Engine 351c Backfiring/ And Not Running At Idle

Discussion in 'Classic Mustang Specific Tech' started by chad ruehlen, May 22, 2013.

  1. Howdy I'm brand new to stangnet so first just wanted to say hi, and thanks for all the help i have received in the past from reading/ learning from all of your post. I am a junior mechanic so I'm really still learning everything and hopefully one day be able to help others.

    As to my problem I recently rebuilt my running 72mustang swapping my 2v heads with some pro rebuilt 4v heads/ headers/ edelbrock airgap manifold/ and a new msd ready to run distributor with a blaster 2 coil. The car will not idle/ will run at 4000rpm and anything less will sputter/ then die/ usually shooting gas in my face.

    I have tried putting the distributor in everyway i can think of and no luck. Last night i pulled the #1 plug cranked it over until it blew my finger, than stuck a plastic rod in the hole to quadruple check that i was at tdc, than lined up my #1 wire on the msd and still not running. I also could not find any vacuum leaks spraying starter fluid around the motor while running

    I checked my compression and all cylinders read 127-130.

    If anyone has any advice for me please let me know. I've been stumped for a month now and i hate losing battles with my beloved car that i have owned for 13 years

    eldlebrock 600 performer carb tried my holley 700 too
    harland sharp rockers
    hooker headers
    lunati cam Adv. Duration 290/300, Lift .536/.562,
  2. sounds like the timing is off... sounds like the intake valve is staying open too long... that is just what i think...
  3. thanks for the reply robert, I too feel the same way but cannot figure it out. I do have the dizzy pointing at the #1 cylinder @ tdc. Any advice on trying something else?
  4. Hi,
    You state you have the #1 @ TDC. verify that both valves are completely closed. If so, re-check your plug wiring, there may be two or more crossed. Where is your initial timing set? How many turns out, are the mix needles? Does it not idle at all?
    If it's backfiring through the carb, It's typically a timing issue, as was mentioned.
    chad ruehlen likes this.
  5. I will double check the valves in the morning? My needles are turned 1.5 turns each. I pray that i dont have two wires crossed after a month but I'll double check that again just be safe:) . It doesn't idle at all, needs a lot of gas to run smooth, which brings me to your next question, how do i do an initial timing without it at idle? thanks a lot for the time and knowledge.
  6. Hi,
    Once you verify the wiring order is correct, and the dist is correctly installed, rotate the engine by hand and note at what degree on the damper, the #1 rotor position sweeps #1 on the cap. This is not perfect, but, I'm thinking you should be somewhere in the 12-14 deg BTDC , at least, based on your cam events. BTW, your needles appear to be, at least, at a starting point. Tuning the carb and timing can only be perfected, once the base operations are correct. I have to mention, your compression numbers seem low. Were they taken using a screw in gauge on a warm engine, plugs removed, and the carb plate fully opened? I guess you don't know what the idle vac is? If your vac is very low, it's possible you're not getting a strong signal for the carb's idle ckt to kick-in.
    What static CR were you shooting for ?Good Luck
  7. What condition is the carb in? New? If used, did it sit for quite a while during the rebuild? Could be plugged idle circuits.
  8. Hack-The carb sat for about a month total, I did try my holley 700cfm with the exact same result.
    poppy- the compression does seem low to me too, motor was warm and carb open with a screw in guage with all spark plugs out, the pistons and rings were put in about 10 years ago going for 10:1. And not getting what you were saying about the screws, looks like a word is missing. Anyway just got home so i'm going to pull vlv covers and check the vlvs at tdc. then put it back togather and try setting timing at 12-14btdc. I'll let you all know in a bit
  9. Are the valves adjustable?Too tight will cause it run rough or pop.
  10. HI,
    Sorry may not have been clear. I re-read when I mentioned "screws", it could have been the carb mix screws. But, I think you have them, at least, in a good starting position.
    "Iskwezm" made a good point about the possibility of tight valves. There is a prescribed sequence to adjusting them correctly. Which begs the question....Did you check for correct "push rod geometry"? Not that the engine shouldn't start if this issue, but, if not correct a whole bunch of other stuff will hit the fan.
  11. I actually did check pushrod geometry this time, it was good times getting the right length push rods before i even tried firing her up. I did just check the push rods and valves and at tdc and valves were closed, and push rods could still spin with what felt like a little tension on them. You'll have to forgive my ignorance fellas but i didn't know you needed to adjust the valves on a 351c. All i did was rotate the motor until both valves opened and closed, cranked a half turn more and tightened up the roller rockers 1/2 turn after zero lash. If thats incorrect i give you permission to kick me.

    After checking the wires again, and that the #1 vlvs were closed, I set the initial timing at what should be 12btdc and fired it up. Well let me just say I lost some more hair rather quickly when a good sized fireball just hit me. lol. back to my endless research on what causes fireballs and how to remove the smell of burnt hair from a garage.
  12. Also as far as distributor install goes let me run how i installed it by you all just in case i messed it up. I first tried install it by simply marking the old one at the base and marking where the rotor was pointing and put the msd in the same spot with the rotor pointing the same way. FIREBALL. next i pulled it along with #1 plug rotated it around until it blew my finger off then stuck a plastic rod into the hole and kept rotating until the piston was all the way up. It verified on my balancer that I was at tdc. dropped the dizzy in, matched up my #1 wire with the rotor at tdc and.......... FIREBALL
  13. :shrug: Just grabbing at straws here... One of my friends once got a bad valve grind (from a professional) and none of his valves sealed. Maybe try throwing some air pressure in a cylinder with the valves closed, and listen for air.
  14. I reads all the posts, and my bet is a timing, firing order, issue. Check one more time for the install of the wires and make sure they are in the correct order in relation to the distributor rotation.
  15. Can you rotate the engine around until the timing pointer is pointing at 0 degree's? Then look under the dist cap and see where the rotor is pointing at? You should either be pointing at number one or be 180 degree off. If you are off a tooth this will help determine where you are at. Make sure the vacuum advance is disconnected when setting your initial timing. I agree it should be at least 10 set based on your cam specs. What rear gears and torque converter do you have to go with the cam?
  16. I have stock 8.78:1 gears, torque converter is a tci breakaway converter in a c6. Not very familiar with the tooth off theory, perhaps someone can enlighten me on that if anyone has the time. As for rotating the engine, the rotor will point at the #1 @ tdc and then the #6 180deg opposite the next rotation
  17. 3.73 gears in an 8 inch carrier?
    Typically on early GM and Chrysler applications, the bottom of the distributor is like a flat screw driver tip. The Fords of the same era have a (distributor) gear to (camshaft) gear set up. So it is feasible to be off one or two teeth compared to where the rotor points, as opposed to being EITHER right on, OR 180 out. A lot of people will either just rewire the cap, or max out the vacuum advance, rather than get it right....
  18. You say that you rebuilt the engine. was it a total rebuild? What about the cam timming being off? Or a stretch timming chain. Just a couple of thing to think about.
  19. nah its a 3.78 in a 9" (code H). I fat fingered it lol. Thanks for the explanation on tooth off, in my mind it just seems like turning your distributor a few more degrees would do the same thing. I'll try to pull it and set it a tooth over when i get a chance and maybe 180 degrees just for fun. I'm working on a oilrig 12hrs a day and really dont have time to work this week on her. I'll let ya all know if that fixes the problem. thanks again for all the help I appreciate it and look forward to talking to you all in the future.
  20. And no it was just a top end rebuild this time. Cam timing was good after last rebuild, the car just ran awesome when i drove it to my new garage a month ago.