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Old 11-07-2017, 08:16 AM   #1
61Chevy454
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Motor hard to start, runs for a couple seconds then dies, backfires through intake

So I'm rewiring my truck, and I'm trying to make it run. It ran before I pulled all the wiring and it will somewhat run now, except after a few seconds of really rough running, it dies. It also backfires through the carburetor. I had to wire in a Mallory HyFire VI box because I have a unilite distributor, and everything worked before I took the wire out. I checked the wiring diagram and everything is where it should be. What should I be looking for? I desperately need to make my car run. It's a 454.

Thanks guys!
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Old 11-07-2017, 10:16 AM   #2
Rickysnickers
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Re: Motor hard to start, runs for a couple seconds then dies, backfires through intak

Did you change the distributor to the Unilite, or was it there already? It sounds like you have a timing issue. Double check that first.
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Old 11-07-2017, 12:35 PM   #3
68gmsee
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Re: Motor hard to start, runs for a couple seconds then dies, backfires through intak

Since you say it was running before the rewiring, concentrate on that. As mentioned above, timing should be checked. An engine needs proper amount of fuel, good compression, ignition and correct timing to run.

The basics:
-check to make sure you're getting fuel and not flooding.
-place #1 cylinder at TDC on compression stroke.
-insure timing mark lines up with TDC (or 0).
-double check firing order clockwise 1,8,4,3,6,5,7,2
-insure you get spark to spark plugs.
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Old 11-07-2017, 02:10 PM   #4
61Chevy454
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Re: Motor hard to start, runs for a couple seconds then dies, backfires through intak

Quote:
Originally Posted by Rickysnickers View Post
Did you change the distributor to the Unilite, or was it there already? It sounds like you have a timing issue. Double check that first.
Quote:
Originally Posted by 68gmsee View Post
Since you say it was running before the rewiring, concentrate on that. As mentioned above, timing should be checked. An engine needs proper amount of fuel, good compression, ignition and correct timing to run.

The basics:
-check to make sure you're getting fuel and not flooding.
-place #1 cylinder at TDC on compression stroke.
-insure timing mark lines up with TDC (or 0).
-double check firing order clockwise 1,8,4,3,6,5,7,2
-insure you get spark to spark plugs.
Based on the list of basics you're giving me:
1. I'm definitely getting at least some fuel from the mechanical pump, and it worked fine before I unwired everything, and I smell fuel in the bowl.
2. The timing was not changed between when I tore out the wiring and put it back in, so I'm not sure it's timing.
3. I'll have to check that.
4. I'm going to double check the firing order when I get home but would having only two wires switched make it not run at all?
5. I'm definitely getting spark to the plugs, as it runs for a little bit.

Is it possible I have the magnetic pickup in the MSD distributor wired backwards to the HyFire box and it's causing it to fire the coil when it shouldn't and the spark is jumping to the wrong plug?

Thanks for the help, yall
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Old 11-07-2017, 07:32 PM   #5
68gmsee
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Re: Motor hard to start, runs for a couple seconds then dies, backfires through intak

I'm not familiar with the MSD distributor but if engine checks out mechanically then something went haywire with the ignition or electrical parts. Could be defective distributor, a loose wire, short, crossed wires or bad distributor cap/rotor.
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Last edited by 68gmsee; 11-07-2017 at 07:43 PM.
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Old 11-08-2017, 12:07 AM   #6
Captainfab
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Re: Motor hard to start, runs for a couple seconds then dies, backfires through intak

So which distributor do you have? A Unilite or a MSD? Was wiring in the Mallory box a part of the wiring you did?

Quote:
Originally Posted by 61Chevy454 View Post
I had to wire in a Mallory HyFire VI box because I have a unilite distributor,
Quote:
Originally Posted by 61Chevy454 View Post
.Is it possible I have the magnetic pickup in the MSD distributor wired backwards to the HyFire box and it's causing it to fire the coil when it shouldn't and the spark is jumping to the wrong plug?
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Old 11-08-2017, 09:36 AM   #7
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Re: Motor hard to start, runs for a couple seconds then dies, backfires through intak

As others were saying, if it worked before your repairs then it is most likely something you did. Rarely do parts go bad just sitting there. Could be you installed a bad part but again, focus on what you just did.
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