68coupe

Is my distributor installed incorrectly?

Hello,
I have a 1968 corvette with a small block 327. The engine was rebuilt last winter and I have been trying to get some of the bugs out. Right now, my major problem is that the header on the left side, passenger’s is running much hotter than the right side, dirver’s. When trying to find a solution, I ran into an interesting point. I checked the firing order of the car and found that my distributor screws (the screws that hold the distributor cap on the distributor) did not line up with the diagram in the corvette manual. The wires are in the correct order, but if you look down at the distributor, the #1 wire is not in the front center like in the diagram. It is in the front left (toward the passengers) side. The wires are still correct based on the screws, but using the screws as a reference, the distributor looks like it is twisted a little bit.



I can post pictures tonight

The current timing is set as follows:
Initial timing = 18 BTDC
Centrifugal timing = 18
Total timing = 36 BTDC at 2100 RPM

Problems
Right now the car idles smooth., but runs very very rich at idle.
Pulled spark plugs and they are black!
Makes a backfiring noise when at cruising speeds.
The header on the passenger’s side is running at over 500 and the drivers side is at 320.

What I have done.
Adjusted carb. It is a Demon 575 cfm. I leaned out the idle screws. They are at .5 to .75 turns out. They are all the same.

Check distributor, other than it looking off, all of the wires went to the correct cylinders.

Bumped the ignition until air was forced out of the #1 cylinder and then looked under the cap of the distrubtor. The metal piece faced the #1 wire on the cap.

Questions:

I have an after-market ignition system composed of an MSD box, an MSD distributor, MSD wires, and Champion plugs gaped at .035.
My original distributor setup was points, with the new electronic ignition, is the firing order different?

Based on what I said in the opening paragraph, is my distributor off. If so, why does it idle okay and why does the metal piece under the distributor cap face #1 cylinder.


Lastly, my brother said that there are two cycles where the piston will push air out of #1 cylinder. How do I know which one is the correct cycle for the metal piece under the cap to face #1. (if that makes sense?)

Really confused.
Thanks,
Joe

CGGorman

Your brother is a Wyotech graduate, right? Why not let him look at it? He can probably get you squared away in an afternoon. With all the trouble you're having it seems like the best route would be to have a professional take a look at the engine so you can get some sleep and actually enjoy the car.

68coupe

I completely agree. And he could probably fix the car in an afternoon, but he is in Maryland and only comes to visit once a year or so and we rarely fix cars. Instead we are usually chasing skirt!!!
Thanks,
Joe

bobs77vet

i think what you are getting confused at is the relationship between parts....the timing bwteen the cranks shaft and cam through the timing chain is very important and must be correct...
the relationship of when the sparkplug fires to the compression stroke is important and must be correct on every spark plug...hence the importance of the firing order.... the relationship of where the distributor is pointing is "relative" as long as you have the rotor sending the spark to the correct sparkplug in relation to the compression stroke you will have an engine that works.... having said that the distributor is normally put in so that it can be rotated so the vacuum advance doesn't hit anything and can be rotated in both directions... sounds like the distributor may be off one tooth... this would effect your ability to control timing in the extremes only if the vacuum advance diaphram is hitting something. i don't think this is your problem....any body else is welcome to improve on my explanation it was harder to write then you may think....

redwingvette

The distributor may not be in the exact place that it was from the factory but that doesn't mean it isn't working right. The only thing that matters as far as the distributor is concerned is that the rotor aligns up with the plug wire at the right time. To put it back where it was originally just moves that point back as well. Even if you put in completely 180 degrees opposite it would work if the plug wires were moved to the same orientation.
If one side is running hotter then the other then you may have a vacuum leak or something wrong with the carb causing that side to run lean.

68coupe

Bob,
Ithink I understand what you are saying. It doesn't matter where the distributor is installed as long as the rotor faces the correct wire at the correct time. But how do I know this? I checked it by bumping the ignition until I felt a burst of air come out of the #1 cylinder, then I looked at the rtor and it was dead on number 1 wire. Does that mean that it is installed correctly. If not, what do I do?

