unfixable idle problem

Discussion in 'General Maverick/Comet' started by CA189HJN, Jun 13, 2018 at 6:10 PM.

  1. CA189HJN

    CA189HJN Member

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    I have an unfixable idle problem with my 1973 Maverick, 302 stock with Motorcraft 2100 carb, and I'm asking for suggestions.

    Because there was hesitation coming off idle, I had carburetor rebuilt last week by a specialty shop. Hesitation is totally gone after rebuild, but now it won’t idle smoothly. Once it warms up, it’s prone to run ragged and quit without warning, which is disconcerting in traffic.

    Runs great during acceleration and cruise above 1800 rpm. Runs ragged at small throttle openings, such as slow-speed cruise. Randomly shuts itself off at idle or deceleration (like the key was switched off), sometimes. Sometimes it will run rough before switching itself off, especially during light-throttle application. Other times, not.

    Same fuel pump, distributor, coil, points, cap, rotor and plugs as before carb rebuild, and all of those are less than 500 miles old. Fresh fuel filter. Fuel less that a week old. Idle mixture screws are 2-1/2 turns out. It runs least bad there.

    All under-hood rubber had been replaced and worked fine before the carb rebuild. Checked for vacuum leaks anyway by disconnecting everything from the vacuum tree and plugging the holes (made no difference).

    Both carburetor mounting gaskets (carb to spacer, spacer to manifold) changed with new Fel-Pro gaskets when carb replaced. Everything was squeaky clean and dry for assembly. Checked for vacuum leaks by spraying carburetor cleaner around the base of carb and egr while car idling (made no difference).

    Throttle linkage setup per for Ford factory service manual (not likely the transition slots are exposed at idle, checked that). Choke operating normally. Ground strap to breaker-plate is good. Battery and engine grounds good. Proper 7 volts to coil. Throttle solenoid works as designed. EGR valve working properly.

    I’m into this particular problem for about five hours of banging my head against the wall. Basically, I've gone through everything at least twice. In addition to my own efforts, I had a shop with vintage Ford experience work on it with no improvement. However, the mechanic did confirm points and timing were set to factory spec. They suggested swapping out components (such as a brand new carburetor).

    Any and all suggestions gladly accepted. After the car cools, I’m going to replace the coil with a known good one. After that, I am at the end of the road. Seriously thinking about how wonderful it would be to roll this hooptie off a cliff. Unfortunately, I'd have to hire a tow truck to get it there.
     
  2. groberts101

    groberts101 Member Supporting Member

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    Check to see if distributor vacuum advance pot has leak via vac test. Quick test is to disconnect from source and suck on the vac hose then plug with tongue for several seconds to verify holds vacuum. Sounds silly but works well enough if you don't have handheld vac pump.

    If good then be sure that line is hooked to full manifold vacuum source. Not ported/timed source where there is no vacuum assist added until higher throttle angles.

    If no love also verify ignition timing with light before tossing parts at it.
     
  3. Krazy Comet

    Krazy Comet Tom

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    Sorry but other than a leak on the intake, vacuum has zero to do with idle(though I would verify the engine has good vacuum).. Ford never used full vacuum on dist but used ported vacuum for years, advance came in almost as soon as throttle is cracked.. Those engines idled without issue, no stalling etc. Rough idle on a 2100 is generally a blown/leaking power valve.

    This could be a ignition issue but at 7v I doubt it's the points, possibly a flaky condenser or coil.
     
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  4. groberts101

    groberts101 Member Supporting Member

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    I kinda figured that, Tom. Although you never know what someone has changed thru the years either. Only thing I had on the quick pop in. Leaking pv should only show once the main circuit has kicked in though.

    More stretching here.. but what about no check ball or maybe little rubber check valve/stopper deal in the accellerator pump? Been a long while.. can't remember exactly what was used in those units. Could cause fuel to drip out nozzle and screw mixture up?

    Is it only ocuuring during idle light cruise? If so seems unlikely to be coil. Better to confirm all baselines first. Look down carb bores.. no leaking fuel. Define the throttle position to home in on fuel circuit involved. Check base ignition timing. All I have time to chime in on now. Good luck!
     
  5. CA189HJN

    CA189HJN Member

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    Thanks. Car has 18-inches of vacuum at crappy idle, +/- 1/2-inch or so. I have a Mini-Mite, so I have systematically checked every vacuum component to see if it will hold vacuum. This car should start and idle like a grandfather clock with all vacuum sources plugged, but connected or plugged makes no difference. Ignition is 6 degrees BTDC. Carb rebuilder said the old power valve had been bad and she replaced it. Possible the new one is also bad. Next thing after the coil to swap out. Off to the auto parts store to buy a power valve and another carb-to-spacer gasket. Thanks again.
     
  6. Krazy Comet

    Krazy Comet Tom

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    I believe without check ball pump shot is nil or at least greatly reduced. It purpose is to keep the passages primed.

    Could check the gasket on power valve, be sure it fits properly.
     
