I have a 1977 351M that has had hesitation issues on and off. It has not been until recently anything that was a consistent issue. It occurs randomly and is always around low to mid range acceleration. By going WOT I am able to get through it and it will go away. I changed out the fuel pump as I had noticed that the fuel filter had some "dirt" in it and ran air through the fuel lines in hopes of clearing any possible issue out.

At first it ran fine but now the hesitation is back and it is happening on the start up. It idles strong but once I throw it it into gear it is worse than ever. I have had to pretty much throw it into reverse and back up about 50 yards and then go into drive and repeat until the hesitation goes away. What is strange is that in reverse there is no hesitation what so ever no matter how hard I hit the gas but in drive it is horrible.

I have also found that by holding the brake down and gassing it until the tires start to give will kill the hesitation and she will run awesome after that. Trying to drive around "normally" will not solve the issue...

Could this be an issue with the carb being dirty?
Maybe the float is not working properly?
It is a 4150 Holley and I am just trying to figure what the next step would be in order to troubleshoot.

Thanks for your time.

 

Hard to diagnose over the Internet but I would look into the fuel system and suspect something has clogged up one of the idle circuits. Especially if you noticed the fuel filter was dirty. You might have some rusty particles in your tank or just got unlucky at one of your gas stations. I noticed the bottom of my plastic 5 gallon jug I use for my mower gets plenty of garbage from a relatively "new" gas station too.

Recommend checking the filter again and replace, then take apart your carb and give it a good cleaning. A rebuild kit runs about $50.00. You'll need some carb cleaner and compressed air and a few hours.

Also recommend not "forcing" your engine when it's running this way hoping that it will clear itself. There's plenty of videos on YouTube to help you if you are not familiar.

 

I would verify that the accelerator pump is working like it should (getting a good squirt when you first actuate the throttle) and then look for a vacuum leak.