The engine runs 155 to 160 with a 180 degree thermostat, unless idling at long stoplights.  At the lower temp idle is perfect, smooth, 600 rpm.  It is pretty cool, actually relaxing with a point in there where a deep base note rolls through.  When the water temp gauge hits 180 the idle changes, very predictably.  Same thing each time...  rougher, uneven. 

I have noticed the coil is hot.  It is an Accel with internal 1.4 ohm resistence without ballast, which was the coil Accel called for to go with their pointless ingition if ballast resistor wasnt going to be used.  Coil is mounted in standard location over intake, with 1/2 in. spacers holding it above intake.

Intake manifold gaskets are wide open at the crossover, and they and the manifold are temporaries waiting for Mummert's release.  Thin stock phenolic spacer between intake and carb.

So what do you think is the cause in idle change?  Heating causing a change in idle mixture or an overheated coil changing its characteristics?  Idle returns to normal immediately after temp drops. 

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

First, verify that the temp is actually 180 with an infrared thermometer. You may have a similar problem as I which is insufficient airflow at idle to keep the engine cool. If it is a cooling issue, you may find it difficult to get a consistent idle.



Assuming it is cooling properly, I think your idle mixture needs to be adjusted - probably leaner.



Lawrenceville, GA

Charlie, the temp gauge is a quality Autometer, and is dead accurate according to infrared thermometer.

When it goes up to say 175 I switch on the elect. fan and the engine will stay at 180 until back underway.

Leaner? 

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

If the mixture is too rich, it may run well when it's cooler under the ho.. wait, do you have a hood? As it warms up, it is too rich because the air is hotter - less air gets into the engine. Idle it in your driveway until it starts to run rough and adjust the idle screws to see if it improves.


Lawrenceville, GA

How about .....change the electrical parts to see if you can rule them out - space the coil off the engine more than a half inch or something like that. Use an old coil and resistor for a temporary replacement. The Accel trigger is just a power transistor that goes to ground like points - at idle a less juicy coil shouldn't be a big deal for it. As long as the total resistance is over 1.4 OHMS (coil and resistor).

Use your infared gun on the carburetor, hard fuel lines and fuel fillter. Mechanical fuel pump? If the engine is thumping along sort of retarded on spark - the exhaust will heat up and start "radiating" everything in the "line of sight' from the heated surfaces. Fuel pressure maybe dropping?

 
 Steve Metzger       Tucson, Arizona

Charlie and AZ, thanks.  It will take a few days to go through all your suggestions.  Oh, it is hoodless.

Mike

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Mike I had a simular problem with my truck when it got warmed up, but I had to slightly "fatten" up the mixture and it smoothed right out. But I'm also at a 2000-2500 ft. altitude also. It also ran a little fast after doing this at idle but after warming up went down to 650-700 RPM and thats with a hand choke.

                                                        Michael

Michael

Sandy Valley, NV

I had a problem similar to yours after finishing a cross country trip in my TBird. Good idle when cool, lousy idle when hot. After much trial and error, I found that the lash on the exhaust valves had closed up. After resetting the valves, the idle was much improved. Apparently, the long trip pounded the seats (probably not hardened seats) . The same problem is coming back, so I am doing a valve job and getting the hardened seats.



Check the valve lash.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Hello; You said you have a 180degree thermostat and you car idles good until it come up to temp of 180 degrees and then it runs not so good. This is just after the thermostat open. Coincidence? Or hot water in the intake manifold raising the temp of the carb. Are you using E85 or gas with ethanol?

[quote]Pete 55Tbird (6/14/2009)

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Hello; You said you have a 180degree thermostat and you car idles good until it come up to temp of 180 degrees and then it runs not so good. This is just after the thermostat open. Coincidence? Or hot water in the intake manifold raising the temp of the carb.

     And making it act rich. That's why Charlie told him to reset the idle hot. Problem is, when he does, it will be lean before it warms up. It's a tradeoff.

Frank/Rebop

Bristol, In ( by Elkhart)