TY250 1974 Spark Plug Gap ?

[YamaDude]

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.

What say you, and what's the source of your info?

Thanks

Edited December 19, 2019 by YamaDude
addition

[guy53]

I run mine at +- .4

Guy

[feetupfun]

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)

[YamaDude]

3 hours ago, feetupfun said:

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.

[USNA22]

 Can I use a BP7ES in place of the B7ES in my 76 TY250? If not, why? I tried it for a short time and it runs well.

 

[lemur]

5 hours ago, USNA22 said:

 Can I use a BP7ES in place of the B7ES in my 76 TY250? If not, why? I tried it for a short time and it runs well.

 

The P means projected.  Does the projected electrode extend further into the combustion chamber and closer to the piston than the correct plug?  If yes then you risk burning a hole in the piston crown by using it.

[feetupfun]

If the reason you asked this is because it is hard to find B7ES plugs for sale, there are other brand plugs that can be used in place of the NGK B7ES.

If you only ever use your TY250 for trials type riding you could probably get away with a BP7ES but if your riding involves sustained riding under load then you are at increased risk of heating up the piston crown compared with a B7ES.