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Discussion Starter #1
Hello everyone,

I am very stumped and can use your help...
Recently had my 1968 mustang engine professionally rebuilt. It is a 302 4V - The original carburetor was re-installed after utilizing a carb kit and the car ran well for a short period (approximately 3 weeks)and then began to leak causing the engine to flood. Re-did the carburetor again and it ran fine for about 2 weeks and one warm and humid evening the car began to `bog` and seem to be choking.... barely made it home. When trying to start the engine it turns over nicely, spark plugs fire, gasoline goes into the carb and `bam` backfires out of the carburetor.

It has now been sitting in a warm underground parking spot. The orginal carburetor was removed and replaced with a brand new Edelbrock 1403 500 CFM - however the engine still won`t start and run. The engine turns over, spark plugs fire, gasoline goes into the carb and `bam` backfires out of the carburetor. I am confused as to why it will not start and run properly.

Any idea what is wrong and how to correct?
Thank you.
 

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Check firing order, timing first, possible spun exhaust lobe on the camshaft. Hope this helps.
 

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Sounds like an ignition problem, as above, check the firing order and make sure the timing is set correctly.
 

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Discussion Starter #4
Thanks guys...
Further to what I have described, thus far have checked the firing order (okay), and timing appears okay, as for possible spun exhaust lobe on the camshaft... have no idea at this point.

Just seems so strange that it was running perfectly prior to shutting down. I have also been "babying" the engine since it is a new rebuild from a reputable shop.

Perhaps it is not at TDC, though we did try to ensure it was... argh.
:-(
 

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Pull the cap and turn over the engine to see if it rotates. Turn crankshaft to shat 0 aligns with pointer, is dist at 1 or 6?

Next use timing light and see where timing is at when cranking the engine and/or running also if it gets to that.

I gasoline of good/known quality? My brother went to a different station from normal and whatever gas they had the car wouldn't start or run when he came out of evening class. I turned the distributor one way then the other when he cranked it over. Finally started hitting on one cylinder, then another until finally without starter helping puttered along with a LOT of throttle until all 8 were firing. JUNK gas!!!
 

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I hope your running zinc in your rebuild. pull the valve covers and turn it over with a wrench from the front. if all the rockers go up and down, you will be just fine on the cam. be sure to run a zinc additive I cant stress that enough.

on the part of the carb, look for a vacuum leak. do you run a spacer or anything of that nature? generally a backfire out the carb is caused by a lean condition. if your timing is set right, I believe this to be the issue. -and I believe its set right because you have been driving it.

a vac leak is basically a very large leaning out of the motor as the air is pulled from some other place then through the carb, thus very little fuel which ignites very easily.

check your base gaskets. I have a good feeling that you have a big vac leak right below the carb. look into that and other areas where vac leaks can occur. youl be surprised, its most likely a very easy fix.

best of luck
 

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Discussion Starter #7
Ok, thanks for the suggestions - will try again tonight or tomorrow and let you know how things go and if "Sally" will be nice and go for a trot. Appreciate your suggestions... if there are more please bring them on.
Cheers! :)
 

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Cough-up through & out of the carb means the cam/crank timing is off...could have jumped a tooth, etc.
Fire with no cough up typically means ignition timing is off....check to ensure the dist, etc is set, rotating correctly, etc.
 

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Cough-up through & out of the carb means the cam/crank timing is off...could have jumped a tooth, etc.
Fire with no cough up typically means ignition timing is off....check to ensure the dist, etc is set, rotating correctly, etc.
I usually would agree with you here, but he did mention that she was running well beforehand. its pretty hard to jump a tooth especially on this new build it is almost inconceivable. all things are possible, its worth pulling a valve cover to get a look see.
 

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You say that the carb has been off twice since the engine rebuild. How tight were the hold down nuts when removing the carb each time? Old studs and nuts could have worked loose over a few weeks and caused the vacuum leak others are talking about.

Is the fuel pump new? Filter new? How old is the coil? None of the fuel lines touching the engine, exhaust, or intake? Was a rag or anything stuffed in the exhaust while the engine was out and could still be in there. It may have moved and is blocking the exhaust. How long between the trouble and the previous gas purchase?
 

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Discussion Starter #11
... follow up

Just to let you all know, still have not resolved the issue. Only thing that is left to change would be the coil - though I seriously doubt that is the problem. I have just responded to a few `mobile mechancis`adds - so I am hoping that one of them knows what the hell the issue is... very frustrating, all things considered - I do appreciate your help though. Once it is figured out (and hopefully it isn`t anything `too` stupid) I will let you know what the fix was.... so much for my Summer ride - once it is fixed off to storage for the Winter.
 

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Discussion Starter #13
Hmm... going back to the drawing board. Did come across this interesting article re: distributor - perhaps that is the issue. The car actually managed to start (seems with the left over gas in the chambers??) and ran for about 20 seconds before konking out. So confused, trying to get a `old time` mechanic accustomed to older classic cars - seems the young lads/ladies depend too much on computers and sensors. LOL

Here is the distributor article... I will check into this (though we have played with it already).

How to Install a New Distributor - Car Craft Magazine
 

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a faulty coil causes related issues too. ironically since this post, I had a coil begin to fail and it had similar symptoms.
 

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Were the plug wires removed or replaced?
I once changed a camshaft on a 289 and the engine backfired and would not start.
The firing order was different from original. 15426378 to 15637248. The middle cylinders fired differently.
It took me days to figure it out.
I called the camshaft maker, "Howard's Cams" and they said that was correct. All their 289/302 cams fired in that order.
 

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You didn't say what ignition you have, if you have points and condensor, one or both is probably bad, or the point gap is not adjusted properly, check the points for pitting, if you have blue streak points, replace them, if you are replacing the points get a set with a phenolic (brown in color) not a nylon (white in color) rubbing block, and carry a spare condersor and a screwdriver with you in the glove box, a condensor can fail at any time, even a new one. Always clean the dist cam lobs and regrease lightly with dist point grease, then put a small dab on the side of the rubbing block opposite the point contact. If your distributor cap is dirty, clean it, if it gets dirty and especially on damp days, it can jump the spark to a different cylinder or not start at all. If you had a bad lobe on the cam, it should backfire every time it hits that cylinder. I don't think your coil is your problem. My 2 cts, from an old mechanic. Good Luck.
 

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Pull the distributor and make sure the gear has all it's teeth. If a tooth is missing, you have even bigger problems because the missing material is in the pan. On the plus side, the distributor can be rebuilt (if you want to go that way).

I agree with others who've already said it - it's most likely a timing issue. Since you've already check the external stuff, pulling the distributor is the next easiest thing to do, followed by removing the timing cover and checking the gears/chain.
 

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Discussion Starter #20
Well thank you everyone for all the wonderful suggestions. I had the car towed to a respectful "old school" garage here in Ottawa - the owner figured out the problem in less than 10 minutes. Turned out that new distributer installed during the rebuild was faulty - it was replaced a "whamo" we are happily back on the road again!!! YAY!!! So happy... so if anyone else encounters this problem this is a good place to look as well.

Small plug to the shop here in Ottawa that did the repair, as well I now have a garage to take my baby to that I feel super comfortable with.
Cheers!

Actek Automotive

Phone: (613) 729-3124Fax: (613) 729-31251050 Somerset Street, Rear, Ottawa, ON K1Y 3C5
- See more at: Actek Automotive Business Review in Ottawa, ON - Eastern and Northern Ontario and the Outaouais BBB
 
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