Could my initial timing really be at 35 deg?

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   My 360 is stock as far as I know except for a edelbrock intake and carb and ebay china hei. I had my timing set at 8 deg and ran out of adjustment room due to the vac assist interfering with PS belt, as a fix I started the timing process from step 1 and pulled the #1 plug.
Upon reassembly of the distributor the engine fired right up but now my timing light says I'm 35 deg advanced. My vacuum gauge shows a peak stable vacuum around 15-16 in hg. If I try to retard the distributor the engine starts running very rough.

Does this sound like the harbor freight timing light is screwed up, or did the engine skip a tooth or two on the timing chain when I readjusted it to the 10 deg btdc mark on the balancer? This time around I did rotate the engine counterclockwise by 5-10 degrees.

I did verify compression was in spec on all cylinders before assembling as well.

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DOJOLOACH Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Fan Joined: Sep/16/2025 Location: Charlotte North Status: Offline Points: 15	Post Options Post Reply Quote DOJOLOACH Report Post Thanks(0) Quote Reply Topic: Could my initial timing really be at 35 deg? Posted: Oct/08/2025 at 7:03am
	My 360 is stock as far as I know except for a edelbrock intake and carb and ebay china hei. I had my timing set at 8 deg and ran out of adjustment room due to the vac assist interfering with PS belt, as a fix I started the timing process from step 1 and pulled the #1 plug. Upon reassembly of the distributor the engine fired right up but now my timing light says I'm 35 deg advanced. My vacuum gauge shows a peak stable vacuum around 15-16 in hg. If I try to retard the distributor the engine starts running very rough. Does this sound like the harbor freight timing light is screwed up, or did the engine skip a tooth or two on the timing chain when I readjusted it to the 10 deg btdc mark on the balancer? This time around I did rotate the engine counterclockwise by 5-10 degrees. I did verify compression was in spec on all cylinders before assembling as well.

White70JavelinSST Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 5168	Post Options Post Reply Quote White70JavelinSST Report Post Thanks(0) Quote Reply Posted: Oct/08/2025 at 10:32am
	Check timing with your light on another known correctly timed vehicle to verify if it is at fault
	70 Javelin SST, second owner, purchased 1972

6PakBee Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Charter Member Joined: Jul/01/2007 Location: North Dakota Status: Offline Points: 5949	Post Options Post Reply Quote 6PakBee Report Post Thanks(0) Quote Reply Posted: Oct/08/2025 at 10:35am
	Timing light says your initial timing is 35 degrees advanced? Wow. I can think of a number of things, you have the pickup on the wrong cylinder, the harmonic damper has slipped, the timing light died on you.....but you can't have that much initial timing.
	Roger Gazur 1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach

bigbad69 Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Jul/02/2007 Location: Ontario Status: Online Points: 7417	Post Options Post Reply Quote bigbad69 Report Post Thanks(1) Quote Reply Posted: Oct/08/2025 at 11:09am
	Set the engine to TDC, compression stroke Verify the timing mark is a 0. Verify the rotor is pointing to cyl 1. I bet you will find one, or both of those, is wrong. I have never heard of a timing light flashing at the wrong time, when clamped to the correct plug wire. In my experience, they either flash (good), or they don't (FUBAR).
	69 Javelin SST BBO 390 T10

DOJOLOACH Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Fan Joined: Sep/16/2025 Location: Charlotte North Status: Offline Points: 15	Post Options Post Reply Quote DOJOLOACH Report Post Thanks(0) Quote Reply Posted: Oct/08/2025 at 6:00pm
	I primarly mean the advance knob on my light got out of calibration. Ok I was going to try on my 4.0 jeep but way too much stuff in the way, I may attempt on a mustang 5.0 tomorrow. However since I couldn't do that I pulled plug 1 and found the compression stroke, using a caliper I roughly found where 40 deg advanced is on the balancer and then double-checked my rotor position, rotor was behind plug wire 1 by about 20 to 30 deg. Then I rotated to 5 deg btdc and it was where I'd expect it to be. With vac advance disconnected i slowly revved the engine up to 4k or 5k and didn't hear any backfires or pinging, but im still getting a fluctuating vacuum of 15-17 in hg at 550rpm and rough idle. Up at 750rpm I'm getting a more smooth idle and vacuum is more stable at 17.5~. Is the low vacuum pressure a concern? Next plan is to go through all my vacuum ports and plug them to see if I have a leak. I also tried spraying propane around the intakes and couldn't hear an rpm increase(not sure my ears would pick that up though). Edited by DOJOLOACH - Oct/08/2025 at 6:14pm

