Help with different Keihin Jets


12 replies to this topic
  • MtnMaster

Posted April 09, 2013 - 10:40 AM

#1

I bought a '09 yz450f, that had a JD kit in it. It was jetted for a different altitude, so I need to lean it out a bit. The Jet on the left is a 170 from the JD kit, and the 2 others are a 168 and a 165 from the local dealer. Notice the "collar" inside is quite a bit deeper on the jets from the dealer than the JD one. Also, the JD one has a little sort of half star design and the others say "AB" on them. Can anyone help me out with the difference between the two? And, will going from a 170 "shallow collar" to a 165 with the deeper one have the same effect as two that are the same?
Any help would be greatly appreciated!

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  • rwebb35

Posted April 09, 2013 - 11:44 AM

#2

Always jet your bike with jets made by the same company. As you explained in your post when you compare a true Keihin jet made by Keihin to after market jet the collar on the inside is at a different depth. Will it work? Yes! Are they the same? In my opinion, NO! I suggest taking the guess work out of it and always jet with Keihin jets, which is the jet you describe as having a half star on it! That half star is actually a K, for Keihin. I don't know what altitude your jetting for but sea level main jet for that 09 is a 160 or 162! Can't remember for sure. I live and ride at 9000 ft and ran a 152 in the colder months and a 150 in the summer when I rode that bike. Great bike! Good luck.

  • MtnMaster

Posted April 09, 2013 - 11:48 AM

#3

Jetting for 3,000 to 5,000 ish With a Dr.D pipe I figured 165 was going to be close. The original owner had a 170 in it.
Well, this kind of sucks, nearest dealer is almost 3 hrs away. I bought those when I was driving through expecting to get close enough to what I needed, that I would be ok. Are you suggesting I shouldn't use them?

  • rwebb35

Posted April 09, 2013 - 12:01 PM

#4

My experience with these motors is yes it will work and work pretty well with the 165 @ roughly 4000ft. However, as I explained your owners manual suggests a 160 or 162 for sea level. If you want the motor to work at it's optimal power and efficiency I would suggest a 155 or 158 for 3-5000ft!

  • TahitianRed

Posted April 09, 2013 - 12:07 PM

#5

Jetting for 3,000 to 5,000 ish With a Dr.D pipe I figured 165 was going to be close. The original owner had a 170 in it.
Well, this kind of sucks, nearest dealer is almost 3 hrs away. I bought those when I was driving through expecting to get close enough to what I needed, that I would be ok. Are you suggesting I shouldn't use them?


Have you thought of ordering online? They will ship to you and if they are out of state you might avoid sales tax.

  • MtnMaster

Posted April 09, 2013 - 12:19 PM

#6

My experience with these motors is yes it will work and work pretty well with the 165 @ roughly 4000ft. However, as I explained your owners manual suggests a 160 or 162 for sea level. If you want the motor to work at it's optimal power and efficiency I would suggest a 155 or 158 for 3-5000ft!


It recommends a 160 for sea level with a stock pipe. But, 165 with an aftermarket exhaust. I was going with a 165 just to be a tad on the safe side. I'm used to 2 strokes where jetting is very crucial, one way makes no power and the other makes a boom lol
How much of a difference will a 165 vs 162 make at 3 or 4,000 ft? Is it that noticeable on a 4 stroke? Also, the JD kit says 165 for 3,000 to 6,000ft

Anyway, The original topic was asking about the aftermarket jets... Is that 165 similar to an actual keihin 165? If not, anyone know if it will run a little richer or leaner? Best thing I can do is ride it, but there is a foot of snow in the valley bottom, still in full blown sledding season.

Edited by MtnMaster, April 09, 2013 - 12:21 PM.


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  • rwebb35

Posted April 09, 2013 - 12:47 PM

#7

Yes, the actual diameter of the hole on the aftermarket jet is probably the exact same as the Keihin jet, or at least it is suppose to be. Most people will tell you the collar on the inside being at different depths makes no difference. To me it does! In the long run try to stick with the same company jets so you can eliminate any problems. A 165 compared to a 162 will be very close and only a few would be able to tell a difference. However putting a aftermarket exhaust on does not make that big of a difference IMO. I suggest over time try all the different jet sizes we have talked about. I bet when you throw a 158 in it you will be amazed at the power increase.

