Back again from my previous "Timing Issue" and "Vacuum Advance" posts. Getting frustrated,

SO with my MSD distributor (ready to run, no ignition box) now working properly I have a pinging problem with the Vacuum advance hooked up. Without the Vac. Advance there is no pinging. The pinging generally occurs under light acceleration or heavier acceleration.

Here are the details: 1965 442 with stock 400 (rebuilt). The Vac advance is hooked up to manifold vacuum as the only ports on the stock carb are located in the base plate. This was discussed in the "Vacuum Advance" post.

Initial timing (with advance plugged) is 8 degrees. I have also tried 10 with same result. The Vac advance is adding 10 degrees to the initial. I have tried a light silver spring (weight springs) , and blue spring, and also two blue springs, same result. The silver/blue combo has a faster timing curve. I have a 25 degree stop bushing which limits total timing to 35 ish (depending on initial setting).

Funny thing is, when I had my distributor issue (see "Timing Issue Post"), where the weights were rubbing against the rotor and not expanding (advancing), I had no pinging.

If it only pinged on hard acceleration, I would change the stop bushing to a lower setting (maybe 21 instead of 25), but the pinging occurs even under light acceleration, so I,m thinking it is not this. (using 93 octane gas)

The engine starts beautifully both hot and cold. Turn the key and it immediately starts (think brand new car). And it it runs at 180° all day long. It's running pretty strong as it will easily burn rubber and chirp the tires into second and third (it's an automatic). I imagine it will get better when the pinging is eliminated. And it is more responsive with the Vac Advance hooked up, so I'd like to solve this pinging issue.

I do also have a rough idle issue, but I wanted to get the timing down first before tackling that. I did check for vacuum leaks with a propane tank, and aside from one carb fitting needing thread sealant, I am unable to find anything else. (when we started the new engine for the first time, the idle was smooth as silk, so not sure what changed).

I know there is a lot here, but any thoughts would be appreciated.

 

The reason your pinging is because you vacuum advance canister is adding too much. What is your total timing with and without vacuum advance?

 

I have a 25 degree stop bushing in the distributor, so without Vac advance total is 35. I did not check total timing with Vac advance, but at idle (highest vacuum) it is adding 10 degrees.

 

So at idle you have 20* with your vacuum advance connected? You need to recheck because it should not ping with a 45* total with vacuum.

 

Correct, 20° at idle with Vac Advance connected (if initial set to 10). With initial at 8, 18° total at idle with advance. My timing curves were as follows (vac adv disconnected). I didn't have time to try the heavy silver springs, which would slow down the centrifugal advance. There was not much difference between the spring combinations, 2 blue may have been slightly better.

1 Light Silver Spring, 1 Blue Spring -

(850 RPM - 10°, 1500 RPM - 18°, 2000 RPM - 25°, 2500 RPM - 30°, 3000 RPM - 32°, 3500 RPM - 35°)

2 Blue - (I retarded timing to 8°)

(850 RPM - 8°, 1500 RPM - 15°, 2000 RPM - 19°, 2500 RPM - 25°, 3000 RPM - 30°, 3500 RPM - 35°)

 

If you declined your initial timing by 2 then your total should have also declined by the same amount. Did you rev the rpm's higher to ensure the advance actually stopped past 3500?

Double check your total with vacuum connected?

 

Can't speak for others, but my 400 never could take 35 degrees of timing. I settled on 14 initial plus 17 mechanical, for a total timing of 31 degrees all in at 2700 rpm. My adjustable vacuum advance was adjusted to 15 degrees, so at cruise I had 46 degrees. No pinging. Max vacuum, at least on mine was not at idle (which was 16") but at cruise which was 20" to 22". Hope his helps. By the by, if you can chirp you tires going into third, you probably have a lot more cam and/or more gears. Oldscutlass is very good on timing issues.


George

 

Thanks for the replies. I’m going to experiment some more, trying the larger bushing to limit the advance to 31 or so, and also try the heavier spring. It has a stock cam and 355 gears. Th400 tranny with stock converter.

 

Along with the timing curves, you could have a lean spot on the fuel side (one of the carb circuits and or a vac leak).

Work your way through the timing first then investigate the fuel. Read the plugs. I always use a vacuum gauge to tune with(max vac signal at curb idle)...along with a timing light.

What is your compression ratio?
At What temperature does the cooling system run?
What octane fuel are you using?
Verify the timing marks are accurate on the balancer.

Try 12-14* base at warm curb idle, vac diaphragm disconnected and source plugged.
Allow another 8-10* at warm idle with vac adv.
Then the centrifugal needs to bring in all the rest (total) by 2700-3000.

My take is that the springs are too light and are allowing the total all in too soon. Do you hear popping at the tailpipes?

 

I used a vacuum gauge to set the timing and mixture screws. Using 93 fuel, car runs at 180, Stock compression ratio is 10.25 to, but the head gaskets are a bit thicker than stock, so may be a bit lower. If I’m to get timing All in by 3k, thicker springs won’t do as the timing is all in at 3k with the lighter springs. The timing mark was spot on when we assembled the engine( 0 degrees with #1 at tdc on compression stroke.

There is no popping, car starts right up hot or cold. Next weekend I will experiment some more with springs and stop bushing.

The engine is shaking at idle, like it has a vacuum leak, but have not been able to find it. I’ll be trying a different carb to see if the vacuum leak is in the carb., but wanted to get the timing set first.

 

For the hell of it increase the spring tension and see if it responds. Your set-up may like 31-3200 rpms or more for the total.

 

So my total timing with advance was 50*. I added a heavy spring to the weight s and still had some pinging. I then changed from the 25* stop bushing to the 21* stop bushing. This helped a lot, but still some pinging, especially when going up hill. Next maybe I’ll try the 19* stop bushing. Lots of experimenting to get there I guess.

 

Do you readjust your timing each time you change your stop bushing and what are you setting it too? All the stop bushing does is cuts down on how much mechanical timing your distributor puts out and allows you to run more or less initial depending on which bushing is installed.

 

Craig442 & Eric (oldcutlass).


When my 67/400E was stone stock, it would idle all day smoothly at 600 rpm, in gear (switch pitch TH400 in high stall at idle). I could get it to idle as low as 450/500 rpm in neutral. My timing ended up with 10 degrees initial, 20 degrees mechanical, then off straight manifold vacuum the adjustable can was set to add another 16 degrees. All timing was in at 3200 rpm. My manifold vacuum, with stock automatic cam, was a steady 18 degrees with Q-jet set at optimum. Of course I ran premium fuel (93 octane). My 400E was prone to pinging with anything over 32 degrees of total timing. If babied it got excellent gas mileage (17.9 mpg). Wonder how the OP's would do with vacuum to the distributor plugged and total timing set to 32 degrees with the two heaviest springs?


George, retired AVCM (E-9), US Navy.

 

I remember yours George. I agree he probably needs to do the same thing.