1977 280 backfiring loss of power where should I start ?

Also exhaust smells rich of unburned fuel

Bad plugs ,vacum leak ,tune up, bad injector??

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77 280 305 BLUE

Rather than ask about the plugs, you could check them and report back so we can help you better. Check the gap also.

Sorry to get technical Greg, but it's important for clarity in this case.

"Backfiring" is a popping of unburned fuel out the end of the car's exhaust system. That's caused by incomplete/partial combustion in the engine, which allows some fuel to come into contact with the hot exhaust system, where it ignites with a bang. "Back flash" (or "Flashback") refers to fuel ignition spitting back OUT of a carburetor instead of being contained in the combustion chamber where it belongs.

There are different causes for each. Which is happening to you? Is it popping out the exhaust, or popping back thru the induction system?

Frank

Backfiring, loss of power.. i'd blame the ignition system at first glance....

This is where its always great to have 2 cars either of your own or a freinds.
Start changing things over ...eg. dizzy...leads.... dizzy cap...
if you get no difference then you can cancel that out...

once you eliminate the probable whatevers left however improbable must be the problem... darn that sounded good

Yes, it did!

"Process of Elimination", we call it. Eventually you swap something which makes all the difference and solves the problem. (At that point you give your mate a cheery wave and drive away with his part, thanking him! )

The back-flashing is usually a timing problem, but it can also be a chipped or broken valve, OR something still glowing inside the combustion chamber when the intake valve opens for the next breath. In your mind's eye you simply have to picture how the ignition flame from inside the combustion chamber is becoming exposed to the fresh, incoming air/fuel mixture. With everything proper, that doesn't happen ~ the intake valve is sealed shut before every plug sparks, protecting that incoming fuel-rich atmosphere in the intake manifold.

When an engine flashes-back thru the carbs, it means SOMEHOW an ignition source is being allowed to remain present when an intake valve opens (like a glowing, overheated sparkplug for example, or a burr on a piston or cylinder head which has reached incandescent temperature).

Improper ignition timing can't happen to only one cylinder ~ it has to happen to all of them at once or none at all. The dizzy simply gets installed wrong or else loosens up and twists enough to provide spark to all cylinders as the intake valves are opening, resulting in the ignition of everything inside the intake ("inlet") manifold.

Backflashing shouldn't happen to cars which use direct fuel injection, since there is no air/fuel mixture in the intake manifold ~ it's just air.

A chipped (or bent, or stuck, or poorly seated) Intake valve can provide a tiny little porthole in one cylinder, which permits the intake manifold air-fuel mixture to have access to the ignition inside the cylinder, resulting in back-flashing thru the carbs.

BACKFIRING can be caused by nothing more complicated than a single sparkplug failing to fire. The raw air/fuel mix from that cylinder doesn't get burned in the combustion chamber, so it gets 'exhaled' out when the exhaust valve opens. When it hits that hot exhaust system, the air/fuel mix ignites, causing a mini-explosion inside your pipe or muffler.

Many racecars can be seen throwing FLAMES out the back as they slow down and approach a turn. That's unburned A/F from the cylinders being ignited on the hot pipes, a TRUE "backfire".

Thanks to all that responded you were all a great help.
Changed out all the plugs found cyl. three not firing and loaded up bad plug I guess also put in a new set of wires, runs like a top now!!

Thanks again to all
greg 1977 280s30 305 blue

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77 280 305 BLUE

well that was easy.....
Make sure ya put NGK plugs in... bosch and champions will do there
5 - 10,000 and then there stuffed.. maybe less than this.. NGK's i know from experience will still be going at 40,000kms. At the same $$$$$$$$$$$$$..

I also found that special high performance plugs on a street car are useless.
You might get 1% increase in power for upto 5x the price...

Hot ignition systems give you power increases but need more regular maintanence... if you have points a hot ignition system will burn 'em out in about 1 - 2000 kms.. standard systems will get more like 5000 kms out of a set of points..
Aftermarket points r made for the entire L series datsun range and i found the dwell angle is always too low. about 30 degress.
I use Nissan points for 240Z. Set the gap and the dwell is always about 50 degress.
Free horsepower.. and they cost the same as aftermarkets......

darn there i go again..rant rant.....

There is nothing wrong with BOSCH plugs.

It was a BOSCH plug that loaded up!! boy your smart. I did put in champion but the next set will be NGKS

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77 280 305 BLUE

I am moderately intelligent. Thank you for the compliment.

BOSCH makes a quality product. If you go by forum BS, then so be it.

I have yet to see any scientific evidence that a Bosch plug is inferior to an NGK. If your decades old engine is the test lab in which we will compare the results of different products, I'll cancel my subscription to that magazine.

No disrespect.

I run NGK plugs and wires, bu,t I'm not so naive to believe a world leading producer of ignition, fuel management and O2 sensor components is garbage because it's "not JDM".

Take better care of your engine and I'm sure a variety of plugs would work fine, if gapped properly under stock and near stock conditions.

WOW sorry I meant no disrespect I'm just lookin for some advice.

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77 280 305 BLUE

I have had nothing but bad luck with Champions in my 240, while they work fine in my family cars and trucks.

In the Z, it seems as if they watch for any storm cloud on any horizon, then use that as an excuse to quit. Hard, hard starts, limited rev limits, backfiring on turns, stuttering when cold, bucking under acceleration.

My manual calls for NGK BP6ES plugs. They never worked quite as well as the 5ES plugs, so that's what my car gets. They make it happy.

I have used Bosch, and they performed well, but they don't seem to last as long in my car as the NGKs do.

Anybody still run Nippon Densus?

Frank

I ran Denso but not in the Z.

Most people don't gap their plugs. Unfortunately you can't expect the companies to make sure they are all gapped appropriately.

At the ages of some of our engines and mods the difference between each motor's combustion characteristics may call for us to slightly change the plug gap for best performance and plug longevity.

Bosch and champion plugs.....
i have found they work fine BUT.... they seem to die when the recomended mileage comes up.. thats what i've found from experience...

I use NGK BP6ES.. works great and last well beyond 10,000 miles.
i've got plugs that i've changed for the heck of it as spares, and they still work fine after years...

SO.... YES.. Bosch and champion plugs work great on Z's... But for the same money you can get the plugs that we all trust and know will go the distance..

NGK r made in japan and the nissan engines were designed with these plugs in mind.

I believe Nippon Denso plugs are actually made by NGK.. or the other way around... These are recommended for my GM V6 3.8L and there still going strong 20,000 miles later.. probly should change 'em soon....

Many times have i changed bosch or champion plugs out because they have just died... This has happened once maybe twice before on me with NGK's so its your own choice...

If you asked me.. No matter what car i'd say put NGK spark plugs in it..