So I may have some dumb questions here. I want to check the timing of my "78 L82. Bought a timing light, did lots, of reading and I could let myself get dangerous

The car runs well once it is warmed up but cold is an issue. Maybe a carb issue, maybe something with the choke. All for a different post. As the sage advice goes, "90% of carb problems are caused by timing". Messing with the timing is all new to me.

To start, with the vacuum advance connected and idling at 900 RPM the timing shows 26 degrees. Disconnecting the vac advance drops RPM to 700 and the advance to 12 degrees. That is good according to everything I've read.

I set the timing light to 36 degrees and pull on the accelerator. By myself so I can't see the tac but by the sound of it, I reach "all in" at about 2,000 RPM. I will do this again tomorrow when I can get someone to read the tac for me.

So, that tells me that I am reaching all in a bit too early?

Is that a problem?

If I need to address this, do I adjust all in by turning the distributor or do I need a set of different springs and weights. FWIW here is a picture of the current springs. Any advice or suggestions appreciated. Thanks, Jim

 

I would recommend doing some cleaning of the weights to make sure they operate freely. Yes turning the distributor will change the static timing.
Send an e mail to Lars and he will send you his tuning papers. It will explain things in great detail. He provides them as a way of giving back but for guys that don't know about things like this he could charge 50 bucks and would be the best deal you ever got so take advantage.once you get your curve and carburetor set up you won't believe the difference.

 

Hey Jim, really no point in speculating until you have someone looking at the tach. If it is a stock distributor/weights, I doubt you are all in at 2000 rpm, and yes that would be too soon.

If you do find the need to make adjustments, a spring kit and adjustable vacuum can will get you there. You may want to look for Lars timing paper if someone doesn't post it or a link.

 

"All-in" means that the mechanical advance has reached the limit of its travel. Keep increasing rpm's until the timing mark on the damper no longer advances. THAT is the 'all-in' rpm reading. If that reading is higher than you want, install softer springs in the mechanical advance unit, so that it reaches max advance sooner.

 

Thanks all.

I will have some help today to read the tach. You're right, for now I'm guessing.

When I say all in - I have the dial on the light set at 36 and no vac advance. As I increase the engine speed the timing marks line up at what I think is maybe 2000 rpm. The marks stay lined up no matter how much faster I go. This is the correct way to measure "all in", isn't it? If I need to do it differently I would appreciate the help and further advice.

I do have several of Lars's papers and have studied them a lot. Those are the main source of what I know or what I THINK I know.

Thanks again for more comments to help me learn this proceedure.

 

You also have to consider when the mechanical advance begins, it varies with every engine so you'll have to look up the spec.

Weak springs will cause it come in at idle which isn't good. The various timing threads up in the sticky section descried placing rubber bands around the weights to check if timing is coming in too soon. If timing changes at idle or just above idle with the rubber bands then the springs are too weak.

P.S. The stickies also contain links to all the papers.

 

if you've got a timing light and learning to use it, you may as well just invest in a good old-school engine analyzer. it will have all the settings and connections for testing points/dwell, volts, and, most importantly, RPM so you can see it under the hood and not rely on someone elses interpretation of a possibly inaccurate guage. They are available used at yard sales and fleamarkets for almost nothing (since nobody but us uses the anymore), but I am sure you can still likely get a new one at HF or the like...SUN used to make a good one, Craftsman had good ones, and there are dozens of other brands you'll likely encounter in the <$10 range used...

 

You are doing a great Job ! First time and your on your way.

So far

Base no advance is perfect (12)
Base plus vac adv perfect (26)

All in I bet is around 2500 or 2800 confirm that with a friend using your tach.


If that confirms you are good to move on to other diagnostic procedures

 

You are determining all-in correctly. I have my L-48 engine all in at 2,500 RPM and the engine loves it.

 

 

Do yourself a HUGE favor and buy a adjustable timing light. Hazard Freight sells them for less than 20 bucks. They are a million times easier to use than a standard light, even for a novice.

In a nutshell.....set dial on light to 26 degrees....turn dizzy until the zero line lines up with timing tab.

DONE.

 

Thanks again everyone. I appreciate the help and encouragement.

I am using a Craftsman adjustable timing light. Nice tool and seems simple enough to use. I set the dial at 36 and read when the timing line and gauge line up.

Tonight I had a helper read the tach while I held the light and adjusted the throttle on the carb. That way I was controlling it while reading the light. As I suspected last night, I am "all in" at about 1,700 RPM!

I forgot about the rubber band technique and unfortunately everyone here has gone home. So I did it myself. Now, to me this is really weird. With the centrifugal taken out of play, the initial timing went to 21 degree's! No vac advance, same idle speed. Am I correct that without the centrifugal timing should have decreased? But it increased. I did this several times with the same result. Each time the rubber bands were still on the weights so I know they were holding the centrifugal in.

