My 340 Flattens Out Above 55 MPH

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hotrod3forty

hotrod3forty

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My 340 flattens out above 55 mph and it won't pick up any more speed and I can't keep up with traffic on the highway. I don't even know where to start to look. Plus it idles rough at a stop and in park but it picks up speed and cruises at lower speeds ok. Is it the carburetor (avs), or ignition, too much timing...??? I can only fiddle with it for so long then I get frustrated. Once again, I'm lost. There are so many smart people on here that I hope can give me a clue.

It's a 69 340 Swinger, electronic ignition, avs, automatic, 3.23 gears. It's my "It used to run fine and now it doesn't" story.

Thanks very much!
 
Just throwing some things out to consider since you said it was running fine at one point. Bad fuel? Dirty fuel filter? Ignition box starting to crap out?
 
What is the engine doing when you hit 55 mph? Does the car have a rev limiter (oh I could tell you a story about having to deal with a motor that had it set lower then my friend wanted but he swore up and down that he set it right)? Any vacuum leaks?
 
sounds to me like its either dumping fuel , losing fuel pressure, or the secondaries arent opening.
 
Id just sell it.... How much you want? Id guess carb. My 340 was running like crap after setting for a while. Hogging up, hitching, skipping, running real rich mine ended up needing the carb cleaned. Looked like dried varnish on the inside of it. Got to love this junk gas
 
Fixed! Yeah.....the Carter AVS was shot! I replaced it with a new Edelbrock 650 AVS. The car runs great now! Just took me a little while to post.
 
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