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hi all I'm new on this forum ,and need some help I have a 71 galaxie Hearse with a 400 running a 600 holley . The holleys new , the dizzy is electronic and new , plugs , leads and fuel filter all new . Car was running well and then developed a shudder and Missfiring .. it now backfire's badly upon acceleration and losing massive power when you accelerate . If you just crawl along it will drive but sounds and shudders like hell . ??!! could it be a fuel blockage ? i feel like i've looked at all the simple things (electrics and fuel filter ..) confused and grumpy with it
 

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Backfiring out of the carb?
Timing is probably out, and needs advancing.
It's a possibility that the roll pin through the gear has stripped, and thrown the timing out..
 

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I have a couple of 400's and have built several more. What you are describing is classic timing chain wear out. Advancing the distributor will help slightly but only make up for the chain slack somewhat, and not at all when idling.

Pull the dist. and look at the drive gear pin like Danv said, and then pull your timing cover. Dimes to doughnuts your chain is stretched sloppy.
 

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Pull your cap and watch the rotor while turning your crankshaft back and forth with a wrench. bet you'll notice a lot of slop in your chain.

Just for fun...have you ran the plug wires? and making sure you're using the correct firing order? That's a real easy mistake/over sight.
 

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my 390 was backfiring out of the carb. It even caught on fire. I changed the plugs and put in a Speed Demon 650. Have not had it backfire since.
 

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Turning the crank while watching the rotor will tell you if you have perceptible timing chain play, but whether it jumped a tooth or not can be easily verified with a timing light, without removing the timing cover. Assuming your timing was relatively close as it ran well before, check the timing and if it's way-off from spec's (usually retarded), and correcting timing only helps a little - that's your problem. If not, you can eliminate that one from the list and keep looking. I would be pulling the vacuum gauge out about now, and if it shows about normal vacuum with a regular tick it's a stuck valve or lobe. If it shows low vacuum and the needle shakes all over like a $5 crack-ho, then it's the timing chain.

David
 

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I had a 71 LTD 400-2V that would bend pushrods every time I floored it...theyd bend enough to not let exhaust open and it would act pretty bad...

I had actually tried to blow it up several times, Dad wouldnt let me put my 429 in it, long as it ran, revving it would just bend pushrods and limp along... Dad would get home, we'd pop the valve covers, pull the bent pushrods, *hammer* them back semi straight, good to go...one bent so bad it wore a hole thru the side of the pushrod rubbing against the head- slipped a piece of bicycle frame tubing over it to support it...
paid 75 bucks for that car, drove it a year and a half, couldnt kill it- went to scrap it out around 1981, called some guys from the newspaper('junk bodies hauled free') they came to tow it, still had plates on it, told them just to drive it...ran great, just drank oil and looked pretty rough...

looking back, was probably the best car I ever had, in a year and a half it cost me a grand total of $145 (+plates/ins/gas/oil of course). for the first year I had it, I cleaned it up real well and it even looked like a real nice car. working in a restaurant, that reliable, but tired old ford really saved me a lot of the few bucks I earned...
 

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Although not mentioned directly above, you may have a bad (or going bad) vacuum advance unit.

As the engine get going, the vacuum port on the carbonator works better and better. It soon then will distort the rubber in the advance unit to it's full potential. As it bends, then vacuum leaks show up and it will not provide any advance beyond some pre-detemined amount. Your engine then is dying for spark advance, and upping it at the distributor is only one way to get there.


Wm.
 

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Discussion Starter #12
thanks to all for advice , have managed to work out that the problem is mechanical for sure . Have removed rocker covers and all is good .. so it seems to be pointing toward the timing chain or around that .. so thats the next exploratory surgery .. wish me luck ! :):confused:
 

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Discussion Starter #13
yes it is backfiring out the carb ... and it seems that ony 5 cylinders are playing ball the rest miss every catch
 
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