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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

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  #1  
Old 01-29-2012, 10:49 AM
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square bore on a spread bore

Hey guys....new to this forumn. Been reading a lot of threads and see some great information here.

I have an 82 F100 that has a 460 out of a 76 T-Bird in it. The issue I have is that is stumbles a bit on take off as well as when I get on it and downshift. I've checked the ignition out well. New distributor, wires, plugs and have set the timing, which did help as it was not right to begin with. The EGR was all plugged up so I disconnected that and that helped out a lot as well...but still hesitating under load. When it's cold it will back fire....acts like it's just getting too much fuel at once.

It does not have the stock carburator on it. It has a Holley 1850 600 CFM vacuum secondary unit on there that looks brand new. But it is a square bore type and the manifold is a spread bore. I've heard that this can cause issues like this but thought I'd run it by some of you experts. Carburation is my week point.

Also seems to surge just a little at idle like there's a vacuum leak. I've checked everything out on top and it all seems tight. Wondering if maybe there isn't a leak on the manifold itself...not bad enough to hear anything.

I'm leaning toward replacing the manifold with a square bore to eliminate either of the issues of it not being the right one or a possible leak
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Old 01-29-2012, 02:01 PM
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I'll show my ignorance, but I didn't realize that Ford used a spread-bore carb, especially in '76. But, anyway, your stumble sounds more like it is lean, probably due to not getting any or enough gas from the accelerator pump, than a rich problem. And, a vacuum leak can easily contribute to the lean condition, which could make the standard shot from the accelerator pump insufficient.

I would spray carb or brake cleaner around the base of the carb as well as the adapter you must have to go from spread to square bore as that's a place where you may be leaking. If it speeds up when you do that you've found your leak. If you don't find a leak there then keep looking as I'd bet there is one somewhere.
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Old 01-29-2012, 02:09 PM
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Ford actually used the Rochester Quadrajet on some of their large engines. I believe they had their own spreadbore Motorcraft carb also.

Using the adapter should not cause you any problems, but like was mentioned if there is a leak around the adapter, that can cause a problem.

Also, take the aircleaner off, and with a flashlight look down the throat of the carb(with the engine off). Two things you need to look for;

1. Two strong streams of gas pouring down the carb when you open the throttle.

2. The rear butterflies should stay shut. If the rear butterflies open, someone has been monkeying with the carb, and that will cause the hesitation problem.
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Old 01-29-2012, 02:11 PM
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Quote:
Originally Posted by Franklin2 View Post
Ford actually used the Rochester Quadrajet on some of their large engines. I believe they had their own spreadbore Motorcraft carb also.

Using the adapter should not cause you any problems, but like was mentioned if there is a leak around the adapter, that can cause a problem.
Cool! A Q-Jet with Ford linkage. Gotta watch for one of those as that's my favorite carb.
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Old 01-29-2012, 04:46 PM
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The ford built spread bore was the autolite 4300, and later the 4350 IIRC. Its the emissions dictated replacement for the squarebore 4100. It makes sence that it was replaced with a holley because the 4300 didn't have a stellar reputation.
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Old 01-29-2012, 05:09 PM
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thanks guys....tried most of the suggestions you all listed...except the carb cleaner looking for a vacuum leak....gotta try that.

One thing though....it does not have an adapter plate on it. The guy apparently just put a square bore gasket on and called it good. The primaries seem to line up right on but he secondaries are obviously not right. It's a pretty thick gasket so it almost acts as an adapter.

I think I'll get an adapter just to rule that out. Will let you know if that makes any difference.

Also going to hand a vucuum meter on to see how it's doing. What would any of you consider a good "idle" vacuum I would expect to see?
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Old 01-29-2012, 05:24 PM
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18" is a fair idle vacuum. But, I can't imagine a square-bore carb fitting a spread-bore manifold as the rear studs are too far apart on the manifold for the carb. What am I missing? Surely it is a square on a square or spread on spread.
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Old 01-29-2012, 06:01 PM
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I don't know if it's considered a true spread bore manifold I guess. I see what you're saying. But the secondary holes in the manifold are clearly about twice the size of the primaries...but has a square bore bolt pattern.

I can't post any pictures but the link below is one on sale on ebay....exact manifold on my 460



FORD 460-429 INTAKE MANIFOLD STANDARD D5VE-9425-A3E 4 BARREL SPREADBORE | eBay
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Old 01-29-2012, 06:04 PM
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Actually the one on ebay is a D5VE, mine is a D6VE....not sure of the difference. May be year since mine is from a 76'
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