1961 Cadillac cranks but won't start what am I missing?

[joeceretti]

Yes a gen light on in that situation indicates stuck points.

[Matt Innocenzi]

Jon and Joe - that was a one time event.  The GEN light now goes off when I remove the key, but stays on while cranking.  It also stays on when the car was running which is what made me replace the battery and polarize which started this whole thing to begin with.  I am thinking it was just a strange coincidence.  At least I learned what makes the GEN light stay on when the key is removed. 

[Jon S]

Matt -

I guess I have a few more questions and maybe an idea.  If it started a few days ago with the old battery, why did you replace it with a new battery?  You say the GEN light came on after you changed the battery; hence the polarization process.  Was there any strange sparking at the battery terminals when you installed them on the new battery?

Does the car have a after-market alarm that grounds out the ignition that needs to be re-set with the change of batteries?  I'm thinking along those lines . . .

[Matt Innocenzi]

Jon,

Brief history - back in the Fall, the GEN light came on.  Earlier this week, we had a cold snap here that killed the battery.  When I put the battery back in charged, I wanted to polarize it since it was removed and make sure that was not what was causing the GEN light to come on.  No sparking on the terminals, all seemed good.  Car will now crank, but won't fire up.  No aftermarket stuff like alarms or anything.

With all the good suggestions and ideas I am planning on doing some troubleshooting tomorrow when it is a balmy 50 degrees.

Matt

[Matt Innocenzi]

OK, I have pulled the distributor and replaced the lead wire, points, and condenser.  Set the gap to spec and installed it with the rotor in the exact same spot, and verified the firing order is correct. 

I also replaced the coil with a known good one, just for good measure. 

I have fuel, carb is good and floats were verified to be in spec.  I can see gas shooting out of the primary discharge jets.

I pulled all of the spark plugs and cranked the engine.  All cylinders are dry and have great compression.

Put everything back together.  Tried starting and bloody thing still will not start.  WTF?!?!? 

In essence, I have spark, compression, fuel, and air.  The last thing I am tempted to try is attach a lead wire from the battery to the positive side of the coil and bypass the car's electrical system. 

Any other possible ideas?

[joeceretti]

Does it even try to start showing that there is some combustion.. or nothing, just cranking?

It does seem like a good idea to wire it up directly like that at least to eliminate the existing wiring as the culprit.

[Matt Innocenzi]

Joe,

It wants to start - when starting, the rpms will pick up like it is about to catch, but then it falls flat.  I also got a HUGE backfire in it that sounded like a grenade went off.  I thought it was a timing issue, but triple checked firing order and timing and they are fine plus none of that was changed. 

Will try the jumper wire idea next.

Matt

[Jon S]

Matt -

Obviously the engine must be flooded and then some.  One last idea before the jumper wire.  Hold the accelerator to the floor for a full minute, then try starting it with the accelerator still fully depressed.  This should unload the carburetor.  If it starts, release the accelerator.

Since you mention it wants to start, I believe it will once you unload the carburetor.  Good Luck!

[Scot Minesinger]

Hope it does turn out to be the flooded carb, push gas pedal to floor resolution.  It makes sense that it would be something simple. 

The back firing is weird because hot exhaust usually ignites unburned air/fuel mixture, but exhaust is not hot - what is source of ignition?

[Jon S]

Hope it does turn out to be the flooded carb, push gas pedal to floor resolution.  It makes sense that it would be something simple. 

The back firing is weird because hot exhaust usually ignites unburned air/fuel mixture, but exhaust is not hot - what is source of ignition?

Scot -

I suspect backfire was via carburetor; not exhaust.  Reinforces my flooding concept.

[walt chomosh #23510]

Matt,
  Back to fundementals: turn motor in correct direction,and with #1 coming up on compression stroke(verify with plug out and finger in hole!) turn crank until timing marks line up on dampner. Then,remove distributor cap and verify the rotor is pointing at #1.(you can even turn the key on when doing this and as the points break open,#1 plug wire should spark) At this point,static timing is perfect! Then,close the choke completely and start. Air,fuel,and spark,it should fire! If it doesn't,apparently the timing chain has slipped.(you should still hear cylinders trying to fire...popping thru exhaust or intake due to incorrect valve timing) Good Luck!....walt...tulsa,ok

[Jon S]

Matt,
  Back to fundementals: turn motor in correct direction,and with #1 coming up on compression stroke(verify with plug out and finger in hole!) turn crank until timing marks line up on dampner. Then,remove distributor cap and verify the rotor is pointing at #1.(you can even turn the key on when doing this and as the points break open,#1 plug wire should spark) At this point,static timing is perfect! Then,close the choke completely and start. Air,fuel,and spark,it should fire! If it doesn't,apparently the timing chain has slipped.(you should still hear cylinders trying to fire...popping thru exhaust or intake due to incorrect valve timing) Good Luck!....walt...tulsa,ok

Since it ran fine before changing the battery, I doubt the timing changed or timing chain slipped.

