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Engine Idle Problem


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Having a problem with the engine idle on my 36 P2.  I drive it several times a week and started having a problem that the engine would quit when I came to a stop sign.  Increased the idle speed some but didn't help.  Got the book out and found the screw to adjust the idle mixture but if I turn it all the way in or nearly all the way out, the engine sounds the same and I still have the problem.  Got a qt of Marvel Mystery oil and put 6 oz in a full tank.  I have run about a quarter of a tank and still the same problem with adjusting the idle mixture.  Any idea how much fuel I might need to run before expecting to see a change or do you think something else is the problem.

Thanks for your help.

Randy

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If it runs with the idle mixture screw all the way in it's probably a vacuum leak somewhere. Spray some starter fluid around the carb base and manifold gaskets . If the idle speed increases you've found your vacuum leak.

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Warmed up the engine, idle mixture needle all the way in, and sprayed the engine start all around the carb and intake manifold, and nothing changed.  Stopped the engine, tightened up the nuts on the intake manifold a little and tested again but everything still the same. 

 

Any other ideas on what might be the problem?

Thanks,

Randy

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It could also be a dirty or clogged carburetor.  My 33 Plym would run ,but poorly, with the idle screw all the way in or a couple of turns out. Changed to a better carb and it runs like a top now with the idle screw 1 1/2 turns out and won't idle with the idle screw all the way in now.

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I had a Plymouth 6 that was starting to be a real "smoker". So I pulled it down and replaced the rings,many were broken, cleaned up the valve seats and replaced the valves (with 1958 Chev 283 ci. exhaust valves). Lo and behold the choke started to "work". I had to keep it out a bit as the engine warmed up before I could push it in just as you would expect of a new vehicle. But my choke never really made any difference before. Then I hooked up a vacuum gauge to the windshield wiper port on the manifold and for the 1st time in a long time there was a "good" point on the air bleed screw! The engine also pulled 15 inches of vacuum at idle. The rings were just "0" standard and I just knurled the cylinders to bring them back to size a bit. I've seen a lot of discussion on the net about engines not adjusting to specs. I think the engines are tired and may need to be "freshened up".  The engine also got a LOT better gas mileage.  Just my 2 cents.    

Edited by DodgeKCL (see edit history)
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What carb are you using, the '36 Plymouth was originally equipped with a Carter B&B carb. If you can find a Motor's Manual for '35 and up it shows detailed info on rebuilding the B&B's  and adjustments. If the body insulator is damaged or warped, it could cause an air leak. Maybe the float level is off which could cause flooding ( if it runs with the screw completely shut or stalling on deceleration due to a low fuel level. Just a thought.

Edited by jpage (see edit history)
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Thanks for all your help and I think I found the problem.  This morning I disconnected the vacuum line at carb that goes to the vacuum advance on the distributor.  Tried to suck it like a straw and to my surprise, I didn't feel any resistance at all.  If I blew thru it, I could hear the air coming out at the distributor.  I assumed the vacuum advance is bad so ordered one and also a set of points and condenser.  Removed the distributor, tore it down and cleaned it and will assemble when I get the parts.  Tried to mark the location of the distributor before I removed it so that it won't need to be timed.  Never have done  that either, but guess I could figure it out if I need to.

 

Also going to paint the distributor base.  It was silver like the engine but was wondering if that is correct or should it be black?

 

Will let you know know how things go after I get it back together and try to start it up.  Took a lot of pictures so think I can get it back together o.k.

Randy

Edited by randyta
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If my understanding is correct, the vacuum advance does not pull a vacuum from the intake manifold. There is a small port above the throttle butterfly that advance gets its vacuum from. The advance diaphragm being bad is a good find however it shouldn't be the potential vacuum leak that's causing you issues.

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Ok, but the port on the carb that it is connected to does not see manifold vacuum until you start to open the throttle, aside from not advancing the timing the blown advance diaphragm was just allowing air to bypass the air filter on your carb. 

 

Another place to look for a vacuum leak at idle is around the throttle shaft, they get ovaled out after many years of use and start to allow air in. I chased that on mine for quite a bit longer than I'd like to admit. 

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Put the distributor back together this morning and didn't have any parts left over.  A good thing, right!  Installed it and tried to start the engine, but nothing.  Forgot to hook up the coil wire.  Did that and started right up.  Took it for a drive to warm it up and the engine runs much better with a lot more pep. Still have the stalling problem when I stop.  Tried to adjust the idle mixture and have the same problem as before.  Guess I still have a vacuum leak somewhere and will continue to look.

Randy

 

 

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I think the problem has been resolved.  This morning I did some more checking for a vacuum leak with starter spray but didn't find anything.  Carbking, Jon, suggested that if all else fails, take off the air breather,  rev up the engine, and temporarily put a metal plate over the carb a few times and if something is stuck in it, it might suck it out.  Did that a few times and idle adjustment seems to be working now.  If I screw it all the way in it doesn't die, but really runs poorly.  Road tested it and it seems to run fine.

 

Thanks to all for your suggestions and guidance.  I learned a lot from this exercise and I'm ready to move on.

Randy

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