Engine nearly stalling at low rpm, hard to start: 73 Comet

Discussion in 'Technical' started by ArchaiTekton, Jun 17, 2021.

  1. ArchaiTekton

    ArchaiTekton Member

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    Hello Everyone, I'm hoping to get some advice on an engine sputtering/stalling problem my 73 Comet is having. 73 Mercury Comet, Auto Transmission, 250 - 6 cyl.

    For background, I purchased the vehicle in 2007 and ran it for a few years with few problems. It had started to stall and shut off at idle/stoplights in traffic, and we couldn't figure out what was wrong, so we parked it and I got a second vehicle when I went to college. Needless to say, it sat for 10 years unmoved.

    During at-home Covid, I decided to work on getting it running again. Wouldn't start, so I got a new battery, replaced the points/condenser, new fuel filter, all new spark plugs, plugged some vacuum leaks, and even replaced carb with a new Carter carburetor (all my novice installation, but we can assume it was done correctly for now). Finally got it started, but still suffered from the same idle stalling problems. Sent it to the shop a few weeks back to have them replace a leaking gas tank with a new one, install new mechanical fuel pump, check air/fuel mixture in carb and fuel pressure, new solenoid, oil change, and just general diagnostic work.

    Came back from the shop running fine enough and is finally drivable, but I am still having issues with difficult starting and low rpm performance. If I go more than a day without starting, it will crank, but takes multiple attempts to get it to turn over. Once it does, it starts fine on repeat attempts, but go a few hours without running, and it goes back to multiple attempts to get it to turn over. (Starts great with a shot of starter fluid in carb, but I know we shouldn't use that, so I have not been using it.)

    Secondly, once I get it started, it seems to idle fine now. But when you begin to accelerate and it hits a certain low rpm or accelerate too quickly (pulling out of stoplights, low acceleration, etc) the engine sputters and seems to want to stall again. I've included a video link below with timestamps to show how it idles fine, sputters at low rpm, then runs smooth at higher rpm. I am also seeing a small bit of smoke from the back of the engine on acceleration with the hood up.



    As an aside, the shop fueled with 90 oct ethenol-free gas when they worked on it. Fuel mileage seemed way lower than I remember when I got it back from the shop, like WAAAY lower. This week I refueled with 87 oct gas because I could not get to an ethenol-free station the gas mileage was so bad, and that is when the low rpm stalling happened. Would this gas difference really cause the stalling? Just looked at car manual, and it recommends min 91 oct, so I will start putting standard 93 oct in from now on, but I don't know how often I can get to an ethenol-free station.

    I have been considering replacing the ignition coil next. I am really novice and new at this, and have very limited tools/knowledge to diagnose problems, but would like to learn more so I am trying. At the least, I'd like to know what to say to the mech shop if I need to take it in when it comes to that.

    Thanks
     
  2. Krazy Comet

    Krazy Comet Tom

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    Ratings for gas in '70s was different than now. Back in day, regular was 94-95 octane while a mid grade 97-98, premium 100+. I use 87 laced with corn squeezins in my stock motor Fairlane, runs fine. In the local area no such thing as ethanol free in any grade.

    http://www.pedrosgarage.com/Site_5/Octane_Ratings.html

    Hesitation/stumble from stop or low speed is 90% a carb issue, accelerator pump linkage possibly set incorrectly. The other 10% could be timing related, set late(retarded) can cause hesitation, poor fuel economy and/or sluggish performance.
     
    Last edited: Jun 17, 2021
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  3. 71gold

    71gold Frank Cooper Supporting Member

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    :Welcome:...:Handshake:
     
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  4. ArchaiTekton

    ArchaiTekton Member

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    I didn't know about the octane difference, good to know. I had always put low oct gas in before and never had any problems, so good to know the oct difference probably isn't the issue. It is just crazy coincidence that the low rpm stalling issue started literally the second I pulled out of the station after the new fill-up.

