Timing question - do I have a problem??

[Wolverine]

I have owned a '76 L82 for the past 4 years, and just did my first complete tune-up. (I'm a novice with this stuff but have been muddling through a lot of repair projects.) It has always run really well and I did the tune-up more for the experience than anything else.

I changed the dist. cap, rotor, wires, plugs (correctly gapped), and coil (with an Accell HEI super coil). I went through all the vacuum hoses and replace a broken EGR thermal vacuum control switch. The last thing I did was set the timing back to factory specs (vacuum advance disconnected and plugged, idle to 1000 RPM's, timing to 12 degrees BTDC). I noted that before adjustment, the timing reading was off the scale (>14 degrees BTDC).

It started right up and ran really smooth -but- without much power. Clearly, the engine wants a lot more advance, and I am going to adjust the distributor back to where it was before. My question is - at factory specs is an L82 really that much of a dog? Or is there something wrong with the distributor? Is there something else I should be checking other than resetting the advance?

Thanks.

 

[wishuwerehere82]

Assuming that you are using good gas at a reasonable octane rating, you should be able to advance it to get more HP.

If you have a dial up advance on your timing light, set your advance for a maximum of 36 degrees BTDC @ 3000 RPM.
Normally, your 12 degree BTDC should be set at 650 RPM.That may be the reason your curve is a little low at top end.
Alternatively, you can advance it by ear until you get to the point that it pings under throttle then retard it until it stops pinging.

 

[RodsnRides]

I have a couple of suggestions:

1. Clean and lube the weights of the mechanical advance under the distributor rotor. Use a lubricant such as that used for contact points.

2. Ensure your vacuum advance is working. Suggest you get one of the hand vacuum pumps such as Mity-Vac. You can check the advance is holding (no leak), and with the engine running, you will see the difference (using a timing light) as well as hear the difference in the engine (speed will pick up).

3. Make sure the hose feeding the advance is getting a good source. It has been suggested here in another post (I thinks it's in C3) that direct manifold vacuum is ideal.

A good rule of thumb is 1-2 degrees of advance for every 1000' of altitude.

Hope this helps.

Rick

 

[Wolverine]

Thanks, guys. Good advice. The vacuum advance does seem to be working. I'll lube those weights in the distributor then reset the timing.

I read something about installing lighter springs in order to achieve total advance at lower RPM's. For anyone who has done this, is there a recommended part number for a HEI distributor and where would I find it? An auto parts store? Is it as simple as it sounds? This is something else I mught as well try while I'm at it.

 

[wishuwerehere82]

The lighter springs might help get you some more low end power, and they are cheap. I wouldn't bother with a new distributer if there's nothing wrong with the one you have.
If you get it timed and still have power loss compared to before you did the tune up, put the original coil back in and try it.

 

[mvftw]

Initial vacuum at 18* - 24* is normal, the 12* was for emissions...wishuwerehere82 is correct, you want 36* in at 2500 - 3000, that's more important then initial timing. Also make sure your running manifold Not ported vacuum advance...You should end up with 52* total advance, you will need a kit for that...

 

[Jack]

Wolverine:
Ditto Rick's tip on lubing mech advance. I'll add that your vac can is probably not optimized. In a word, it's all in the ignition "Curve". There are a coupla very good tech articles here in CAC database on how curve parts work-interact and how to choose-match the right ones ... P/Ns are there. Do Read Them! Alternately, I have a coupla brand new performance Accel HEI dist that are fully adjustable on both mech & vac advances; your new coil will match perfectly. Firm $125 each and I'll pay ground ship to MI. email if interested: qaferret@aol.com
JACK:gap

 

[Bob Chadwick]

The Chevy small block wants 36 degrees of mechanical advance all in by around 3,000 rpm. The idle advance is not as big a deal as the total advance, I think it is more of an emissions thing but am not sure, so what happens is that a lot of people advance their initial timing to get a higher timing curve closer to the 36 degrees. The vacuum advance then adds additional advance under no load conditions to get total advance to about 52 - 54 degrees at or above 3,000 rpm. Any load on the engine, such as putting your foot into it at speed, and the vacuum disappears and advance drops back to 36 degrees.

It also adds advance at idle. As other's have pointed out, you have to be running manifold vacuum or this won't work correctly. If you source has vacuum at idle and disappears as you load the engine, you are using manifold vacuum. If I remember ported vacuum correctly, there is no vacuum at idle but otherwise it works the same. If you don't run manifold vacuum, you won't get the added advance at idle.

You have to be careful though. On my car the stock distributor kept advancing as long as I gave it gas. It never got near 36 degrees even at about 4,000 rpm so you have to be sure of what your distributor is doing from and advance perspective to make sure that if you get 36 degrees at 3,000 rpm that the distributor does not continue to add advance above that. Certain to create a pinging situation or worse.

This prior post I made when I replaced the distributor has some additional info and references.

I was surprised that your 76 wanted 12 degrees of initial advance. According to the sticker on the firewall of my 77 mine is supposed to be set at 8 degrees. When checking the timing at 1,000 rpm you probably have some mechanical advance introduced into the timing equation.

 

[Wolverine]

Thanks for all the suggestions. This is a geat learning experience.

Bob, in response to your coment about the 12 degrees of advance at 1000 RPM's, this is the spec for the L82 engine. I believe the '76 and '77 engines are exactly the same.

My timing light does not have a dial on it. I assume a dial must be necessary to adjust to 36 degrees at 3000 RPM's, or to get any measurement other than initial timing. Is my option then to tune by ear (unless I get a better timing light)?

Is there any way that by adding the Accel super coil, it could have actually reduced engine power? If I get the advance set right, wouldn't the stronger spark from that coil help combustion?

One last question - my vacuum advance hose connects to a port at the base of the carburetor. This means that I have manifold vacuum - right?

I'll definitely find those articles in the archives on timing. Thanks again for all your help.

 

[Bob Chadwick]

Bob, in response to your coment about the 12 degrees of advance at 1000 RPM's, this is the spec for the L82 engine. I believe the '76 and '77 engines are exactly the same.

I have an automatic. I think you said your's is a four speed. That may make the difference.

My timing light does not have a dial on it. I assume a dial must be necessary to adjust to 36 degrees at 3000 RPM's, or to get any measurement other than initial timing.

You can get a timing tape for the specific size balancer or divide your balancer evenly into ten marks, of which the first would be 36 degrees.

Is there any way that by adding the Accel super coil, it could have actually reduced engine power?

Not unless the coil is bad.

One last question - my vacuum advance hose connects to a port at the base of the carburetor. This means that I have manifold vacuum - right?

Mine is on the top of the carb. Pull the hose from the vacuum advance. If you have vacuum at idle, that goes away when you place a load on the engine, then you have the right source.