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Yes the video explains a lot but I’m not sure if that’s my issue on this. The drop in RPMs is my bigger concern
Ignition coil supplies increased voltage required to fire each spark plug in each cylinder igniting fuel mixture causing each piston to move/down contributing to the turning of the engine crankshaft measured in RPM. If you're delivering less than the required voltage to fire each spark plug, or no voltage to one or more spark plugs, expect the RPM to decrease, generally when you accelerate & a load is placed on the engine; yet, this can be manifested also by a weak RPM at idle often accompanied w/ rough idling. The engine struggles to maintain RPM. Clearly, you require a solid delivery of high voltage to every spark plug to achieve steady combustion. If you have arcing it's likely an electrical issue e.g. points, condenser, distributor cap, rotor, maybe IGN coil itself. As stated, if you have badly worn distributor shaft lobes this is going to adversely effect your ability to provide a steady stream of high voltage as the field collapse becomes intermittent/inconsistent resulting in poor voltage delivery. With the issue(s) you're having w/ the GEN, I would not be running the engine at all until the GEN is repaired. What "may" be a salvageable GEN, will be rendered non-salvageable if you continue to run the engine with your current faulting GEN.
Ignition coil supplies increased voltage required to fire each spark plug in each cylinder igniting fuel mixture causing each piston to move/down contributing to the turning of the engine crankshaft measured in RPM. If you're delivering less than the required voltage to fire each spark plug, or no voltage to one or more spark plugs, expect the RPM to decrease, generally when you accelerate & a load is placed on the engine; yet, this can be manifested also by a weak RPM at idle often accompanied w/ rough idling. The engine struggles to maintain RPM. Clearly, you require a solid delivery of high voltage to every spark plug to achieve steady combustion. If you have arcing it's likely an electrical issue e.g. points, condenser, distributor cap, rotor, maybe IGN coil itself. As stated, if you have badly worn distributor shaft lobes this is going to adversely effect your ability to provide a steady stream of high voltage as the field collapse becomes intermittent/inconsistent resulting in poor voltage delivery. With the issue(s) you're having w/ the GEN, I would not be running the engine at all until the GEN is repaired. What "may" be a salvageable GEN, will be rendered non-salvageable if you continue to run the engine with your current faulting GEN.
I agree but it never did this rpm drop until I fixed my timing. And everything with the ignition system is new. And after watching the video about rebuilding the gen I found out the wires that are connected to the brushes or least one of them should be insulated and neither of mine are so it may be arcing causing it to go out. I’m definitely pulling it apart today. But going back to the rpm yeah doesn’t make sense that it never did this until I set timing. I haven’t replaced my dis cap but it really isn’t bad. Could the drop in rpm be a ballast resistor?
I’m not sure if I was on this thread, but I think I was telling how ever since I set my timing, my car will run normal at idle the sometimes just drop like it’s barely staying alive. I thought it was the points were slipping or opening too much Also on the lobes in the center, if some are worn more than others, should I set my points gap to a worn lobe or a higher one?
The lobes will all wear evenly, if they wear at all.
The shaft bushings inside the distributor however do wear out.
This will cause dwell variations, and make an engine run poorly.
To check the distributor shaft, remove the cap and rotor. Grab the shaft and try to wiggle it side to side.
If you can feel any play the bushings are worn.
Everyday Performance in CT re-bushed my distributor, good service.
The lobes will all wear evenly, if they wear at all.
The shaft bushings inside the distributor however do wear out.
This will cause dwell variations, and make an engine run poorly.
To check the distributor shaft, remove the cap and rotor. Grab the shaft and try to wiggle it side to side.
If you can feel any play the bushings are worn.
Everyday Performance in CT re-bushed my distributor, good service.
Your ballast resistor just allows a full 12 volts on start up then reduces voltage from 12 volts to 9 volts while the engine is running, this saves the points from burning. The whole system is designed to run on 9 volts while running, and has nothing to do with your timing or dwell, if these parts are set correctly look for something else. Try and fix one thing at a time, don't throw new parts into the mix till you find out what is wrong with the old ones. You need a few diagnostic tools and for sure an Oldsmobile motor manual so you can understand why we are telling you what we are speaking about.... Tedd
Your ballast resistor just allows a full 12 volts on start up then reduces voltage from 12 volts to 9 volts while the engine is running, this saves the points from burning. The whole system is designed to run on 9 volts while running, and has nothing to do with your timing or dwell, if these parts are set correctly look for something else. Try and fix one thing at a time, don't throw new parts into the mix till you find out what is wrong with the old ones. You need a few diagnostic tools and for sure an Oldsmobile motor manual so you can understand why we are telling you what we are speaking about.... Tedd
I haven’t gotten other nee parts yet. Which diagnostic tools can I get that aren’t too expensive? I just pulled the carb and cleaned it out again so that should be fine. I’m wondering if the rpm drop is that it’s cutting off on a couple cylinders then picks up when I rev it. I know the manual is on the top of my list.
