Backfiring

[Disposition]

I am new here. I owned an '80 ZX model in High School and parted with it in college for some stupid reason. I finally found a 240 I was in love with and I am in the process of restoring it.

I have been reading these forums all weekend and have found many solutions to problems that I have been having with my '72. The search engine has been very helpful.

Since this is my first restoration project, and first experience with SU carbs I have a lot to learn.

One thing I wasn't able to find in the search was where to sniff out backfiring problems. I'm honestly not sure where to start. I replaced one of the hoses on the carbs that was blocked, which helped, but I was wondering if this could even be an exhaust problem.

If this is a stupid question my apologies in advance, but I don't want to replace the entire exhaust system if it's not necessary.

Thanks, D

[MikeW]

I would suggest starting with reading old posts regarding tune ups. Backfiring is an indication that unburned fuel is getting into the exhaust system which is certainly not the fault of the exhaust system.

[2ManyZs]

If you are talking about a loud "bang" or "pop" as the backfiring, it's usually due to a carb, timing or ignition issue that is out of whack.

Do a complete tune-up, and check your timing before you do anything else.

[Disposition]

I'll check the timing first. Thanks

[Bambikiller240]

After having made sure that the engine is in full tune, if the symptom still persists; you may need to look into the condition of the Anti-Backfire Valve which is part of the emissions controls (if your car still has them installed).

[Chino 240Z]

Tune up, tune up, tune up. But also make note of when the backfiring is happening, on the gas? off the gas? idle? Out the back? Up under the hood? The carbs can backfire out the carbs in a lean condition, and from inside the car can sometimes seem like it's out back. Exhaust systems shouldn't be causing the problem, but some performance exhaust systems can sure amplify a problem to make it more noticeable. Do what basic tuneups you can do, a little investigative research in your problem and these guys here will help you get down the right road!

Cheers

Craig

[240ZX]

Technical information

BACKFIRE is through the carbs

AFTERFIRE is out the exhaust

Yea I know, everyone calls it a backfire when it come from the exhaust. I just had the urge to get technical on you all.

[gundee]

Still got the air pump hooked up? Remove the belt and try it out.

If you do have a exhaust leak it will detonate in exhaust even if all the other settings are correct. All the exhaust detonations I ever had on cars were traced to an exhaust leak.

[Gav240z]

oh me me me

I know this one .

Seriously it could be any number of things you need to describe when it's happening and how often.

Just one other thing to look for though is if the carbs are too rich? If they are really rich it can foul up the plugs and it can splutter and backfire and carry on.

It's nothing to do with your exhaust system more your timing. Your valves could need adjusting because if there not fully closed on the firing stroke you could get the firing noise through your exhuast.

Check your spark plugs also and your electrical timing.

As i say any number of items could cause it.

:cheeky:

[sjcurtis]

Hi Guys,

this looks like mixture theory 101

BACK FIRE - thru the carby = "lean mixture seeking Fuel".

AFTER FIRE - thru the exhaust = "rich mixture seeking Air".

These two theories apply to normally aspirated carb & injected

and both types of boosted engines using a 4 stroke cycle.

My 2c

cheers

Steve

[Disposition]

Thanks for all of the suggestions. I will tune it up this weekend. That needs to be done regardless.

However, my instinct tells me my air/gas mix is off. It will spatter gas out the tailpipe when cold and choked.

The fumes are pretty intense as well. I am going to try and get my hands on a air flow meter and follow the advice on tuning carbs from one of the old threads.

I'll get back here with my findings.