backfire out the tail pipe question
Hi all, I'm trying to start a 1967 390 motor that has a lot of unknowns. The guy I bought it from said it had NO spark at the plugs a couple of years ago when he last tried to start it. Well he was wrong, it does have spark at the plugs. However he had the wires on the wrong plugs. I compared them to my 1959 352 motor and wired them to the distributor the same way. From what I found online that is supposed to be correct. If anyone can confirm that I would greatly appreciate it.
When I tried to start it (using some starting fluid) it wouldn't fire at all. After a few attempts, and a few more shots of starter fluid it backfired out the exhaust. The neighbors loved it! Can anyone tell me what this might mean? Could it be a timing issue? Like I said, it didn't fire at all while cranking the starter. I think the fuel pump is working because I pulled the hose off the carb and it was wet.
I didn't want to run gas through the old lines and rusty gas tank so I used a gas can as a fuel source. I ran a line from the fuel pump into a gas can as my fuel source.
Any ideas or procedures that you guys have would be greatly appreciated.
thx, Dave J
The firing order is the same; 1-5-4-2-6-3-7-8. I would start with the basics. Bring the #1 piston to TDC and check the rotor position. It sounds like a timing issue to me. Verify that the points are set correctly also. You can rotate the distributor one way and then the other a little and see if it starts.
Your distributor cap should have a "1" on the top (and no other numbers). This is #1 spark plug tower.
Just to verify, crank the engine to TDC then pull the distributor cap off. The rotor should be pointing at either #6 or #1. If it is on #6, you can rotate the crank one more turn, and the rotor will be pointed at #1. If it points to any other tower, your wires are off.
If your rotor is pointed between two towers, your distributor may be off by one tooth.
So, to directly answer your question... it sounds like your wires are firing on the exhaust stroke instead of the power stroke. If you follow the above directions and it still won't fire, you can pull the rocker cover off the driver's side and check your lifters (in case your timing chain is off).
Let us know what you found. - Dave
Thx gents, I'll check it out tomorrow in between turkey, football, beer, and naps.
Have a great holiday!
No start ...
Sounds like the dist. could be 180 deg out. When bringing it up to tdc on #1, make sure you are on the compression stroke. often when they have been "worked on" this is a common error. Mike
Hm, maybe I did do it 180 out - I got turned around the first time I tried so I just went by my 352. Here's what I found online;
When I read that the engines were all the same I just went by my T-birds 352 cuz I knew it was correct.
I'll check it out today one more time - I was in a bit of a hurry yesterday.
thx, Dave J
Alrighty then, I did as SimplyConnectd said. First I corrected the plug wires. Got it to top dead center and the rotor was in between number 1 and number 5 - it was closer to number 5. I compared that with my 352 at top dead center. I noticed the 352's distributor was advanced (or retarded) more than the 390 so I adjusted the 390 distributor to match my 352 - that caused the rotor to point to number 1 (like it should). Thinking all was well I tried to start it, now it back fires out the carburator. It doesn't backfire flames, it just pops and spurts gas.
Any ideas on what to try from here?
thx, Dave J
David, I would normally start by verifying the timing chain is set right. For now, I will shoot from the hip and assume it is***.
At TDC your rotor should point directly at #1 (not half way to another plug tower). While pointing to #1, your points should have just cracked opened.
What could be wrong? Simply turning the cap will NOT correct the situation because of a few reasons:
There are 8 towers but your distributor has 11 gear teeth. That means each tooth represents 32-degrees but each tower represents 45-degrees. Notice they do not match.
If your distributor is one tooth off, it is impossible for the rotor to point at #1 tower when the points open. Being off one tooth puts the rotor inbetween spark plug towers (like yours is) causing the spark to 'jump' to the wrong plug wire at the rotor.
Set the crank damper at TDC and pull the distributor out. Turn the rotor so that it does point at #1 when you slip the distributor back down in the hole. If the distributor doesn't go all the way down, leave it there while you slowly turn the crank either way about 1/3 turn and it will drop in place.
Now, put the timing marks on 6-degrees BTDC. The rotor should still be pointed at #1. Rotate the distributor slightly until the points just open, and tighten the distributor hold-down bolt. Your engine should start and run smoothly. If it doesn't, your timing chain has jumped a tooth and it must be replaced. - Dave
To verify cam/crank timing is correct:
Pull the valve cover off of the driver's side and 'bump' the engine. Pay attention to #6 pair of rocker arms (second set back from the front). First the exhaust rocker will open and close. Immediately after, the intake rocker will open and close. Then a long pause before the next cycle.
Why #6? Because in the firing order (1-5-4-3-6-2-7-8), #1 is opposite #6. So, at TDC, both #1 AND #6 are BOTH at top dead center at the exact same time. When #1 is on its power stroke, #6 is on its exhaust stroke.
If you watch #6 rocker arms and stop the crank just at the point where the exhaust is closing and intake is just starting to open... when these two rocker arms are dead level (use a straight edge), your timing marks should be exactly at TDC. If it is not, the timing chain is off at least one tooth and must be corrected.
I understand how the engine and parts work, but I had no idea how to troubleshoot things. Your instructions are perfect - just what I needed. Hopefully I'll have some time tomorrow to go through them and see just what's up.
Thx a ton!
Very good, David. Those instructions pertain to ALL V8 engines, even though the firing order may change. For example, a Chevy uses 1-8-4-3-6-5-7-2 firing order. Notice that #1 and #6 are opposite? All the rules still apply.
Also, if you have a hot cam, the exhaust and intake valves overlap (for scavenging). No matter... when the rocker arms are dead level, the piston should be at TDC.
I am big on cam timing. It costs nothing to do and you would be surprised at how many engines are far off from the factory. I caught 460's off by 15-degrees. Later, I discovered Ford set them that way from the factory for emissions. That's why these engines were DOGS! Correcting the cam and crank timing properly, unleashes big HP.
Stretched timing chains retards the cam by ~2-degrees which puts in a 'gas pedal lag' at the light. It also lowers manifold vacuum. Whenever I change timing sets I use a 4-degree cam key to advance the cam. That brings the torque curve closer to 'street' performance, raises vacuum, and it 'builds-in' compensation for later on, when the new chain stretches.
Good luck in your findings. - Dave
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