I haven’t gotten other nee parts yet. Which diagnostic tools can I get that aren’t too expensive? I just pulled the carb and cleaned it out again so that should be fine. I’m wondering if the rpm drop is that it’s cutting off on a couple cylinders then picks up when I rev it. I know the manual is on the top of my list.
oh and I moved the shaft under in the distributor and there was no play so that’s good
Still think you have an accelerator pump issue, unless I have missed a post somewhere. Fuel squarter fluid must hit the carb immediately, or you will have a bog. As far as inexpensive equipment goes, you should be able to find a multi meter at Harbor Freight for cheap, they used to give you one with every promotion...Tedd
A vacuum gauge is another diagnostic and tuning tool that is good to have for these old cars.
A dwell meter will help verify your point adjustment,
In fact, points can be adjusted with the cap and rotor off, while cranking.
With a dwell meter.
E-Bay is loaded with slightly used versions of these tools.
I have a multi meter it was like 5 bucks but I only know the setting to check my battery. My dis cap doesn’t have the little side door to adjust points while it’s running. The vacuum gauge sounds cool and handy I’d like to find one of those. And yes my accelerator pump is still off but it’s ok I know that’s an easy fix. I just need to find the correct part number and order it. I did some tinkering today and got rid of the low rpm issue.
Still think you have an accelerator pump issue, unless I have missed a post somewhere. Fuel squarter fluid must hit the carb immediately, or you will have a bog. As far as inexpensive equipment goes, you should be able to find a multi meter at Harbor Freight for cheap, they used to give you one with every promotion...Tedd
hey tedd, so we talked about setting dwell, timing then air mixture screws. I didn’t all that and the car runs decent most of the time but it still not starting that easily, ever since I set my timing. Before I did the timing I used to start it and let it warm up shut it off for a couple min and it would fire right back up from a quick key bump. Now it will start when it’s cold and when it’s warmed up it will try to start but I have feather the gas pedal. Does timing affect how it starts? I pulled that carb off again and it is spotless and everything is functioning good even accelerator pump.
Chris - If you're confident of both your dwell & your timing settings, Charlie offered good advice. Get yourself a vacuum gauge. Not only do they provide the ability to set the A/F mixture screws correctly, but it's a good way to validate several other readings/findings. They're relatively inexpensive. They run ~$15 - $20.
If you do not own a vacuum gauge, you can establish the best vacuum (most often) using your ears & watching (listening for) RPM.
You need to be certain you have no leaks - that includes any cracks in the vacuum hoses. All vacuum hoses must be attached and in good condition - this is key.
Adjust EACH A/F mixture screw one at a time. Adjust one A/F mixture screw to the highest RPM you can achieve (at idle) on one A/F mixture screw then perform the exact same adjustment to the other A/F mixture screw. Do not change dwell &/or timing once you establish A/F mixture. If you do re-adjust dwell &/or timing, you need to readjust A/F mixture (as the final setting). Many, many times these old beasts have tell-tale cracks in the vacuum hoses. If you have bad vacuum hoses, you can experience the types of conditions which you may be experiencing.
The importance here is this:
You must set dwell first;
You must set timing next;
You then adjust A/F mixture.
The above steps must be performed in order. Any time you change dwell or timing, you need to adjust A/F mixture ratio as the last step.
With a vacuum gauge, you can visually identify you are achieving the highest possible vacuum which is the optimal (nominal) air:fuel mixture ratio for your engine. You measure vacuum in inches of Mercury (Hg).
Last edited by Vintage Chief; January 3rd, 2024 at 08:13 AM.
With a vacuum gauge you can perform some very good rudimentary tests which can provide hints to basic overall engine tune.
ok yes I’ve been wanting a vacuum gauge I’ll go see if I can find one. I read online that if my timing is too off then it could mean a long start like the battery is dead and that’s exactly what mine does when it’s warmed up. My only concern with the vacuum gauge is that I’m not sure where to hook it up because I have a solid metal vacuum line going from carb to distributor so I would have to make sure it has a fitting that can screw into my carb I’m guessing?
Chris, E-Bay is full of vacuum gauges, both new and used.
Most auto parts stores either have them or can get them.
You want to tap into manifold vacuum with the vacuum gauge.
The vacuum in the line from the carb to distributor is ported vacuum. and is not useful.
