Help with diagnosis regarding ford 360FE

We're having some issues regarding the 360 in our 69 F100. In 2014 I rebuilt the carb and did a tune up on it and got it running well, drove it for a few months and then let it sit. Since then we've started it up  but it won't reliably run. We've put a new rebuilt carb on, put electronic ignition in with a new coil, as well as new plugs and wires. It'll start right up and idle, and drive around town just fine, but it will start to backfire and spit if we try to accelerate under load, like if we're in 3rd gear going 50-55, we can't accelerate because it just coughs and backfires. To me this sounds like a timing issue. 

Ive checked to make sure the balancer and TDC is correct, which it is. Checked timing, which was at 12*. would backfire off idle if I did anything less then 12*. Plugs seem to look good, doesn't appear to be running too rich or lean, and the accelerator pump appears to be working.

Thoughts on this? 

In reply to NBraun :

Are you getting timing advance?

Yep, I checked and mechanical advance was around 25*

Float level? Fuel pump? Fuel filters, including any fine screens in the carb?

Sounds possibly lean under high fuel demand?

May not be *running* lean, just unable to keep up when you go to accelerate when already under load, do might not show lean on plugs?

Balancer slipped?

Verify TDC mark.

Tdc has been verified, new fuel pump, new fuel filter. Will pull the top and check float level and other filters though.

I had similar issues with one and it was a vacuum leak at the base gasket. Easy to check by spraying some carb cleaner at the base of the carb.

Float was set too high. Adjusted it back down to ford spec. 

No vacuum leaks, voltage is correct at coil. Going to pull the fuel filter and see. It feels lean going through 1st gear and when in second it coughs because not enough fuel I'm assuming.

Pulled fuel filter and it's spotless

Look closely at the hard line from the tank, especially in the areas that it is higher than the fuel level in the tank. I have seen several cases where there is a slight rust hole in the line that sucks air in but does not leak fuel out because of altitude. I have also seen on one occasion a line that rusted internally enough to block under suction. Check the actual output from the pump, volume, not pressure. Carefully!

Could be overly rich.   What do the exhaust pipes look like?   Does it smell of unburned fuel?  Any black smoke during acceleration?

My Harley, only carb vehicle in the fleet, was way too rich.   It refused to pull cleanly at higher revs and broke up badly.  Wouldn’t go faster than about 60mph and adding throttle would make it stumble.  Pipes were black and kind of wet/gooey.  Reduced jet sizes and it now revs and runs much better.   

Sock in the tank is possibly filthy / plugged.

Disconnect the ignition, remove the plugs so the engine turns over easy. Put a hose on the output of the pump and turn it over until you pump out about a quart of fuel.

You're watching for the  pump output to drop off as it sucks the hard line dry.

Alright, ended up pulling the fuel boosters(?) and cleaning out the fuel passage. That seems to have fixed the running lean while driving. However, now it will backfire through the carb if we hit the throttle off idle. I've checked and the accelerator pump is squirting fuel just fine. It seems like it's a timing issue, but it doesn't seem to change whether if it's at 4* or 15*.

Is it a Holley carb?

Did you get the accelerator pump cam in the correct hole when you put it back together?

The accel pump should start squirting fuel as soon as you move the throttle. Not at 1/8 open or anything like that.

First, what kind of backfire?  Bangs out of the exhaust?  Or pops back through the intake?

The first one indicates rich, which could be carburetion or late spark.  The second one indicates lean.

Autolite 2100 2 barrel. It's a lean backfire, as it backfires through the top of the carb

Slack in a worn timing chain? Just throwing darts.

Recheck that the ignition wires are on the correct cylinder.   And go back to the basics in the book.

   I have run across this before back in the days of distributor ignition.  One crossed wire and it only shows up under load.

Also possibility is bad spark plug wires arcing across.  If you start the engine in the dark you can see the flashing when you rev it up.

Backfiring through the carb is a sign of a spark plug firing while an intake valve is open.    A sign of a crossed wire.

ddavidv said:

Slack in a worn timing chain? Just throwing darts.

Quite possible.  Usually a 360 will run fine with chain slack given the light valvesprings, but it is very possible.  Normally the chain gets enough slack that you hear it dragging and slapping on the timing cover before you get other issues, but it's easy enough to check.

It's an FE motor, so no fuel pump pushrod.  The pump arm rides directly on the eccentric.  Just yank the fuel pump and use a telescopic magnet on the timing chain to see how much slop there is.  Rotate the engine backwards and forwards and test in a few spots to make sure tension isn't being held on the chain by the valvesprings.

jharry3 said:

Backfiring through the carb is a sign of a spark plug firing while an intake valve is open.    A sign of a crossed wire.

Big difference though between a plug firing during IVO versus a lean "sneeze."  I agree that backfiring through the carb can be caused by a spark during IVO, but I wouldn't go as far as to say it's a sign of it.  If you've ever really experienced a spark igniting the intake charge, chance are you are now deaf and there is a dent in your hood above the carb.  

Curtis said:

jharry3 said:

Backfiring through the carb is a sign of a spark plug firing while an intake valve is open.    A sign of a crossed wire.

Big difference though between a plug firing during IVO versus a lean "sneeze."  I agree that backfiring through the carb can be caused by a spark during IVO, but I wouldn't go as far as to say it's a sign of it.  If you've ever really experienced a spark igniting the intake charge, chance are you are now deaf and there is a dent in your hood above the carb.  

Well...Considering it sounds like someone is shooting .22 from the engine bay I wouldn't rule it out. I'm going to pull all the plugs and double check gap, then double check the wires. If that doesn't fix it we'll pull the pump and check the chain.

Curtis said:

jharry3 said:

Backfiring through the carb is a sign of a spark plug firing while an intake valve is open.    A sign of a crossed wire.

Big difference though between a plug firing during IVO versus a lean "sneeze."  I agree that backfiring through the carb can be caused by a spark during IVO, but I wouldn't go as far as to say it's a sign of it.  If you've ever really experienced a spark igniting the intake charge, chance are you are now deaf and there is a dent in your hood above the carb.  

i have seen cross wiring happen multiple times in a mechanic shop I worked in, 1970's.  It is not like you describe. 

 I did it myself once on my 289 ford with 11:1 compression ratio when I crossed wired two plugs while putting the wires back on when it was almost dark.  It sounded like a light miss when I drove away, I didn't floor it. cause the engine was still cold, so I turned around, re-checked, and found the culprit (me of course), switched the wires around, and that was it.  

I have seen some cross wiring  cause flash out at the carburetor with a popping sound but nothing like  you describe.  Itt depends upon the firing order and where the mismatch occurs in it as to the severity.

NBraun said:

Curtis said:

jharry3 said:

Backfiring through the carb is a sign of a spark plug firing while an intake valve is open.    A sign of a crossed wire.

Big difference though between a plug firing during IVO versus a lean "sneeze."  I agree that backfiring through the carb can be caused by a spark during IVO, but I wouldn't go as far as to say it's a sign of it.  If you've ever really experienced a spark igniting the intake charge, chance are you are now deaf and there is a dent in your hood above the carb.  

 

Well...Considering it sounds like someone is shooting .22 from the engine bay I wouldn't rule it out. I'm going to pull all the plugs and double check gap, then double check the wires. If that doesn't fix it we'll pull the pump and check the chain.

Ah... gotcha.  If it sounds 22-ish, then quite possible.

Plug wires 2 and 3 were switched around. Fixed that and we're back in business. Thanks for the help!