Dynojet Vs. Keihin Sizing

[NCexRider]

Ok, someone set me straight. I have always understood that Dynojet jets run leaner than stock. Example, A DJ 165 would let less gas through than a stock (keihin) 165. Or like if you need a 155 stock main you would use like a 160 DJ. Stock is bigger. But i've also heard it the other way around. Which is it?:confused:

[JOEX]

I belive it's the opposite. Someone posted this here awhile back, I can't vouche for it's accuracy......

hole-----Kehein #--- DynoJet #---Mikuni #
0,0570----147,5------ 136--------127,5
0,0580----150-------- 138--------129,4
0,0590----152,5------ 140------- 131,3
0,0600----155-------- 142--------133,1
0,0610----157,5------ 144------- 135,0
0,0620--- 160-------- 146------- 136,9
0,0630--- 162,5------ 148------- 138,8
0,0640--- 165-------- 150------- 140,6
0,0650--- 167,5------ 152------- 142,5
0,0660----170-------- 154------- 144,4
0,0670--- 172,5------ 156------- 146,3
0,0680--- 175-------- 158------- 148,1
0,0690--- 177,5------ 160------- 150,0
0,0700--- 180-------- 162------- 151,9

[Buffalo400]

I try it and keihein is very similar to dynojet (I check the size of the hole with a needle).... Dynojet isn't realy as bigger as what it said upper...... maybe a little bigger...

[04'400ex'er]

Heres the difference. Traditional Kehin jets come in sizes such as 148 152 155 157 160 162 165 and so on. with the Kehin style jetting you just richen the main jet until you get the bog, and then back off a size. (or something to that similar effect) then you also have the pilot jet to play with in turn for your bottom - mid range power. Also the clip on the needle

Now, that said, here is the DynoJet way. Dont try to compare the numbers on the dynojet mains at all because they in no way are related to the kehin numbers. DynoJet uses a different tapered needle with their kit, which in turn allows you to leave your stock pilot jet in the carb whether you have a slip on or a 460 stroker. All you have to worry about is the main jet size and clip spot on the needle, which is all explained to you in the kit's instructions.

The 400ex kit comes with 134 138 142 146 150 155 160 165 170 mains.

Stage 1: The 132 - 146 mains are for the stage 1 jetting with stock or aftermarket exhaust at sea level to 6000 ft.

Stage 2: The 150 - 170 mains are for the stage 2 jetting. EX. if you have an aftermarket exhaust and no airbox lid, and are at 3000 ft or below, you use the 170 main, the biggest in the kit. This jetting setup will stay untouched if you build a 460 stroker. still use the 170 main. this is due to the taper of the dj needle. thats what im at.

The kit comes with VERY detailed instructions and pictures to go along. Nice Kit to have and saves ALOT of headaches.

BTW I have a complete kit for sale. $35 Shipped

[coryatver]

I researched it a while ago and I found out you can not compare the sizes between the 2. They are totally different. There is no pattern like dyno jet is 3 sizes smaller. YOu just have to do plug runs to test it.

[NCexRider]

Originally posted by 04'400ex'er
Heres the difference. Traditional Kehin jets come in sizes such as 148 152 155 157 160 162 165 and so on. with the Kehin style jetting you just richen the main jet until you get the bog, and then back off a size. (or something to that similar effect) then you also have the pilot jet to play with in turn for your bottom - mid range power. Also the clip on the needle

Now, that said, here is the DynoJet way. Dont try to compare the numbers on the dynojet mains at all because they in no way are related to the kehin numbers. DynoJet uses a different tapered needle with their kit, which in turn allows you to leave your stock pilot jet in the carb whether you have a slip on or a 460 stroker. All you have to worry about is the main jet size and clip spot on the needle, which is all explained to you in the kit's instructions.

The 400ex kit comes with 134 138 142 146 150 155 160 165 170 mains.

Stage 1: The 132 - 146 mains are for the stage 1 jetting with stock or aftermarket exhaust at sea level to 6000 ft.

Stage 2: The 150 - 170 mains are for the stage 2 jetting. EX. if you have an aftermarket exhaust and no airbox lid, and are at 3000 ft or below, you use the 170 main, the biggest in the kit. This jetting setup will stay untouched if you build a 460 stroker. still use the 170 main. this is due to the taper of the dj needle. thats what im at.

