Since you've checked the obvious ( mixture, etc.) I'd suspect an exhaust
leak near the front. The additional air a leak lets in can allow the last
unburned fuel air charge POP inside the exhaust.
----- Original Message -----
From: "Mike H." <twobeaners@earthlink.net>
To: "Datsun list" <datsun-roadsters@autox.team.net>
Sent: Tuesday, November 06, 2007 7:57 PM
Subject: [Roadsters] Tailpipe backfiring when shut off
> Hello list,
> Well I haven't updated my stroker project since July, so here it is:
> I built the 1600 stroker using the stock head (un-ported, stock valves),
stock
> intake manifold (also un-ported, un-modified), 4:1 headers, and stock 1600
> carbs with ADQ needles, Boone EI dizzy, standard U20 flat top pistons and
U20
> rods, and last but not least, the NISMO stroker crankshaft ($$$). The only
> other upgrade to the engine was the Isky DR-66 cam, a little more lift and
a
> little more duration than the stock cam. I cc'd the head's chambers, and
> several online copression calculators indicated this engine would have
> approximately 9.4:1 compression. I also rebuilt and added the 5-speed to
> complete this upgrade. The rotating components were then balanced at a
local
> speed shop, I was told to within .2 of a gram. It sure runs like it! It is
> smooooooooth! Well worth the $175! IMHO.
>
> After putting 1500 miles on the engine I have routinely cruise at 4500 rpm
in
> 4th and 4000 in 5th,and recently started winding it further to 5000 during
> 3rd, 4th, and 5th gear shifts. It fairly screams and really seems to
"like"
> shifting at this rpm range. Must be a "torque curve" thing or something!
> Anyway, I'm starting to wonder how far it will eventually wind out in 5th?
My
> problem is I'm already pushing close to 90 in 5th at 4k. How fast can one
go
> to "test" his engine? ! :-).
>
> Everything is wonderful, except: It backfires loudly (one loud bang out
the
> tailpipe) when I turn off the ignition. I've checked mixtures, timing, and
> valve clearance. Compression is good and leakdown testing tells me there
are
> know valves leaking.
> Any suggestions, opinions, or comments?
>
> Thanks to all the listers who have provided help and advice to my project.
> Mike Hudson '67 - stroker / 5speed
> ________________________________________
>
> msedlack@neo.rr.com
>
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>
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>
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