setting engine timing -- vacuum advance mid 20s?

[kajsdf]

after installing new lifters (which took care of my clicking problem) we are now trying to properly time the engine and fine tune my new 2150 (thanks gronk).  base timing was set at 8 degrees. not 100% sure on idle rpm (no tach) but we managed to get it quite low. however, as soon as we hooked up the vacuum advance, it jumped to approximately 25 degrees at idle. 

a trip around the block indicated that under load it advances itself so far it almost wants to die; it's necessary to back off the gas a bit to keep it running.  there is no evidence of knocking or pinging and other than having to back off the gas, it runs smooth as eggs.

vacuum lines are set up properly, computer is bypassed correctly. 

any thoughts?  the vacuum advance seems to be far too high, but i am not sure what it should be.  i didn't see anything of much help in the tsm, unless i missed it, nor was it mentioned in the timing article in the eaglepedia.

oh, and if anyone has some good mixture settings to try for the carb, that would be much appreciated.  it's guesswork at this point.

thanks

[mudkicker715]

Vac advance for dissy is ported correct.

[kajsdf]

it's from the port directly below the choke housing.  is that correct, or did i hook it up backwards?

[kajsdf]

which port on the carb is ported vac?

[kajsdf]

this is where it's currently hooked up...that was the only remaining port on the carb.  the other was the elbow that leads to the air cleaner housing that was already capped when i got it.  so by process of elimination i assumed this was the correct port as it's supposed to be directly from carb to distro if i am understanding this correctly.

[projectscreamingeagle]

we set base timing with vac advance unhooked and port on carb plugged. after half a pack of cigerettes a 20 minute drive home and pacing back and forth in the house the "falling on its face issue" just leads me back to the carb and just having to do some fine tuning (by the way gronk its a very nice piece and i shouldve definatly got one off you when i built mine lol) its not knocking pinging nutn purrs like a kitten. off the stop sign idle circut is fine and accelorator circut is fine but once the squirt burns off i had to get out of the pedal to keep it running, no biggie just some fine tuning needed. in park throttle responce is good and crisp, hold at approx 2000 and cracking it was one the money. we let it idle for at least a good 30 minutes or so and the temp guage didnt go above the colder end of the green line.   wich that could be somthing else (had heat tho) it would start fine didnt knock even on shut down didnt diesel or knock. it just kind of weirded us out as soon as we plugged the line in it jumped that much.

[kajsdf]

just realized we forgot to disconnect the 2nd connector from the ignition box (2-wire)

could this be the source of our issue?

[BenM]

Did you bypass the plug to the ECM, it sounds like it's still controlling the spark.

You don't have the 3-wire plug on you ignition, do you?

[GRONK]

What is your elevation?  I will respond with correct timing deg for you.   Note:  To set timing, you must disconnect the vacuum to the distributor and make sure your choke is OPEN all the way and your fast idle cam has dropped so you are riding on the curb idle screw.

Set your timing at 650RPM and you will be good to go.

I'm assuming you have PCV hooled up and all manifold vacuum sources sealed tight.

[kajsdf]

there is the one with 3 wires going to it (orange wire from distro spliced to green where orange continues on the other side, if that makes sense) and 4 going from connector to box.  the connections look just like they do in the diagram:



the other is the 2 wire connection.

gronk, all pcv is hooked up and all other vacuum is good.  new caps on unused ports, new hoses on everything still in use.  elevation according to wikipedia for clovis, nm is 4,268

[GRONK]

Set timing at 12-13deg at 650ROM, choke open, engine warm, etc.

Use a vacuum gauge (manifold) to dial in the mixtre screws/timing after you reach a good base.

[kajsdf]

still need to disconnect and jumper 2nd connector to ignition box, correct? or is this not necessary with the n u t t e r b y p a s s ?

and what numbers are normal for the vacuum advance after it's hooked back up?

[Bird-o-Prey]

I am running an MC2150 off of a mustang.  I have a GM HEI distributor which is run off of manifold vac (on top of manifold behind carb by the firewall).  My carb only has i port on it which is for the choke pull off.  My engine is timed to 8* BTDC with the vac line plugged.  When I tried to run the car off of the ported vac the engine ran like POO!  I switched the vac line to manifold vac and it smoothed out and stopped stalling.  I have run the car this way for 2 years now.  I had the vac line plumbed like this before I switched to the HEI (but with the MC2150) and the car still ran fine.  Perhaps a different configuration in the carb?

[projectscreamingeagle]

im still not understanding why if we are in the correct port its pulling full vac advance at idle lol. does one of the wires that plugged into the distributor from the ignition box run to the computer some how? i know a newb question but i havent done anything with the stock ignition i went straight with the HEI

[BenM]

AMC used two setups, one with a separate wire on the ignition module - the yellow grommet ignition module and the one with the the ECM spliced into the wires between the sensor and the ignition module - with a blue grommet. The blue box is much more common, that's what the diagram above shows. Sorry if it was confulsing, but asking about unplugging the other connector made me wonder, the yellow box also has a third 3-pin connector that needs to be unplugged.

This is where the wiring should end up:


My understanding is that the start wire to the module retards the timing to make starting easier, but you need that plug. The other plug goes to the coil and to the sensor.

If the wiring is all clean and good, and nothing is plugged in backward then try a new module. The timing will jump around on a dying module, especially after 20-odd years.

Also, if you have advance at idle, you're on a manifold source or you have your idle set way too high. Factory setup used a ported source with no idle vacuum, but everyone had a setup at one time that used temperature switches and regulators between vacuum ports and the distributor. If you have any of that disable it until everything is working correctly.

First, I would try running with no vacuum to the distributor. Make sure it's disconnected at both ends.
Second, if it still feels like the timing is changing then look at the wiring and make sure it's correct. You may have a wire that is shorting out somewhere.
Third, I'd go get a spare box. Worst thing is you have a $25 spare part in case it goes bad. They may even be able to test your old one.