emissions failure

["Robert H. Hughes" <robhughes100@domain.elided>]

Harvesters

I don't remember who asked about a failed emissions test, but I haven't
seen many responses, so I thought I'd jump in.  I'm sure the digest will
let us know if my advice is bad.

I've failed emissions tests two years in a row (though I've eventually
gotten it to pass -- took me 5 tries the first year, 3 last year), so I
feel like something of an expert.

My understanding is that a high HC count is a result of poor ignition,
that is, and incomplete burn, whereas a high CO count is due to a rich
mixture.  Since your CO is fine, I think you can leave the carb alone.

That leaves ignition.  You've already replaced plugs, wires, cap and
rotor, right?  A few other ideas:

--Gap the plugs a bit wider, maybe?
--Play with the timing - I would guess advance it
--Replace the coil

Also, I think you stated that you failed the high rpm test, but you
didn't mention failing the idle test.  That might be a crucial clue.
What does the ignition system do to compensate for increased engine
speed?  It advances the timing via the mechanical advance.

Check this by hooking up a timing light, then have a friend rev it up
(if you're working solo, you can reach over the carb and open the
throttle yourself).  The timing should advance noticeably.  If it
doesn't, you might have to replace the mechanical advance springs --
someone else will have to guide you in that endeavor.

You might want to check the vacuum advance, too, though I doubt it is
related to your emissions problems.

Rob H.