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engine backfire

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striker308
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engine backfire

Postby striker308 » 18 Nov 2007 22:32

Why does my 1976 TR7 backfire when I shut it off? It does seem to shudder when I turn off the engine and lately it's been doing a noticable backfire.

I close my eye and wince everytime I shut it off. Any thoughts?

Thanks,
Karl

Karl
1976 TR7
1982 VW Scirocco

jclay (RIP 2018)
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Postby jclay (RIP 2018) » 18 Nov 2007 23:03

Is your air pump still installed?

Have fun, drive fast & safe, be kewl,

jclay

striker308
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Postby striker308 » 19 Nov 2007 00:27

It's physically in the engine bay, not pulley plate or belt and just the hose connections attached.

Karl
1976 TR7
1982 VW Scirocco

Hasbeen
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Postby Hasbeen » 19 Nov 2007 06:46

Karl, are you talking about something through the carby, or the exhaust?

Hasbeen

bmcecosse
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Postby bmcecosse » 19 Nov 2007 12:43

Engine 'running on' is down to something glowing red inside the combustion chamber - and this keeps the engine going even when the plugs aren't being fired. Could be carbon deposits - or the plugs themselves. Also can be down to very retarded ignition timing causing overheating. Worthwhile changing the plugs. Otherwise a de-coke may be required. A true 'backfire' is caused by unburned fuel getting down into the exhaust system - and igniting there. Is the engine idle speed perhaps set too high ?

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striker308
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Postby striker308 » 19 Nov 2007 13:19

It's from the exhaust. I do have hard cold starts and once I drive it aroundt he idle speed is way too high around 1200 - 1500. I also have black deposits on the exhaust tip.

The plugs were changed 150 miles ago. I replaced with Bosch platinum's and new plug wires.

Karl
1976 TR7
1982 VW Scirocco

bmcecosse
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Postby bmcecosse » 19 Nov 2007 15:17

Well -it sounds as if running too rich - and way too high idle speed. When you switch off it's pumping unburned fuel into the hot exhaust.

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Beans
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Postby Beans » 19 Nov 2007 18:39

But first check if your ignition timing is correct.
Work from there on

<center>Image
<font color="blue"><i>1981 TR7 FHC Sprint (better known as 't Kreng)
1981 TR7 DHC (not very well known yet, but back on the road)
Also a 1980 TR7 DHC, 1980 TR7 DHC FI, 1981 TR7 FHC
http://tr7beans.blogspot.com/</i></font id="blue"></center>

striker308
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Postby striker308 » 24 Nov 2007 22:34

bmcecosse, what's a de-coke? I did notice that the damper oil level was very low. This seemed to help a little, but I still can't seem to get the idle right. It also blows out a lot of black soot on my drive way, when running it.

Karl

Karl
1976 TR7
1982 VW Scirocco

Hasbeen
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Postby Hasbeen » 25 Nov 2007 00:54

Karl, your car is far too rich. It could be the wrong needles in
the carbs, or perhaps the jets are worn due to incorrect set up. Or
it could be that the needles & seats are shot, & your carbys are flooding.

Someone could have fitted a replacement fuel pump whit too high fuel
pressure.

Do you have an FAST, [auto choke device] or a manual choke? These
things often cause fast idle, & may cause rich running. Run a search
for SSTs [forum member] post on how these work.

De-coke, is to remove the head, & clean out the build up of carbon
in the combustion chamber. Not realy probable cause of your problem.

Not trying to be unkind, but it sounds as if you should find some
help, to get things sorted, & learn a bit,then start doing your own
work, when things are a little bit easier.
There are so many things, or combination of things, which COULD be
causing your problem, it can be hard to find whats wrong, even if
its reasonably simple, & you have lots of experience.
Its often a matter of trial & error to find & sort the cause, & thats
where experience counts.

Hasbeen

striker308
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Postby striker308 » 25 Nov 2007 01:31

Hasbeen, you're not being unkind. I really don't know anything about carbs or in my situation "A Carb". My 1976 is a California model with only one carb.

Yes, it has the auto-choke. My only other experience with working on a car is my 1982 VW Scirocco........but it's fuel injected.

Thanks, for the advise.

Karl
1976 TR7
1982 VW Scirocco

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