99 WR400 Dyno Tuned -- The results are in...


25 replies to this topic
  • Shred Jesse

Posted May 08, 2011 - 02:32 PM

#1

Posted Image

So I wanted to dial my WR400 in so it would be spot on for trail riding. After installing a full FMF powercore exhaust I completely lost my over rev, and the bike just felt extremely down on power.

I purchased a JD jet kit, and went about redoing my jets. I also cleaned out my pilot jet very thoroughly, and installed the jets recommended in the kit. After riding it a bit, and seeing some advice on here, I didn't wind up using the main jet included in the kit (170) and tried a jet size larger than the kit, a 172.

Here's video of my two dyno runs:

http://www.youtube.com/watch?v=5Bw9RC3A82g

Here's the dyno sheet:

Posted Image


First run (blue lines):

Big lean spots, and the bike was a bit anemic in a few spots, and at risk for burning up the motor it was so lean in said spots. This definitely called for a larger main jet, and given my main jet was already larger than anything provided in the JD jet kit... I can't recommend buying it. Jet's are cheap ($4-6 each dependign) and $75 for just a needle isn't worth it.

I reinstalled a 178 main jet, and then had my second run.

Second run (red lines):

Peak power did not improve from the first run, however all the excessively lean spots disappeared, the engine really settled in. The engine was smoother, it's response was stronger, and MAN did it deliver! I took it out for a spin before the dyno testing, and sure enough the bike stood right up with some serious gusto! WOOHOO!



So yeah, a 178 main jet is apparently the way to go. I'm still a bit lean, but given the temperature today (55 ish degrees) this leaves room for warmer days, where there will be less air, reducing my air to fuel ratio, and bringing me closer to the target mixture represented by that red line there.



(Popping on deceleration still to be resolved. I'm somewhat convinced it's an air leak now at the intersection of the header and the engine. More on that to come though when I try and suggest solution to the problem)

Edited by Jnicola, May 08, 2011 - 02:55 PM.


  • Shred Jesse

Posted May 08, 2011 - 02:55 PM

#2

Oh, and the forum restricted the size of that picture.Here's a link to the full size image!

  • CanadianWR450

Posted May 08, 2011 - 04:04 PM

#3

A 178 main just sounds whacked, but I simply do not have a argument...kinda hard to argue with a dyno....lol
There is a dyno shop about a hour from here, and now you have me REALLY tempted to go take my bike done there "just because"......

  • Shred Jesse

Posted May 08, 2011 - 06:25 PM

#4

He's done other WR400's, and they go larger in main jet size than this even!

Another forum member posted in my fire spitting post about how they dyno tuned theres as well and they wound up WAY above a 170.

  • shelbyguy

Posted May 08, 2011 - 09:51 PM

#5

A 178 main just sounds whacked, but I simply do not have a argument...kinda hard to argue with a dyno....lol
There is a dyno shop about a hour from here, and now you have me REALLY tempted to go take my bike done there "just because"......


as he stated...


i ended up on my 444 project 47hp- 39ft lbs at the tire(and this was with a head gasket that was leaking when the bike was under a load)

the bike had a pretty flat power band.
had a 168 in it to start i could tell it was running awfully lean all over the place.
jetted it to a 170 and it got a little better.
after about 8 pulls on the dyno and drilling my 170 out to a 184 the bike has perfect, flat air fuel ratio.


and dont for what its worth nels is the man he has done all 6 of my bikes, that i have now...so nobody can say different dynos read different....the 2 bikes were done on the same machine.


nice numbers...like how flat the power is. should be fun.

  • Shred Jesse

Posted May 08, 2011 - 10:23 PM

#6

Yeah he mentioned running your bike and compared mine to yours... although you've got 44cc's on me, but are losing some compression.

If I can fix this exhaust leak I'll be happy with the bike. Right now it's engine braking is funky. It hangs a bit and then pops and drops down. Definitely got to fix that!

  • CanadianWR450

Posted May 09, 2011 - 01:40 AM

#7

I wonder if it is a difference between the 400 and the 450?
I'm not doubting the results or numbers, I just can't imagine a main that big in my bike.

  • miweber929

Posted May 09, 2011 - 04:28 AM

#8

Since it's a Dynojet dyno, what are the odds the jets they are using are numbered via DJ's numbers, not Kehin? Thats the only thing I can think as well as those jet numbers are WAY huge for "normal" jets.

But, like was just mentioned, it's a 400, not a 450 and uses a totally different carb than the 450's do. Could it be an anomaly from running it on a dyno and not in the field? A dyno pull is different than normal dirt bike running where you are on and off the throttle and the accelerator pump wouldn't come into play.

