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Discussion Starter · #1 ·
Got a 302, '69,. Slow from the get go and in the Custom 500 that is a lot of weight to make it slower. I replaced the stock carb a couple of months ago with a Holley 2300. Had the carb adjusted by someone that definitely knows what they are doing. Picked it up, ran fine. I drive it about once or twice per week. In the last month it has been losing more and more power.

Example of power loss. 4% grade up a mile and a half, no problem, maintained speed limit and stayed with traffic. Now, same mountian road and another not even close to a 4% grade up 1/8th of a mile, can get no higher than 17 MPH.

Had no problem until a month ago on level ground keeping up with traffic rolling 70 or 80. Now I am running 58 MPH tops. That's nearly pushing my foot through the floor.

Although some of this is not going to matter. Has new plugs, fresh oil change, had the shop go over the car, check everything, everything is (was) fine. When I put the Holley onI did not use the Holley spacer, I used the stock spacer. The engine had a bunch of chrome on it. I changed all the chrome out with the original parts, which I had with the car. That included replacing the chrome open air filter housing with the original.

Does not hesitate at initial acceleration, just has no power.
Vehicle did come with emissions.
I found no vacuum leaks.

What could be causing this major power loss?

Thanks
 

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check your compression and timing. something's degrading. also make sure the choke isn't sucking shut
 

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put the aftermarket air filter back on and test again.
^^ this. But before you put the aftermarket air filter back on, see if the choke closes all the way, drive it and see if the choke is open all the way.
 
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Clean the carb. It could be starving for fuel at higher RPM's. If the choke was sticking open you could probably smell the excess fuel and the fuel consumption would go up. Alternatively, is the throttle linkage operating properly? Do the throttle blades open fully when the pedal is to the floor? Are you getting wide open throttle?
 

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Discussion Starter · #9 ·
That's not being a wise ass, legit question. Because that was over two months ago and it ran perfectly fine for over a month and a half. Actually I think it was over three months ago now that I think about it. This is a big shop, not free and definitely not cheap. I have doubts that it was something they/he did considering it ran perfectly up until a few weeks to a month ago. I am going to go with all the recommendations first. If everything fails or I cannot ID the problem then I will take it back over.
 

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As Galaxiex suggested it sounds like a restriction. Get a vacuum gauge and connect it to the manifold. Gradually open the throttle and watch the needle. If the vacuum stays steady then the exhaust is clear, but if it decreases and starts looking like air is trying to come out of the carburetor as you open the throttle then try loosening the exhaust pipe to the manifold and see if there is a difference.
The only other thing could be a timing chain about to let go.
Usually when there is a fuel restriction there is a surging effect.
 

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I had a set of points wear the rubbing block wore out and it just slowly layed down on me. No back fires or anything, would idle fine but wouldn't pull a load. Just guessing but maybe check points and dwell.
 

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Discussion Starter · #15 ·
I checked everything and did find the problems. (Plural). I checked it with a vacuum gauge a couple weeks ago and no problems . Turns out it did have a vacuum leak. I'm no carb expert but the diverter valve (?) was capped with a vacuum cap. The vacuum cap had deteriorated and there was a crack all the way down one side. Valve that comes out of the front of the carb. Not sure if that is a diverter valve or not. Went to NAPA, bought a $4 box of vacuum caps and got it close back to normal running. No doubt the open air filter housing is going to have to go back on. It's simply not getting enough air. but primarily that little black vacuum cap was the culprit.
 

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I checked everything and did find the problems. (Plural). I checked it with a vacuum gauge a couple weeks ago and no problems . Turns out it did have a vacuum leak. I'm no carb expert but the diverter valve (?) was capped with a vacuum cap. The vacuum cap had deteriorated and there was a crack all the way down one side. Valve that comes out of the front of the carb. Not sure if that is a diverter valve or not. Went to NAPA, bought a $4 box of vacuum caps and got it close back to normal running. No doubt the open air filter housing is going to have to go back on. It's simply not getting enough air. but primarily that little black vacuum cap was the culprit.
Old vacuum lines are the source and big problem to find the leak. Power brakes, dist diaphrams, vacuum lines to head away headlights, cruise controls, etc, etc, etc.
 

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Glad you found it. with the lack of quality in vacuum cap rubber overt he past decade plus, I've learned to carry a few spares in the tool kit in the car just incase one decides to give up the ghost.
 

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Discussion Starter · #19 ·
Glad you found it. with the lack of quality in vacuum cap rubber overt he past decade plus, I've learned to carry a few spares in the tool kit in the car just incase one decides to give up the ghost.
I was going to say that cap was only about two months old. I bought that Holley brand new. Five cent part caused a 40% power reduction. I think the caps from NAPA are better than the black cap. They fit tighter and are the exact length of the valve so they fit perfectly. Think I will take some engine photo's tomorrow.
 
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