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have a 65 gt fastback A code and the other day i got on the interstate and couldnt get over 80 as a matter of fact i bogged and sputtered in fourth but was fine when id throw it back in third. whats going on? help please
 

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too much fuel maybe? vacuum leak could be anything
 

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I dont know about the sputtering and all but what gear ratio is in your rear end? Some 4.10 gears could really effect top speed.
 

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Agree with above, I'd change the fuel filter first. Have you tested your dist. vac. advance to see if it's working? Remove your dist. cap and look for the little arm that extends from the vac. adv. to the plate in the dist. Now remove the vac. hose from the carb and suck on it, watch to see if the arm pulls into the vac. adv., if it doesn't the diaphragm in it is shot. You can get replacement adv. at the parts store.
You can check the points with the cap off, take a small flat blade screw driver and lightly pry them apart if they're not open, look at the contacts on the points with a flashlight and see if they look burned, you can smoothe them somewhat with an emery board, fine metal sandpaper, etc. To adjust them you need a gap blade and a shop manual wouldn't hurt.
Jon
 

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Why would you want to go that fast on a public highway? Isn't it illegal? :gringreen:gringreen:gringreen
 

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But all fun aside -- check the fuel filter and get yourself an electronic ignition module.
 

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Are you saying that the engine runs OK at higher RPMs in 3rd? Does the engine run OK at lower RPMs in 3rd? The only time that you experience this problem is in 4th gear?
 

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If it's got problems under load, like when you are in top gear, my guess would be spark related. Maybe a bad coil, plug wires, etc. I wonder what happens if in third, at a fairly low speed, and then you floor it?? Or maybe up a hill in third at a fairly low speed?
 
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