My '72 1800e w/ a b20f has been backfiring lately all at engine speeds below 3000 rpm. Also below that mark power is nearly gone and the engine seems to be crusing at hwy speeds at about 700 rpm less than normal. i'm a novice DIY'er and don't know where to start to look at. Please help.

Thank You,
TurboZamboni

There was one time when I had to have my 1800 towed to a mechanic because it exhibited the symptoms you describe but worse. Eventually the car died in a fit of popping and lurching. I was quite embarassed when I discovered the condenser mounting screw, which also serves as its ground, had been taken out by me to replace a lost trigger contact mounting screw. One new screw and I was on my way, and the mechanic and tow company were enjoying themselves too, I'm sure.
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Justin 66 122E, 71 145S
Read vclassics!

1st, clean and set your ignition points.

I suspect the ignition distributor. It has a timing retard mechanism, I believe in the '72, if injected. Sounds like maybe this isn't working. I doubt, without serious other symptoms, that your engine is actually running slower at highway speeds. Since the tachometer is signalled by the ignition, usually through a distributor connection, I again would suspect connections at the distributor.

Basic things to do:
Remove distributor cap, inspect for dirt, corrosion, clean. Clean points. Cceck and clean all electric and vacuum connections. COuld be the vacuum retard mechanism.

Less likely, although possible, if D-jet injected, are the lower set of F.I. trigger points in the bottom of the distributor, although these usually work or it only runs on two cylinders.

700 rpm less? Is this an auto tranny? Although even then I don't know why it would change anything...

Backfiring could be a number of things. Could be some sort of lean condition (check the plugs). Could be something with the valves (a very tight intake valve, a flattened exhaust valve lobe). Could be shorts in the distributor cap. Could be timing way off.

JohnMC
It's a manual tranny, m41. Now that i think about it it might have been tach error, engine speed sounded normal, just a lower reading. checking that darn distrubutor now and will be back with my findings
Thanks
TurboZamboni