Question on setting my timing

[Michael L.]

Re: Question on setting my timing

Thanks so much for the help Duke. I will get those things for you in the next couple days when I get back to my shop. Part of the problem is the car is running so bad it may be hard for me to get the vacuum numbers but I'll try.

Mike

[Michael L.]

Re: Question on setting my timing

That cam has the same .050" lifter rise duration as the OE L-46 cam, but the narrower LSA, 110 compared to 114 means a lot more effective overlap. Assuming the distributor is OE and not modified, it needs to be, and if you provide some information I can help get you get it optimized.

First, give me the centrifugal and vacuum advance specs from the CSM or AMA specs from the GM Heritage Web site, and there are two other things I need.

1. Idle vacuum in neutral: report as xx" Hg @ xxx RPM.

2. The data stamped on the VAC bracket. You may need to loosen and move the dist. cap out of the way to see.

Duke

I got back into the shop today. The marking on the VAC bracket is B1. I was able to get the car to idle for a few minutes with great difficulty. While warming the car up it was popping and back firing. After getting it running and idling, while nursing the throttle, the vacuum needle was very rapidly oscillating from about 3 to 5.5. I used my mightyvac to do this, I assume it works for this purpose. I realize this means something is very wrong. I've been working on cars my whole life and nothing has challenged me like this car. After seeing this reading I carefully looked over everything on the car, double checking with my AIM to see if I did something wrong. While doing this I realized that I'm missing something the AIM refers to under the carb called a "baffle" I have no idea what this does or if it could affect how the car is running. Any thoughts?

Mike

Mike

[Duke W.]

Re: Question on setting my timing

The B1 is a boat anchor... takes up to 18" to pull to the limit. Your engine likely pulls in the range of 10-14" at the lowest you can get it to idle, say 750-900, with acceptable idle quality, so you'll probably need a 8" B28 or 12" B26.

I believe you may have an improperly assembled and/or installed distributor. You need a 1969 Chassis Service Manual and a '69 Chassis Overhaul Manual may be helpful, too. Distributor installation is NOT in the AIM since the dist. was installed at Flint.

Let us know when you get at least a CSM. Don't touch the car until you do.

If I had a hundred bucks for every screwed up distributor assembly/installation I've corrected or helped owners fix over the phone, I'd be richer than Jeff Bezos.

Get the missing part for the carburetor installation and get it back to the GM design. I have a feeling that bubba has been all over your car.

Duke

[Michael L.]

[Duke W.]

Re: Question on setting my timing

C3 small block distributor installation is different than C2s. Review the CSM, which should describe cap wire indexing and show the relative angular orientation of the cap. No need to remove it now. Post a photo.

Has the distributor been moved or removed/installed since the dyno test?

Duke

[Michael L.]

Re: Question on setting my timing

I followed the CSM to the letter for the distributor install. Yes the distributor has been removed since the dyno test several times. Part of this saga also included an inability to fire the motor once it was in the car that took me forever to figure out. I pulled the distributor and put in a total MSD system with a 6AL MSD box and the car ran fine with it. I would then put the distributor back in and the car wouldn't fire. Long story short the distributor wire to coil was bad. It took me forever to figure this out because I assumed it was good since A) Jerry Mcneish rebuilt it, and B) the wire is used to wire in the MSD system so if it worked for the MSD I assumed it would work with the conventional ignition. Turned out that the wire was bad but worked in the MSD system because in that system the wire only acts as a trigger and doesn't have to pass much in the way of current, whereas in the stock ignition it has to carry much more current. (On the dyno it was also wired into an MSD system.) I replaced that wire and the car fired up. To make matters even more confusing, I re-set the ignition timing last week before I swapped the Q-jet in and the timing light worked perfectly firing consistently every time. Now when I run the car the timing light fires very randomly, indicating there is something wrong again with the ignition system. I thought I had the ignition system, except for dialing in the timing, totally figured out, but it seems that's not the case. So frustrated. Here are the pics of the distributor and the AIM page:

dizzy A.jpgdizzy B.jpgAIM dizzy inst.jpg

[Lawrence M.]