  • MtnMaster

Posted April 09, 2013 - 02:20 PM

#8

I'm not scared to go a little lean if there's power to be gained! Once riding season hits, and I get a chance to do some testing, I will definitely try out a few smaller sizes.... What is the sacrifice or dangers of running lean on a 4 stroke? I've got some very modified 2 strokes, but always left my 4's fairly stock, other than a pipe and a few other small mods. Mostly spend my time in the chassis and suspension department.
I know running lean in a 2st can be detrimental, but are 4st as finicky to lean out?

  • rwebb35

Posted April 09, 2013 - 02:47 PM

#9

In my opinion the jet sizes I recomended for your elevation are not to lean! I ran a 155 main in denver(5000ft) at the moto tracks in my 08 and 09 for years. Try it, check your plug color. It will not be to lean! I can promise you if you run a 162 or 165 @ 3-5000ft your plug will be black and wet! Good luck.

  • slothman

Posted April 09, 2013 - 03:08 PM

#10

I'm not scared to go a little lean if there's power to be gained! Once riding season hits, and I get a chance to do some testing, I will definitely try out a few smaller sizes.... What is the sacrifice or dangers of running lean on a 4 stroke? I've got some very modified 2 strokes, but always left my 4's fairly stock, other than a pipe and a few other small mods. Mostly spend my time in the chassis and suspension department.
I know running lean in a 2st can be detrimental, but are 4st as finicky to lean out?


lean is mean. You also roll the dice lol....don't go too lean or you'll be rebuilding the engine real quick ;)

  • MtnMaster

Posted April 09, 2013 - 03:59 PM

#11

In my opinion the jet sizes I recomended for your elevation are not to lean! I ran a 155 main in denver(5000ft) at the moto tracks in my 08 and 09 for years. Try it, check your plug color. It will not be to lean! I can promise you if you run a 162 or 165 @ 3-5000ft your plug will be black and wet! Good luck.


If its going to be that rich, I'm surprised the JD kit recommends a 165 :excuseme:
I'm leery about going any lower than a 160, but that is only based upon what I've read. Have not done any testing myself, but time will tell. On my 4 strokes, I've always just done a JD kit, pipe and then rode the bejeezus out of them. Never really did a whole lot of fine tuning, because they always seemed darn close. I will definitely do some experimenting this year. :ride:

  • grayracer513

Posted April 10, 2013 - 06:54 AM

#12

In my opinion the jet sizes I recomended for your elevation are not to lean! I ran a 155 main in denver(5000ft) at the moto tracks in my 08 and 09 for years. Try it, check your plug color. It will not be to lean! I can promise you if you run a 162 or 165 @ 3-5000ft your plug will be black and wet! Good luck.


First, you can't use plug color to determine anything about your jetting if you run unleaded fuel. Any plug that doesn't foul in 15 minutes will come out white to light tan regardless. It was the lead in gas the produced the color.

Secondly, I run either a 165 or a 168 (summer or winter) in my '06 with a 45 pilot everywhere from 100' below sea level to around 4000 feet and never have a problem with it. Given that, a 160/42 should be at least close. OTOH, 155 doesn't seem completely unrealistic, either.

I don't care for most of the jet kits because the jets don't perform the same as factory jets. This makes it difficult to compare or predict the results you get with a kit jet to that of a factory jet. Say you have a OEM 165, is a JD 168 2% richer? Maybe, but maybe not. In answer to the original question, I don't use them, and so I don't know exactly how a JD jet compares to OEM, but I do expect them to be different.

Four strokes don't turn into cutting torches like pingers do just because they get a little bit lean, though, either. Under normal circumstances, the bike will start to run unacceptably badly before it gets lean enough to hurt itself. Really long full throttle runs like you'd get on a dry lake bed, or maybe at a super moto race could be an exception to that statement.

The OEM needle (NFLR) needs changing for lower altitudes, 0 to around 4000, but might be just about right at 3000-5000. If you find the bike runs alright from 1/3 to 3/4 throttle, but stumbles a bit coming off idle, try an NFLQ (5TA-14916-L1 ).

  • rwebb35

Posted April 10, 2013 - 08:52 AM

#13

Thanks for the reply Gray. I'm always willing to be educated on the facts. I must say that I have always ran unleaded fuels in sleds, Jet skis, and Moto and have had different color plug readings depending on my jetting. Not saying you are wrong, just telling my real life experiences.





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