Problems with 340 timing

My long term project 72 340 Duster is acting strange. When I try to get it to idle and punch and sound normal, it isn't responding normally to minor tuning - idles mixture, turning the distributor for timing changes, trying different vacuum advance ports. I decided to get out the Innova digital advance timing light that I bought but haven't used til now. I had a lot of initial timing dialed in - 33 degrees . I had the vacuum advance disconnected and the port plugged at the carb. When I rev the engine up to 3000 - 3500 the timing mark goes the wrong way ( retards 20 degrees or so) and returns to the initial timing spot even though the engine is still revved up. I'm new to the advance light and don't know what's up with the Duster readings. It has Mopar Performance electronics conversion distributor, a chrome box, a pertronix coil. I tried it on another project - 71 Challenger 440 engine msd 6 box, proform ? procomp? something like that for a distributor, Mallory street strip coil - the engine runs pretty good and the timing acts like I expect. It advances some and holds when I rev it up. So I don't think it is a timing light problem. I hooked it up the same. What's wrong with the Duster 340 ? Distributor all messed up? Just not getting a good reading?

with a 1&1/4" socket/breaker bar set the dampener on 15 BTDC. turn housing slightly till magnet is dead even with the closest tooth which will have the rotor under either the #1 or the #6 plug wire (holler if it is way off). cap the vac can port at the carb. have the dialback knob back to zero. start/idle it & see what you get for initial. this'll get us started & also note the RPM it is idling at. holler back

Rapid -
Hey I'm trying to get some ideas on this. What are you suspecting with this test? I'm wondering if a couple of wires are swapped at the distributor or control box. I probably won't run the car for a couple of nights - give the neighbors a break.
Besides I have other fun in the heat such as mowing and garden related. I'll ponder this Duster issue in A/C til the weekend probably. Moparts is a good place for that ! My timing retards as I rev it then goes back to the initial number. Maybe I should trade in for a Smart Car !

the symptoms ain't making sense so I figured we might go back to some basics to try & get a handle on this. 15 BTDC is a good/reasonable start. You've likely already double checked your connections. I could see the MSD wreaking havoc on the dialback but if I am reading this right it is the other way around. Dont get a smart car, we WILL solve this! I see one every day in a companys' parking lot when I am out jogging & it caught my eye cuz it is so tiny (VG mileage I would assume). Do you have or can borrow a non dialback light for a quick repeat test?

This Duster has a Mopar chrome box and mopar electronic distributor. The 440 I tried it on had the MSD which proved the timing light works I think. Still, giving another light a chance on the Duster might not hurt. I have 3 of those regular lights around here. Usually one of these cars will tune up fairly good just by ear. But this one just seems a little rough on idle and just doesn't feel quite right. It will go in gear and drive down the road, although I haven't done it with the most recent ear and guess tuning. Where it was at for the dial back light test. It seems very slow to warm up and run right with more electric choke, less electric choke, more or less vac secondary. I'm afraid the retarded timing results might somehow be real.

with a bit of thought someone had a similar problem & the plug wire clamped was evidently too close to another one & the magnetism from the spark in the nearby wire was jumping over to the clamped wire giving a false flash location on the dampener. EDIT #3 is gonna fire 270 deg later around the dampener than the #1 will (& that is assuming it is a clean jump)

I found a guy on the internet who had a Trans Am with the same symptoms as my 340. He was on a forum asking what could cause this backwards advance reading. One of the guys said he was 90 % sure that the weights in the distributor were installed incorrectly and showed a picture of one installed wrong.

the early 241/260/270 Hemis have a dist with the same lower shaft length (3&7/8) as a SB & I am just assuming they rotate clockwise which I would think could cause this if one of those dists is in there but the eng could barely run & if it did it'd be way hot from the retarded timing exposing more of the cyl wall length to combustion. we're missing something simple here. confirm the spark ain't jumping over (move the clamp closer to the plug so the plug wire is isolated). SB adv weights look like a comma at the beginning of a sentence & BB's at the end of a sentence. the only way they will interchange is if you slip em on the post upside down & the pins the the slotted plate slides on would then be upside down so it would not work. Pics please! EDIT meant to say CCW on the rotation

If you put a BB Mopar distributor in a LA motor the advance will retard when revved up, trust me on making that mistake, once
if that is a 440 distributor get the correct one for the 318/360 motors and you will be good

Huh? How'd ya bolt it down and NOT notice the gap? Lol.

