Backfire between shifts?

[Draker]

I've got a hole in my exhaust so there is a bit of excessive noise, but at lower speeds say between 1st 2nd 3rd gear shifts I hear a bit of a backfire, louder the higher the rpms.. shifting between 3-4 and 4-5 there are no backfires. I am wondering is this just more amplified because of the hole in the exhaust or do I have an issue with my carb?

[datzenmike]

I've got a hole in my exhaust so there is a bit of excessive noise, but at lower speeds say between 1st 2nd 3rd gear shifts I hear a bit of a backfire, louder the higher the rpms.. shifting between 3-4 and 4-5 there are no backfires. I am wondering is this just more amplified because of the hole in the exhaust or do I have an issue with my carb?

 

 

Have you removed any of the pollution 'stuff'?

 

Cut a soup can and wrap it over the hole with two gear clamps. Fixed.

[datsunaholic]

Could be too much ignition advance, could be normal. Best advance at load is too much at high RPM with the throttles closed. Distributor vacuum advance doesn't react that fast to a quick throttle close. The hole in the exhaust makes it more noticeable.

[sedition88]

I have hardly any exaust on my 620 and it does the same thing, and it's because of the exaust leak. Agree with the King Rat I do with the fix.

[ggzilla]

Why fix it? A little carbon monoxide never hurt us ...yes it's normal to have a little "burbling" in the exhaust. However, a sharp backfire shouldn't happen with a modern EFI-emission controlled engine.

[banzai510(hainz)]

I think my car did this when it was reaaly worn timming chain. But this ran points back then also. So could be a combonation of both (timming)

[Draker]

Thanks for the replies. I'll do the soup can fix and see where that gets me. I noticed actually it's not even between shifts as much as it is just on falling RPMs. If I am in neutral and rev it up and let off it does the same thing. I do get sharp backfires too.. I'll check the timing. Currently I've got 138k on this truck, all original.. no odd noises from the timing chain. All emissions stuff is still in place.

[blackwolf]

i have an 84 720 KC and its always backfired since the day my parent bough it new off the lot replaced the engine 3 years ago and it still backfires but run great and still gets 22-23 city and 25-26 highway wouldnt worry unless your mileage changes

[datzenmike]

This topic is 10 months old.....

[ggzilla]

So what? Good information never dies.

 

 

[izzo]

So this still backfires even with new exhaust. I've removed all the emissions stuff. Timed it to factory spec. Adjusted air fuel and idle speed. It calmed it down but hadn't stopped it

[banzai510(hainz)]

 

 

Izzy

I had points ignition and changed condensor, points or worn dist bushing causing slight backfire

 

ck the cam timming and see if the marks line up correctly when you put crank on Zero

 

 

ck valve lash as a last hail mary pass

[datzenmike]

Stock carb? If you pulled 'all that emission crap' off you also removed the anti back fire valve and plumbing.

 

 

Turn the idle mixture screw up as rich as you can and try that.... or was it a lean as you can. Try both.

 

Also your BCDD may be set to low and not coming on when decelerating. Turn CW to increase the sensitivity but if the idle fails to drop back down when you come to a stop you went too far. Then turn CCW.

 

Nice to see you posting again Tim

[debugish]

Having the exact same symptoms, and i'm not using the stock carb. I haven't looked through the exhaust but plan on having that addressed here soon. If that doesn't do the trick, I wonder if this has anything to do with not having a "Boost Controlled Deceleration Device" which I believe is installed in the stock carb.

 

Any thoughts on this perspective or updates on what has worked appreciated.

 

Thanks!

[captain720]

Mine does the exact same thing every time my exhaust leaks come unglued.

[Mavwinchester]

I had this problem until I removed the hoses from the front of the breather and used one to tie the hard lines together. You can also cut and bend them but I'm not interested in aesthetics so I figured why take a chance of them leaking?