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TUNING AND TIMING PROBLEMS

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MGerdau View Drop Down
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    Posted: Jul/08/2020 at 7:34pm
I'm trying to tune and time my step-son's 1978 Pacer. It has the 6cyl with a Carter YF (or it maybe the YFA) carb. I rebuilt the carb but the car dies when I unplug the solenoid. Then when I try to start the car it won't start unless I close the choke, it'll run as soon as I let the choke open and if I have the solenoid plugged in. I've been able to get the idle down to 800 rpm and then set the timing to 8 degrees; all with the distributor vacuum advance unplugged and the vacuum line plugged, the air filter on and plugged in, and the car in drive. But when I unplug the solenoid it dies. All of the anti pollution devices are plugged in with the exception of the smog pump which was frozen up. Any suggestions?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Jul/09/2020 at 4:23am
You say it dies if the throttle holding solenoid is unplugged. That's basically what it's supposed to do. The solenoid holds the throttle at proper idle speed. The solenoid de-energizes when the ignition is switched off to prevent the engine from dieseling or "run on". Just don't unplug the solenoid. Let it do what it's supposed to do. Problem solved. 

Cold engines always need choked to start with few exceptions. Once started, they will run with partial or no choke. Again...normal and problem solved.

I'd put more timing into it. It'll want 10 degrees at a 600 RPM idle. The mechanical advance is kicking in by 800 RPM so you probably should see 12-15 degrees at 800 RPM. Timed and tuned right, it should happily idle as low as 500 RPM and I've even taken mine down to 250 RPM in a slow idle contest. Still...550-600 is where you want to be. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGerdau Quote  Post ReplyReply Direct Link To This Post Posted: Jul/09/2020 at 1:43pm
Thank you!

Am I, maybe unplugging the wrong thing.  The timing instructions said to unplug the, I thought, solenoid.   
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Post Options Post Options   Thanks (1) Thanks(1)   Quote wittsend Quote  Post ReplyReply Direct Link To This Post Posted: Jul/09/2020 at 2:20pm
As noted above the solenoid is designed to shut off the flow of fuel..., or completely close the throttle blade. In either case the engine should not run if it is disconnected (de-energized).

I'm not sure if the design you have closes the throttle blade, but, if it does then there likely is some form of adjustment at the solenoid to adjust idle. That is unless there is a convoluted multiple linked linkage where the idle air speed is adjusted independently..., after the solenoid engages. Sometimes careful observation will show the logic (or lack of) in the design.

Unfortunately 70's/80's engine systems were Rube Goldberg designed in accordance with Murphy's law. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2020 at 12:20am
There will be an adjusting screw down low on the carburetor near the throttle shaft for adjusting the throttle opening with the solenoid off. It's the only idle speed adjustment on cars without the solenoid. 

The solenoid has it's own adjusting screw, of course. 

So the engine has two idle speeds to set: the base idle speed and the solenoid idle speed. Both should be listed on the emission certification label under the hood.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGerdau Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2020 at 8:15pm
Thank you! 

While rebuilding the carb I saw a place for a screw that would adjust the throttle idle but there was no screw.  I figured the solenoid would take care of all of the throttle idle.

I'll put a screw in there and try adjusting the idle down to 500.

Before that I have to deal with a coolant leak.  Also, check the exhaust pipe to make sure there are no more squirrel nests in there.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2020 at 2:29am
500 RPM in neutral is a pretty common specification for the throttle screw because it's fast enough that the engine will idle on it but it's slow enough and the throttle is closed enough that it won't Diesel. 

If there is no specification, I just back off all screws until the throttle plates physically jam in the throttle bores then turn the throttle screw until is just barely cracks the throttles open. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MGerdau Quote  Post ReplyReply Direct Link To This Post Posted: Jul/14/2020 at 10:38pm
I couldn't get the idle down below 700.  But I do have a pretty smooth idle.  I think some of the smog devices may be malfunctioning.  I did drive it around our driveway and sent a video to our son.  Thanks for all of the advise - you guys rock!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2020 at 3:25am
Something is going on, because you should be able to shut that throttle down far enough to make it idle below 400 RPM if you so desire. I have the same engine and carburetor that you do and I think I took mine down to like 300 RPM just because I was curious. 
1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
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