Hey guys! I am restoring a 79’ Bronco, 351M.. used by previous owner to play in mud.

Recently it’s started stumbling then stalling out when I hit 40+ MPH. Mechanic said it was the carburetor.. another mechanic said it was the fuel pump.. fuel filter.

Well I replaced ALL THE ABOVE. New carb is a Summit Racing M2008 Series, 600 cfm, electric choke. After installing everything and tuning the carb, I was able to hit around 50mph before the stumbling began.

I’ve had the new carb tuned at least 3 times and still she’s not running good at all. Usually she stalls out after stumbling. Sometimes she doesn’t start right back up. Today after stalling out, it wouldn’t even crank so I sat for about 10 min and then she started up but stumbled and stalled out again. Sometimes it will crank but not start, so I have to sit a couple of minutes then it starts up and runs but I can barely get it past 25mph before stumbling again. I checked the clear fuel filter and it’s not gummed up with anything..

Mechanic says it is flooding out still and he needs to tune it some more but I don’t know about that now. He says everything is checks out fine..spark plugs, hoses, wiring.. all good, so I’m at a dead end right now.

I’ve read it could be the gas.. or the gas tank, but I replaced the gas tank months ago due to the old tank rusting out and got a whole in it. Mechanic recommended I get the new plastic tank to prevent rust so I did. I’ve put Lucas Fuel treatment in the tank prior to all this and still the same result.

I’m thinking about changing from a carburetor to a Fitech Fuel Injector System because of this but who’s to say the same thing wont happen and it’s something else wrong.

Any ideas will help..I’m begging!

Welcome to FTE Broncogirl

No carburetors have been installed on any production engine in something like 33 years. So... finding someone who is both willing and able to work on them is tough sometimes. Are the mechanics working on your Bronco old enough to be your grampa? Or are they young enough to maybe asking you out for a date? Because that's probably what you want for your Bronco (Grampa, not the young guy) if you take it to a "regular" shop, they may not be familiar with carburetors in any meaningful way, or engines that don't throw codes and the rest of it. Not really a criticism just an observation, know what I mean? You need to find some ornery older guy with proper old school test equipment who does this kind of thing on the side as extra beer money or a hobby. It is true, many times the carburetor is blamed when something else is the actual issue. Ignition problems particularly.

You have some choices, the main one is either you, Broncogirl, dive into the shop manuals and get smart and do the troubleshooting & repairs yourself or, hire someone else to do do it and hope that they know what they're doing. It doesn't sound like that now necessarily. They usually have to charge an arm & leg just to look at it, because every minute of their time has to make money for them and they have to work fast or the charge builds up faster. Maybe ask around at NAPA or wherever if they know some locals working out of their garage, retired guy who works on "vintage" cars maybe something like that.

Thank you BrutalBronco for your suggestions!! I will definitely tell my mechanic to check the coils. Cables from the battery & alternator checked out good. Will report back with update!! This issue has been a mystery for a lot of people!!

I would have a new fuel filter ready, pull off the old one and cut it open. If there is any crud or particles in the old filter, remove and clean or replace the fuel tank. Also inspect the tank pick up closely.

By the way, I’m 69 years old and have seen more than my share of carburetors.