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Cylinder works vs Athena BBK for KFX 400, Which is better and what jet kit?

701 Views 13 Replies 3 Participants Last post by  JOE G
Hi, I am looking for a Big Bore for my sons KFX 400, He has Stage 2 Hot Cams and Dyna tek with Full exhaust, I know there info out there when searching but everything I find is 10 plus years old, Is there any updates? Which kit is better and why? What jetting should I start with? Get a Jet kit ( If so which ) or buy individual jets. Thanks.
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I have the Athena 434 kit with pretty much the same setup as you but I have a fcr carb. I love mine and it really gave it a boost.
As far as Jetting goes, it's cheaper to buy individual jets, but a kit like Dynajet gives you an adjustable needle as well, that works great in these quads.
Do you guys think the Jetting will change with BBK? I have heard it does not. I ordered the Athena kit since the CW is back ordered all over.
I changed mine but I can’t remember to what… but I also have the fcr carb so I takes a lot more fuel
Do you guys think the Jetting will change with BBK?
You should go one or two jets sizes larger on the main, and might want to richen the the fuel screw a bit, IMO.
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Which base gasket should I use? DRZ E Gasket with this kit? It comes with Copper washers for the head bolts should I re use the factory stainless steel ones?
You can use either base gasket. Thin one will give you more power/compression, but you will need to stick to high test fuel. Not sure on the copper washers, I have only re-used my stock ones on the kits I have had.
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Athena kit going in, Using single layer base gasket and going to use the oem steel head bolt washers instead of the copper ones in the kit. I will do a search for base line jetting instructions, for needles and seats and what not.

What Pilot should i use, I believe it is factory at the moment.
You will probably be ok just turning out the fuel screw with the stock pilot, if it is clean. 3 turns out is about max. You can also go up one size and adjust to your liking.
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As of right now, I put the Dyno jet stage 2 recommendations in the carb. I believe it is 160 Main, Stock pilot 3 turns out and DJ needle on 3rd clip. I Have to replace 1 way as the factory ( 1 year old ) crapped out and once it started it went fast. I have the L&L Extreme one to put in. The Carb had a 150 Minuki Jet in it.
Is that dyno jets recommendation for 400? I would go one more for a 434. 150 Mikuni is the same as a 160 DJ, btw..
Yes it is there suggestion for the mods I have besides the Big bore, Most people say I probaly don't need to jet up just because of the BBK. But I honestly do not know. Quad seems to run good.
bout 5 Hrs of ride time on it and it is running good, I broke it in on Honda Dino oil and will be switching to Amsoil shortly.
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