Hopefully someone with more experience than me can help me with this problem.

I am working on tuning a 1984 300 6cyl and can't quite figure out what's going on with the ignition timing. It has the duraspark distributor and non-feedback carb. I can crank the engine and get it running smoothly by tuning the timing and carb with a vacuum gauge. However, when I check the timing with a timing light, I'm reading 40 degrees advance with the vacuum advance unhooked.

Here are my questions:

1) There are timing marks cast into the timing cover, and a timing "tab" on the block on the passenger side of the water pump. Which one should I be checking the timing on? My 40 degrees advance is referenced from the timing tab on the passenger side of the engine.

2) There is a mark and a notch on the crank pulley about 45 degrees apart. Which one should I be using to check the timing?

3) Is the pulley "keyed" to the crankshaft such that it cannot slip, or is it just a "press" fit such that it may have slipped causing the marks to be off?

4) Is there a harmonic balancer on this engine?

Thanks in advance.

 

I gave up trying to time my 300 with a light for the same frustrating reason.
I tune it roughly by ear and then tune using a vaccum gauge. Bring it to the highest vaccum by twisting the distributor. Then back it off a inch or two of vaccum. Another FTE guy taught me this Works great.

In awnser to 3 and 4-
The crank pully is the harmonic. it can slip around the center section if the rubber degrades, though there is a woodruff key holding it in place.

 

Timing an engine with a vacuum gauge will result in severly over-advanced timing, which expalins your 40 degree reading. This is why flipklos backs his off a tad.

On my '79 300, I use the timing marks on the passenger side. They're on a small tab above the crank pulley. There is a single notch on my crank pulley that serves as the timing mark.

In general, if you ever have any doubts, you can remove the number one spark plug and put your finger over the hole. Move the engine over by hand and you will feel the compression on your finger. Move the engine to the highest point of the compression stroke, and that will be TDC for the first cylinder. Since your timing marks are referenced from the first cylinder, that will help you orient yourself.

 

I've used the vacuum gauge method for years. Obtain the highest steady reading and back off 1-2 hg for a starting point. Drive and try. Adjust accordingly.

 

I guess that if the pulley and damper are the same unit in this case, it would make sense that it is very possible that it may have slipped. I've seen sbc dampers that have slipped 20+ degrees, and they don't have pulleys attached to add to the torque that the damper sees. But, they also rev up alot higher than my 300 will ever see. Thanks for the replies.

 

Ok, I after confirming that #1 cyl. was a TDC, I figured out that the timing tab on the passenger side of the engine corresponds to the mark on the pulley and not the notch. Now, can anyone tell me where the base timing should be set? The label on the radiator support states something to the effect of setting base timing at 0 degrees and adjust for best performance; for propane conversion, set at 12 degrees BTDC.

I'm sure 0 degrees is ultra-conservative just for initial startup. What do you guys recommend?

Problem #2 relates to the vaccuum advance. I set the base timing at 0 degrees with the vaccuum advance vaccuum line unhooked and the carb port plugged. I confirmed that I get roughly 10 degrees mechanical advance at 1500 rpm. Also I get 5 inches vaccuum at the carb advance port at 800 rpm.

When I hook the vaccuum hose back up, and check the timing, I get no additional advance at idle. When I get to 1500 rpm, I only get 10 degrees advance (mechanical?). Does this mean that the vaccuum advance module is faulty or not receiving vaccuum?

 

As far as I know 8 inches is right about where a vacuum advance will start to adjust timing. Full advance coming around 14 to 18 inches.

Are you sure the decal didn't have a 1 smudged out and it really means 10 when it looks like 0? I would set the base timing at 10 degrees and then while the engine is running plug the vacuum advance into a full manifold vacuum port and see if the RPM's change. Or better yet, if you have a Mityvac hand vacuum pump with gauge, plug the vac. advance into that and slowly pump and see what vacuum numbers do what to your engine speed.

Despite what your decal says, I would set the base timing at 10 degrees, adjust the idle speed to 700 or so, and rev it up with your timing light just to verify your mechanical advance is working.

After doing that you could also disconnect the vacuum advance and plug all ports then top off your tank, drive about 40 miles of constant high-speed light throttle driving then top off again and check your mileage. Then plug the vac. advance into the timed vacuumed port and do the same thing. The plug the vac. advance into a full manifold vacuum port and do a third mileage test. Listening for ping the whole time.

If mileage is the same on all three, the vac. advance is not working. If it improves on both of the last two, plug into the port that gave the best mileage and call it good.

 

Thanks guys. I determined that I had 2 problems. First, I checked the vacuum advance with a vacuum pump and it would not even budge. Must be a hole in the diaphragm. Second, after replacing the vacuum module and seeing a slight change, I determined that there was a leak in the vacuum line going to the vacuum advance module. Fixed that and checked it with my timing light.

Set base timing at 6 deg. BTDC. Confirmed ~6 deg. mechanical advance. Hooked up vacuum advance, and got 45 degrees total advance at 1500 rpm. I'd say it's working now!

Then, per suggestions in another thread, I hooked up the vacuum gauge to manifold vacuum and tuned the carb to the highest vacuum (~16.5 in.)

I do have one more problem. Although I couldn't test drive it because of the weather, I noticed that upon hard acceleration (revving it up in the garage) I get a loud "pop" in the carburetor. This only happens when I go directly from idle to WOT. If I hold it at ~1300 to 1500 and go directly to WOT, it doesn't happen. Any ideas?

 

Just don't floor it right from idle. Accelerator pump dumps a wad of gas down the intake that your engine can't deal with right at idle

 

Makes sense. I hope to get it back on the road tomorrow and check it out.

 

Got it back on the road and after a little driving and tuning, it seems to like 9 degrees base timing and makes about 18 inches vacuum at 800 rpm. It has an intermittent miss at about 2500 rpm, but other than that, it's silky smooth and pretty quiet too. Thanks for the help.

 

Id check for the cause of that miss. Wires, if old are prone to wear. check cap rotor and everything else too. If the problom presists I would try twisting the dizzy back another degree and it should disapear.