The kit comes with VERY detailed instructions and pictures to go along. Nice Kit to have and saves ALOT of headaches.

BTW I have a complete kit for sale. $35 Shipped

Thanks for the info man! Here's the deal, I already have a Dynojet jet kit installed, and I'm running the 165 main. When i installed it I was running no airbox lid & it was great. Well, not running a lid was quickly ruled out due to the trail riding I do, therefore I drilled some (6) of those little Uni filters into my lid and put it back on. Since then I have fouled my plug every 3-5 rides so I'm figuring I'm too rich and want to back it off. I was going to put in the 160 but now I'm thinking of running the DJ 155. Any thoughts on the matter? And thanks for the pilot jet info, I was about to change that too.

[JOEX]

Originally posted by 04'400ex'er
Heres the difference. Traditional Kehin jets come in sizes such as 148 152 155 157 160 162 165 and so on. with the Kehin style jetting you just richen the main jet until you get the bog, and then back off a size. (or something to that similar effect) then you also have the pilot jet to play with in turn for your bottom - mid range power. Also the clip on the needle

Now, that said, here is the DynoJet way. Dont try to compare the numbers on the dynojet mains at all because they in no way are related to the kehin numbers. DynoJet uses a different tapered needle with their kit, which in turn allows you to leave your stock pilot jet in the carb whether you have a slip on or a 460 stroker. All you have to worry about is the main jet size and clip spot on the needle, which is all explained to you in the kit's instructions.

The 400ex kit comes with 134 138 142 146 150 155 160 165 170 mains.

Stage 1: The 132 - 146 mains are for the stage 1 jetting with stock or aftermarket exhaust at sea level to 6000 ft.

Stage 2: The 150 - 170 mains are for the stage 2 jetting. EX. if you have an aftermarket exhaust and no airbox lid, and are at 3000 ft or below, you use the 170 main, the biggest in the kit. This jetting setup will stay untouched if you build a 460 stroker. still use the 170 main. this is due to the taper of the dj needle. thats what im at.

The kit comes with VERY detailed instructions and pictures to go along. Nice Kit to have and saves ALOT of headaches.

BTW I have a complete kit for sale. $35 Shipped
How does the needle taper have an effect on the pilot jet?

[NCexRider]

Originally posted by JOEX
How does the needle taper have an effect on the pilot jet?

Wondering the same thing. Doesn't the pilot control 0-1/4 throttle fuel delivery? How about my previous question on which size main?

[blue150]

What type of jets have RD stamed on them

[400exstud]

Originally posted by 04'400ex'er
Heres the difference. Traditional Kehin jets come in sizes such as 148 152 155 157 160 162 165 and so on. with the Kehin style jetting you just richen the main jet until you get the bog, and then back off a size. (or something to that similar effect) then you also have the pilot jet to play with in turn for your bottom - mid range power. Also the clip on the needle

Now, that said, here is the DynoJet way. Dont try to compare the numbers on the dynojet mains at all because they in no way are related to the kehin numbers. DynoJet uses a different tapered needle with their kit, which in turn allows you to leave your stock pilot jet in the carb whether you have a slip on or a 460 stroker. All you have to worry about is the main jet size and clip spot on the needle, which is all explained to you in the kit's instructions.

The 400ex kit comes with 134 138 142 146 150 155 160 165 170 mains.

Stage 1: The 132 - 146 mains are for the stage 1 jetting with stock or aftermarket exhaust at sea level to 6000 ft.

Stage 2: The 150 - 170 mains are for the stage 2 jetting. EX. if you have an aftermarket exhaust and no airbox lid, and are at 3000 ft or below, you use the 170 main, the biggest in the kit. This jetting setup will stay untouched if you build a 460 stroker. still use the 170 main. this is due to the taper of the dj needle. thats what im at.

The kit comes with VERY detailed instructions and pictures to go along. Nice Kit to have and saves ALOT of headaches.

BTW I have a complete kit for sale. $35 Shipped


Lets go back to basics.

Your saying that a bike with a pipe and filter will use the same jetting as one with a full race motor?