  7. Craig Selvey

    Craig Selvey Indiana State Rep - MCCI Supporting Member

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    You stated: Idle mixture screws are 2-1/2 turns out

    I have always rear 1 1/2 turns is what is recommended.
     
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  8. Krazy Comet

    Krazy Comet Tom

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    If you mean heard, I agree.
     
  9. Maverocket

    Maverocket Bob Williams Supporting Member

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    I’ve always heard 1-1/2 for Holley and 3 for Ford.
     
  10. Crazy Larry

    Crazy Larry Member

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    You said it idles good until it warms up. Sounds like choke to me.
     
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  11. groberts101

    groberts101 Member Supporting Member

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    In a perfect world you can get close by using the typical factory setting. But it's far from a perfect world with these old motors so you should ALWAYS use a vacuum gauge directly ported to a full manifold vacuum source to set idle mixture screws.

    You should also confirm float level settings and adjust if necessary. Very easy to do on those carbs by bending the small needle hanging/seating lever/tab on the end of the float. Some kits used to have the small paper float adjustment gauges not sure if they still do but close to level or even slightly downwards angle is far better than being too high.

    Have you also visually checked for raw fuel dripping from boosters during idle?

    And like I said above, always best to eliminate the other circuits by determining when it happens. You said idle and light cruise?.. if only runs rough during idle and very light cruise(constant lower throttle angle) then that should mean it's specifically located within those circuits. But if it does the same when accelerating at higher throttle angles, say 1/4 - 1/2 throttle?.. then you are out of the idle and transfer slots domain and into the main jet/power valve metering circuits.

    You also need to be damned sure the distributor is functioning properly as well be verifying base timing plus constant rise of the mechanical portion without the vac advance pot hooked up. Then verify what and how much the advance pot is adding when reconnected. Regardless of the factory hooking it to ported/timed source.. it WILL run better overall with a full manifold vacuum source. 6° base timing is horrid and why the factory did that had nothing at all to do with mileage or performance and is another whole discussion in itself. And even if you don't want to deviate from the factory's ported source, it's very easy to hook it to the full source for quick testing. Given these symptoms it seems very unlikely that will be the problem here but you are doing your engine no favors by keeping it on the ported source which does absolutely nothing for cleaning up the idle and very light cruise rpm's when the ported source has not yet built enough vacuum to assist light throttle combustion and efficiency. Being that you have near 18" of manifold vac with only 6° of base timing, I'm guessing it's already hooked to full manifold vacuum anyways but just trying to help.
     
  12. groberts101

    groberts101 Member Supporting Member

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    Good catch there, Larry. This is why it's so hard to help on a forum. Things get breezed over when people come flying through, terminology is easily misconstrued, testing/troubleshooting is incomplete, and OP's don't give nearly enough clarification or follow up to get reliable and specific troubleshooting.
     
  13. Eastern Raider

    Eastern Raider Member

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    Ca 189 , it sounds like you have a Pro Carb Builder! Couldn't they Trouble shoot the Car as a whole, while running it? It sounds like a cheep, quick Fix. Beware of carbs with holes drilled in the choke plate, for they are independently set!
     
  14. Krazy Comet

    Krazy Comet Tom

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    I suspect the op has enough awareness to know whether the choke is open or not. As long as it's at least mostly open when engine is warm, that ain't your problem.

    I've fixed(uh sidestepped) sticking chokes by clipping a clothespin to carb housing so it couldn't fully close.
     
  15. CA189HJN

    CA189HJN Member

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    Me again. Mostly there.

    - Replaced coil and condenser,

    - Replaced power valve

    - Reset linkage to factory defaults

    - Set idle mixture to 2-1/2 turns out (more on this later)

    - Used Hi-Tack when seating spacer-to-manifold gasket

    After fully warming up, the car now idles at about 600 rpm in drive. It’s still not as smooth as I want, but it’s an order of magnitude better than two days ago. It drives well, the hesitation is still gone, but there’s still a something a little “off.” I have yet to make any mixture or linkage adjustment, other than those I made on the bench, so it’s bound to get a little better.

    Expectation management fully is engaged, as this is a 45-year old economy car. It's never going to run like a Lexus, but that's okay; I'm just trying to get it to run as well as a 1973 Maverick has a right to run.

    Note to Eastern Ranger: The Carburetor Factory, in Antelope, California, just does carbs. You drop it off before 10, they have your rebuild ready in the afternoon. Great service. But they don't work whole cars.

    The shop manual says to use 1-1/2 turns out for initial idle mixture, but since this engine had been exhibiting signs of lean combustion, I figured it’s not going to hurt to richen the idle mixture a little. The final setting isn’t going to be too far off from this. I'll use the vacuum-gauge method; it's worked for me int he past.

    Thanks to all of you for your help. While I can't point to any specific thing, my gut says it was several things. As they say, 90 percent of all carburetor problems are in the distributor.

    Hope to see some of you at the Spanky’s Pizza car show in Placerville June 24. And thanks again.
     

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