Hissing sound - Loss of power

Need help diagnosing,
65 mustang 200 ci with a Carter YFA from a granada 250. Electronic ignition (ford factory DSII). Stock coil.
I have been driving with this setup for two years with no problems, Last night coming home I had a loss of power and heard a little more hissing sound coming from the carb.
The car seems to be only able to rev to about 4000 and then back to idle it is rough. Playing with the accelerator a bit and it will idle ok but once you gas it it will go back to rough.
Plugs were a bit fouled due to me flooding it in this cold weather, and number 5 had some crusty crap on the plug.
What I've done so far-
Was running a little rich- reset float (brass), changed plugs and checked dist. cap and rotor (no change).
Checked fuel filter (fine) checked oil and water for contamination (none)
Checked for vac. leaks and (found none) Pcv seems fine.
Checked timing (good)
I'm down to trying to figure out if this is fuel or ignition. If its fuel then maybe the carb?, coil or Ign. box? Head gasket?
Anyone experience these symptoms? Any help would be appreciated.
This car is a daily driver.
Thanks, Mike

start with a can of carb cleaner. my car was being a PITA a few days ago, running rough, stalling, etc, and that straightened it right up.

to my knowledge, an ignition module will never cause it to run poorly, when they fail, it will run great and then suddenly quit.

i can't say what coil problems would do, but would be interested to learn from someone who does know

most head gasket problems involve water, but its possible for it to only blow between 2 cylinders. a compression test will pinpoint that if its the problem, but i wouldn't expect it.

sounds to me like the carb needs the usual going-over

Bad tank of gas?

If it was bad gas I probably wouldn't be able to get it to idle good. Rough choppy idle, but if you feather it a bit it will smooth out. Its starting to sound more like the carb but I wanted to see what everyone else thought.

Hissing might be a vac leak, which might be affecting the advance timing.
So check all the vacuum hoses and connections.
But the carb itself emits a hissing sound that's quite normal, I think.

I think Jackfish is right on with his assesment. There's a leak somewhere whether or not it's the carb, distro, or PCV. Something is leaking. Check every hose by taking it off and really scrutinizing for cracks. Take a good look at the carb base plate. That non-hot rodded engine should be pulling close to 18-20" of vacuum. If the PCV has a plastic top look very closely for cracks there too. Use your hand and cup around some of the vacuum connections and if it's sucking air then the tone will change. If you have power brakes check there too. Both ends of the hose. It's a big hose and a small crack will leak.

In my experience hissing is always a vacuum leak. Not to be confused with the sucking of the carb.

I have checked and rechecked vac lines, of course theres only three, dist, pwr Brakes, and pcv. Only one outlet which is a tree. Not it at all unless I'm pulling a vac from a gasket leak somewhere which is why I posted because it seems I heard that the HG can blow between cylinders. I am at the firehouse today but plan on ruling that out with a compression check tomorrow. As for the hiss It almost sounds like a Turbo whistle which gets louder as you rev.

Have you checked your carb base gasket?

Checked that first, also put new gasket just in case. Definitely not it. I thought it may have jumped time so I pulled the timing cover and found the timing chain and gears very loose but it had not jumped. Going to put a new set in this week and if no change I'm pulling the head. This is frustrating.

I checked the compression yesterday but my tester was screwed so I will have to borrow one and get back on it tomorrow. I mean guys I have checked and rechecked all the small stuff, I even changed Carbs with the one off my fairlane and was still making the whistling sound and no power. Has anyone had a cracked head or a Blown head gasket make a noise like this? My buddy say a loss of power like mine is that it seams to be more like timing than the head or head gasket, I will be putting a new timing set on tomorrow , mine is extremely loose and re-adjusting my timing and then I guess compression check and off with the head.

It sounds like you are on the right track.

It's got me stumped.

BTW, maybe I missed it, but did you do a vacuum test at idle? What was the reading?

Yesterday got the timing set in. Today, I changed out the vac advance from my parts shelf, went through the old carb, did a compression test on the cylinders- all good. So its running fine at idle and low speeds but falls on its face when revved. After revving when it comes back to idle it stumbles but you can feather it and it idles back smooth. So with my head hurting an my pocket shallower the only thing I can think of is maybe the fuel pump is sucking air??? What made me think about this is after it was idling for a few minutes I shut it off and changed my fuel filter incoming near the fuel pump and it was dry. Which leads me to think that all my fuel drained back to the tank. It sustains enough fuel to idle and take off but not enough to run at higher RPM? whistling could be sucking air or introducing air into the fuel bowl? That will be my last try and then I will be completely stumped. Does this sound likely?

Does anyone know what the pick up coil in a DSII dizzy would act like if its going bad? Low spark for instance?

Between the orange and purple you should read 400-800 ohms, either one to black more than 100k ohms if I remember right. They usually just go bad completly.

Its finally fixed! and am I mentally drained! This thing had a clogged exhaust pipe in the straight section just under the seat. Dont know Why, How, or What but dropping the exhaust at the manifold told the details. I dropped the pipe from manifold and found it was definately clogged, so Thinking the muffler was clogged I drilled a hole just before the muffler and hardly any pressure, then about midways and the same results, the last hole I drilled was about a foot back from the exhaust manifold and that got it. so all my efforts were not too bad she needed a timing set bad anyway. Thanks for all your help.
Mike

ahhh glad you sorted it! Had a similar problem in a friends van, it seems you can never predict when your exhaust may get blocked!