First of all a full race motor uses much more oxygen than a piped motor. This requires more fuel.

Second how can a tapered needle make it unnecessary to change the pilot or main settings. The needle's range is only from about 1/4 - 3/4 throttle.

[NCexRider]

So even with the Dynojet kit I should still bump my pilot up to a 40 or 42? What size Dynojet main are you guys running, and please tell whether you're running an airbox lid or not.

[underpowered]

Originally posted by coryatver
I researched it a while ago and I found out you can not compare the sizes between the 2. They are totally different. There is no pattern like dyno jet is 3 sizes smaller. YOu just have to do plug runs to test it.

there has to be some pattern, they dont just randomly size them. the difference between sizes may differ slightly, but there is a pattern.

[04'400ex'er]

The DynoJet Kit's instructions say no matter what to stay with the stock pilot jet. They basically tell you what to set the air fuel screw at also, within a turn or so. Im not for sure how the taper of the needle affects the pilot, that is what I was told when I bought my kit at SandTrax. Im not sure if your familiar with them but they are a VERY respected engine builder in Tulsa, OK. The 170 main is for basically all majorly modded bikes near sea level. The only possible thing you would have to change with a fully built motor compared to a piped motor is the clip on the needle.

NCex, tell me what your elevation is and what mods you have. id think with just the little lid filters, you would prob be best to stick with the jetting instructions for having the lid on.

[04'400ex'er]

Originally posted by NCexRider
So even with the Dynojet kit I should still bump my pilot up to a 40 or 42? What size Dynojet main are you guys running, and please tell whether you're running an airbox lid or not. Im at 1000ft. above sea level, with a Hotcams Stg. 2 and full HMF and no airbox lid: Running the largest main in the kit, 170, with stock pilot, and clip on 3rd. groove on the needle. af screw at 3.5 turns.

[jason43050]

i got everything stock on my 2005 400 ex. the stock jet was a 148. i put a 150 jet in and spark plug was brown and insulator was white. backfires from time to time. is it lean and need bigger jet or what?

[04'400ex'er]

Originally posted by jason43050
i got everything stock on my 2005 400 ex. the stock jet was a 148. i put a 150 jet in and spark plug was brown and insulator was white. backfires from time to time. is it lean and need bigger jet or what? was it backfireing before you put in a 150? if it backfires on decel then its your pilot jet and af screw

[jason43050]

i put the stock baffle back on its not backfiring anymore. i just want more response from it.

[NCexRider]

Get a pipe and filter.

[04'400ex'er]

Originally posted by jason43050
i put the stock baffle back on its not backfiring anymore. i just want more response from it. When you took the baffle out it leaned the bike out. that was your problem.

[larry171]

if i got a 42 pilot jet and no choke holes in the airbox lid and live in michigan it wants to pop and sputter do i change the jet go up down a on the clip . i have a 400ex stock exaust no other mods help!!! please

[04'400ex'er]

Originally posted by larry171
if i got a 42 pilot jet and no choke holes in the airbox lid and live in michigan it wants to pop and sputter do i change the jet go up down a on the clip . i have a 400ex stock exaust no other mods help!!! please If it is poping and sputtering on decel most likely you are lean on the pilot jet. but you might want to bump up one size on the main along with that 42 pilot. most likely that is the solution.

[larry171]

thanks for the info but it pops when it acceleratesreal bad when it tries to start not to bad after it is warm

[Sleeper]

Originally posted by 400exstud
Lets go back to basics.

Your saying that a bike with a pipe and filter will use the same jetting as one with a full race motor?

First of all a full race motor uses much more oxygen than a piped motor. This requires more fuel.

Second how can a tapered needle make it unnecessary to change the pilot or main settings. The needle's range is only from about 1/4 - 3/4 throttle.

I can't say anything about the needle but, The reason you need to change a jet when you do the pipe and filter (as I understand it) is because you are decreasing the vacume in the carb. by creating a more free flowing system there for less fuel gets sucked out of the jet. If you bump your cc's up to 460 you are sucking more air threw the setup you already had creating more vacume at the same time, so it's totaly possible you could remain with the same jets as a lower bore engine and still have plenty of fuel.

imho

Sleeper