Maybe that's it ! I didn't know a big block one would fit a 340 at all. I'm sure I ordered a small block kit ( I think ). You guys are geniuses , no ? No kidding, thanks for that tid bit of info. You know I was thinking of ordering a new Proform distributor. I might have fixed it never knowing what was really wrong. How much of a gap we talking? I was dealing with oil leakage back there also. LOL. Thanks guys. I'll check my files and see if I can find that receipt and find a part no. on the distributor ! LOL - thanks all . Way to go Moparts !

close your fist & set it on top of the vac can. open your fist & let your fingers curl around the dist housing/cap the way they would naturally cup it. this is your direction of rotation. let us know what you get & if you pull the dist you can turn the housing in your hand just right till you can see enough of the weights to see if they are CW or CCW rotation. plus measure the dist shaft (Darthvdr is wondering)

Which fist? What is this?

whichever fist (L or R) that when sitting on top of the can will let your fingers open naturally & cup around the cap (it'd be the opposite of where the can nipple that the hose pushes on to is pointing). if your fingers are reaching around clockwise then CW rotation

OK - I'll take a look at that. I looked up the old receipt and the number for the electronic ignition kit was P3690426C the number tracked to a small block distributor. OK beer break !

alright, how about we move the clamp closer to the plug and grab one of you regular lights

I took the distributor out. I was going to look it over and measure the shaft which was 3 7/8 inches mounting surface to end of shaft. Normal for a small block one. B engine is supposed to be 3.5 inches and RB at 4 inches.

I put another distributor in there and same thing - running a little funny and timing still retards instead of advancing when revving up the motor. I finally got around to reversing the coil wires to see if that helped and it did! The engine runs smoother.
But with the timing light the mark still retards instead of advancing when revving up. So there's more than one problem. I figured both problems were tied to the same thing. Beer Break !

I have two cars now that run better with the coil wires reversed from what the Mopar conversion kit schematic calls for! Both are chrome box installations but two different coil brands. Also one is small block and one is big block. That's afu . Oh and I thought I'd mention I repositioned my Duster's distributor drive shaft to the proper position when I changed the distributor . I had moved my cap wires to fit the one - tooth - off position that I had it stuck in.

is the black/yellow wire going to coil neg primary?

The black / yellow stripe wire is going to the positive connection on the coil on both cars to run best.

hi,just a reminder to check if you have correct balancer and the correct timing cover. I think they moved timing marker to opposite side after 68 model year? not sure exactly but worth checking out.

The timing mark is on the driver's side. The timing cover and balancer are original 72 340 parts that came off this car and engine to the best of my knowledge and memory. The timing mark lined up when I re-stabbed the distributor drive and distributor. And the rotor pointed reasonably well where it should. My 1972 Plymouth shop manual shows a picture of the timing mark on the driver's side of the timing cover.

Have you physically checked to make sure the distributor has the proper mechanical rotation inside ? The shaft would be the same for either rotation , if it has the wrong reluctor cam it could move the timing in the wrong direction.

But if you have 33 degrees initial you should have a locked out distributor ???

I don't know that I have watched rotation with the engine turning over. But I have figured out how to tell if the distributor is correct for a small block or big block. I have also tried a second distributor. Swapping the coil wires made the engine run better while the weird timing light readings continued. Now I'm more thinking I'm not getting noise free pickup. I have Spiral Core wires and the wires are a little close together. I haven't really started those checks yet : moving wires around, moving the pickup around, clamping on another plug wire. Maybe even trying some RF shielding of some sort. My symptoms include a strange move back to the initial timing, which may indicate a reset of the timing gun. This idea came from another site where a guy was warning of interference from racing wires or other non - stock wires.