Thanks guys...good advise.
Yes, the 1955 235 is a truck engine,it's in my '51 1/2 ton.
No, the noise isn't excessive, and it only lasts for a couple of miles until its warmed up. Then it doesn't happen again till the next morning, sometimes not for a few days.
I shall stay away from STP, and also leave well enough alone. It runs great since we put in a new fuel pump and cleaned the carburator of 50 years of gook accumulation last month.
I always appreciate the expertise from you guys, Thanks.
Bart
