Help..Rebuilt 289 engine will not start, backfires thru carb, Cam setting wrong? - Vintage Mustang Forums
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Old 10-22-2003, 12:40 PM   #1 (permalink)
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I just rebuilt, rings - bearings - valve job ect, a 289 motor, installed it into the car and went to start it,
has backfires thru the carb, checked timing with a timing light while engine cranks and timing is good
so i assume that must mean the dist is in the right setting, the points appear correct so its either
the 4100 type 4bl carb that has been sitting for years is screwed up or I somehow got the
cam set up wrong I tried to line a dot on the upper timing gear with the woodruf key pointing up
on the cam shaft, but the "how to rebuild your engine book" showed the eccentric cam that
runs the fuel pump having the detent in it pointing down towards the woodruff key.
mine did not line up that way...Need some help on what to do..thanks Bob
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Old 10-22-2003, 12:53 PM   #2 (permalink)
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Checked timing while cranking? That's a new one to me, I've never heard of such a thing.

Why don't you just hand rotate the dizzy while someone cranks until you can get the car to run and then try to set the timing?
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Old 10-22-2003, 01:00 PM   #3 (permalink)
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Did you replace the cam and if so what is the firing order of them? It could be a 302 or a 351W firing order.
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Old 10-22-2003, 01:03 PM   #4 (permalink)
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I'm with dodgestang on this one. Sounds like timing to me.
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Old 10-22-2003, 01:09 PM   #5 (permalink)
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Sounds like it's 180* out of time.

Swap each of the sparkplug wires at the distributor cap with the wire that's directly across from it.

Anytime you're dealing with backfires, keep a fire extinguisher handy.
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Old 10-22-2003, 01:10 PM   #6 (permalink)
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I'll take this one....been there, done that.

Either your distributor is 180 degrees out or your cam is a 302 late model cam. Sometime around 1983 or so, the firing order on the 302's was changed. My engine was recently rebuilt and the shop ordered the later model cam. I built the engine and once I tried to start it up, it backfired out the carb. Once I went back and saw the part number of the cam they ordered, I relized the firing order was different. I redid the plug wires to the new firing order and it started right up...

Good luck.
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Old 10-22-2003, 01:23 PM   #7 (permalink)
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You didn't state that you changed the distributor, so it will be assumed that it is the old dizzy you had on the car when you tore it down. Most likely you are 180 degrees out, so take your dizzy out and turn it around. After you get the car started, you can adjust the timing. You can't do that unless the car is running. Then adjust your points, then go back and re-adjust your timingl.
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Old 10-22-2003, 01:26 PM   #8 (permalink)
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Just went through the same thing as have many of us. Are the plug wires on the distributor counter clock wise?

Just wondering! ::
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Old 10-22-2003, 01:34 PM   #9 (permalink)
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I'm with everyone else. Check your dizzy. Make sure you aren't 180 out. Also look at your cam specs.

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Old 10-22-2003, 02:05 PM   #10 (permalink)
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i went through something like that... turn the crank over and watch the rockers to be positive on which cam you have. If you have the right fireing order its, just one less variable to worry about
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Old 10-22-2003, 02:15 PM   #11 (permalink)
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Sorry, I'm not sure I understand how you set your cam? Did you align the the timing marks? Are you just saying the key was off compared to the book? Oh, did you replace any of the cam, timing chain or gears? Its possible the timing is off but you can verify it is the ballpark by removing the valve cover and watching the valves on #1 as you turn the engine (by hand) to TDC . No offense but you might also want to check that the valves are not set too tight and are closing completely.
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Old 10-22-2003, 02:45 PM   #12 (permalink)
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If you have 1 or more intake valves not closing all the way, it will back fire through the carb.

A lean condition can also cause backfire.
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Old 10-22-2003, 03:19 PM   #13 (permalink)
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If you lined up the marks on the timing gears correctly, the position of the fuel pump eccentric makes no difference.
My vote is for something simple, like wrong firing order, or crossed spark plug wires. Easy to check and fix, best to start there.
If you timed it while cranking, I doubt the distributor timing is too far out (for you unbelievers, that's exactly why you would do this. Not to time the engine, just to make sure it's in the ballpark and NOT 180 out-a useful trick).
Of course the trouble may lie in the other stuff mentioned and more besides. Start with the simplest things and go from there. Carb trouble is possible, but considereing what you've been doing to the engine, it would about last on my list. Much more likely you didn't get something back together just right. Happens to everybody.
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Old 10-22-2003, 03:31 PM   #14 (permalink)
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At 180* out, the timing marks will still line up - remember, the crank turns twice as fast as the cam in a 4-cycle engine.

BTW, I've always used a timing light while crank to get things "close enough".
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Old 10-22-2003, 03:39 PM   #15 (permalink)
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I am with Gene_J on This one, DO the easy thing first MAKE SURE THE WIRES ARE ON COUNTER CLOCKWISE.
I did the same thing on the 429.
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