MMJ

I have a problem that has me stumped. I have a 69 with an L-46 (350/350). It ran fine when I got it. One day it started running rough and kept getting rougher and rougher, then started backfiring bad out the exhaust (afterfire). It has electronic ignition on the original distributor, so I opened the cap and saw that the red wire going into the ignitor was broken. I assumed that was the problem, so I ordered a new electronic ignition kit. When I got the kit in, I took out the distributor to make sure that I had all the correct clearances. I checked the timing and found that when #1 piston was at top dead center the rotor was pointing to the wrong plug wire. So I changed the wires to correct spots according to Haynes manual. (How did it run before like this?) Now when I try to start it, it doesn't backfire, but it won't run. The fire out of the plug wires seemed like it wasn't very strong and was erratic, but had good fire coming from coil. Then I thought, well, maybe I got a defective electronic ignition. So I dug out my old one with the broken wire, soldered it back together and tried it. Same thing. Then I thought, I'll try putting the plug wires back in their original spots like the p.o. had them. BOOM! Huge backfire, this time out of the carb. Does anybody have any ideas here? Could the original violent backfiring have damaged something, like the timing chain or something else? I'm stuck.

RobRace10

Are you sure you had it on the compression stroke when you checked TDC?

MMJ

Yes, checked it 3 times.

RobRace10

Distributor gear worn out?

Mike Ward

How did you verify it was on the compression stoke?

PS- throw away the Haynes manual.

MMJ

I don''t think so, it looked good when I had it out. Teeth looked almost new. Can all that backfiring cause something to get so far out of time that it's difficult to get it back in. Could timing chain be stretched or broken?

MMJ

I took out #1 plug, put my thumb over hole, and cranked it until I felt air blowing out hole, then kept turning engine until piston reached highest point and lined timing mark up with zero. And you're right, the Haynes manual for the Vette stinks compared to ones I've used for other cars.

Mike Ward

That method is unreliable. Take the valve cover off and make sure both valves are closed while #1 piston is at TDC.

Take off the distributor cap. The tower closest to the where the rotor is pointing is #1. Reposition all the wires accordingly.

MMJ

Ok I'll try that. Thanks!

MMJ

Ok, took valve cover off and tried this method. The problem I had was that there was quite a bit of travel on the crank after both valves are closed. It's hard to tell exactly when they close. But I moved wires clockwise one spot according to where the rotor was pointing, but still had same result. It hits every once in a while, but won't run. I've tried rotating the distributor a little too, both ways, but still nothing.

Scott's 73

Stupid question but your sure your on the No 1 cylinder? not #2
front cylinder on the driver side is #1
I can admit I have made that mistake myself.

MMJ

Yep, that's the one I'm on.

kjb13

Maybe the timing chain jumped a tooth or two.

Scott's 73

I would pull out the #1 spark plug and put it back in the spark plug wire and ground the plug on the intake or something. then hold your finger over the empty spark plug hole and have someone crank it over and listen to make sure the air escaping from the cylinder is happening at the same time as the spark jumps in the plug. you will need to crank the engine over many revolutions to see if its firing in time. Its kinda primitive but it will help to determine if you have everything set up correct.

MMJ

That's what I am wondering. Is there any way to tell without actually seeing the chain?

MMJ

I will try this after church tomorrow. Thanks

Brcmpbl

If you've been trying to start it repeatedly, I would pull a couple of plugs on the right rear and make sure they are not covered in fuel.

MMJ

Ok, I'll do that. Why the right rear?

Brcmpbl

Fuel tends to run that way from my experience. I have a 70 L-46 that I had a hard time starting after running new wires. My distributor is also set up differently than it was when it left the factory - #1 is the front right post on the cap instead of front left. Going to change it back once I'm motivated. Anyway, I had the wires in the wrong spot as a result of consulting the shop manual and couldn't get the car to start, of course. Once I sorted out my wires I still couldn't get a start other than a few short catches, so I started pulling plugs. I had flooded the right bank badly and the left slightly. Cleaned them up and problem solved.

Fuel is pumped into the carb every time you try to start it, so if it doesn't start after a bunch of tries...the fuel has to go somewhere.

MMJ

Makes sense, I'll post later if it helped. Thanks