I don't know, just thinking out loud!!!

Interesting dyno numbers and chart. Never thought they'd look so flat! Cool!!

Mike

  • shelbyguy

Posted May 09, 2011 - 07:12 AM

#9

I wonder if it is a difference between the 400 and the 450?
I'm not doubting the results or numbers, I just can't imagine a main that big in my bike.


these bikes run notoriously lean.
does your 450 have big bore, compression, cams, exhaust, and a 40mm fcr?

Since it's a Dynojet dyno, what are the odds the jets they are using are numbered via DJ's numbers, not Kehin? Thats the only thing I can think as well as those jet numbers are WAY huge for "normal" jets.

But, like was just mentioned, it's a 400, not a 450 and uses a totally different carb than the 450's do. Could it be an anomaly from running it on a dyno and not in the field? A dyno pull is different than normal dirt bike running where you are on and off the throttle and the accelerator pump wouldn't come into play.

I don't know, just thinking out loud!!!

Interesting dyno numbers and chart. Never thought they'd look so flat! Cool!!

Mike


the jets are keihn, mine actually was a keihn jet that was drilled out via a drill gauge and carb guru david alexander in between his races...that bore he fit after all said and done was the same as a 184, with the entrance of the jet drilled and reamed to a 188 to provide a smooth transition of fuel flow...

  • CanadianWR450

Posted May 09, 2011 - 08:17 AM

#10

[quote name='shelbyguy']these bikes run notoriously lean.
does your 450 have big bore, compression, cams, exhaust, and a 40mm fcr?

It has an Athena 480 big bore, stage 1 hotcams, FMF megabomb/Powercore 4combo, and the stock FCR.

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  • Shred Jesse

Posted May 09, 2011 - 09:29 AM

#11

Big bore kits move more air, so they actually go down in Jet size to get a better air to fuel mixture.


It was a dynojet dyno setup, however it was just used for parts. All jetting changes were merely suggestions from the operator, and he is in no way associated with dynojet, so his recommendations are not based on them.

  • miweber929

Posted May 09, 2011 - 10:33 AM

#12

Big bore kits move more air, so they actually go down in Jet size to get a better air to fuel mixture.


Not 100% sure I understand this statement as it makes no sense to me....how can a larger piston (hence a larger motor size) that burns an air/fuel mixture move more air and not require more fuel to keep that ratio correct?

Bigger motors need bigger jets as they need more fuel to run. Bigger CARB would require smaller jets to maintain the correct ratio.

By that above statement a 50cc lawnmower motor would need a HUGE jet then, right? If bigger motors require less fuel?

Guess I'm confused.......

  • shelbyguy

Posted May 09, 2011 - 11:59 AM

#13

[quote name='CanadianWR450'][quote name='shelbyguy']these bikes run notoriously lean.
does your 450 have big bore, compression, cams, exhaust, and a 40mm fcr?

It has an Athena 480 big bore, stage 1 hotcams, FMF megabomb/Powercore 4combo, and the stock FCR.[/QUOTE]

that should make some "real mans power" as a coworker called it.

until you actually have a sniffer up the pipe you cant see air/fuel mixture
but i can tell you that bikes will make more power when you lean them out,
it may be a huge jet in most peoples opinions...but im very content with the fact that my a/f is spot on @12.5-13.2

  • CanadianWR450

Posted May 09, 2011 - 03:34 PM

#14

[quote name='shelbyguy'][quote name='CanadianWR450']

that should make some "real mans power" as a coworker called it.

until you actually have a sniffer up the pipe you cant see air/fuel mixture
but i can tell you that bikes will make more power when you lean them out,
it may be a huge jet in most peoples opinions...but im very content with the fact that my a/f is spot on @12.5-13.2[/QUOTE]

It does work good :thumbsup:.

Again though, I'm not disagreeing with you guys, or questioning your dyno results, it's hard to argue against dyno charts. I'm simply really surprised by the setup, and would not have expected it. I'm still kinda wondering if it is something that the 400's favor/like more then the 450's for some reason.

I have never had my bike on a dyno, and simply go with seat of the pants tuning, and even then, I go for a compromise setup to get me through all my riding seasons (spring/summer/fall). But as I originally mentioned, I may just have to go for drive to a dyno shop about a hour from here after seeing your results, and this thread..

  • Leardriver

Posted May 09, 2011 - 04:52 PM

#15

A bigger bore and higher compression can often pull more fuel through the same jet.

  • Shred Jesse

Posted May 09, 2011 - 09:54 PM

#16

A bigger bore and higher compression can often pull more fuel through the same jet.


This.

