65CopCar
Well-Known Member
It was a great pleasure to help today!
Yes there are things that could be improved (my ultrasonic probe indicated potential significant vacuum leak in one corner of the carb and an electrical abnormality at the coil), but they probably are not the main issue.
The spark plugs are probably WAY too hot. They are Champion RN14YC. The engine just quit after we took it for a nice spin while idling. When tried to restart it and it sounded like it wanted to blow up and it spit some smoke out of it to boot. Started it up again and it died after a minute or two.
So decided to see what it sounded like while only cranking it. So I pulled the spark plug wire out of the coil so it would not fire - impossible for it to run with the coil wire pulled.
Much to our surprise it basically ran for a couple of seconds. Ok - THAT'S A PROBLEM! The most obvious cause is too hot of a spark plug. 14 is too hot. 440 Source says 12 is their standard recommendation, and I think that is too hot for a 10.5:1 motor. This is a 520 CID. To put it in perspective, granted it was better heads and higher compression, I ran a 7 heat range in my 528. I recommended a 10 heat range, and the NGK should be a bit colder than the 10 so should be a good start in my opinion.
Will it totally solve the problem, maybe or maybe not. But for sure its a major problem and it needs fixing before any other troubleshooting takes place. Pretty obvious the dieseling is being caused by the spark plugs, but if its not the cause, then there is a serious combustion chamber problem and I seriously doubt that.
Yes there are things that could be improved (my ultrasonic probe indicated potential significant vacuum leak in one corner of the carb and an electrical abnormality at the coil), but they probably are not the main issue.
The spark plugs are probably WAY too hot. They are Champion RN14YC. The engine just quit after we took it for a nice spin while idling. When tried to restart it and it sounded like it wanted to blow up and it spit some smoke out of it to boot. Started it up again and it died after a minute or two.
So decided to see what it sounded like while only cranking it. So I pulled the spark plug wire out of the coil so it would not fire - impossible for it to run with the coil wire pulled.
Much to our surprise it basically ran for a couple of seconds. Ok - THAT'S A PROBLEM! The most obvious cause is too hot of a spark plug. 14 is too hot. 440 Source says 12 is their standard recommendation, and I think that is too hot for a 10.5:1 motor. This is a 520 CID. To put it in perspective, granted it was better heads and higher compression, I ran a 7 heat range in my 528. I recommended a 10 heat range, and the NGK should be a bit colder than the 10 so should be a good start in my opinion.
Will it totally solve the problem, maybe or maybe not. But for sure its a major problem and it needs fixing before any other troubleshooting takes place. Pretty obvious the dieseling is being caused by the spark plugs, but if its not the cause, then there is a serious combustion chamber problem and I seriously doubt that.
