missfire at higher speed/rpm

On the way home today the 55' (F134) started missing and ran out of power around 45 mph in top gear. It has been running great until the ride home. Checked wires, plugs, etc and all seems fine. Any ideas what could cause this all of a sudden. It idles and drives smooth as silk untill you get to the top of the rev band in all gears any thoughts?

 

Vacuum leak?

 

That's what I thought, can't find one...sprayed with carb cleaner everywhere
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Points?

 

Vac is reading at 20, might be points but they are fairly new and it was running great this morning on the way to work.
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Fuel delivery. Last fillup was when? Check fuel filter, pull line and check flow while cranking, maybe some H20 in there too? A round of J8's if they're not real new already.

 

Vac is E
20, Timing is good, dwell is around 38 ( a little low), no vac leaks that I can find. I filled it yesterday, bad gas maybe? I will get some dry gas and re fill it somewhere else. The plugs have less than 500 miles on them, they look good but maybe a touch hot???
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Well now its doing it all the time, runs but has a spitting sound from exhaust. Engine idle ok but not as good as it did. I'm at a loss, going to drain the tank and put in new plugs and see how that goes. It's just wierd that it started all of a sudden on the way home
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This sure sounds like a fuel problem. How old is the float? Old enough to leak a fill with gas? Float needle stuck in the seet?

 

Brand new solex carb
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I would put my timing light on it and rev it up while watching the light for even flashes. High rpm with even flashes will tell you it is not ignition. Bad or low fuel will not effect the opening or closing of the points or coil operation.

 

Walt,

Even flashes all around, are you saying its not fuel?
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Well new plugs, fuel filter, dry gas, and still no change. Its really not a missfire per say but its a spitting sound from the exhaust through the whole rpm range and even though it still gets up to around 45 or 50 it is def. a loss of power. I am lost on this one. It went from running mint to this all of a sudden while cruising around 40 in top gear
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No I am saying if you have even flashes that your ignition is good.. If your timing chain does not have a bunch of slop in it and timing and dwell is good then it looks more like a fuel problem Sorry F head has gears.. Was looking at your Avatar..

 

Ok, yeah ignition seems good, but I can not find were the fuel issue might be. The solex is new and as been running great for at least a 100-200 miles then all of a sudden his issue pop up. I can not seem to see anything that is any different than before today.

 

What is the status of fuel volume and pressure? Could it be the pump has gone south?

 

I do not have a fuel pressure gauge, how do I find this info out?
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Do you have a vacuum gauge? Mine has both vacuum and pressure.. Your fuel pres should be 2 1/2 to 3 3/4 lbs. To check your pump volume output -- get a 1/2 pint bottle and remove lint at carb. remove ign wire going to the plus + side of the coil. crank engine until you have fuel spurting out of line. Then hold bottle to line and crank engine continuous for 20 complete turns of the engine. If that did not fill the bottle then you have bad pump or line restriction or crimped line or plugged line at bottom of tank or something like that. HTH

 

A weak coil will keep up with low demands but stumble under higher loads.

 

Your right but the timing light flashing would stumble during this time and tell you it was ignition.