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My Stock 1977 Luv is experiecing a nasty miss at varying speeds. I lose power suddenly, if I back off the gas and downshift( its a 4 speed stick) I can regain power. I can't drive on the Freeway anymore. I've changed points, plugs and wires, and distributor and cap. Maybe a valve adjustment? Anybody have any suggestions.

Bad Coil, Bad Fuel Pump, Vaccum Leak, Blocked Fuel Filter

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1980 4x4 KBD40 ISUZU/Chev Luv
Factory Fitted c190 Diesel Engine, ARB BullBar, Ramsey Winch, Custom Tilt Tray,

Look at the fuel pump, lines and filters, as Oz said. Sounds like a fuel restriction issue. How's the carb?

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"If we did the things we are capable of, we would astound ourselves" - Thomas Edison

Thanks guys. I'll examine your suggestions. A vacuum leak is very possible. I'm due for my Bi-Annual smog check(since Swarze took over in California, the 30 year exemption was repealed), and I have numerous vacuum ports in this system. I'll post my results.
Could a bad Rear Axle cause a feeling of lost power?

Take a look here if your emissions sticker is missing. I think it should be the same as your '77 -> viewtopic.php?f=5&t=17617

A bad rear axle usually indicates it's 'badness' by making some sort of racket, whine or clunk.

Again, not my area of expertise, but if you suspect the rear axle, check for brake drag first. If that doesn't turn up anything, then check for a slipping clutch. Here's an easy way to do it -> viewtopic.php?f=5&t=16991&p=128470&hilit=slipping+clutch#p128470

A common cause of vacuum leaks is the EGR port, cracked hoses, and misrouted hoses. Use WD-40 or carb cleaner and lightly spray around various parts of the engine while it's running. If the engine speed increases, you've found the general area of the leak. Watch for overspray. I was convinced I had a bad shaft bushing in my carb, but it turned out the spray was drifting down to the EGR. That's where my leak ended up being.

I'm basing these recommendations on a very general t-shooting concept, you've indicated that you seem to be lacking power. If you find I'm way off base, just wait. Better mechanics than I will surely jump in to assist you.

Still having an issue? Keep posting questions (after you've used the search feature, of course) ...

Good luck.

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"If we did the things we are capable of, we would astound ourselves" - Thomas Edison

I'm with nukeday on this one. Fuel filter, also filter inside the pump, restiction at the fuel line pick up inside the tank.

Good way to check for vacuum leak that doesn't make a mess: use a propane torch with the gas valve cracked open, but don't ligh torch. Just spray the propane around intake and fittings etc. and the engine will speed up when propane gas is sucked in.

JimmieD rocks. What a cool idea...

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"If we did the things we are capable of, we would astound ourselves" - Thomas Edison

The exact opposite happens when you spray air at a slightly low volume/pressure all around where you suspect a vacuum leak might be. The engine will tend to slightly drop in rpm's and/or miss if you hit the right spot directly. A sensitive enough external tach and/or vacuum guage should pick it up.

That's just one more way I've used to verify that I found it. The unlit propane touch trick works well too, and so does using WD-40 and carb cleaner. Just be careful...after all that stuff is flamable and carb cleaner is not very paint-friendly.

have you seen it miss with a timing light thats what mine did my coil was bad

Good tip, luvnluvs, saved me a couple of times! Sure beats trying to pull plug wires and having them disintegrate.