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 Backfire 
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Firing on two.

Joined: February 17th, 2009, 8:43 pm
Posts: 508
Location: NOrWAY
Post Backfire
Hello Folks

The engine backfires up the carb, one of 5 times when hot starting.
It never backfires when cold. Valves adjusted and it has a DG-nition.

It's been doing this for 11000km. Doesn't get better, but doesn't get worse either. The engine runs great once started, hot and cold. The airfilter is in bad shape though, because of all the backfiring.

Something with the valves, even though they are checked? Only one exhaust valve needed a little adjusting. Intake valves was good.
Or may it be the DG-nition? Anyone had issues like this with an electronic ignition?

Regards Eirik

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Vennlig hilsen, Eirik
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Five 2CV's, DS 21 ieh Pallas -70, DS 23 h Pallas -75, CX 25 GTi automatic -89, XM 2,0i -90


January 17th, 2020, 8:41 am
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Firing on two.
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Joined: March 24th, 2009, 9:18 pm
Posts: 232
Location: 15340 Mourjou France
Post Re: Backfire
Never with 1-2-3, and I have it on all three vehicles (and the H-Van). Mostly because it's hard to find reliable condensors, and they always fail when it's raining or snowing or both....

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Dennis usually in the Cantal

1964 HY 72 (Type H, campervan)
1969 AZU 250 (formerly French Post Office van)
1982 Red Special
1983 Burgundy/Black Charleston
2017 Skoda Octavia Estate 1.4 DSG


January 18th, 2020, 2:01 pm
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Firing on two.
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Joined: March 21st, 2013, 12:04 am
Posts: 1048
Location: Exeter, Devon
Post Re: Backfire
Greetings :D

Possibly electrical, in that a connection is expanding when warm and causing a bad contact.

Probably running weak when hot. Poor condition air filter won't help. Also check air filter unit isn't rattling around in the air box.

Check float height and test for air leaks at carb and cylinder head.

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If you can't fix it with a hammer, it's probably electrical (or, an electric fuel pump!) ....


January 18th, 2020, 3:13 pm
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Firing on two.

Joined: February 17th, 2009, 8:43 pm
Posts: 508
Location: NOrWAY
Post Re: Backfire
Thanks guys. I have been thinking it might be the ignition unit, but maybe it is a weak mixture. I don't think there's any leaks at the manifold but I'll check. I'll have a look at the carburettor too.

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Vennlig hilsen, Eirik
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Five 2CV's, DS 21 ieh Pallas -70, DS 23 h Pallas -75, CX 25 GTi automatic -89, XM 2,0i -90


January 21st, 2020, 7:15 am
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Firing on two.

Joined: February 17th, 2009, 8:43 pm
Posts: 508
Location: NOrWAY
Post Re: Backfire
This makes me crazy. I can't find the fault.... This is turning into those cases where you just live in the garage and nothing improves.

So, the car started backfiring up the carb before the trip to the worldmeeting in Croatia. Did 11.000km with it. Blowing the shit out of the air filter in the prosess. But no way am I doing mechanical work on my trips, as long as the car gets me where I wanna go. Witch it did. This summer I've done 6000km so far, and it doesnt get worse, or better.
Also can mention, that when switching off the engine, it tends to do some "overrrun" before it stops. It's been doing this for years. Nothing I do changes this. Have changed carbs, sparkplugs and done all normal maintenance.

I dont think it's the ignition. I have changed the carburetor to one I have overhauled. When I changed the carburetor, I discovered that the two nuts in the front of it, was loose. I could see that it had sucked air in between the carburetor and the distance/heat piece. I was super happy, that must be the reason. I try not to over tighten these, as that will pull the base of the carb crocked. So last time I probably didn't tighten enough. Even put on a new airfilter, confident as I was. Well, the starting is now perfect. It starts so easy, just a touch on the key. But the shattered airfilter proves the backfiring on hot starting is not solved. Fuck me I tired of this. When driving along on flat surface with no acceleration, one can feel it running rough. Probably lean. It did not do this with the other, loose carb, orignal jet, though. When accelerating or driving under load, it runs really great.
The new carb has a 105 jet. Although when I tried to put in a 105 drill through the jet, it will not go through it. So, either the drill is lying, or the jet is lying. Drill from ebay, jet from a german parts supplier I dont use anymore. Why cant things you buy, just be as promised? Anyway, this is not a jet issue, as my other 2CV's run fine with original jets.

I have tried squirting brake cleaner and start gas on all parts of the intake, with no result. I even tried it on the carb base on the loose carb without noticing any change in the tickover. So I am not sure how much to trust this method. The other day I thought I noticed a slight change when squirting brake cleaner on the intake manifold to head gasket on one side. Yeyyy, went and ordered new gaskets. They haven't arrived yet, but when repeating the test, I now cant hear any change in tickover at all.
I am dreading that I'll to the full manifold off-struggling with exhaust nuts and bolts, loosening and tightening heads, valve adjustments and bejeesus knows what more, just to end up with no improvement at all.

I NEED ADVICE :)

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Vennlig hilsen, Eirik
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Five 2CV's, DS 21 ieh Pallas -70, DS 23 h Pallas -75, CX 25 GTi automatic -89, XM 2,0i -90


July 13th, 2020, 8:15 pm
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Firing on two.
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Joined: March 21st, 2013, 12:04 am
Posts: 1048
Location: Exeter, Devon
Post Re: Backfire
This stuff can really be a pain, and when you solve it, the clues were all there, and it should have been obvious. At least, thats the way it usually is with me .... :roll:

What carb is it?

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If you can't fix it with a hammer, it's probably electrical (or, an electric fuel pump!) ....


July 13th, 2020, 8:54 pm
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Firing on two.

Joined: December 21st, 2014, 7:33 pm
Posts: 715
Location: Rhayader Mid Wales
Post Re: Backfire
Timing is spot on? Too far advanced would run great, too great perhaps. try retarding the flamer.
Try cooler plugs?
Any service history helps you, and still the list could go on and on,and before you know it, the heads are off and the valves are re-ground in...
Good luck! and don't give up troubleshooting :).


July 14th, 2020, 12:04 am
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Firing on two.

Joined: February 17th, 2009, 8:43 pm
Posts: 508
Location: NOrWAY
Post Re: Backfire
Thanks for replies. I've driven this car for 14 years, always kept it well serviced. It's got a DG-nition ignition for years, after the 123 gave up the ghost. Not touched it since it was installed. I might check the timing just to be sure. The carb is the latest type for a 2CV6. I have 3 of them on the shelf. Tried two of them, after checking them. Backfires with both of them.
It's running lean, I belive so. I just dont know why. I guess the manifold has to come off.... Maybe try to machine the base of the carb.
If the fuel pump had a problem, the car would have a problem at full throttle, yes? It doesnt.
Oh well

Overhauled the breather yesterday. With the Burton kit. That was a success, at least :)

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Vennlig hilsen, Eirik
Image
Five 2CV's, DS 21 ieh Pallas -70, DS 23 h Pallas -75, CX 25 GTi automatic -89, XM 2,0i -90


July 14th, 2020, 6:04 pm
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Firing on two.
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Joined: March 21st, 2013, 12:04 am
Posts: 1048
Location: Exeter, Devon
Post Re: Backfire
Is the choke pull off diaphragm perforated?

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If you can't fix it with a hammer, it's probably electrical (or, an electric fuel pump!) ....


July 14th, 2020, 6:09 pm
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Firing on two.

Joined: March 26th, 2010, 8:41 pm
Posts: 233
Post Re: Backfire
Try some different plugs ?


July 15th, 2020, 8:14 am
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