    My guess is also either carb/fuel/air related or timing, just can't pinpoint it. I didn't mess with the accelerator pump because I bought a brand new carb, so assumed it should be factory correct. It is a Carter Model RBS 1-V Carburetor, matched what was on it before. I don't have the tools to confirm if idle/fuel/air screws are correct, so left them as is. The fast idle cam does kind of seem "off" though, not 100% sure it is sitting right. I do notice that the choke plate isn't fully closed when not running. It defaults at sort-of half open, half closed. I can push the plate open and closed easily, but it sits half open, even after sitting "cold" (not winter cold, as it is summer of course, but "not started for a few days" cold).

    I'm not ruling out that I could have messed up the timing when I put in the new points/plugs. I tried my best with suggested gaps. Not sure I have the equipment/knowledge to diagnose incorrect timing. This was done a year ago, so I would have assumed when I took it to the mechanics shop to have them put in a new fuel pump, that they would have noticed a timing issue, since they'd be related to fuel pump issues.
     
  5. mojo

    mojo "Everett"- Senior Citizen Supporting Member

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    Installing points/plugs will not affect timing; loosening dist. fastner and rotating it will move timing. I not quite sure what your conveying about choke, AFAIK choke should stay pretty much open at operating temp. If your having stalling issue might be choke contributing to problem.
     
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  6. Constable

    Constable You have the right to remain silent....or not!

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    Here's something to think about. After a while once I got mine running again after it's long sleep, it also wouldn't idle well. I went the carb route at first and timing until I got thoroughly frustrated. Then I had a thought and something told me to replace the coil. I bought a good one, MSD, and lo and behold it seems to have fixed the issue. The car not only idles much better, it runs a bit stronger than it did before the swap. I do remember that the charging systems in these cars aren't as robust as more modern ones especially at low revs. That might have something to do with why an apparently weak coil won't fire off as hot at low revs than a new one will. Anyway, food for thought.
     
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  7. ArchaiTekton

    ArchaiTekton Member

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    I won't mess with the points/plugs for now then.
    I was just reading that the choke plate should be closed for cold starts, and noticed mine is always open when I have the vehicle off and am looking into the carb. If the links work, the attached pic is how the carb looks when parked, not running. 20210618_101338.jpg The other two pics are the fast idler position. 20210618_101628.jpg 20210618_101922.jpg

    Changing the ignition coil was my next thought too, as it seems easy enough, just a part change. It's ordered and on the way, so replacing it next. We'll see.
     
  8. mojo

    mojo "Everett"- Senior Citizen Supporting Member

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    Choke plate open on cold start = hard start & poor drivability b4 engine warms. Assuming you have elec. choke, check to see if ur getting voltage w/ ign on.
     
  9. Constable

    Constable You have the right to remain silent....or not!

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    If you ordered a universal coil, which they basically all are in this style, you will have to change the wire ends attaching to the coil. The original Ford attachment is a clip on type where most of the universal ones use terminals as the coils use a screw retainer. Easy fix so long as you have the terminal ends and a crimp tool.

    Oh, and I'm curious. With the common access to electronic conversions for points like the Pertronix units which make the car much more driveable and dependable, how come you haven't done away with the points? They're not an expensive swap or complicated to do.
     
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  10. ArchaiTekton

    ArchaiTekton Member

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    Hmm, If you can see these pictures, this is the old coil that I am replacing: 20210619_103746.jpg 20210619_144754.jpg . The new coil I purchased is linked: https://www.autozone.com/ignition-t...igh-performance-ignition-coil-8202/139528_0_0 . I just set the nut/washers aside and hooked it up just like the old one. 20210619_150559.jpg Do these wire ends look correct? Car started and runs just like it did with the old one, so that didn't fix the problem.

    I've thought about converting to electronic ignition a few times, but kind of always liked the idea of keeping it as close to stock as possible, but I'm starting to think now it will be better to move away from a points system, so I might look into it more.

    Feeling way out of my element here lol.
     
  11. Krazy Comet

    Krazy Comet Tom

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    Through the points era, Ford coils used stud. Beginning with electronic ign, switched to slide on double connector that are trouble prone. Terminals on coil resembled a rivet.