Air moving through the carb causes vaccum in the float bowl, and fuel is sucked up into the engine. For any given vaccum, a given jet size will allow a specific amount fuel through. If you increase vaccum (engine size) for the same jet size, more fuel is being pulled through. To my understanding, the gain in vaccum tends to be less than the gain in fuel, as they are not directly proportional. Thus the mixture actually becomes richer for the same carb settings.

  • miweber929

Posted May 10, 2011 - 04:27 AM

#17

A bigger bore and higher compression can often pull more fuel through the same jet.


This.

Air moving through the carb causes vaccum in the float bowl, and fuel is sucked up into the engine. For any given vaccum, a given jet size will allow a specific amount fuel through. If you increase vaccum (engine size) for the same jet size, more fuel is being pulled through. To my understanding, the gain in vaccum tends to be less than the gain in fuel, as they are not directly proportional. Thus the mixture actually becomes richer for the same carb settings.


How, it's a fixed orafice? If you had vastly different valve cycle time maybe but intake is directly based on the time the valve is open, the needle position, the amount of fuel in the float bowl and jet size. Suction (as your are both describing) would only be changed if any of those variables change.

Not arguing, I just think these are flawed statements. The reason you have a jet is to meter the amount of fuel your engine can ultimately "grab" and use. A larger motor with a higher compression needs more fuel to complete it's 4 stroke cycle, understandably we are talking relatively minor differences (say 20-30cc's) between a big bore and standard but I am not seeing the logic here in tge above statements.

Again I say, huge V10 motors with much more pull would need very little fuel compared to a 50cc weed eater by your logic.

William? What am I missing here? Not knocking the findings, just not 100% sure where this logic is. I still say (not knowing anything much about them) it's the differences in the actual size and/or operation of the different carbs between the 400 and 450 then its motor size.

Mike

  • Shred Jesse

Posted May 10, 2011 - 10:56 AM

#18

How, it's a fixed orafice? If you had vastly different valve cycle time maybe but intake is directly based on the time the valve is open, the needle position, the amount of fuel in the float bowl and jet size. Suction (as your are both describing) would only be changed if any of those variables change.


The engine displacement increased, so it is pulling more air. More air results in more vaccum accross the jet, which in turn pulls more fuel. While being a fixed orifice, it's potential isn't fixed. It's relative to the vaccum above it. Hence a 178 main jet in my bike will not deliver the same amount of fuel as a 178 on a wr450. It's all relative.

The reason you have a jet is to meter the amount of fuel your engine can ultimately "grab" and use.


Again I say, huge V10 motors with much more pull would need very little fuel compared to a 50cc weed eater by your logic.


This is where you are making the mistake. You are thinking that any given jet size will only move a particular amount of fuel regardless of vaccum above it. This is incorrect. Any given jet size will move a different amount of fuel based on the vacuum across it.

If a jet did provide a fixed and metered amount you would be correct, however that is not the case. There are other factors as well, such as throttle body diameter, ram air induction (on some bikes, but that requires vacuum balancing between the airbox and the float bowl).


The factors are dynamic, and jets do not deliver a fixed amount of fuel.


It's this misunderstanding that causes people to put a big bore kit on the DR350 I bought, jet it wrong, then sell it to me for almost nothing because they don't know how to jet their bikes right :thumbsup:

  • William1

Posted May 10, 2011 - 01:08 PM

#19

How big is the opening in the airbox? For a given engine, the power produced does not increase if you make the hole larger than a certain size. For a 400, this is about nine square inches. If you make the hole larger, you will not get an increase in power. However, the drop in vacuum singal from the easier breathing opening causes a weaker signal at the venturi and you need a larger main to compensate for it.

You would of seen a lot more power had you had a street tire on it at 35psi. The knobby lost a lot, I bet over 5 Hp, possibly more.

Did you do any runs to part throttle to check the needle?

  • shelbyguy

Posted May 10, 2011 - 02:45 PM

#20

How big is the opening in the airbox? For a given engine, the power produced does not increase if you make the hole larger than a certain size. For a 400, this is about nine square inches. If you make the hole larger, you will not get an increase in power. However, the drop in vacuum singal from the easier breathing opening causes a weaker signal at the venturi and you need a larger main to compensate for it.

You would of seen a lot more power had you had a street tire on it at 35psi. The knobby lost a lot, I bet over 5 Hp, possibly more.

Did you do any runs to part throttle to check the needle?


not to derail.

but i cannot imagine he would have seen that much more power with a street tire vs knobby.

that bike is pretty stout 41hp and 29ft lbs isnt anything to shake a stick at considering its stock bore and stroke..

what did the bikes make from the factory- 37-39hp if that.




 
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