Specs: 1983 F-100 XLT, 300 Straight.

Vac lines are a little sketchy, it does have gas, new fuel pump is kicking gas out well. Carb spits back fuel when cranking (new definition for feedback carb?).
Like I said, vac lines are unhooked in several places. Also, the EGR is sketchy really bad. The spacer's hose hookup to the exhaust is a bit worn where its supposed to be threaded. Idk if I can get the exhaust hose back on, we will see.
If not, how to cut out EGR system from the loop. A hole under the carb is prolly not gonna help in the future. For now it is blocked though. What are some things to check? Batt voltage is good. Gapping is good on plugs and they are firing, although I used the plugs and the ground out on the engine trick, not a bona fide spark tester (I understand the tester is more definitive as it takes ~25,000 volts whereas normal plugs take ~3,000)

Help me please. Other things to check?
Additional info just ask.

 

Well, unhooked vacuum lines will cause mondo problems unless every vacuum port on the intake is capped.

The exhaust line to the EGR is isolated from the intake unless the EGR valve is stuck open. There's no reason to remove it and would require some sort of tall spacer because of how long the carb studs off the intake are.

What does the carb spits back fuel mean? You can see gas pouring out while cranking? Has the carb been rebuild recently? Sounds like a bum needle/seat.

 

What does the carb spits back fuel mean? You can see gas pouring out while cranking? Has the carb been rebuild recently? Sounds like a bum needle/seat.

The choke plate opens up when I crank and it sprays fuel out the top. It was re-manufactured in May 2012. I also had my dad rebuild the needle/seat and all of that. Idk all the names of the pieces, but he put the standard rebuild kit from Advance Auto (GP Sorenson) on it.

The exhaust line to the EGR is isolated from the intake unless the EGR valve is stuck open. There's no reason to remove it and would require some sort of tall spacer because of how long the carb studs off the intake are.


Not sure if the valve is stuck open, I DID put a vac guage and the EGR didnt hold any pressure, so I know its bad. Does that mean its stuck open or stuck closed, idk.

Im taking a trip to the junk yard tomorrow, I saw a yard on facebook and in one of the pics there was an '83 F-250 with the 4.9. It was complete as of April 15, hopefully I can get a new spacer for the EGR valve, as the one I have, the threads might be screwed up.
I had real difficulty finding the 3/8 carb studs. Apparently they arent used often, Auto Zone, Advanced Auto, and O'Reillys all treated me like I was stupid. I ended up buying 3/8 bolts and putting the carb on with them.

ALSO: I checked the firing with a true spark tester, it still jumps the gap with the tester set to 35,000 volts, although its a pretty small spark. It seems alright though.

 

 

This is a video o me cranking the engine. You can see the gas spitting out of the top o the Carb.

 

Yep, spitting back through the carb. Careful, you could be one spit from a fire. Keep face and body well back!!!

A common cause of spit-back is a mixture that is way too lean.
Some things to try:

Unbolt EGR valve, and make sure that the valve's pintle (the pointed part that moves) closes tight, not blocked open (even a little bit) by chunks of carbon. If there are chunks of carbon, scrape them away, and use solvent to clean the pintle and seat, so it closes tight. It doesn't take much of a leak in a EGR Valve to dilute the mixture too much.

Mark, disconnect, and plug every vac port on the engine. In effect, isolate the engine's intake manifold from everything else. This will greatly reduce the possible vacuum leaks, just down to engine basics. Speaking of engine basics, verify that all carb gaskets are present and correct, like carb to spacer, spacer to manifold. Yeah that seems obvious, but you can get the wrong gasket, I did on a 460 once, had a wide thin vac leak on secondary barrels on the back of the carb, ran like crap till I found it. Gasket had a tab missing that should have covered up a PCV Spacer slot. Didn't catch it, with carb on couldn't see it. Had to troubleshoot to find it.

There are other possibilities for spit-back, like ignition timing way off, or an intake valve not closing all the way, etc. but I would start with the too-lean idea above, as that is more probable.

What is the history here? Was this truck running recently, or is it being brought back from the dead, or ? Sometimes knowing the whole story helps

 

cstephens,

Agree with above posters. Fix all vacuum leaks. Snug up carb and intake bolts. Your video shows a classic vacuum leak. Other things can cause the backfire through the carb, but check the easy things first.

Tote

 

I started paying on the truck in October. It "ran" then, but idled terribly. It would shake really hard when ya got it to start at all.
I hauled the truck home with a backhoe (I know a guy) and since 2 weeks ago, I have been plugging leaks, went to the scrap yard and purchased a new spacer, this one had a stopper in one hole (and the hose).
I thought I put it in time on the distributor, but idk enuff about it to say for sure. I DO know that it is firing on all the plugs, but it keeps flooding. I can look in the intake with the Carb off and see gas on the walls. So we're good on gas.
To me it seems like the dizzy timing. I just don't know how to do it right. Well, actually I have the idea from a post by AbandonedBronco (I think), I just need another person to do it