    Your old coil was a replacement. In 55 years of vehicle ownership, I'm yet to see a actual bad coil. Seen plenty with burned/arcing towers, caused by bad spark plugs or wires. Did have a replacement on a '74 Mustang II that would cause a transinsistor in tach to short. Ran fine.

    The red wire should connect to the + terminal.
     
  12. Constable

    Constable You have the right to remain silent....or not!

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    I bought the same MSD coil and my car does in fact run better. Kraz, maybe you haven't seen a coil go bad but I have and mine obviously was weak or why did replacing it fix my driveability issue? The wires and plugs are all new. I've replaced a number of coils in newer vehicles and each time they were the offending actor in why the car was acting up. Single coil in a Jeep 4.0, multiple COP failures in a Ford 4.6, etc. You've been lucky never needing one in 55 years. Bought my first car in 1975.

    Now, Arc, you have me intrigued. We've ruled out several potential issues. Still the car isn't running right. I really hate to see you throwing parts at it in the hope of fixing it before the parts bill gets too big. At this point, ,given the symptoms, I'd still suspect carb, vacuum issue, points and/or condenser which is what we're attempting to do here. Hell, I might even look at the distributor if all else ends up being ok. Bottom line is that it's hard to diagnose a car by remote control. Once in a while, you can hit it right away when the issue is painfully obvious but with general driveability issues, it can be a plethora of possible culprits. In my case, it did take going through the vacuum system, carb, timing, to see what the problem was and was glad I had a factory shop manual along with some other vintage repair papers to use for reference and to help diagnose the problem. I also suspected the electronic ignition module and was debating about the distributor, later the coil which ended up being the problem child. The coil was a parts throw but turned out to be the right call and really didn't bother me if it was a wrong call as I was replacing a 46 year old coil and that's never a bad thing.

    Might be cheaper in the long run at this point to see if there is someone local who can take a look at the car. I applaud you for trying to take matters into your own hands but sometimes when we get overwhelmed and a bit past our pay grade, we have to take it on the chin and get some professional help. With all the experience and knowledge and tools I have, I still have been in that position a time or three. Sometimes it is worth the expense to save the stress alone.
     
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  13. Krazy Comet

    Krazy Comet Tom

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    I wasn't including COPs, yes are famed to be junk(in my opinion, ill gotten reputation). I replaced a set of those on my '98 4.6. Didn't fix problem, turned out O rings on Dorman intake were slightly leaking. Ran horrid below 50-55*, at higher temp or warmed up, was fine. Mostly COPs fail because of excessive plug gap, that engine had plugs replaced at 65K mi(Dorman intake installed) & again at 35K, original coils were still fine. Now have spares.

    Bought my first car in '66.

    Yes I've tried a few replacement coils, always something else. In points systems, weak condensers are famed for erratic operation. Resistance plug wires were lucky to make 25K mi. Installing a Crane Hi-6(their version of 6AL) & MSD Blaster coil on my 428 improved cold start & operation plus greatly extend plug life. Now hasn't had plugs in over 20 years. Fairlane still has it's points ign system & coil, runs fine. BUT it has new plugs(at least were 3K ago). Back in day we were lucky to get 3K on a Hi-Perf engine before misfires set in(moving one range up, did net 6- 7K in my 428). Racers ran plug gap at .025 & under to achieve max performance(minimise misfires). Modern systems easily fire pugs in excess of .060 - .080. BUT large gaps do contribute to coil, dist cap & plug wire failure. Gap should be limited to .045-.050 if using orig small dist caps. The Comet has points but are triggering a '90s Ford TFI module, sparks a stock E-coil.
     
  14. Madmave72

    Madmave72 Member

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    Hope you got your car running well but I have had similar issues you said you replaced the carb my motor is just a 200 with yf not rbs but all the carbs I can find the venture is to big and causes acceleration issues or dies if I give it to much throttle to fast can be fixed for the most part with going bigger jets just a thought
     

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