Had the chance to drive a clean 85 Eldorado Biarritz today. What a beautiful car! The car is all original and has a rebuilt HT4100 engine. I have always heard that engine was not enough to power this model, and I experienced that today. The car "labored" to enter the freeway as I depressed the accelerator. It did accelerate, but there was a slight labor popping sound -- nothing metallic -- just a very light popping noise as I depressed the accelerator hard. It stopped as the car gained highway speed - the car ran and rode beautifully then. It also has no noise or issue during in-town driving. It's the acceleration. Is this a normal feature for this car? Thanks

 

Sounds like it could be spark knock, not that unusual for 4.1-4.9l push rod engine, normally related to carbon build up on pistons or in EGR system. Should you decide this the car for you it should not cost very much to correct. It might be worth getting professional opinion from a qualified local tech to be sure this is not the start of something more serious.