John Mitchell wrote:
<I remembered that a couple weeks back I had tried the
external oil feed line. I had so much oil to the head, is was being
sucked into the carbs, and apparently had completely plugged the
evaporative canister. I replaced the canister and the problem was
solved. I guess the oil saturated charcoal was acting like the
anti-run-on valve and choking the engine.>
I'm sure listers are tired of my harrang on canisters, but here's a concrete
example (abeit extreme) of how the seemingly benign charcoal canister can
cause problems. I've advocated removing the thing and I was told by an
othewise astute lister, that removal was "ill advised" and that as long as I
installed new hoses and clamps, the canister couldn't possibly affect
performance.
Unfortunately, checking the canister through-flow is never part of the
diagnostic our repitoire. Over time, as the engine ages, oil blowby through
the valve cover port can foul the charcoal, even with the valve cover baffle
in place. This is obvious if there is substantial oil residue at the entrances
to your ZS carb ports. As a forensics exercise (sort of TR6 CSI, with darkened
garage lights and the works) I disassembled my canister and poured the
charcoal into a container. It was a mess and couldn't possibly have been
effective in absorbing fuel vapors or anything else. This thing was designed
for an evaporative emissions system in 1973 before catalytic converters or
closed loop systems with sensors, and after 3 days w/o running the car, fills
up with vapors and is marginal anyway.
Take a look at Triumph Service Training Notes, p. 65 for symptom 10 on
http://www.mv.com/ipusers/last/emissions/booklet.pdf Also look at p.54 on the
operation of the anti run-on system. In my view, this is the best diagnostic
document available to owners of our LBCs, and I would advise listers to
download a copy in case this link goes south.
The alternative to canister removal, is to engineer emissions systems
work-arounds to address its weaknesses. First of all, a separate PCV valve
(ala GoodParts, see http://www.goodparts.com/shop/index.php?categoryID=8 )
then route the output to your intake manifold and route the carbs directly to
the canister port. If you are using a valve lifter feeder line and/or a valve
cover w/o a baffle (as I am) , an oil separator is essential to route the oil
directly back to the crankcase. If you don't want to spend $139 for a
GoodParts oil separator, Paul Tegler has a simpler design using a modified
aluminum electrical conduit box that drains back through the valve cover port
and doesn't require a separate return to the crankcase. See
http://www.teglerizer.com/triumphstuff/emissions/emissions_67t_filter.htm.
In addition, I've added a roll-over check valve ($11) to my fuel tank vent
line and attached it to the tank along the side in the vertical direction to
prevent fuel from flowing into the canister and catching fire in a roll-over.
Along with the roll-over switch (from ebay for $9) for my electric fuel pump
will make the car safer in the event of an accident.
Jerry
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