Tuning newbie
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Tuning newbie
I've got a 64 F100 with 292 4 speed manual. No power brakes, Motorcraft/Autolite 2100 2bbl w/ manual choke. It's a brand new reman. Pretty much bone stock. Here's my questions.
1. I've got a vacuum gauge and am trying to adjust my idle mixture. Whether they're 1.5 turns out or ran all the way in, no change in idle speed or vacuum. It's pulling between 13 - 15 at idle, but it's searching. 20 at 2k ish rpm and steady needle on the gauge. Could timing being off cause this? Or should I start looking for vacuum leaks?
2. Should I have to adjust or check point gap and dwell on a new distributer?
3. The only vacuum port I can find is on the bottom of the carb. Will that make a difference in tuning with a vacuum gauge? All the videos I've watched on it, they're using the power brake port.
1. I've got a vacuum gauge and am trying to adjust my idle mixture. Whether they're 1.5 turns out or ran all the way in, no change in idle speed or vacuum. It's pulling between 13 - 15 at idle, but it's searching. 20 at 2k ish rpm and steady needle on the gauge. Could timing being off cause this? Or should I start looking for vacuum leaks?
2. Should I have to adjust or check point gap and dwell on a new distributer?
3. The only vacuum port I can find is on the bottom of the carb. Will that make a difference in tuning with a vacuum gauge? All the videos I've watched on it, they're using the power brake port.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Welcome to FTE!
You'll have to find a source of constant vacuum from the manifold to use the gauge properly. The reason is that accurate vacuum readings are taken at factory idle (550-650 tops), the port on the carb won't allow for this. On mine I installed a fitting just forward of the carb for taking vacuum readings.
13" to 15" sounds real low. A healthy stock cammed 292 motor at Sea level should draw 18" or more. It could be late ignition timing, or valve lash needs adjusting. It is very common for the old vibration absorber/damper ring to slip off its clock and bugger the timing marks. It should be replaced if this is the case.
Carb idle mixture adjustment can be tricky, make sure timing and valves and everything is where you want it. Definitely want to set the points with a feeler gauge first to get in the ballpark, then set the dwell. That's the accurate method. Btw- Modern manufacture points and especially condensers are junk. Use good quality points (expensive) or old school NOS if you want to run points.
Anyway make sure the butterflies are nearly closed, it's possible they are too far open and the transition circuit is in play at idle. It's either that or a bad vacuum leak, make sure the carb gaskets are good and the carb is snug. Snug, don't overtighten.
http://members.tccoa.com/392bird/tuning.htm
You'll have to find a source of constant vacuum from the manifold to use the gauge properly. The reason is that accurate vacuum readings are taken at factory idle (550-650 tops), the port on the carb won't allow for this. On mine I installed a fitting just forward of the carb for taking vacuum readings.
13" to 15" sounds real low. A healthy stock cammed 292 motor at Sea level should draw 18" or more. It could be late ignition timing, or valve lash needs adjusting. It is very common for the old vibration absorber/damper ring to slip off its clock and bugger the timing marks. It should be replaced if this is the case.
Carb idle mixture adjustment can be tricky, make sure timing and valves and everything is where you want it. Definitely want to set the points with a feeler gauge first to get in the ballpark, then set the dwell. That's the accurate method. Btw- Modern manufacture points and especially condensers are junk. Use good quality points (expensive) or old school NOS if you want to run points.
Anyway make sure the butterflies are nearly closed, it's possible they are too far open and the transition circuit is in play at idle. It's either that or a bad vacuum leak, make sure the carb gaskets are good and the carb is snug. Snug, don't overtighten.
http://members.tccoa.com/392bird/tuning.htm
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Good news: confirmed TDC mark on balancer is accurate.
I'm going to install a fitting where that plug is to get an accurate vacuum reading.
New question: is it normal for the idle to raise when the vacuum advance is plugged in vs when it is unhooked and plugged off?
I'm going to install a fitting where that plug is to get an accurate vacuum reading.
New question: is it normal for the idle to raise when the vacuum advance is plugged in vs when it is unhooked and plugged off?
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
But it does sound like the base idle RPM might be a little bit on the high side then. Normally, there is no vacuum at the carb port running at factory idle RPM. Disconnecting and plugging the vacuum is done when setting the initial timing for just this reason, it can interfere with accurately setting the timing.
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Thanks for the help by the way, it's been SUPER useful!
I set the timing with the advance unplugged and port blocked off. My idle does seem too high with every thing hooked up. Just got a tach, but haven't hooked it up yet. What should the RPMs be at idle? I thought I read around 700 rpm. Also, know off the top of your head what the thread is on that plug I took a picture of?
I set the timing with the advance unplugged and port blocked off. My idle does seem too high with every thing hooked up. Just got a tach, but haven't hooked it up yet. What should the RPMs be at idle? I thought I read around 700 rpm. Also, know off the top of your head what the thread is on that plug I took a picture of?
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
3/8" NPT
The manual for 64 sez 500-550, can set it wherever you like or sounds best. Speaking of, you REALLY want a Ford Shop manual, and maybe an older (1950s) MoToRs manual, for these beasts.
The manual for 64 sez 500-550, can set it wherever you like or sounds best. Speaking of, you REALLY want a Ford Shop manual, and maybe an older (1950s) MoToRs manual, for these beasts.
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