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Vacuum Gauge |
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63RumbleRambler
AMC Fan Joined: Aug/06/2021 Location: California Status: Offline Points: 22 |
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Posted: Jul/06/2022 at 12:00am |
Ok stupid question time-but no better place than to ask you guys: I would like to use a vacuum gauge to tune my carb and to set the timing. Plus I would like to get an idea what psi it runs at while happy. it is a 63 classic with a 196. Freshly rebuilt Carter 2bbl WCD. Vacuum wipers/vacuum pump on the fuel pump…
Edited by 63RumbleRambler - Jul/06/2022 at 12:13am |
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rgsauger
AMC Nut Joined: Aug/17/2014 Location: Houston,TX Status: Offline Points: 311 |
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That’s done every day, although I prefer a timing light for setting timing over vac gauge. What’s your question? Hint, bigger diameter gauge beats a smaller one.
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Mr_Roboto
AMC Apprentice Joined: Jun/12/2022 Location: Wisconsin Status: Offline Points: 221 |
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I like vacuum for base timing, although I will admit that you may leave some power on the table in terms of overall timing. I just set to maximum vacuum. My experience with it has been you'll end up close to where the factory had recommended timing if you use a vacuum gauge. You typically wouldn't use the vacuum pump on the engine (unless doing diagnostics of it) you'd use engine vacuum for such adjustments. In terms of the carb setup I'd much rather use a wide band O2 if plausible. I realize it's probably out of place if you're doing something more "period correct" but man they really do help with a calibration. That said, if your carburetor and engine are stock and running well they should be fairly close.
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63RumbleRambler
AMC Fan Joined: Aug/06/2021 Location: California Status: Offline Points: 22 |
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Thanks guys, I should have read my post a little more! I am trying to figure out which line to hook the vacuum gauge up to? Do I disconnect the line running to the wiper motor? Thanks!!
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troutwilly
AMC Addicted Joined: Sep/14/2007 Location: Carriere, MS Status: Offline Points: 991 |
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You want manifold vacuum, so any port from the manifold would work. And I thought the vacuum for the wipers came from the fuel pump, no?
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Bill O.
70 AMX |
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63RumbleRambler
AMC Fan Joined: Aug/06/2021 Location: California Status: Offline Points: 22 |
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You are correct, the line running to the wipers is coming from the vacuum pump. So there are 2 bolts in the manifold plate-in the front of the plate. These currently have bolts in them…since these are the only two access points on the plate, would I just unbolt-find a fitting that works and run the vacuum gauge?
Thank you
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Mr_Roboto
AMC Apprentice Joined: Jun/12/2022 Location: Wisconsin Status: Offline Points: 221 |
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Are there any ports that are unused in the intake? That's where I'd start. Quite honestly you're supposed to set base timing with the dizzy disconnected from vacuum, so I'd be tempted to "borrow" that line and hook up the vacuum gauge there to set base timing. If you're talking about driving around, if you have a port available on the base of the carb you could use that or the plugs (not bolts) in the intake could be removed to add a hose barb if you want to drive around. It should be readily available at an auto parts store though you may have to ask. Also, I would probably advise using a 6 point socket not a 12 point just because it may be fun to get out after the decades.
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63RumbleRambler
AMC Fan Joined: Aug/06/2021 Location: California Status: Offline Points: 22 |
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Thank you! No plugs or ports on the manifold plate. This idea makes sense since the vacuum line is disconnected from the dizzy when setting timing. This is the line that runs from the base of the carb so I should be able to get a vacuum reading off it.
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troutwilly
AMC Addicted Joined: Sep/14/2007 Location: Carriere, MS Status: Offline Points: 991 |
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Post seems to be bouncing around, so here's what I (would) do. You're free to follow other methods but this seems to work for me. For ignition timing, you don't use vacuum. Disconnect the vacuum line to the distributor and plug it on the source side so there's no vacuum leak. Set your timing with a timing light and lock it down. Reconnect the vacuum line. For the carburetor, I use a dwell/tach, just the tach function. Advance the throttle stop to about 1,000 RPMs. Adjust your idle mixture screw(s) for maximum and smooth RPMs. Repeat until your happy with the results and set your throttle stop at the correct RPM. For a vacuum gauge you have some options. There are ports on the carburetor but you need to know which are metered and which are not. Could be none are metered in your case, but metered to me means different than straight vacuum. Best to use a dedicated port straight from the intake manifold. Remove a plug/bolt and install a barb fitting, but mind the caution on the 6-point socket/wrench as yours are probably rusted in quite well.
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Bill O.
70 AMX |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4741 |
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The base timing setting that produces the highest vacuum reading at idle tells you nothing about whether that is the best base timing setting for engine speeds above idle: as in where it really counts for moving the car down the road.
Follow the factory recommended timing setting first. Check the base timing and the timing advance systems. Go for a test drive and note the full-throttle power. Then advance the base timing 5 degrees and go for a test drive again. If it has more power, leave it. If it doesn't seem to have more power, take it back down to the factory setting. Rev the engine to 2000 rpm and see if it surges. Light throttle surging means over-advanced. Setting the idle mixture is easier with a sensitive tachometer than it is with a vacuum gauge. Adjust the idle mixture screw for the highest idle speed then turn the screw leaner (clockwise) in 1/2 turn increments until you notice the engine slow down slightly, then turn it back rich 1/2 turn. This will put you at the highest idle speed, but within 1/2 turn of slowing down from being lean. This is the ideal idle setting.
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