Bruce Clarkson Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Feb/09/2013 Location: New Bern, NC Status: Offline Points: 594	Post Options Post Reply Quote Bruce Clarkson Report Post Thanks(1) Quote Reply Posted: Oct/12/2025 at 9:49pm
	Please disregard if you've already checked this but the dampers on these can very well slip. This will make the results from your timing light look funny since the mark will be in the wrong place. BTW, that will also impact engine balance in a significant way. Both my 343s were in that condition when I got them. They can be rebuilt for reasonable money. Good luck
	Bruce Clarkson

DOJOLOACH Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Fan Joined: Sep/16/2025 Location: Charlotte North Status: Offline Points: 15	Post Options Post Reply Quote DOJOLOACH Report Post Thanks(0) Quote Reply Posted: Oct/21/2025 at 4:07pm
	Wow, well I'm getting a measurement of 40deg btdc at idle according to the indicator on the balancer and a separate timing light, degrees advance did not change either when I held 3000rpm. Could the balancer slip just by cranking the engine over with a breaker bar/socket when I found tdc? I've literally only rotated it 10 deg backwards one time but that math doesn't even add up. Just replaced all the vacuum lines and tried plugging some to verify no leaks. I had also broken the rotor that came with this chinese hei cap so in a pinch I replaced it with a seemingly dimensionally identical rotor made for an 80s Chevy. Timing light flash tends to jump around 5 degrees every rpm sometimes, not as stable as it used to be. Maybe the rotor I put in is not gapped correctly with the cap buttons? Or spark plugs are too fowled with running rich? Edited by DOJOLOACH - Oct/21/2025 at 5:32pm

BassBoat Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Aug/29/2008 Status: Offline Points: 1931	Post Options Post Reply Quote BassBoat Report Post Thanks(0) Quote Reply Posted: Oct/22/2025 at 3:52pm
	you could mark the balancer so if it keeps moving you can tell. When you say the timing doesn't advance, I wonder if you are getting centrifugal advance at idle.

DOJOLOACH Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Fan Joined: Sep/16/2025 Location: Charlotte North Status: Offline Points: 15	Post Options Post Reply Quote DOJOLOACH Report Post Thanks(0) Quote Reply Posted: Oct/24/2025 at 6:01pm
	Well I'm confused even more now! I disassembled the distributor to check out the slop in the spring weights and inspected the coil. Reassembled and had my wife feel for the piston stop lifting, then again to feel when it started dropping. Dead in the middle of my two marks was the original timing mark, pretty much dead on with the TDC mark. I reassembled and was 20 deg advanced at idle so turned it back to 10 deg at 550 rpm, following directions in the service manual. Then reset idle to 750. Unless I just rotated the distributor to quickly that the engine died when I was at 40, I really don't know what changed. Still have poor vacuum at 15-16 in hg though, I tried spraying propane around different areas but didn't get any feedback, Maybe I moved the gas torch to quickly

BassBoat Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Aug/29/2008 Status: Offline Points: 1931	Post Options Post Reply Quote BassBoat Report Post Thanks(0) Quote Reply Posted: Nov/07/2025 at 11:49am
	My guess is that your driveability will improve, and idle vacuum, if you advance the timing to 20 at idle. That sounds like a lot when you reference the manual, but it isn't really for a low compression 360. To complement that initial timing, you might want to reduce centrifugal advance travel with a bushing. Total advance somewhere between 36 and 40 will run the best. good luck!