Thanks,
Joe

68coupe

Thanks for the reply.
I thought that was the case. As long as the rotor lines up with the wire when it is on the compression cycle I am fine right? How do I know that for sure. What about the firing order for points vs electronic ignition. No difference right?
Thanks,
Joe

bobs77vet

sounds right...and you know this by having an engine that works....just like yours does...your problem is in the fine tuning dept.... if it was off too much the car simply would not start and backfire as the spark is getting sent to the cylinders with valves open...


edit: is your vacuum advance on the dist uptight against something ...if not I don't think you have to worry about it

68coupe

I have no vacuum advance.
Thanks,
Joe

Garys 68

Your distributor sounds fine. Dont worry if it's off 1 tooth as long as the timing, relative to the crank is correct. You can reinstall to get it facing forward, but that wont change anything if the ignition timing is set to specs.
You did adjust the timing with the vacuum advance disconnected?
It sounds to me that there's a problem with the carb. If it was a holley, I would suspect a mis adjusted float or blown power valve. Not sure about Demons.

68coupe

Thanks for the reply.
I have no vacuum advance. When I timed it, I checked it at idle and then advanced it to 18. Then I reved it to 3000 and checked it. It was at 36.
I think you have a good point. It started when I installed the new demon. The float level was stuck all the way down, but I fixed it. Now the float level is at 1/2 filled, but when I shut the car off the fuel is no longer in the sight glass. (I think, it is really hard to see in that glass.) stuck needle maybe??
How do I check the power valve or needle?

Thanks,
Joe

bracketshark

To check for TDC on the compression stroke the method I use is remove the drivers side valve cover and watch the #1 intake valve. I bump the motor over slowly and watch the #1 intake valve, when it opens then closes I watch for the timing mark on the balancer to come around, when it meets zero on the tab the motor is at TDC compression stroke. You can make the #1 plug wire face any direction on the distributor from here as long as the firing order remains correct (1,8,4,3,6,5,7,2). Is the backfire issue you spoke of thru the exhaust or the carb.?

bobs77vet

?????we are talking about vacuum advance diaphram it looks like a triangular cone thing on your distributor below the cap that has a vacuum hose coming out of it... you should have one of these...atlhough i guess you could have a distributor w/o one ?????????

87bob

When you feel the puff of air the timing mark should line up on the balancer and the rotor. If it doesn't then your out of time. Once you have checked that then disconect and plug the vacuum line and use your timing light. Remember that a lean running engine can also run hot.

68coupe

The noise is through the exhaust. Not a full backfire though. It is a loud rumbling noise that decrease as I increase pressure on the trottle.
Thanks,
Joe

lars

The distributor can be installed in any position and correctly timed if the wires are located to match the position. The "correct" installed position is simply the position and wiring location chosen by the factory. It is, therefore, the position most of us like to duplicate when installing a distributor. You don't have to have it installed in this way.

If you have your total timing set to 36 degrees, there is nothing wrong with your distributor installation. It may not be "correct," but you will not gain or change any performance parameters by orienting the distributor to the "correct" orientation. If #1 is firing at 36 before, you have an optimum setup. You have no problem even if you won't win an NCRS show with the incorrect orientation.

On custom engines, I will often change the distrubutor orientation and the plug wire placements in order to "clean up" the engine compartment. By locating the #1 wire in the cap over towards the driver's side of the engine (this was done by Chevy when they came out with the HEI systems), it is possible to create a less messy plug wire routing. Many people will do this when installing aftermarket components - sounds like that's what you have, and there's nothing wrong with that.

68coupe

I do have adistributor without one.
This is the distributor I have:
http://www.msdignition.com/dist_10.htm
Thanks,
Joe

68coupe

Thanks.
I tried that once already. I had to shift the harmonic a little bit by hand to get it to line up and then I looked at the rotor. The rotor was right on #1. I then timed it, I do not have a vacuum advance, and set the total to 36 and initial to 18.

Thanks,
Joe

lars

Joe -
You've done everything right - you don't have problem. Your timing (both initial and total) look great - perfect setup for a mechanical advance distributor.

SanDiegoPaul

I would check two things in this order: firing order and valve adjustment