[Roadsters] Tailpipe backfiring when shut off

[Mike H.]

Hi Al,
Thanks for your reply.

Thats' what I was thinking too. I run a "Boone" EI Distributor, so it's not
a points issue. Plugs at this point show a light tan/grey color, this is
what I have assumed for the last 40 years to mean a balanced fuel mixture.
It does seem to run smoother, and at a faster idle, at another 1/4  turn
leaner on the mixture nuts. It will run up to 90 mph without any hesitation
or high speed miss. When I look at the plugs using this leaner mix, they are
a lighter, almost white color, but no specks or evidence of excessive
heating that most sources say  would mean it's "too lean". I've heard that
these engines like to run lean, but I've also heard of several people who
have melted pistons, and warn against excessively lean mixtures. I've always
thought if you're running too lean, the engine will start to miss at higher
loads. ???
Mike

----- Original Message ----- 
From: "Al Boettcher" <datsunsports at rogers.com>
To: "Mike H." <twobeaners at earthlink.net>
Sent: Saturday, November 10, 2007 2:50 PM
Subject: Re: [Roadsters] Tailpipe backfiring when shut off


> you are most likely running too rich or if using points your gap has
changed
> Al...68 solex..


> ----- Original Message ----- 
> From: "Mike H." <twobeaners at earthlink.net>
> To: "Datsun list" <datsun-roadsters at autox.team.net>
> Sent: Tuesday, November 06, 2007 3:57 PM
> Subject: [Roadsters] Tailpipe backfiring when shut off
>
>
> > Hello list
> >
> > 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
> > ________________________________________