Sputtering And Stuttering

I need advice, please.

Just got my 1964 with a Buick 3.7 back from mechanic. It had been idling rough, lots of vibration, and hard to start. He found that one of the previous owners had cobbled together the distributor and when I replaced cap and rotor with correct ones, plugs were misfiring. So, he rebuilt distributor to correct, and now it idles great.

However, he couldn't seem to get the carburetor adjusted. It's a Carter BBD 2 barrel, and it's running a little rich. Not really a problem at low speed, Jeep runs like a scalded cat through all 3 gears until about 60.

At highway speeds it starts stuttering, shaking and sputtering. It gets better when I let off the gas but will do it again after a few minutes. Nothing at lower speed, just when I get to 60. I lose power, naturally, and speed drops to about 30. Let off gas, and it accelerates normally until it happens again.

Plugs are new, wires are new, fuel filter just a couple months old. I'm out of ideas and looking to tap the collective expertise of this forum.

Thanks in advance.

 

That sure sounds like a fuel delivery problem. Check fuel pump output, both pressure and volume. Check fuel filter. Check condition of any rubber lines in the fuel system.

 

I'll get on that this weekend. Awesome! Thanks!

 

What Doug said. Another factor that isn't an infrequent occurrence is a clogged pickup in the fuel tank-same result.

 

What makes you think it is rich?

Might check the float level. If it is too low or the float is sticking, the carb can run the bowl dry under high demand situations.

 

I have had this before, self-inflicted. Try and run the bowl as low as I could to help with off camber flooding

 

The mechanic told me when I picked it up, he felt it was still running a little rich. I'll check. Thanks!

 

Clean. Jeep has side exhaust, and I don't notice any smoke or fumes.

 

Lets see. Mechanic, cobbled distributor, firing wrong, rebuilt distributor, cap and wires, rough idling and loses pep at higher RPM.
Mechanic says it's rich but doesn't smell rich. Too much going on here and would need to start with all the basics. How many
mechanics have dealt with this particular engine?

 

Does the symptom seem more aggravated under sustained load, e.g. pulling a hill for instance? Then that may be confirming a restricted fuel supply, as above.

But yes, always, start with the basics... a by-the-book tune up to FSM spec, and done in the correct sequence. Diagnosis starts from "known-good," not random guesswork.

 

What do the spark plugs show?

 

Yep. Disconnect the fuel line and give it a good blow back towards the tank. If there's anything in there between the filter and the tank pickup, it should free it up enough to get a test run in for a little bit. Might even be worth draining the tank to see what hidden gems are lurking haha. I drain mine every couple seasons and there are always crumbs of varnish and misc stuff that somehow magically appear.

The first time I did it, there had been a decent sized insect/critter clogging my line.

 

Just possibly this could be a reaction to the vacuum advance and timing settings, or points gap adjustment/cleaning. Start with checking the tuning specifications. Per FSM.

 

Could be the points are floating at higher rpm's.

 

Maybe with Omix-ADA points but with the stock GM version I doubt you would be anywhere close to floating the points at any sensible rpms in a Jeep. I've run stock Delco points to 7k in a sbc.

 

So I was tracing fuel lines and noticed that the steel line coming from fuel pump had an extreme turn. I attached a photo, unfortunately it's not very clear, but you can just make out the flat spot in the bend. Could this be the issue?