1974 250 Supersport: chain size?

[sandman]

Quick question for 250 egg motor owners (Supersport, Sprite, Barracuda, more, late 60's-early 70's):

What's the correct original chain size? The best info I've found is in my original factory shop manual tech page: 1/2" X 5/16". No numerical size is given. A little search shows these dimensions as being a 428 chain- is this correct?

I appreciate any helpful responses, and will no doubt have a question or two in the future. I'm determined to get this once neglected '74 250 Supersport back to the condition it deserves to be!
Alex

[sandman]

Forgot one more important question to ask, as long as I potentially have other egg motor owner's attention. Hope you can be so kind...

What is the modern equivalent and correct standard spark plug to use these days?

[mckvny]

425 and 109 links should do it on the chain.

Mac

[mckvny]

Forgot one more important question to ask, as long as I potentially have other egg motor owner's attention. Hope you can be so kind...

What is the modern equivalent and correct standard spark plug to use these days?

NGK B6ES or BP6ES or BPR6ES


Mac

[FBM]

428 chain. I've got an extended swingarm, so the link count does you no good. I always order longer and remove links as need be.

for chain data, see: http://www.sprocketsunlimited.com/Ch...fications.html

heres a quick mock up, before I got it running. she's a runner now, just need to finish off the details.

[sandman]

FBM-
Your Motobi looks lovely, I'm looking forward to seeing updated pictures here of it as it is now.

Thank you for taking time to reply and verify the 428 chain size, I think that this is correct.

Mac- where did you find 425 chain size specified for 250 egg motor Supersports? That's an oddball/unusual one. Unfortunately I do not have my old chain to compare or check sizing, which is why I'm asking here for advice as my restoration proceeds.

[sandman]

NGK B6ES or BP6ES or BPR6ES


Mac

Doing a little more checking- the odd thing is my spare motor came with a
NGK B8ES in it...wonder which is correct?

[sandman]

Also, must consider that my other motor had a Champion RN3C in it (not a fan of theirs).