Timing Problem -- Carburetor or Ignition?

[TallCowGirl]

Hi Guys...I'm having a problem with the timing on the 383 in my '73 Blazer. It has a stock QuadraJet carburetor and HEI distributor with an MSD ignition coil and module. The problem is that when the engine is cold, I have to advance the intial timing (i.e. rotate the distributor counter-clockwise) so I can start the Blazer, and then retard the timing again to keep the engine from pinging while driving. The 383 in my truck was custom built for me and has a 9.1 compression ratio. I have Taylor spark plug wires and platinum spark plugs. Running high or low octane gas makes no difference so I've just been using 87 octane unleaded. I have stock .073 jets and .044 metering rods in the carburetor. I also have an oxygen sensor installed in the header collector and a gauge on the dash so I can check the air-fuel ratio. I put the stock jets back in after moving from the mountains in New Mexico so the motor's not running too lean. Do I have a carburetor or an ignition problem? As long as the engine is warm, I don't have to adjust the timing but after it gets really cool (and now that it's winter here that means just a few hours) I have to advance it again to start the truck. Is something else going on? It didn't start doing this till late this summer. If you guys have any suggestions as to what my problem might be it would be a big help.

Thanks,
Diana

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[burbBoy]

Is the vaccume advance hooked up on the distributor? Some advance curves are very steep especially later in the years. With the engine warm and at idle with the vacume unhooked and plugged it should be 8 - 10 deg advanced.

If the vaccume advance is hooked up try unhooking and plugging it and see if it still pings after warming up.

 

[TopOff]

Check your mechanical advance, and vacuum advance.

Where do you have the vacuum advance hooked up? Ported (get vacuum only when off-idle) or non-ported (vacuum at idle and off-idle) on the carb?

Which carb? (If it's the edelbrock... how does it run? ) These jets tend to get sensitive to any little dirt. I recommend a fuel-injection type filter.

I had an adjustable vacuum advance tear and no more vacuum advance.

You really need to know what your base timing is (vacuum disconnected) idling at or below 600 rpms. Should be ~8 degrees.

You also need to know what your mechanical advance is at ~2500 or 2800 rpms. Should be ~28 - 32 with NO VACUUM advance.

Vacuum advance SHOULD only be a factor for freeway gas mileage. With your compression, non-EGR vacuum advance should be ~12-14 degrees. If your running EGR then vacuum advance should be ~16-18 degrees. This is ABOVE your mechanical.

So idling (set at 8 mechanical) with VACUUM connected (after adjusting and putting stops in) you should be ~20 degrees at idle! This makes a good jump/torque off the line.

Or for better gas mileage if you do more stop-n-go traffic, put the vacuum on ported-port on the carb for no vacuum, and you should be at 8 Degrees at idle. You will still get good freeway mileage.

Good luck!

 

[TallCowGirl]

Took Off the Vacuum Advance...

I disconnected the vacuum line going to the vacuum advance on the distributor. That worked. My engine is running a lot better. Now how do I adjust the vaccum advance and the mechanical advance to get this right? I've been using the same distributor that I got with the truck so I have no idea what weights and springs are in it. Which port do I use for the vacuum advance on the carburetor? I'm using the one in the front of the Quadrajet on the right side just above and to
the right of the large port for the PVC valve line.

Thanks,
Diana

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[wasted wages]

Re: Took Off the Vacuum Advance...

Unless you are wiling to pull the distributor out and send it to a shop with a curve machine, it will trial and error.

Get an advance kit from Accel or MSD,they come with a curve chart for the different weights and springs and bushings, that will get you in the ballpark.
The rate at which the curve comes in is as important as the inital and total amount of advance.
Many factors such as vehicle weight, gear ratio,stall of the torque convertor,etc affect how fast the advance comes in.
each vehicle will be a little different.

I run two different color/weight springs and all of my advance is in by 2500 rpm.
no vacuum advance.

 

[TopOff]

Re: Took Off the Vacuum Advance...

The trial-and-error is pretty good description/instructions with the Accel mechanical and vacuum advance kit.

That's how I did mine. I was getting great off-idle torque and driveability with ~15 mpg with my 383 and Howell TBI. I was getting 16MPG with towing my boat with the Edelbrock Performer carb. /forums/images/graemlins/eek.gif

Good luck.

 

[Grim-Reaper]

Hmmmmm I have had some simular problems with my 75. Didn't have a start problem but I did have problems with Ping.
Aircleaner was part of it. Thermac was not swtiching over to cool air after it started.
I also swapped to a 85 Aircleaner with a Snorkle to the grill to get rid of the restrictive air cleaner and to get cold air.

Pull the cap and button. flip the weights arond and make sure they snap back. If they hang or don't come all the way back then you have a coked up'd distributor and it's giving you advance problems. Pull the distributor. On the gear is a roll pin. Drive that pin out and remove the gear. Remove the advance springs and the weights. Now you8 can slid the inner shaft out of the outer shaft and clean it. A light coat of high temp white lithium grease to lube the shaft and weights.

The last thing that was messing with me is a problem with my down shift cable. It's too short and locked me out of the 4bbl. So at highway speed I was pulling more then the primaries could deliver when I hit a hill
There is a device on the choke linkage that will do the same thing. It's a lever that locks out the 4bbl till the choke is off. It's on the passenger side of the in the middled of the main body and it locks out the bottom shaft of the secondaires. You can criple it with a thin zip tie.

Are you running the stove type choke or did you go electric? The stove type is a little cranky sometimes. I finnaly ditched it and went to a newer hot air choke that I then converted to electric. Works great now.