So, where I am at this point: With only centrifugal advance and 900 RPM idle, my timing is at 12 degrees. As it should be.

With the vacuum advance connected I top out at 46 degrees, which again is spec.

So if I may, ask three questions:

I am all in at as low as 1,700 RPM which is too low. Is this a problem?

Should I be investigating the purchase of some weights and springs? If so, any suggestions?

Why would cancelling the mechanical advance INCREASE my initial timing?

Thanks again for all the help.

 

All in at 1700 RPM is most likely way too early. (I say "most likely" because every engine like something different, but 1700 RPM is VERY early). Somewhere between 2700-3200 RPM is typically what people shoot for. When I had my stock 79 L48 with an automatic, it liked about 2800 RPM - but you have to experiment to see what your engine responds best to.

More than likely, you can purchase a set of springs and experiment with different advance rates to see what your engine responds to - they are usually fairly cheap.

Those kits will come with weights, but most folks I know don't use them, as long as your existing weights are in good shape.

Speaking of that - have you cleaned up the weight/advance mechanism in your pictures? Those are rusty enough that I would worry that they may stick and not fully advance. I would try to clean those up before I changed any weights out. I am betting your springs are just shot, and a stiffer spring would get you between 2500-3000.

 

If you do decide to clean the weight/advance mechanism be careful. The ignition pickup sits directly below it. The pickup is a live magnet and will collect any ferrous particles removed. I just went through this myself and pulled the shaft from the distributor housing. I submersed the mechanism in navel jelly a couple times and it came out looking like new.
Brian

 

ALSO-----upon cleaning the weights, etc., be sure to put a drop of Marvel mystery oil,
or a good grade thin oil, on all the pivot points in this mechanism....
I had a problem wif my ole' '76 Harley once when it was idling high at stoplights....and....since I'm a wrench, I knew that was prolly the problem...I took the cover off of the points mechanism, & took the oil dip stick out & put a tad on all the pivot points....never idled high again!!

 

Pick up a vacuum gauge and measures vacuum at idle. The distributor vacuum can rating should be less than manifold vacuum at idle. Gauge needle should be steady. A bouncing fluctuating needle is indicative of other issues.

How's the timing mark under the light? It should be steady, if it bounces there're other issues, distributor may need shimming or something else.

 

To adjust it you need to get a spring kit and put heavier springs on the mechanical advance it may take a few tries but you will have no issue getting it all in at 3000 if that is your goal.

MR Gasket has a mechanical advance spring kit which is very inexpensive

 

"All in" with mechanical advance and NO vacuum advance should be at 32* BTDC. If it isn't at that point on the damper, then the mechanical advance mechanism in the distributor is jambed. Just ceasing to increase from 1700 rpm doesn't really mean anything, by itself.

If you are getting 32* BTDC at max mechanical advance (at 1700 rpm), then, YES, it is way too early for that. You would need to put stiffer springs on the mechanical advance system so that it would delay that advance until 2500 MINIMUM. Otherwise, you are going to get bad detonation and possible engine damage.

Read Lars paper on setting advance for "performance" again. I think you don't quite understand what is needed to set the distributor curve properlly.

 

You are right 7T1, I need a better understanding of this. Thats why I ask the questions here and get great help from guys like you and everyone else who is responding.

Today I am going to clean up the distributor. Then I will read it all again. I will reread my lars papers. One thought is I will set the dial at a different setting that lets me read the mark but maybe finds a different max advance level? I'll report back with my findings.

I measured the vaccum but dont have my notes here. I'll report those number later.

 

Worked with it again today. I cleaned the weights and springs. I noticed that the bushings on the weight pivot shaft are gone. Probably an issue there.

I did several tests; First with vacuum advance connected, idle at 900 RPM I have 15" manifold vacuum and 11" at the distributor. Timing is at 26 degrees. I raised the speed until the timing mark stopped moving. By the sound of it, I am about 2,000 RPMS.

Next I removed the vacuum assist. idle at 800 RPMs and timing at 16 degrees. Again increased the RPMS until the timing mark stopped moving. I am guessing by the sound of it I'm at 2,000 RPM's +/-. Adjust the timing dial to zero and shows 36 degrees.

Earlier today I did have some help and ran this same test but was able to confirm that the timing mark stopped moving at 1,700 RPMS. Did this several times.

My next test I removed one of the springs. Idle at 800 RPM and timing at 24 degrees.

Lastly, I removed the weights. Timing is at 4 to 5 degrees, RPM at 600. No change in timing with increased speed.

Car runs OK. Took it for a short test drive. No knocking when I lug it. No real torque either.

So, either I am not doing this correctly or my timing is coming in way too early. I think my next move is to have someone with more experience with this look at it. After that decide what to do about maybe replacing weights and springs.