HELP! 418W problem during initial start-up

[REPLIMOD #17]

Fired the motor for the first time, and it sounds even meaner than I had expected....however, I'm getting a backfire whenever I let the car idle below 1,100 RPM I've varied my timing from 6 degrees all the way to 17 with no luck. It's currently set at 14 which is were it seems to be the happiest. My idle mixture and float level are dead on. I'm reading between 15-16 vaccum, and the needle is fairly steady with a tiny amount of bounce.
It will backfire when it is allowed to idle below 1,100 RPM it is sparadic and in no way consistant. It will also backfire if I quickly stab the trottle. This is also sparadic.

I'm going to take the following steps in an attempt to cure my problem, but if you have had any similiar experiences or wisdom in this area please chime in...

1. Check for vaccum leaks by spraying ether aroung carb base and intake.
2. Swap carbs
3. Set valve lash
4. Ask for more help on stangnet....
5. Possibly give up and call for help...(I hate it when that happens)

The engine was built by Creb Racing Engineering out of RI. I'm running AFR 205 heads, 750 Bigs stage 5 carburetor, Engle hyd. roller cam, and 1.6 roller rockers...

 

[HookandLadder]

Make sure you have the correct firing order for the cam you are using.

 

[REPLIMOD #17]

Firing order

Make sure you have the correct firing order for the cam you are using.

I'm currently running the old 351W firing order. Would the engine even start if my cam was looking for say a 302 type firing order? If it did start wouldn't the engine consistantly missfire instead of being so sporadic?

I can call my engine builder just to be sure...

 

[dennis112]

Do you have an exhaust leak?

I would first concentrate on the ignition.

As mentioned, ensure you have the correct firing order. How is your balancer? Could the outer ring have slipped and be giving you the wrong timing marks?

An engine will can backfire at idle if your carb is too rich and fuel is allowed to accumulate in the manifold.

 

[WORTH]

is it backfiring threw the intake or the exhaust?

 

[REPLIMOD #17]

Do you have an exhaust leak?

I would first concentrate on the ignition.

As mentioned, ensure you have the correct firing order. How is your balancer? Could the outer ring have slipped and be giving you the wrong timing marks?

An engine will can backfire at idle if your carb is too rich and fuel is allowed to accumulate in the manifold.

I re-torqued all of my header bolts after my initial start, and I don't see any black soot around my headers, so I think I can rule an exaust leak out.

I pulled my plugs after my initial start and they indicated a rich mixture, so I cleaned them, and then set my idle mixture using a vaccum gauge to insure that I got it right. My carb does have 4-corner idle adjustment, and as of right now each screw is about 3/4 turn out.

With the #1 piston at the top of it's stroke my balancer reads 0 degrees.

I did notice late last night that the problem doesn't exist for the first 30 seconds after start-up. Then the car will idle and rev fine, but after that you can forget about it.
The car will backfire out of the exaust at a low idle, and if you crack the throttle she'll send a nice flame out of the carb.

 

[REPLIMOD #17]

is it backfiring threw the intake or the exhaust?

At Idle it backfires throught the exhaust.
When I give it gas it backfires throught the intake.

 

[WORTH]

At Idle it backfires throught the exhaust.
When I give it gas it backfires throught the intake.

backfiring threw the intake is generally too lean, which is backed up by it being fine when it's cold if the choke is partially on at the time. Try giving it a bit of choke and see if the problem goes away, if it does you'll have to start looking for a vacuum leak, or possibly adjusting the accelerator pump.

 

[REPLIMOD #17]

backfiring threw the intake is generally too lean, which is backed up by it being fine when it's cold if the choke is partially on at the time. Try giving it a bit of choke and see if the problem goes away, if it does you'll have to start looking for a vacuum leak, or possibly adjusting the accelerator pump.

I'm running a dominator style fuel bowl, so I don't have a choke.
I'm going to search for a vaccum lead on my lunch break. I know that all of my vaccum ports are plugged and My intake should be sealed well consider the fact that I used an ample amount of RTV when I installed it. I'll replace the crappy paper thin gasket which is installed between the carb and intake and see if that helps.

What's the chances of a bad plug, wire, or coil. causing this?
They are all new and I'm running an MSD 6AL with a blaster II

 

[Jc69Stang]

You could also be a tooth off on the dist. Double check that as well. It happened to me once....

 

[REPLIMOD #17]

You could also be a tooth off on the dist. Double check that as well. It happened to me once....

