Hi guys I need some assistance or advice regarding a issue on my truck.

Setup: 1979 F100 inline 6 with standard single barrel carter yf carb, headers with freeflow exhaust. Replaced auto choke with a manual choke.

Problem: i have been using the truck as a daily driver for about 2 years now. Everything running smoothly and truck runs great. At one stage i had a issue where the truck will randomly shut off while driving. Then after i stopped. Switch everything off and on again then there we go again. Was very intermitted. Eventually i found it was a vacuum leak. And problem solved.

After abouth a month or so after that i got this simular issue that while driving i will loose power and what sounding like one or more cylinders that are flooded(maybe not the case but just a description) then a loud back fire and I will pull over, let it idle for a while and then everything is fine again. Then i can drive off again. This would happen maybe once a month randomly. It became worse. Over a weekend i would go over the basics to try and find the issue but the issue happens intermittedly and very difficult to find when its not present. Other than that the truck drives great. No miss on acceleration. Fuel usage is good. Relly no other problem. Starts fine

My knowledge is limit but thats why i have the truck and thats why i am trying to solve the issue.

Over a peroid of a month I have done the following.

Changed all vacuum lines, all fuel lines, flushed fuel tank, replaced fuel filter couple of times, rebuilt the carb, checked timing, replaced spark plugs, replaced leads, distributer cap and rotor, replaced fuel pump, adjusted carb and idling.

Cant say if any of these improved anyting because i can get in the truck and drive it for the next few weeks, and then suddenly this issue will appea when I am going camping for a weekend. Then i really dont want get stuck in the middle of nowhere without any power.

I apologize if i cant discribe the problem to clearly. But thats part of the problem...

My question: is there anything else that i can check or test to see if its a spark or flood issue. Can it maybe be a dodgy ignition module? Or something in the carb?

It will be very hard getting a solution with a problem with so many variables. But i have restores my entire truck from the advice i got from this site so anything is possible.

Thanks in advance

 

Intermittent problems can be very exasperating.
The ignition modules have been known to cause strange intermittent problems. If you have a spare module, you could give it a try. If you don't have a spare, you should buy one and always carry it with you. Frequently they don't give any warning before failing completely. I once had one quit in the Arizona desert. If I hadn't had a spare, it would have been very sad. Sometime the pickup coil in the distributor can also become intermittent, but the module is usually more problematic. Since you've already rebuilt the carburetor, that will eliminate my second choice. The ignition components usually do worse when they get hot. Be sure to have a lot of ventilation around the module. If you get it resolved, we'd like to hear about it. Best wishes.

 

Thanks for the heads up. My next step will then be to replace the module. And keep a spare! Thanks for the advice!! Will keep the post updated with my findings!

 

Where does it backfire from, the exhaust or the carb? If its the exhaust, which I suspect is what you'll say, you have an intermittent issue with spark. What happens is fuel is drawn into the cylinder from the rotation of the engine, and if there is no spark in that cylinder to ignite it the unburnt fuel gets pushed into the exhaust and the next cylinder to fire because the spark reappeared, its hot exhaust gas ignites and explodes the fuel in the exhaust. Definitely check your ignition module as mentioned, and the interconnecting wiring for loose/corroded connections.

 

Jip you are correct. It backfires through the exhaust. From your description I can picture that is whats happening. At first I thought it was a float/carb issue causing it to flood. After I rebuilt it there was defenitly an improvement on how the truck drives. But after a few trips the issue appeard again. Will defenitly replace the ignition module and check all wires and connections in the process. Thanks again!! Will keep you guys updated.

 

Seems to be going around. Spent an hour or so tonight laying in a rain puddle trying to get mine running. Bought new fuel pump, filters, bypassed dual tank switch thinking that was the issue. Plumbed both tanks to the fuel pump, ran fine for a while. Then twice in last week, it's died for no apparent reason. Started replacing rubber fuel line. Rerouted metal fuel line out and around from sources of heat. Now I've blocked off the rear tank entirely, and running off of aux tank. That was fine until today. So I took rubber line off of fuel pump, put a gas can in my engine bay, hooked rubber hose back up to pump and drove home. It's so frustrating. Can't trust it to take it anywhere