Timing problem on a 400
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Tuned
Joined: Sep 2006
Posts: 250
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Timing problem on a 400
I am in need of a little help. I have just completed a restoration of a 150 shortbed 4x4. I used a 78 400 that had been professionally built and had a few hundred miles on it when I found it in a local bone yard. This restoration has taken three years and the motor has been on the stand for that time. I have never driven the truck and have just completed the restoration. I drove it for the first time today. Motor runs normal in neutral, no miss or backfire. even at hirer rpms. Under load it backfires and misses hard. I put the timing light on it- and it is running way advanced- off the dial- maybe 30 BTDC or better. When I try and retard the timing to say 8 it still will run but is absolutely unresponsive and just barely stays running on the road. Could this distributor be 180 out? What else would cause this? I have no way of knowing what kind of cam is in it or if it has been advanced at the timing chain- does anyone have any suggestions?
Elder User
Joined: Feb 2008
Posts: 640
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From: US/Baja border
Yeah it wouldn't start 180 out and I have a hard time believing it would at 30 advanced too. With a couple hundered miles on the engine I would assume all is ok with the engine.
This may sound dumb but double check to be sure you are setting it to #1 and that the firing order is correct, most of the time problems like this are the kind you hope nobody sees.
This may sound dumb but double check to be sure you are setting it to #1 and that the firing order is correct, most of the time problems like this are the kind you hope nobody sees.
Elder User
Joined: May 2008
Posts: 508
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From: Wasilla, AK
I concur with mrjones111! Either the distributer is a tooth off (I would check that first)then I would check the insides of the distributer to make sure you didn't lose an advance spring or something. Then again, it's quit possible it could be that when they built it they got the timing chain cam and crank sprockets misaligned. Might of been why it was in a bone yard?
Thread Starter
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Tuned
Joined: Sep 2006
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All great advice- I will verify the wiring is right first, then the distributor is not a tooth off. if it was a tooth off would it explain the breakup under load? It starts right up an idles in the driveway smooth?
Senior User
Joined: Nov 2007
Posts: 340
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From: Near Madison, WI
Do you have the vacuum advance hooked up to a ported source, or is it getting direct manifold vacuum?
-Jared
-Jared
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Tuned
Joined: Sep 2006
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vacuum advance is running off a tree on the back of the manifold-should it go somewhere else? I checked the wiring-good, did back the distributor up a tooth and retimed. Still- good in neutral in the driveway, responsive- at idle and reving, but under load on the road-still backfiring thru exhaust.
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Elder User
Joined: Feb 2008
Posts: 640
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From: US/Baja border
Also if the dist. is off a tooth or two it will not make a difference in the timing, you will just need to turn the dist. to a odd postion to time it right.
The plug will only fire when the rotor aligns with the connector in the cap and it doesn't matter how the dist. is pointing. I know lots of people who simply drop a dist in and then put the wires on to make it work, #1 can be anyplace as long as the #1 wire is on right along with the proper firing order. All that matters when setting the timing is for the rotor to align with the cap at the degree you set it for.
If this doesn't make sense I will try to explain it further
Senior User
Joined: Nov 2007
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From: Near Madison, WI
-Jared
Senior User
Joined: Jul 2005
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From: Mountville PA
mine did the same thing one time, I had 2 spark plug wires switched 6 and 7 the bad thing was somebody else saw it before me, goes to show you that everybody does something dumb every now and then and just to add to what oldmetal was saying the #1 spark plug is the front pass side (I,ve ran across some people who didnt know that about ford) and I put a 400 in a truck that came out of a car that had the timing pointer and mark on the balancer on the driver side Ive only seen the pointer and mark on balancer on the pass side in the trucks so make sure your not mixing and matching the two
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Tuned
Joined: Sep 2006
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OK- I pulled the dist out back up a tooth and that gave me the timing marks in the right place. checked the plug wiring, pulled the plugs-all are burning normal. Replaced the advance vacuum line to carb- plugged the vacuum tree. Again, it idles good-starts right up, and I can rev it up without a miss or backfire in neutral. Put it on the street-especially in third gear and it has a miss or backfire through the exhaust? I even swaped the carb out- still had the same problem?? I know it something simple, but just cant nail it down.
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Tuned
Joined: Sep 2006
Posts: 250
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Just another thought- thinking about what Jared wrote. I am running a Holley 600 carb and it has two vacuum ports on the passenger side. One half way up the carb behind the front bowl and the other under the bowl on the front of the carb. Does it make a difference which I use to get ported vacuum?