by Fred Stoermer
A common emission test problem for upright fan [type 1] engines with a few miles on them is caused by blowby/crankcase fumes being re-ingested through the air cleaner and carburetor and throwing the tailpipe readings way off.
There's a simple fix.
Using a longer piece of hose than is already there reroute the crankcase fumes out of the compartment via a "road draft tube". Standard fitment/procedure for most older vehicles. Just remove the preheated air hose from the air cleaner, temporarily, and route the road draft tube under the engine tin through that opening. After the test replace the hoses in the appropriate arrangement.
This procedure was suggested to me a few years back by a state-certified emission test/control technician, and it worked like a charm.
Whatever approach you take it's imperative that you get all the machinery
thoroughly warmed up pre-test. Our local state testing station checks this
pre-test, and will send folks back to the freeway if necessary to avoid
wasting everyone's time and money.