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Backfiring....
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bug..bug
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Joined: September 18, 2018
Posts: 6
Location: SOUTH KOREA
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PostPosted: Tue Sep 18, 2018 7:38 pm    Post subject: Backfiring.... Reply with quote

Hi..
I am suffering from backfire for many years.
I need help very much .....

I have been struggling for the past two years due to the backfire of the engine.

Two or three years ago, from winter, suddenly backfire occurred to engine.


1973y, Thing(181)
1600cc dualport, stock Engine.
AB Case.

I did not find a vacuum leak.
And,
Ignition timing BTDC 7.5" adjustment.
Valve gap adjustment(0.15mm)
Crankcase Rebuilt(cam and crankshaft timing mark Confirm.)

The following items were exchanged.
1. carb(34pict-3,EMPI)
2. Distributor(043, SVDA, Point gap 0.4mm)(kuhltek)
3. Fuel Pump, Fuel Filter.
4. Intake boots and Head Intake gasket(EMPI).
5. Cylinder Heads(EMPI)
6. Spark plugs, wire set, Ignition Coil.(BOSCH).


I checked and exchanged for the last two years.
But, The backfire is still there. Yet.......

What should I do more?
Help Me..


Backfiring Cam.
https://www.youtube.com/watch?v=JW3wb49th44

Idle Cam.

https://www.youtube.com/watch?v=55LlPpDG6TI[/youtube][/url]
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Arkansauced
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Joined: November 11, 2014
Posts: 38
Location: Stockton, CA
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PostPosted: Tue Sep 18, 2018 8:55 pm    Post subject: Re: Backfiring.... Reply with quote

Iím not seeing any mention of looking for exhaust leaks? Thatís probably where Iíd look next. I learned to put a piece of hose to my ear and start poking around near all the joints.
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carsdlt
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Posts: 250
Location: So. OC, Calif.
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PostPosted: Tue Sep 18, 2018 11:00 pm    Post subject: Re: Backfiring.... Reply with quote

Had a similar problem. Replaced all exhaust gaskets and heat riser gaskets- problem solved. Good luck.
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Thanx, DLT
'73 181 stock 1600 - "Dr. Bombay"

"If it works, don't fix it....let it break on its own."
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bug..bug
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PostPosted: Wed Sep 19, 2018 2:27 am    Post subject: Re: Backfiring.... Reply with quote

Arkansauced wrote:
Iím not seeing any mention of looking for exhaust leaks? Thatís probably where Iíd look next. I learned to put a piece of hose to my ear and start poking around near all the joints.


Thank You..
I did not think the exhaust leaked.
Why do you think, exhaust leaked are related to backfire?
I sincerely look forward to your reply.


I got hope from your reply.
In the winter when backfire started, I changed the exhaust.

The exhaust that was fitted before the change was a product made in the aftermarket.

Very loud...,and, The heat riser was "off".
So, I changed the stock style exhaust.. and all gasket.

I'm going to go out now and see if there's a exhaust leak exhaust.
But the exhaust sound did not sound strange.
Do you backfire even with very small leakages?

I want to know why exhaust leaks and backfire are related.
Can you tell me?
I will wait for your reply.

Thank you..^^You gave me hope....
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bug..bug
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PostPosted: Wed Sep 19, 2018 2:39 am    Post subject: Re: Backfiring.... Reply with quote

carsdlt wrote:
Had a similar problem. Replaced all exhaust gaskets and heat riser gaskets- problem solved. Good luck.


Your answer, Thank you very much.

Do you think the exhaust leak ?

Thanks to everyone's answer, I'll check the exhaust leak once again.

But I want to know.
Why is exhaust leak and backfire related?
But my engine's exhaust sound was not strange.
If it is a leak, is it a very small leak?


Thank you..^^
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74 Thing
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PostPosted: Wed Sep 19, 2018 6:24 am    Post subject: Re: Backfiring.... Reply with quote

Search for "backfiring on deceleration" and read up
https://www.google.com/search?source=hp&ei=y02...-Y8szTMzEA
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bug..bug
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PostPosted: Thu Sep 20, 2018 6:17 pm    Post subject: Re: Backfiring.... Reply with quote

74 Thing wrote:
Search for "backfiring on deceleration" and read up
https://www.google.com/search?source=hp&ei=y02...-Y8szTMzEA


Thank you.
I exchanged all of the exhaust gasket(s) yesterday.
I also checked the exhaust leaks.
I could not find an exhaust leak.

hummmmmmm....
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EDragnDean
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PostPosted: Thu Sep 20, 2018 6:28 pm    Post subject: Re: Backfiring.... Reply with quote

bug..bug wrote:
74 Thing wrote:
Search for "backfiring on deceleration" and read up
https://www.google.com/search?source=hp&ei=y02...-Y8szTMzEA


Thank you.
I exchanged all of the exhaust gasket(s) yesterday.
I also checked the exhaust leaks.
I could not find an exhaust leak.

hummmmmmm....


All? the gaskets on the heads also? How about the front of the motor? The connections on the j tubes?
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Last edited by EDragnDean on Thu Sep 20, 2018 6:28 pm; edited 1 time in total
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74 Thing
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PostPosted: Thu Sep 20, 2018 6:28 pm    Post subject: Re: Backfiring.... Reply with quote

How did you check for exhaust leaks?
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bug..bug
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PostPosted: Thu Sep 20, 2018 7:24 pm    Post subject: Re: Backfiring.... Reply with quote

EDragnDean wrote:
bug..bug wrote:
74 Thing wrote:
Search for "backfiring on deceleration" and read up
https://www.google.com/search?source=hp&ei=y02...-Y8szTMzEA


Thank you.
I exchanged all of the exhaust gasket(s) yesterday.
I also checked the exhaust leaks.
I could not find an exhaust leak.

hummmmmmm....


yes.
all gaskets changed.
Including j-tube gasket.

What about mean " front of the motor?"

Thank you.

All? the gaskets on the heads also? How about the front of the motor? The connections on the j tubes?
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bug..bug
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PostPosted: Thu Sep 20, 2018 7:40 pm    Post subject: Re: Backfiring.... Reply with quote

74 Thing wrote:
How did you check for exhaust leaks?

Hi..

I checked the soot around the exhaust every joint..
and The sound of the exhaust is felt without any abnormality.
I looked around the exhaust joint with my eyes. and I only heard the exhaust sound.
and
I exchanged all of the exhaust gasket(s) yesterday.
Is there a good way to find a little exhaust leak?

Tomorrow I am going to look for exhaust leaks using soap bubbles in idle state.
Tomorrow ... I pray to solve the problem ... ^^

I think a small leak is the cause of backfiring.
I have already checked the engine timing, vacuum leakage and so on ....


Thank You..
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74 Thing
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PostPosted: Sat Sep 22, 2018 8:55 am    Post subject: Re: Backfiring.... Reply with quote

It is almost impossible to check visually and through hearing since it is so loud.

Using a spray bottle with water and a little soap looking for bubbles is the way to go. Find yourself a small shop vacuum that has a blower mode and switch it to that. Place the nozzle into the exhaust tip with a rag and hold it there and spray the joints with your soap solution. If it bubbles then you found your leak.
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Wildthings
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PostPosted: Mon Sep 24, 2018 8:29 am    Post subject: Re: Backfiring.... Reply with quote

Your engine sounds weak when you rev it. Try setting your timing to 28-30į BTDC @ 3500+ rpms and see what effect that has.
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