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Old tricks to determine if Cam has been upgraded

Tim Chavez said:
It’s HEI now. It wouldn’t run whatsoever before I replaced the distributor and ignition system. After I replaced it I’ve had it driving but never easily (lots of keeping slight throttle and fiddling to keep it running). I rebuilt the carb and have been fplaying with timing ever since. and that’s where I’m at now. It seems like if I have the timing set one way it starts without issu but pops and backfires with any throttle. Set it the other way and it takes 30 seconds to a minute of cranking to start But will wrap the tach well over 5500. Both posted videos are at the same timing setting.
Click to expand...

The distributer probably is not curved correctly for this engine. The curve is determined by how much base timing you have, the speed at which the mechanical advance comes in, and the total amount of mechanical advance allowed. Can you map the curve? Do that by starting the engine and writing down what the timing is in 500 RPM increments from idle to the point where the timing does not advance any further. If you do this and report back with those numbers it will be much easier to determine if the problem is inside the distributor.
 
Tim,is that a new HEi or used?
Check to see if you have a bare wire on the
advance ,it's down inside.On some older
ones I've seen them rub & eventually break.
Could be shorting out against case?
 
Johnpat said:
Tim,is that a new HEi or used?
Check to see if you have a bare wire on the
advance ,it's down inside.On some older
ones I've seen them rub & eventually break.
Could be shorting out against case?
Click to expand...
It is a new unit, it’s an all in 1 two wire HEI distributor. I’ll double check connections but it’s only Been I. The engine for a year and has seen maybe an two hours of total run time, if that, since.
Paul_G said:
The distributer probably is not curved correctly for this engine. The curve is determined by how much base timing you have, the speed at which the mechanical advance comes in, and the total amount of mechanical advance allowed. Can you map the curve? Do that by starting the engine and writing down what the timing is in 500 RPM increments from idle to the point where the timing does not advance any further. If you do this and report back with those numbers it will be much easier to determine if the problem is inside the distributor.
Click to expand...
I can try to free up a buddy to map the timing. I can never be a simple fix can it
 
Tim Chavez said:
It’s HEI now. It wouldn’t run whatsoever before I replaced the distributor and ignition system. After I replaced it I’ve had it driving but never easily (lots of keeping slight throttle and fiddling to keep it running). I rebuilt the carb and have been fplaying with timing ever since. and that’s where I’m at now. It seems like if I have the timing set one way it starts without issu but pops and backfires with any throttle. Set it the other way and it takes 30 seconds to a minute of cranking to start But will wrap the tach well over 5500. Both posted videos are at the same timing setting.
Click to expand...
Ok 2 wires to distributor right , try switching them. Sometimes on HEi if they are backwards it will advance timing and make it hard to start but runs OK after starting.
 
A quick, easy way to measure the cam lift if you have a dial indicator( preferably magnetic base)... stick it on the valve cover, pop out the oil breather or PCV and put the probe down through the hole to the top of the rocker and turn the motor by hand... Watch how much the dial moves as the valve opens and closes
 
Jackpot50 said:
Ok 2 wires to distributor right , try switching them. Sometimes on HEi if they are backwards it will advance timing and make it hard to start but runs OK after starting.
Click to expand...
I’ll flip them when I get home and give it a shot
 
Hold the #8 spark plug wire while someone cranks the engine
(I have actually seen this)
compression test time
then squirt some oil in and check them again
might as well do them all
throttle open , choke open
and ignition disconnected or whatever works with your ignition system
 
The plot thickens.. good spark and

CC3924CA-8632-4349-9644-D8F204D3B809.jpeg
 
Paul_G said:
Why do you suspect #8 is not firing? What readings did you get on the other cylinders?
Click to expand...
The other 7 show around 490 to 550 degrees on the header tubes when checked with my laser thermometer. cylinder 8 was 120 degrees.
 
Does the intake runner for #8 have a vacuum port in it? If so cap it and see what changes.

Do all 8 cylinders read compression about the same or close to the #8?

I would try swapping plugs and wires from another cylinder to #8 and see if the problem stays in 8 or follows a part to another cylinder.
 
I had a cracked distributor cap make me nuts, couldn't see the crack
 
I just had on on a v6 Cirrus engine light on and code for number 4 not working- car was overdue at the smog test shop and license was expiring
then one for the cam position sensor
compression good- that's good for both of us
grabbed a bunch of parts at pick a part (the CPS is in the distributor and pricey)
come to find the shaft is a different size so the rotor did not fit but the cap looked like new, fit, and worked- car passed smog
now back to my regularly scheduled work list
 
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