening. I assume i am doing something wrong, but can't figure it out. Regardless, the effect is working correctly as it if it is tuned adequately, so who knows.
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Lead Driver
Joined: Jul 2017
Posts: 9,606
Likes: 1,175
From: San Jose, CA
Where are you taking the reading from? Perhaps it's a restricted port on the carb. If you're using the manifold directly I would say to still verify the gauge is correct by attaching it to any semi-modern vehicle that is still stock.
Paul
Paul
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