Hi everyone, can someone tell me what size main jet I need in my 76 dt125? Looking in the manual, one section says 100 main and onother says 140. What is correct?

Which model (electric start, 12v?) and which country of origin?

Yes it is a 12 volt electric start. United states

Thanks.

Whilst I wouldn't take it as absolute gospel (after all, Yamaha parts lists are known to contain the odd error  ), parts list on CMSNL shows 100 as standard.

I'd wait for others to confirm (or otherwise!), just to be sure.

What size was fitted in the carb when you got it?

Both of my 74 Dt125a’s, almost the same, came with 140 main jets. 

yamaha-enduros.com/index.php/workshop/wiki/101-1976-dt125c

tech library link for yours

Factory Tech Sheet for the DT125C says main jet is 100.  Earlier models were 140.

Emissions (both noise and exhaust) became much more of a problem in the USA in the mid-70's...  air filter housing may have received "muffling" modifications and often became more restrictive to lower noise levels.  Several Yamaha models had significant main jet size changes in 1976 that went along with air intake changes to meet noise emissions requirements...  RD350 is one of them.

Thank you all for the replys. I wasn't able to read the jet that was in it, but I think I will try a 140 and go from there.