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Old 05-12-2010, 08:47 AM   #7 (permalink)
Ryland
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Join Date: Jan 2008
Location: Western Wisconsin
Posts: 3,903

honda cb125 - '74 Honda CB 125 S1
90 day: 79.71 mpg (US)

green wedge - '81 Commuter Vehicles Inc. Commuti-Car

Blue VX - '93 Honda Civic VX
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I never tried the pulstar plugs on my cvcc engine but my other Honda did not like them and it caused the engine to run poorly and a slight drop in mileage, copper core NGK V-power plugs have always worked best for me in Honda's, I've tried iridium tipped, platinum tipped and have a drawer full of plugs that saw 2-3 tanks of gas.
Stock exhaust, if it's over sized it will make your mileage drop, even more so with this engine, it's all in the math of pulsating flow.
If you can do a compression test with a warm engine and check your valves with a cool engine (50-90F) I've only seen a few that were in poor shape, but when they do have compression issues it will hurt things bad.
Tires! to wide is common and is not good, I think stock tire size is 155/80R13 and pump them up.
Is your engine warming up fully? if not then the carb adjusts to run richer.
Is your warm air intake intact and working? if not it will dump more fuel in to keep the engine from over heating and burning it's self up.
If one of the vacuum hoses is missing or cracked and leaking it will also cause the engine to run poorly and often burn more fuel.
You might also try running premium gas in it for the next few tanks as the cvcc engine doesn't always agree with the fillers, like alcohol that are in cheaper gas.
If you need any tune up specs let me know, I have a shop manual that covers the 1981 civic sitting on my book shelf.
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