Re: Question on setting my timing

Hi Mike,

On the subject of your missing stainless steel carb base baffle I have attached an article by the late great John Hinckley . If I recall correctly he may have also covered this problem in some threads on the Tech Board. I hope the attachment is large enough to read. Also Mr. Gasket makes a Q-Jet carb base gasket without the heat slot under part numberMRG-56 which can be used with the


baffle to help further isolate the carb from the excessive heat.John Hinckley.jpg

[Duke W.]

Re: Question on setting my timing

A common problem with the distributor is the ancient ground wire crimped/soldered to the breaker plate that grounds through one of the VAC attaching screws breaks because it is constantly flexed by rotational movement of the VAC, so check that, assuming it still has a breaker plate with some kind of switch either mechanical or electronic.


Before removing the dist. set #1 at the normal initial timing point (NOT TDC!). Disassemble and check the ground wire. Chances are very high it is brittle with broken wire strands. NAPA has replacements, or you can fab your own. Upon reassembly be sure the dimple on the side of the gear is facing the same direction as the rotor tip. Disassembly/assembly is in the COM, but it may not mention proper dimple orientation.

Once the distributor is seated, rotate it CW to the limit then back CCW until the points just begin to open. You can do this visually or with an ohmmeter. Once the points just begin the open or the meter goes to infinity, the initial timing will be within degree or two of where you set the balance notch on the tab. This is called static timing the engine, and it should start right up.

Duke

[Michael L.]

Re: Question on setting my timing

Thanks Duke. I've already replaced both the ground wire and the distributor to coil wire. I did this previously after the car wouldn't fire initially. I also don't think the timing is the primary issue anymore. Now with the intermittent firing problem as evidenced by the intermittent timing light, something else seems to wrong. Gonna pull the carb and look at the gasket and wait until the baffle comes in until I try doing anything else.

Mike

[Rocco S.]

Re: Question on setting my timing

Mike,
Intermittent timing light readings? Interesting. Have you checked for a cracked distributor cap or faulty rotor?

[Michael L.]

Re: Question on setting my timing

Thanks for the input guys. Rocco, the distributor and rotor look fine. Larry, I was able to read the Hinkley article. I'm going to seal those passages as he recommends, but after pulling the carb off I think I discovered a big part of the problem I've been having. If you look at the attached photos of my carb gasket and the bottom of my carb you can see that failing to put the steel baffle in place results in direct contamination of the fuel intake with exhaust gases. Can't believe I missed this when I first installed the carb. I'm sure this is why I've had so much trouble getting this car to run with the Q-jet carb. Although this problem was also present on the Holley spread bore I installed, the completely different way in which fuel is metered in these two carbs must have resulted in the Holley carb being less affected by this. I've ordered the baseplate and will also plug those passages and hopefully this will go a long way to solving all these vexing issues that I've been having. This has been going on for a couple of years already. Of course, I've not been working on this continuously and have been doing other projects, but I'm starting to see the light at the end of the tunnel, I think (hope it's not an oncoming train!).

Carb gasket no baffle.jpgcarb base no baffle.jpg

[Timothy B.]

Re: Question on setting my timing

Huge vacuum leak plus very dangerous with hot exhaust under the carburetor, the engine will run entirely different after you install the stainless baffle.

Do some research in the archives about plugging the hot slot holes in the intake manifold while you have it all apart, that will ensure the carburetor stays much cooler.

[Michael L.]

Re: Question on setting my timing

Yeah that's what I'm guessing/hoping. I already plugged them with some 7/16" freeze plugs coated with some Indian head gasket sealer. Just waiting for the baffle to come in. Thinking of putting in some fresh spark plugs too, just to sorta start with a clean slate when I start it next.

[Duke W.]

Re: Question on setting my timing

Okay, assuming the wires are okay... could be a shorted capacitor or points.

Duke

[Timothy B.]

Re: Question on setting my timing

Yeah that's what I'm guessing/hoping. I already plugged them with some 7/16" freeze plugs coated with some Indian head gasket sealer. Just waiting for the baffle to come in. Thinking of putting in some fresh spark plugs too, just to sorta start with a clean slate when I start it next.

My feelings are with that kind of vacuum leak there is not enough of a combustible mixture getting to the cylinders to burn hence the erratic spark.

The plugs are sooted so just clean them good and try the engine.