Timing Question

[Allen9878]

I have an 80 CJ5 with a AMC 258 i6 / 4.2l engine. The AMC 258 i6 / 4.2l is a 1987. What is the best timing for this engine?

 

[Allen9878]

Anybody? I could use the help!

 

[Buuushman]

There should be an emissions tag under the hood that will give you you the proper info on timing. If the tag is missing, I would start at @ 5-7 degrees below T.D.C., drive it, and advance the timing a degree at a time till the engine starts to ping under load, then back it off a few degrees.
Hope this helps.

 

[Allen9878]

It definitely does, thanks!

 

[Old Dog]

I would start at @ 5-7 degrees below T.D.C., drive it, and advance the timing a degree at a time till the engine starts to ping under load, then back it off a few degrees.
Hope this helps.

I think he means before T.D.C. At least thats where I would start.

 

[IOPort51]

do you own a service manual?? if not, why not??

 

[Cheepjeep85]

does the motor have all of the emissions stuff still on it? is it computer controlled like it was in the yj it was pulled from? or do you have the 1980 stuff on it? alot of people recommend 8deg btdc, mine is set at 9deg thats just where it seems to run the best.

 

[Old Dog]

my haynes yj manual says if it's carburated it should be 9-11* BTDC.

 

[Allen9878]

It doesn't have all the computer controlled stuff anymore. It has some of the simple emissions stuff but I cut out most of it.

 

[derf]

Best way to set the timing is to use a vacuum gauge while you're doing it. Some people can tune by ear but having the vacuum gauge telling you what's going on is much more reliable.

You can pick up a hand operated vacuum pump with a gauge at any parts store. It should have a manual that will get into using it to adjust your timing. If not, there's plenty of sites to google that have instructions for vacuum timing.

In a nutshell, you disconnect the vacuum advance and hook up the vacuum gauge to a manifold source. Start at something low and advance the timing slowly. As you advance the timing, the vacuum should increase. Once it peaks and starts to fall off, back it up until you're at the peak again. Then back it off 1-2 degrees and lock it in. Reconnect the vacuum advance and you're done.

While you're in there, you can also use the vacuum gauge to adjust your idle mixture too.