Whilst looking for a new clutch cover for my TY175 I came across this on ebay.

Looks like a TY engine but it has two spark plugs.

Is this a common engine?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280614254910&ssPageName=STRK:MEWAX:IT

I suspect the second plug is filling the hole that a decompresor was fitted in

Based on my TY175 and pictures of TY125's I've seen the spark plug is normally central and vertical. Never seen a decompressor on a TY before, but I am a novice on TY's?

I had a 1973 twinshock DT 175 (in '76) and that had two spark plugs fitted when i bought it.

I left well alone, and just used it a a spare plug.

A fresh plug seemed to be necessary quite often in those days!

Back in the days we used to just mix 30 weight motor oil with gasoline at 20:1.....sometimes a spare plug was a good idea and a lot of bikes had an extra spark plug hole. Some people would fit a compression release to these holes and use the compression release when descending muddy hills as the rear tire would keep turning and not lock up as it would if you used the brake too aggressively.

If you put a second plug in.....you must put one that is the correct heat range in the extra hole. One mistake people would make was to take out their compression release if it was acting up and just borrow a spare spark plug from someone to fill up the hole. Although the plug is not connected to the coil wire - it still is exposed to the combustion chamber and if the heat range is too hot it can cause the engine to detonate....or if the plug is a really hot one the electrode can melt and during the process it sometimes melts a hole in the piston.