Vintage Dirt Bike Q & A

I have a 78 cr250 that I'm racing, it has a Keihin carburetor.

I would like to purchase 2 throttle slide needles for it, one that is one size richer, and one that is 2 sizes richer.

The one in it is marked "AJM".

Can anyone tell me what needles I will need? and where to possibly by them?

Thanks for any advise you can provide.

That AJM needle is really lean. Here's a chart:

http://www.jetsrus.com/a_jets_by_carburetor_type/needle_keihin_N427-48.html

The needles listed at the bottom of the page are the ones that are still available.

Here's some additional relative info on some of the OEM Honda 66mm needles - only the diameters are precise, sorry:

31A: D .106"/ 2.705mm (leanest) 16201-430-000 '79-'80 CR125/'78-'80 CR250/'81-83 CR480 opt.
31C: D .106"/ 2.705mm (much leaner) 16203-430-000 " "
ECA: D .1025" / 2.604mm, medium L1, medium taper (leaner D1, otherwise lean to medium)
271006: D .0983", short L1, shallow (dual?) taper (medium) MR250 34mm
271302: D .0988", long L1, shallow taper (leaner) '76 CR250M 36mm
271309: D .0972", long L1, heavy taper (richest) '73 optional 36mm

L1 can have a big effect on throttle response, especially if the straight diameter, pilot jet, and throttle slide cutaway are close to ideal.

Jets 'R Us and Sudco should have the needles, and I couldn't really suggest anything without knowing the complete carb setup.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thank you for the response and information.

I also found this link which has been very helpful.

http://www.duncanracing.com/TechCenter/ ... etting.pdf