The lines that run to the power brake unit or the fuel pump from the manifold are the ones you need to tap into .
Chris, E-Bay is full of vacuum gauges, both new and used.
Most auto parts stores either have them or can get them.
You want to tap into manifold vacuum with the vacuum gauge.
The vacuum in the line from the carb to distributor is ported vacuum. and is not useful.
The lines that run to the power brake unit or the fuel pump from the manifold are the ones you need to tap into .
I don’t have power anything. I have the fuel pump but do I tap into the middle of that line with everything still hooked up? I’m confused on how the fuel pump will help the AF on the carb
That line supplies manifold vacuum to the upper chamber of the fuel and vacuum pump.
This vacuum pump boosts the vacuum to the windshield wipers, so they can work constantly even under acceleration.
You won't be using wipers when tuning the carb, so you can just leave it disconnected temporarily.
Connect your vacuum gauge to the port on the manifold where the fuel pump line was connected.
I want to add something here. (1) You need to measure the intake manifold vacuum somewhere; therefore, you can select any point where a vacuum hose is attached to the intake manifold - this then is your intake manifold vacuum i.e. the amount of intake manifold vacuum your engine is producing (at idle); (2) Obtaining this measurement with the vacuum gauge attached allows you the ability to adjust (set) each A/F mixture screw to achieve the highest available vacuum your engine can produce. You WANT the highest available intake manifold vacuum your engine is capable of producing. So, you're measuring the intake manifold vacuum and you're going to adjust that intake manifold vacuum w/ each A/F mixture screw to its highest achievable intake manifold vacuum.
I want to add something here. (1) You need to measure the intake manifold vacuum somewhere; therefore, you can select any point where a vacuum hose is attached to the intake manifold - this then is your intake manifold vacuum i.e. the amount of intake manifold vacuum your engine is producing (at idle); (2) Obtaining this measurement with the vacuum gauge attached allows you the ability to adjust (set) each A/F mixture screw to achieve the highest available vacuum your engine can produce. You WANT the highest available intake manifold vacuum your engine is capable of producing. So, you're measuring the intake manifold vacuum and you're going to adjust that intake manifold vacuum w/ each A/F mixture screw to its highest achievable intake manifold vacuum.
only place I can think of to hook vacuum gauge is where it’s hooked to the spring flap the opens and closes on the carb which down a little tube into the the manifold. Will that work?
only place I can think of to hook vacuum gauge is where it’s hooked to the spring flap the opens and closes on the carb which down a little tube into the the manifold. Will that work?
Trace your vacuum hoses - where do they come from & where do they go? You insert a "T" into any available intake manifold vacuum hose and measure the vacuum; or, you can measure the intake manifold vacuum directly from any intake manifold vacuum port located on the intake manifold. Close off (plug) the vacuum hose which was attached at that port so as to have a closed vacuum system when measuring the vacuum of any port or any vacuum hose.
Can't recall what the carb looks like on your 1955 Oldsmobile. However, the very bottom plate of a carburetor is where intake manifold vacuum can be measured and it is where devices which use intake manifold vacuum obtain (source) their intake manifold vacuum. Any vacuum port located "above" the base carburetor plate is considered a "ported" vacuum source and not an intake manifold vacuum source. Have a look-see of a basic carburetor so you can identify ported vacuum vs. manifold vacuum.
There are several (numerous) discussions of the 4GC carburetor and associated vacuum hoses. It will take some leg work on your part, the other guys on this thread are FAR more knowledgeable than me on measuring your vacuum on your engine w/ a 4GC carburetor mounted onto your intake manifold. Additionally, we're assuming (IMO) you have a 4GC carburetor - a PO might have/could have installed a different carburetor (just saying).
There are several (numerous) discussions of the 4GC carburetor and associated vacuum hoses. It will take some leg work on your part, the other guys on this thread are FAR more knowledgeable than me on measuring your vacuum on your engine w/ a 4GC carburetor mounted onto your intake manifold. Additionally, we're assuming (IMO) you have a 4GC carburetor - a PO might have/could have installed a different carburetor (just saying).
I have two at the base of the carb but the other guy says those are ported. The on the back is for the whipers but they have never been hooked up it’s plugged right now. The fuel pump vac lines aren’t hooked up. Let me show a pic of where I think it will work.
OK. I'm going to need to stop because I just don't have the experience to accurately tell you which ports on your 4GC carburetor are ported and which are intake manifold vacuum port. So, wait for one of the other members who can specifically define for you which is which. I can say you need to measure intake manifold vacuum, however.
