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Old 03-02-2013, 06:54 AM
Russ McClay's Avatar
Russ McClay Russ McClay is offline
Motorized Bicycle Senior Member
Join Date: Jan 2013
Location: Taipei
Posts: 85
Default Replaced the Factory Plug on a 66cc China Girl Motor -Wow!

Yes. It is almost a mantra here to change the factory plug for a better one.
I decided on an NGK BP7HS - 5111 for a variety of reasons. Unfortunately
that plug is difficult (impossible?) to find here in Taiwan. So I bought one from
MFG Supply in the States. It arrived yesterday.

I already have over 350 miles on the bike with the factory plug and it has
worked well. Idling no problem. Plenty of power. But I wanted to follow the
advice of changing it.

Eagerly I installed the new plug. I don't have a feeler gauge, so I didn't
bother gapping it. Visually the gap was the same as the factory plug, which I
also didn't bother gapping. According to NGK, the factory gap is: .027"
(0.7mm). And since the threaded end is shipped with a cardboard cylinder
protector around the threaded's highly likely that's what the gap is.

Fired it up...first thing is the idle was too high! I had to back out the carburetor
idler screw a full turn out right away. This meant the plug was igniting
fuel more efficiently (which of course translates to better fuel economy, more
miles/kilometers per gallon/liter).

It was raining so I didn't take it out for a run.

But today I took it out...and whoa...the difference between the performance
is remarkable! I ride the same set of steep mountain roads with their
switchbacks almost daily. So based on my digital speedometer I know very
well what my average speed is on the steeper sections. These are sections
where I usually have to add a little pedal power (at around 13 mph) to keep
the momentum a 2-stroke engine needs.

Well after installing the 2 dollar NGK plug...the machine is powering at least 2
mph faster in all gets up to speed faster. The combustion sounds
better. More robust. Better performance. Better gas mileage. Overall a
significant improvement just from changing the plug.

And here's the sweet understated benefit of this NGK plug: the factory plug
has two thin, hard steel washers which have a gap at the ends. The only leak
(very minor) I've had on my engine was from the spark plug. The NGK plug only
has one washer. It is thick and tapered and is "soft". When you tighten in
the plug that washer "melds" with the head. Perfect seal! if you're a newbie like me...take heed to the old-timers here who
say replacing the factory plug with a better plug is one of the first things you
need to do!

Motor on!
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