Igniton timing mystery
croozertoo
12-30-2003, 11:02 AM
Hello, just joined this forum to see if anyone can solve this mystery.....
After rebuilding my daughter's 1982 Jeep Scrambler with the 2.5 liter Iron Duke 4 cylinder, we started the engine and did the normal break-in run on the cam. The engine ran slightly rough due to minor carb problems, but everything was normal during the 1/2 hour run at about 2000 RPM. I took a timing light read and adjusted the advance until the engine ran smoothly at 2000 RPM. I noticed that the advance seemed way high, but the engine continued to run normally.
We then changed the oil and restarted the engine, this time allowing it to idle with the vacuum advance disconnected and plugged. To my surprise, the timing light showed about 25 to 30 degrees of advance at 700 RPM! This is approximate since it was way off the scale. Revving the engine with and without vacuum advance showed normal advance range as RPM's increased, but still way too much - from 25 to about 50 degrees!
I then rechecked that the timing mark on the balancer was 0 degrees at TDC on the #1 piston. It was exactly. I haven't checked the rotor position at TDC in the distributor yet. When I installed the distributor, I set the rotor to the #1 contact with the #1 cylinder at TDC on compression. I then wired up the firing order. My timing light is not adjustable.
Basically, the engine runs fine. It can't really have 25 degrees of advance at idle, so I suspect something is out of whack, but I have no idea what it might be. I've rebuilt and run several engines, mostly V8's, and have never had a problem like this!
Any ideas???
After rebuilding my daughter's 1982 Jeep Scrambler with the 2.5 liter Iron Duke 4 cylinder, we started the engine and did the normal break-in run on the cam. The engine ran slightly rough due to minor carb problems, but everything was normal during the 1/2 hour run at about 2000 RPM. I took a timing light read and adjusted the advance until the engine ran smoothly at 2000 RPM. I noticed that the advance seemed way high, but the engine continued to run normally.
We then changed the oil and restarted the engine, this time allowing it to idle with the vacuum advance disconnected and plugged. To my surprise, the timing light showed about 25 to 30 degrees of advance at 700 RPM! This is approximate since it was way off the scale. Revving the engine with and without vacuum advance showed normal advance range as RPM's increased, but still way too much - from 25 to about 50 degrees!
I then rechecked that the timing mark on the balancer was 0 degrees at TDC on the #1 piston. It was exactly. I haven't checked the rotor position at TDC in the distributor yet. When I installed the distributor, I set the rotor to the #1 contact with the #1 cylinder at TDC on compression. I then wired up the firing order. My timing light is not adjustable.
Basically, the engine runs fine. It can't really have 25 degrees of advance at idle, so I suspect something is out of whack, but I have no idea what it might be. I've rebuilt and run several engines, mostly V8's, and have never had a problem like this!
Any ideas???
KC Ron Carter
12-31-2003, 07:49 AM
It sounds like you have a vacuum retard, not unusual to see.
Most consider setting the max and letting the idle be what ever.
The manufactures provide the idle setting since that is the easiest to set.
Later,
Most consider setting the max and letting the idle be what ever.
The manufactures provide the idle setting since that is the easiest to set.
Later,
MustangRoadRacer
12-31-2003, 08:31 AM
could be bad timing light or the marks could be off, but barring that, what KC said soundas correct.
Automotive Network, Inc., Copyright ©2026