Round Mikuni Main Jet conversion

[oldyzman]

My KX250A4 has a 170 Round main jet fitted, i believe a 165 is standard,
Can i use hex main jets for this carb, there a conversion chart available but my jet needle 283 is not listed. so i am not sure..

http://www.ozebook.com/compendium/t500_files/mikuni.pdf

Brett

[John Orchard]

The threads are slightly different but you can still use the hex jets but why don't you just get some round-head?  I changed the the stock 172 in my KX250A5 to a 168.

[oldyzman]

Thankscfor the info john,
My bike has
170 main        165 std
50 pilot                50 std
Cutaway 2.5          3.0 std
Jetneedle 283   R2     Q8 std
Needle 6f28                    24std
This is all seemingly a bit richer than std
I have not ridden it much as i  have been con centrating adding size to the house incl 100sqm garage.
How does this compare to yours i know yours is 1979
I will order a couple of round ones

[John Orchard]

My A5 is ...

168 MJ,  stock 172
40 PJ,  stock 50
2.5 slide,  stock 2.5
6F21 needle,  stock 6F21
#3 clip, stock #3 (but thinking of going to #2)
R4 NJ, stock R4 (but will try to find a R2 if needle clip change won't clean it up)
1.0 turns mixture screw, stock 1.0 turns.

With 30:1 Castrol R30

[oldyzman]

Yep,
First i will give it a run at hartley 300 meters above sealevel in two weeks, Will run at nepean dirt track soon after that. If it ru s abit rich at hartley then it may be ok for nepean.
Thanks again

[JohnnyO]

My KX250A4 has a 170 Round main jet fitted, i believe a 165 is standard,
Can i use hex main jets for this carb, there a conversion chart available but my jet needle 283 is not listed. so i am not sure..

http://www.ozebook.com/compendium/t500_files/mikuni.pdf

Brett

Are you aware that the hex and round jets are caliberated differently so it's not an easy swap.

[JohnnyO]

My A5 is ...

168 MJ,  stock 172
40 PJ,  stock 50
2.5 slide,  stock 2.5
6F21 needle,  stock 6F21
#3 clip, stock #3 (but thinking of going to #2)
R4 NJ, stock R4 (but will try to find a R2 if needle clip change won't clean it up)
1.0 turns mixture screw, stock 1.0 turns.

With 30:1 Castrol R30

How does yours go with a 168 main jet? I tried a 168 in mine and it was flat on top and i ended up going richer to a 178 and it pulls so much stronger now..
I run a 45 pilot and a 6FL28 needle on the 4th clip and mine has a R2 needle jet and 2.5 slide. Quite a bit different.

[John Orchard]

Yeh I think your settings sound good, with a 172 MJ I had a fluffy top-end, I've gone to a 40 PJ to clean-up the low-end but a 45 PJ would be better combined with an R2 NJ, I'm having trouble finding the correct type needle jets, the 38mm carb runs a longer needle jet than most other Mikuni carbs; I'm not sure of the 'type' code, do you guys know?

[JohnnyO]

My needle jet is a 283 series, you may be able to get 1 from TD Hatrick in Townsville otherwise genuine Kawasaki but parts for them are few and far between.

[oldyzman]

Yep thanks for that johnny re conversion, i was mainly interesfed in conversion if i was to renew the carb. I have usually found that i have to go leaner than std on jetting as mine was allready richer i was considering getting  std jet and leaner. But from what you say johnny maybe its on the right track . The firstbtime inrode the bike was 6 mths ago and it was flooding, i finally worked our that the little cap that goes over the main jet was the plastic type and was rubbing on the lever which goes from the plastic floats to the seat and needle. So i should test it in a week or so.
BRETT

[Peter Villacaro]

I know this is an old thread but it caught my attention for a couple of reasons.

I gather most overlook the air jet/needle jet correction factor on most carburetors as well as the fuel used, both are a huge consideration when quoting jetting for any application.
The other is the needle jets themselves, be careful comparing OEM spec jets to Mikuni general consumer parts, many times the OEM spec has marking like the standard parts but is in fact quite different, shroud length for example changes everything.