Do you mean that the distributor gear could have engaged the cam gear in the wrong position? Correct me if I'm wrong but if that was the case my Initial TDC timing would have been of, but it would have been corrected when I set the timing with my light. I might have to turn the distributor a little further to reach my timing mark, but 14 degrees would be 14 degrees regardless of whether or not the gears were off by a tooth or so????

 

[milner351]

I just ran across a wierd problem that kept me thinking it was a carburetor, but it turned out to be the distributor advance mechanism.

Get the engine warm and put your timing light on it, slowly accelerate the engine while looking at the balancer, the advance should be smooth and the timing mark should be steady. If it jumps around there is a problem with the advance mechanism inside the distributor, or, with your electronic ignition control unit.

If your plugs looked black when you pulled them out, perhaps the carb is jetted too high, that would explain the exhaust backfires, but through the intake, that would say lean mixture or ignition issue.

 

[REPLIMOD #17]

I checked for vaccum leaks, and there are none.

Jesse at bigs reccomended that I change the stop bushing in my distibutor to lower my mechanical advace. He then suggested that I bump my initial timing up to 19. He also walked my through a fine tunig of the carbs 4-corner idle circuits...But the problem still persists.

I'm having to keep it above 1200RPM to avoid backfires. This makes it nearly impossible to get an accurate timing or carb adjustment.
I'm concerned about causing engine damage due to the backfires because they seem to be some of the worst I've heard...I have to wear earplugs to keep my ears from ringing.

I'm going to do a valve adjustment next...

 

[Jc69Stang]

Exactly, my car would idle ok and then as soon as I drove down the street it would spit and puke and backfire through the carb. I thought the dist was set perfect so for the sake of it I re-stabbed the dist, problems all went away. This was after a cam swap so I checked all the wiring etc as well.
You have to be carefull because the way the two gears mesh, it can easily wind up a tooth off. Worth a shot anyway, just make sure you on TDC to do it right.

Do you mean that the distributor gear could have engaged the cam gear in the wrong position? Correct me if I'm wrong but if that was the case my Initial TDC timing would have been of, but it would have been corrected when I set the timing with my light. I might have to turn the distributor a little further to reach my timing mark, but 14 degrees would be 14 degrees regardless of whether or not the gears were off by a tooth or so????

 

[iskwezm]

mine did the same when i first got it fired, it was the wrong firing order, which the builder assumed i would know .ran ok at idle, just rough and would pop every few revolutions.

 

[REPLIMOD #17]

mine did the same when i first got it fired, it was the wrong firing order, which the builder assumed i would know .ran ok at idle, just rough and would pop every few revolutions.

I thought that there was only one firing order for the 351W...If there is another please let me know what it is and I'll give it a try...

I knew that the standard 302 and the 302 HO use a different firing order, but I thought all 351W were the same...I don't like to be wrong, but In this case I'm begging somebody please tell me I'm wrong....

 

[brianj5600]

The only difference in 302 and 351 cams is the firing order. My 351 has early 289/302 firing order. If you have the cam card, it should be on there.

 

[Capt Dan]

http://www.mustangandfords.com/techarticles/28738/index3.html

Many neophyte Ford freaks don’t realize that the firing order of the early 351W engine is different from the 221-, 260-, 289-, 302- and late 351W engines. The early 351W’s firing order is 1-3-7-2-6-5-4-8, while the smaller Windsor engine’s firing order is 1-5-4-2-6-3-7-8. What makes this interesting is that 289/302 cams are completely interchangeable with 351W cams, providing you match the firing order to the camshaft. If a 289/302 cam is used in a 351W engine, the firing order must be changed to the 302 sequence by moving the wires on the distributor cap. The same procedure is used if a 351W cam is used in a 289/302W engine where the firing order in the distributor cap must match the camshaft.

 

[WORTH]

Do you mean that the distributor gear could have engaged the cam gear in the wrong position? Correct me if I'm wrong but if that was the case my Initial TDC timing would have been of, but it would have been corrected when I set the timing with my light. I might have to turn the distributor a little further to reach my timing mark, but 14 degrees would be 14 degrees regardless of whether or not the gears were off by a tooth or so????

You are correct, it doesn't matter where your distributor points at TDC as long as you put the wires in the cap to align with the rotor. You can be 180 out and just move the wires on the cap to match.

 

[HookandLadder]

So what did the cam card say the firing order was? Curious about the outcome of this caper. Been there done that..............like to see him lick this problem.