I use NGK B6ES with 0.5mm gap with a standard ignition TY250 engine and B6ES with 1.0mm gap with an aftermarket electronic ignition TY250 engine. On both engines the spark plug gets looked at about once per year. They usually start to get rounded edges after about 5 years.
I've been setting the plug gaps on my trials bikes with points ignition at 0.5mm for about 45 years now and have no recollection of where the 0.5 mm first came from.
A B7ES is a conservative plug for a TY250 twinshock and was recommended by Yamaha because they wanted to minimise the risk of customers melting a hole in the piston crown when they went flying along the road on a TY250 (like commonly happened in the 1970s)
Thanks for this info, Feetup. It was informative.
I also benefited from your detailed responses in 2018 to questions about timing the TY250A.
I just did a top end rebuild on my '74 TY250 and it is running great.
Wanting to make sure all of my settings are correct, I checked my original Yamaha 1974 TY250 service manual (Copyright 1974) for the spark plug gap for the NGK B-7ES.
In the specs section, page 4, it says 0.4 - 0.5mm
But on page 29 it provides 0.5 - 0.6mm as the plug setting.
Trail & TrialsUK sells the B-7ES plug with the notation 0.3 - 0.4 mm plug gap for a points ignition, which I have.
A google search did not provide me with any other sources.
From what I see in your photo the drive fits into the end of the crankshaft unlike my C model which means no extra parts inside the clutch cover, get the blanking plate kit from B&J Racing or TY Trials & block the other end of the oil line which should be into the side of the intake port on the A model - a short 6mm bolt & fibre washer will do that
Run a good oil at 40-50:1 & you should be fine with no other changes needed.
I am in the process of going to pre-mix with it, and therefore removing the autolube pump.
I pulled the pump today, and the pump drive shaft came out with it (see attached picture).
So, it seems that all I need to do now is attach a block-off plate (I've studied this procedure, and I will be fabricating one) on the case, am I correct?
Or do I necessarily need to pull off the engine side case and remove other bits, such as a gear, which was suggested in a previous posting. Not sure what gear that would be, although that member (Tony 76) had a '76 TY250, which appears to be configured differently.
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TY250 1974 Spark Plug Gap ?
in Twinshock
Posted
Thanks for this info, Feetup. It was informative.
I also benefited from your detailed responses in 2018 to questions about timing the TY250A.