Chrysler 120 won't idle

[Charlie75]

Hello,

It seems to be an impossible task to get my 1975 Chrysler 120 to operate properly at idle speeds. Fuel pump, spark plugs are new and the carbs have been overhauled with new gaskets, needles, seats etc. Float levels are in order.
The original Magnapower II system has been removed at some point and replaced by the newer Magnapower III/ Prestolite ignition system. It operates OK and timing is correct.
The engine operates perfectly when above idle speeds and performance is ok. The compressions are also checked and are fine.
The engine starts normally and has a smooth operation during warm up, but as soon as the rpm level is lowered to normal (900) it will operate just a few minutes and then it dies. The funniest thing is, that after normal cruising when the throttle is gradually lowered to idle speeds, the engine will first operate for a while with higher RPM (1600) when the lever is in neutral, and after that it will stall within a couple of minutes. This is harmful to the clutch and gears.
The linkages and towershaft are checked and the lever returns to idle position as it should. Adjusting the idle speed and mixtures wont do any good, the same basic problem remains.
The reeds and the reeds in the cylinder drain and fuel recirculation system seems to be in a proper working condition.

Any ideas what could cause such an irritating problem?

 

[Frank Acampora]

Re: Chrysler 120 won't idle

An idle speed of 900 IN GEAR in the water is too high. 900 in neutral is too low.

I suspect that the synchronization of carbs and timing is off. Correct idle depends upon the correct relation of throttle opening to timing, correct low speed mixture needle setting, and good compression on all cylinders. SO: First recheck the compression and then clean the plugs again.

Then, buy a Clymers manual and set the synch according to their procedure. It is rather long and I don't want to repeat it here. Hmmm! Maybe I'll make a sticky.

Check that the trigger assembly or the distributor (depending upon which one the engine has) is moving freely and smoothly. These can cause problems with the linkage binding, shifting in and out of gear, and idle not dropping down to its correct RPM

 

[Charlie75]

Re: Chrysler 120 won't idle

Thanks Frank,

I have tried over and over to get the idle speed set @750 in gear, but so far - not a chance... With the engine running in gear, and the RPM lowered to below 1000, it wont?t run for more than just a few seconds.

I have both the Clymers and the Seloc manuals and have checked the syncs on the carbs and the linkages. (quite simple as the 120 have only two carbs) The trigger assembly under the flywheel moves freely.

Double-checked the compressions and the timing - they are ok. Deposits on the plugs are normal and don't indicate any uneven mixtures between the four cylinders so I assume that needle settings on both carbs are at least almost correct.

When the RPM is lowered, and the engine quits, it somehow feels like too rich a mixture... Opening the throttle and restarting and, wrooom - the engine immediately comes back to life.

Not quite sure about the cylinder drain system though... The small reeds and poppet valves are clean and the hoses are not cracked. What else could be wrong here?

I wouldn't want to give up yet. I like the looks and sounds of the old Chrysler and it has a tremendous amount of power.

 

[Charlie75]

Re: Chrysler 120 won't idle

The investigation continues... Took the boat out for a test run today, and it seems that when the engine reaches normal operating temperature, the problem worsens.

When cold, the idle is fairly good, but after a short cruise the symptoms are exactly as if the mixture gets way too rich. The screws are open ca. 1 complete turn. Leaning the mixture will result in heavy coughing and spitting when cold and an immediate cut out.

The operating temp is normal, the cooling and thermostat is ok.

 

[1990_Bayliner]

Re: Chrysler 120 won't idle

The investigation continues... Took the boat out for a test run today, and it seems that when the engine reaches normal operating temperature, the problem worsens.

When cold, the idle is fairly good, but after a short cruise the symptoms are exactly as if the mixture gets way too rich. The screws are open ca. 1 complete turn. Leaning the mixture will result in heavy coughing and spitting when cold and an immediate cut out.

The operating temp is normal, the cooling and thermostat is ok.

I have the same issue with idle except my problem is opposite of yours when warmed up it idles fine, on the other hand, when cold it will not idle on it's own.

 

[Charlie75]

Re: Chrysler 120 won't idle

I have the same issue with idle except my problem is opposite of yours when warmed up it idles fine, on the other hand, when cold it will not idle on it's own.

Try enriching the mixture a bit (1/8-1/4 turns on each carb) and then rise the idle RPM as needed using the idle stop screw to compensate. This should give a better idle when the engine is cold.

 

[1990_Bayliner]

Re: Chrysler 120 won't idle

Awesome, Thanx I will try that and let you know how it went!

 

[1990_Bayliner]

Re: Chrysler 120 won't idle

Try enriching the mixture a bit (1/8-1/4 turns on each carb) and then rise the idle RPM as needed using the idle stop screw to compensate. This should give a better idle when the engine is cold.

Which of these screws is the idle screw?

Just go to www.gts1.00show.com click on engine to see the images. Thanx

http://www.gts1.00show.com/images/engine-2.jpg
http://www.gts1.00show.com/images/engine-1.jpg

 

[Charlie75]

Re: Chrysler 120 won't idle

Sorry for the late reply,

The marked screws on the second pic are the mixture setting screws. (I would start with 1/4 turns) The ones on the first pic are just the choke linkage sync shaft screws. Don?t touch theese.

Then you have adjust the idle stop screw a bit clockwards after opening the mixture screws. You will find the stop screw on the towershaft. You can see it on the second pic, just under the grey fuel hose going to the fuel pump. It has a stop nut on it. Loosen the nut and screw the whole inwards a bit until you have the right idle speed and then retighten the nut.