'71 Thunderbolt 500 not firing on #1 cylinder.

[WoodOnWater]

I'm tracking down what I believe is a fault in my ignition system. The engine stopped producing full power on my last outing and fuel consumption was high for the power it was producing. I initially thought it was a carb issue and have cleaned the the carbs. Further investigation has revealed the #1 cylinder is not producing power. I swapped the #1 and 2 spark plugs and the miss remained with the #1 cylinder.

I feel that that the issue is in ignition system associated with that cylinder and would like direction in taking the proper steps to correct the problem. In retrospect, I had noticed on the last couple of outings, it felt like the motor was idling less smoothly than normal, but power was normal. On the outside chance that I have a compression issue, I have acquired the tools for running a compression check, but haven't been able to do the check just yet.

I stopped my ignition trouble shooting when it looked like I might have to tear deeper into the ignition system and maybe open up the distributor(?) assembly. Thanks in advance for any guidance in helping with this issue.

 

[racerone]

Post the results of the compression test.----And tell us if spark on # 1 is good.---Does the spark jump a gap of 3/8" or more , yes or no ?

 

[merc850]

It could be a bad spark wire or there's a short between the wire and the block, run the motor and move the wire away from any part of the block and cowling support and see if it improves. Another way is to run it in the dark and look for arcing.
The next area to look at is the cap, there could be carbon tracking or corrosion.

 

[WoodOnWater]

I'm back finally. I did the compression check so we could move past of that point. Cylinders check at. 109 psi, 108 psi, 110 psi and 111 psi respectively.

Moving forward with ignition diagnosis, all cylinders are getting spark, but both 1 and 2 were weak at around 1/4" of arc give or take, number one being the weakest. Number 3 would do a 3/8"arc and number 4 could jump a 1/2" arc.

I'm not really sure of the right path to go now. Does the whole ignition module (distributor?) have to come out or can it be disassembled in place? I'm concerned about unnecessarily disturbing ignition tuning.

Thanks in advance. What a great forum.

 

[racerone]

Just remove the bottom half of the distributor.----Timing will not change then.