L26 blowing back through the carburator

[amplogic]

Sorry, I missed the 2 posts previous to this.
I live west, a few miles north of Douglasville. Maybe a half hour or so from the downtown ATL area. I bought the car from a guy in Monroe, about a couple months ago or so.

The ignition issues were all electrical. The previous owner had installed a used MSD 6AL that had a blown output diode. But he didn't know that, and I didn't either until I drilled out the rivets and took it apart. I have a GM HEI module installed right now, because the module that came with the distributor doesn't work. The HEI module works pretty well though. Strong blue spark at every plug, even with a cheap generic coil I had lying around. And as inexpensive and butt simple as it gets.

Edited August 31, 2015 by amplogic

[amplogic]

I just looked at it again, and did find a mark that looked like a center punch. No idea why it's there, but it's actually inside one of the holes and not on the collar of the sprocket where it would normally be. I'll post a picture in a little while, after I've had a chance to get it off the camera and resize it.

[amplogic]

 

It's been known to happen that the cam shaft dowels have sheared, so even though in theory the worst the timing could be is at spec., or 8 degrees advanced, it's possible that things are totally screwed up.

 

 

I loosened up the bolt enough to slide the fuel pump cam out of the way.  The sprocket didn't seem loose, and I wasn't able to spin it on the shaft at all.  So I don't think the dowel is broken.

 

 

So have you verified that at TDC #1- compression stroke- that the dizzy shaft is at the proper 11:25 position and that the rotor is lined up with 1 plug?

 

Yes, and yes.

 

 

Might be easiest to assume the PO knew what he was doing and work on everything else until cam timing is the last possibility.  Or replace that sprocket with one that has the notch.

 

I more or less assumed that the PO did know what he was doing.  Aside from the am sprocket not having the standard timing mark groove, I haven't seen anything that really looks awry.

I mentioned in my previous post that I found something that looks like a center punch mark in one of the sprocket holes.  It could be nothing more than a mark left from the casting process, but it sure looks like a punch mark.  No idea what it's there for, and it may be nothing at all.  I just thought I would mention it in case someone has seen it before.  I lined it up with the cam reference mark just for giggles, and it hits right on #4 exhaust and #6 intake.

 

 

 

[amplogic]

This is probably a dumb question, but I've never been one to shy away from an entertaining dumb question :-)

Theoretically speaking, would it be possible for enough fuel to enter a cylinder to raise the compression enough to force a valve open? The PO installed an electric fuel pump and disconnected the mechanical one. There isn't any sort of pressure regulator or return line, and I have no idea what the fuel pressure is. I haven't really messed with the Holley carb, other than to wire up the electric choke, but I need to check the bowl levels to at least see if they are right.

[Zed Head]

I mentioned in my previous post that I found something that looks like a center punch mark in one of the sprocket holes.  It could be nothing more than a mark left from the casting process, but it sure looks like a punch mark.  No idea what it's there for, and it may be nothing at all.  I just thought I would mention it in case someone has seen it before.  I lined it up with the cam reference mark just for giggles, and it hits right on #4 exhaust and #6 intake.

 

Looks promising.  If it was correct, cylinder #1 would have intake and exhaust lobes up, and the damper pulley timing mark (for setting ignition timing) would be on zero.

 

Not sure what you mean with the 4 and 6 comment.  You should really get a timing light and set timing.  It's time.

 

You can't force a valve open from inside the cylinder.

[amplogic]

 

Looks promising. If it was correct, cylinder #1 would have intake and exhaust lobes up, and the damper pulley timing mark (for setting ignition timing) would be on zero. Not sure what you mean with the 4 and 6 comment. You should really get a timing light and set timing. It's time. You can't force a valve open from inside the cylinder.

 

I do have a timing light, but the engine won't idle long enough for me to check the timing. That, and with fuel blowing all over the place every few seconds, and having had excess fuel in the carb ignite a couple of times, it will be a little tricky.

Never mind about the #4-#6 valve comment.  It was a dumb way of stating that the mark most definitely didn't line up with #1 cylinder lobes in the correct position.

Edited August 31, 2015 by amplogic

[beermanpete]

It sounds like you have a motor at least. As has been stated already, fix the other small stuff not that you have verified the compression. Check the fuel pressure. It should be in the 3 to 5 PSI range for the Holley. With the electric pump you can do this without running the engine. Anything more than 5 PSI can force open the float valves and cause flooding. Also, since you are having what sounds like a rich condition and its a Holley, check the power valve. If it is bad it will cause flooding. Once you solve the fuel problems you can set the timing. If it won't idle you can set it at a high engine speed (3K RPM) for the full advance point, typically about 26 to 36 degrees depending on which distibutor you have and wether or not you are using the vacuum advance. Unhook the vacuum advance first. If the distrubutor is working correctly it will end up close enough at idle speed to idle if everything else is in the ball park. Really, you should be able to move the timing while the engine is running and set it by ear to get it close enough to idle.

[amplogic]

Sounds like a plan.

I went ahead and adjusted all the valve clearances to where they are supposed to be.  The fuel system will be the next thing I'll dig into when I get some time.  I did check the bowl level, and they were a tad high, even with the adjuster very nearly at its lowest limit.  I'm pretty sure I also have a vacuum leak after really looking all around and under that carb.  I see a couple of small fittings that aren't connected to anything, and I'm pretty sure that they are supposed to have vacuum lines connected.  I'm going to feel like a big dummy if all these issues are from vacuum leaks.