Timing jumping a lot

[Anonymous_User]

Specs: '86 TI shortblock, slightly ported 782, one piece intake, '87 wiring, older +40 cal (ND), +40's, 3-bar

Had it running, but it wasn't running very good, so I tore into it tonight to double check cam timing, spark timing, fuel pressure. Cam timing was a tooth out - corrected it. Couldn't find my fuel pressure gauge - that'll have to wait. Hooked up the timing light and the timing mark was jumping about 10 degrees.

With the car idling, I set the timing at what looked like an average of 12 degrees BTDC. Trying to start the car, it would fire, run for a second or two and then die with a slight backfire sound. If I start it and immediately give it some throttle, it will rev to 3k, die, catch itself before completely dead, and repeat.

It was getting late and running only through the swingvalve, it was a little noisy to continue. I bumped the timing a "wee bit" retarded. Now it fires up and idles. I don't know exactly where the timing is now until I put the light back on it tomorrow.

Is it normal for the initial timing to jump so much. If not, is there a cure?

[cordes]

I have had it jump about 2* or so each side of the mark, but 10* is a huge jump. I would check for a vac leak, make sure that the CTS is unpluged of course.

It might be some thing with the dist for it to be jumping that much.

[87glhs232]

Maybe a dumb Q but you are disconnecting the temp sensor on the water block right? Another thing that comes to mind is what cam are you running? '88 or newer roller, or a slider?
Is the idle smooth when the timing jumps, or does the engine surge? Codes?

[MiniMopar]

Assuming that you did disconnect the temp sensor, I'd remove the dist cap, grab the rotor twist it...checking for play. Remove it and the HEP and check that the shutter wheel it still attached to the distributer shaft. Also check your timing belt tension.

[GLHSKEN]

^^^^^ All likely culprits

[Anonymous_User]

Maybe a dumb Q but you are disconnecting the temp sensor

Apparently not a dumb question. LOL..... Sometimes we all have that stupid brain fart!! I can't believe I'm actually admitting to this. Uh.... It was late, dark, and I was tired? LOL Thanks.

[mech1nxh]

Apparently not a dumb question. LOL..... Sometimes we all have that stupid brain fart!! I can't believe I'm actually admitting to this. Uh.... It was late, dark, and I was tired? LOL Thanks.

well...dont feel to bad ....I spent an hour going through the same
checks, untill I found the crack in the rotor body (as previously suggested)
doh!!!