Yes, measuring that vacuum is key. You should be able to measure 15"Hg - 22"Hg. Once you get your vacuum gauge, your reading(s) should be rock steady, no bouncing about - whatever the reading(s) is/are. The vacuum gauge will identify significant & pertinent information.
Yes, measuring that vacuum is key. You should be able to measure 15"Hg - 22"Hg. Once you get your vacuum gauge, your reading(s) should be rock steady, no bouncing about - whatever the reading(s) is/are. The vacuum gauge will identify significant & pertinent information.
so when the gauge is on, I’m adjusting it til the needle is at 15 to 22 with highest idle point ? I’m still curious where I’m gonna hookup to
As stated multiple times you adjust A/F mixture screws until you achieve the highest available intake manifold vacuum.
Thats what I’ve been doing just clarifying. Vacuum gauge would be great in my case because my exhaust is all shot to hell so it’s hard to hear certain things. I saw one for like 20 bucks I’ll pick it up tomorrow. I just order that shop manual should be arriving this coming week, that will help me a lot!
I have two at the base of the carb but the other guy says those are ported. The on the back is for the whipers but they have never been hooked up it’s plugged right now. The fuel pump vac lines aren’t hooked up. Let me show a pic of where I think it will work.
No, that is not a vacuum line.
Neither is the other line in the picture that runs from carb to distributor
Connect your vacuum gauge to the port on the back of the carb where the wipers would have connected.
Last edited by Charlie Jones; January 4th, 2024 at 08:24 PM.
Hey guys, as I mentioned a couple weeks ago, I was explaining having no power stepping in the gas going up hill. I was told to plug the open vacuum line, I did that and it seemed a bit better. My accelerator pump is shooting fuel right on spot but it seems I should have some more power. Is there something else I’m missing? And I think I stated before that I squirted fuel around the intake and cylinder heads and the engine did not get richer so I don’t think there’s a vac leak there.
The reason I ask is that a lack of power going uphill can very much result from improper timing. How do I know this? I spent month's working on an old 1992 Fleetwood Bounder RV with 454 throttle body injection that had a ton of issues (I took it in as a trade for something I didn't want anymore). After checking everything (vacuum leaks, cleaning/testing injectors, exhaust back pressure, and timing) the thing ran great at speed but as soon as I would press the accelerator more than just slightly, it would lose power. When checking the timing again, I discovered that someone had set it to 4° ATDC instead of 4° BTDC (the marks were easy to confuse). Essentially, it was running 8° retarded. Once I corrected that the beast leapt up hills (well, as much as a 10,000 pound RV with a 454 can leap).
Not that you needed to hear that whole story, but the fact that the vehicle can run so good at speed but lose power when stepping on the accelerator (like when going up a hill) is the point. If your timing is set correctly, the other thing to check is the vacuum advance on the distributor. If it's not working properly or you've connected it to the wrong vacuum port on the carb (manifold vacuum vs. ported vacuum), that can also cause the issue you describe.
The reason I ask is that a lack of power going uphill can very much result from improper timing. How do I know this? I spent month's working on an old 1992 Fleetwood Bounder RV with 454 throttle body injection that had a ton of issues (I took it in as a trade for something I didn't want anymore). After checking everything (vacuum leaks, cleaning/testing injectors, exhaust back pressure, and timing) the thing ran great at speed but as soon as I would press the accelerator more than just slightly, it would lose power. When checking the timing again, I discovered that someone had set it to 4° ATDC instead of 4° BTDC (the marks were easy to confuse). Essentially, it was running 8° retarded. Once I corrected that the beast leapt up hills (well, as much as a 10,000 pound RV with a 454 can leap).
Not that you needed to hear that whole story, but the fact that the vehicle can run so good at speed but lose power when stepping on the accelerator (like when going up a hill) is the point. If your timing is set correctly, the other thing to check is the vacuum advance on the distributor. If it's not working properly or you've connected it to the wrong vacuum port on the carb (manifold vacuum vs. ported vacuum), that can also cause the issue you describe.
that makes sense. My timing is at 14 degrees BTDC. I’m over 7,000 feet above sea level though. My last job working on these old hot rods is where my boss told me the timing needs to be 2 degrees for thousand feet which is 14 so that’s what it’s at. It was way lower when I got the car. The idle screw was all the way in just to keep it running. But I was also told that I need to adjust my TV rod because when I smash on the pedal it’s not dropping to a lower gear like it should which is true since I’m the one who put the transmission in the tv could be off
I grew up in Albuquerque (60's and 70's) and I always set timing at 1° advanced for every 1000 foot of altitude (for ABQ that would add 5° to the timing. Your timing seems WAY to high for Santa Fe.
December 27th, 2023, 06:44 AM
