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IM FAT, YOUR UGLY!
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3,783 Posts
Discussion Starter #1
OK i have my 1985 BKO with a eldelbrock 1406 4bbl Carb. Fresh Air Filter, Fresh Carb Fuel Filter and such. So far as I can tell no fuel leaks, as for pressure im not sure but it starts, idles, runs absolutely fine on the streets.

On the freeway when i hit past 55mph it starts to bog down and lose power. It will do that till i remove my foot from the pedal and let it go down to like 45 and it will keep doing it but only after a mile or 2..

I was thinking Fuel Pump, but it runs fine on city streets, although reading through my chiltons is says bad pressure at high speeds can cause problems.

Ive searched through most threads and have looked at most peoples solutions..

Catalytic Conv, Fuel Line next to exhaust getting heated, Clogged Fuel Filter, Fuel Pump, Vapor Lock and such..

So what do you guys think the problem might be?

I might have a small vacuum leak inside the brake booster but im sure thats not the problem, either way the boosters being fixed soon.

Can it be the fuel pump? Or the cat?

ill check the fuel line placement to see if its too close to the exhaust and such.

Any suggestions would be fine
 

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Satyr of the Midwest
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17,734 Posts
Fuel pump flow, float level, and jet resizing would be on my short list.

Is the ignition advancing the timing like it's supposed to? What's your baseline timing? Is the vacuum line hooked to the correct port?
 

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IM FAT, YOUR UGLY!
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3,783 Posts
Discussion Starter #3
timing is i think at 12 but im not too sure on that, and everything was checked over correctly by my mechanic and said it was all fine, dandy and hooked up correctly.

I was thinking fuel pump or cat.. Either one isnt too expensive, fuel pump is $30 and cat is $60

So since its more than likely the original fuel pump and cat, should i replace them both? high flow cat should help alot also?
 

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Registered
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777 Posts
I've seen the internal spring on a mechanical pump go weak, and the pump volume at speed is reduced.

I would say diagnose the cat issue first with vacuum gauge. You can get inexpensive vacuum/pump pressure gauges pretty cheap, and would help diagnose either issue.

If it isn't the cat, then put a tee in the fuel line, and put the pressure test gauge on the fuel line, and, with the test gauge mounted OUTSIDE the passenger compartment, go for a drive and see what the fuel pressure does.

This is the tool I'm referring to here

and how to diagnose engine problems with a vacuum gauge info here
 

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IM FAT, YOUR UGLY!
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3,783 Posts
Discussion Starter #6
ok ill test both as soon as i get a chance.

Also its been taking 3-5 times to start the engine, earlier it didnt take that long, so fuel system is the way ive been leaning too.
 

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IM FAT, YOUR UGLY!
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3,783 Posts
Discussion Starter #8
the exhaust from the cat back is a brand new 3" flowmaster exhaust system..

im thinking of replacing the cat and the pump
 

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I never regreted changing that cat and by the way, sounds awesome. Wish I'd done it sooner. My 84 really acted up when it got hot or under load.
 

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IM FAT, YOUR UGLY!
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3,783 Posts
Discussion Starter #13
ok so its between the cat and the fuel pump/system.

Now can anyone recommend a good high flow cat?
 

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IM FAT, YOUR UGLY!
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3,783 Posts
Discussion Starter #14
ok well finally starting doing this to me on the streets so now I know its the fuel pump, gonna switch to an electric fuel pump while im at it.
 

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IM FAT, YOUR UGLY!
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3,783 Posts
Discussion Starter #16
no problem has been found and being fixed. it was the fuel pump causing all of it. Im just debating on whether or not to put in an electric or keep it mechanical.
 

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what would be the reason in switching? what do you hope to gain from it?

I'm not telling you not to switch, just curious.
 

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IM FAT, YOUR UGLY!
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3,783 Posts
Discussion Starter #18
what would be the reason in switching? what do you hope to gain from it?

I'm not telling you not to switch, just curious.
was told better performance at the high rpms and such but im not too sure, trying to get more info before i decide
 

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IM FAT, YOUR UGLY!
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Discussion Starter #20
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