Been wrenching for 35 years and got a brain buster. Been spoiled with obd 2 that really helps narrow down issues on my daily drivers. I got the scan master on the gn which helps a ton too. My 70 gs 455 recently started surging at cruise speed 40-50 mph. It hasn't challenged me in 18 years since I built it now obd2 can't help and I have to go back to using my brain. The disty is an hei and it looks pretty clean inside. Carb is an edlebrock that has never given me an ounce of trouble. I need to put a timing light on it to see what's going on with timing. The centrifugal advance seems loose but it springs back when you twist it. Any suggestions on other possible causes ?
Changed fuel filter lately? Sounds like a lean condition. Could be the filter clogged or not enough fuel supply to carb due to pump issue or restriction in fuel system. If its not a dead misfire then i would check your fuel system
Are there nylon bushings on the pivot points for those advance weights? Do you drive it pretty regularly? Carb might have deposits in it from dried up corn gas.
The ole GS is once again running sweet as ever. turned out the idle air bleeds on the carb were dirty/plugged. A blast with some carb cleaner was all it needed. I'm embarrassed it got this far because this is not unusual for my set-up and ive done this numerous times before on the GS after spirited driving which kicks around settled dirt , but the old brain and old eyes sprayed the carb cleaner in the wrong place the first time around but with cheaters and an inspection mirror I found the bleed tubes. Getting old is not fun. Good news is it caused me to do a full inspection on the disty and found the advance weights were hanging up a wee bit and in need a minor cleaning and a few drops of oil. She's a street beast once again.