Matt - Your comment "I pulled all of the spark plugs and cranked the engine.  All cylinders are dry and have great compression." bothers me as I would have expected the plugs to be dripping with gasoline and the cylinders to be wet!

[Bobby B]

Matt,
  Back to fundementals: turn motor in correct direction,and with #1 coming up on compression stroke(verify with plug out and finger in hole!) turn crank until timing marks line up on dampner. Then,remove distributor cap and verify the rotor is pointing at #1.(you can even turn the key on when doing this and as the points break open,#1 plug wire should spark) At this point,static timing is perfect! Then,close the choke completely and start. Air,fuel,and spark,it should fire! If it doesn't,apparently the timing chain has slipped.(you should still hear cylinders trying to fire...popping thru exhaust or intake due to incorrect valve timing) Good Luck!....walt...tulsa,ok

Walt,
You beat me to it. After reading all the previous posts there are not many avenues left to go down here. Matt says he pulled the distributor. Very easy, and a common mistake, to be 180 degrees out. I've done it myself and it exhibits the above symptoms, till you realize what you've done. The only other possibility I can think of is that it did indeed jump time, and it could be totally coincidental, but stranger things have happened. There usually isn't a warning sign when an engine jumps time, it just happens. So we really can't rule that possibility out. All the pieces seem to fit, but it's not lighting off. When Matt states that it seems to speed up while trying to fire is usually an un-timed compression stroke due to the valve openings not being in concert with the piston stroke. I'm out of ideas and just trying to help because I know something like this is frustrating when you have covered all the obvious bases. At this point it's either something so trivial or something major, which we hope not. Just because it was running before doesn't mean that something didn't happen in the interim.   
                                                                                         Bobby

[joeceretti]

General rule.. too rich, backfire out exhaust. too lean, cough out the carb.

[Scot Minesinger]

What is the source of ignition for backfire?  It cannot be hot exhaust.  Carb does not create a spark.  My inexperience is showing here, but do not get how a backfire can occur here on a cold engine.  Perhaps it is the spark igniting the exhaust gas being pushed out of the cylinder during exhaust removal stroke and distributor is 180' out? 

However, it seems weird that the timing would have jumped to create the need for matt to remove the distributor that was not 180' in the first place, so maybe it is the chain jumped a bunch!?  There must be a test to determine if the chain is way off.

It sure is tough to diagnose this type of problem over the internet when you know Matt has restored many RWD V-8 cars of the 50's and 60's including dismantling engines; heads off, oil pans off and etc.

[Raymond919]

I am definitely no expert on this but can only relay my experience. My '49 was running fine on the highway and suddenly I got a loud backfire like a grenade same as Matt. Big cloud of black exhaust smoke and I rolled to a stop.
The car was flat-bedded back home and we noticed that the wire from the coil to the distributor had come loose at the coil where a nut had loosened and the wire completely disconnected. The wire was re-attached and the nut tightened. The car was easily re-started with no other problems and ran as before the problem started.
I would check all connections first. Perhaps that 'jump' as mentioned would reveal a lot.
Ray Schuman
#26141

[Jon S]

I'm still hung up on the  "All cylinders are dry and have great compression as I would have expected the plugs to be dripping with gasoline and the cylinders to be wet!

The timing issue is the most logical; but as Matt states, the car started last week before the battery died.

A very lean condition (dry cylinders/plugs) could also cause a carburetor back fire.  I was going to question the distributor 12V wire also.

[Bobby B]

The baffling part is that he says there's spark……So, are we ruling out an electrical issue? Hard to help without being there.
                                                             Bobby

[joeceretti]

has to be electrical.. even if the timing chain jumped a few teeth it would likely still fire and generally act like an angry dragon.

Or, if the cylinders are nice and dry then it's the carb/fuel pump. If it is the carb or fuel pump then putting a bit of gas in the carb will tell the story...

[Jon S]

Best way to load gas in the carburetor is with an eye dropper in to the vent tubes to fill the bowl as opposed to pouring it down the throttle plates.