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Strange jetting carb behavior?


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45 replies to this topic
  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted July 27, 2016 - 03:37 AM


This may be because I´m stupid and I don´t know anything, but i came across something strange.

 

I checked the jetting thread last winter and jetted my bike after what i saw was the closest to what others had done who had done the same mods as I.

 

I also followed the carb tuning advice in the sticky.

 

The bike has been running Ok this summer, but a bit rich.

 

I also changed the exhaust from some European GYTR thingymajingy to a full YZ450F exhaust with a modded long original WR450F can.

 

Now i have to go down a size in pilot jet because i can screw the fuel screw all the way in?!

Earlier the fuel screw was about 1,5 turns out.

 

How can a pipe change have this effect?

Especially with a bigger higher flowing pipe?

 

When i reach the bottom of the fuel screw, the bike is nearly dying, so do i really need to re-jet?

I do not want to change the jetting each season, so if i can leave it as is, and adjust the fuel screw this winter, i would be really happy, 

 

but what say the experts?

Is it bad to have the fuel screw in the bottom?

Can i go down a size in pilot jet and still have it run great this winter with only a fuel screw adjustment?

 

I´m going back in the carb anyway this fall to add a easy adjust fuel screw, so changing the jet is no problem, I just don´t want to to it again next summer.

 

In the summer we can reach 95F and in the winter -31F ~

 

Best regards, the newbie


Edited by Agazza, July 27, 2016 - 06:10 AM.


  • Krannie McKranface
36,164 posts
Location: California
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Posted July 27, 2016 - 05:28 AM


Any change in the pipe affects jetting.....but it's more about carb condition and fuel screw tuning.

 

Ignore how much 'die' you get when closing the fuel screw: it's about turns out.

 

You want a pilot that puts the highest idle at 1.5-ish turns out.  That would be a 45p on 99% of the bikes.

 

You must have a hot motor, and start with 1.0 turns out and a low idle, and then turn the fuel screw out for highest idle.

If it's too high, lower it with the idle screw, and re adjust the fuel screw.

 

The hot start, slide plate, slide plate seal, choke plunger, needle jet (emulstion tube) and pilot jet condition all affect this.



  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted July 27, 2016 - 06:49 AM


Any change in the pipe affects jetting.....but it's more about carb condition and fuel screw tuning.

 

Ignore how much 'die' you get when closing the fuel screw: it's about turns out.

 

You want a pilot that puts the highest idle at 1.5-ish turns out.  That would be a 45p on 99% of the bikes.

 

You must have a hot motor, and start with 1.0 turns out and a low idle, and then turn the fuel screw out for highest idle.

If it's too high, lower it with the idle screw, and re adjust the fuel screw.

 

The hot start, slide plate, slide plate seal, choke plunger, needle jet (emulstion tube) and pilot jet condition all affect this.

 

What is my highest Idle?

 

Do i know when i know?

 

thank you, i´m on it right now



  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted July 27, 2016 - 07:17 AM


When I sett it to 1 turn out, with low idle, the idle goes down and it stalls if I turn out the fuel screw more, about 2 turns out, the idle never goes up. It stays basically the same then it dies.

It's also easier to start with the fuel screw all the way in, no hot start needed.

It's also remarkably hot outside

I have the JD jetting kit.

I have the blue needle, a 48 pilot jet (only one in the kit, sadly), and the 168 as main jet.

The bike came with a 50 pilot jet and a 178 main. I do not own a 45 pilot.

Edited by Agazza, July 27, 2016 - 07:20 AM.


  • Krannie McKranface
36,164 posts
Location: California
Garage View Garage

Posted July 27, 2016 - 12:09 PM


When I sett it to 1 turn out, with low idle, the idle goes down and it stalls if I turn out the fuel screw more, about 2 turns out, the idle never goes up. It stays basically the same then it dies.

It's also easier to start with the fuel screw all the way in, no hot start needed.

It's also remarkably hot outside

I have the JD jetting kit.

I have the blue needle, a 48 pilot jet (only one in the kit, sadly), and the 168 as main jet.

The bike came with a 50 pilot jet and a 178 main. I do not own a 45 pilot.

 

right, so it is telling you to put in a smaller, 45, pilot.



  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted July 27, 2016 - 12:40 PM


right, so it is telling you to put in a smaller, 45, pilot.


I understand that, I just don't get why I need it when so many others have success with the 48 JD, with what I understand, is less fuel demanding mods.

Could it be something else that is worn in the carb, or is a lot of people riding with badly tuned carbs in the forum?

Anyhow, I will order the 45, thank you for your know-how!

  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted July 27, 2016 - 12:48 PM


Somewhat related are these Chinese jets OK or should I be looking for something specific?

http://www.ebay.com/itm/321709420521

  • Krannie McKranface
36,164 posts
Location: California
Garage View Garage

Posted July 27, 2016 - 02:40 PM


I understand that, I just don't get why I need it when so many others have success with the 48 JD, with what I understand, is less fuel demanding mods.

Could it be something else that is worn in the carb, or is a lot of people riding with badly tuned carbs in the forum?

Anyhow, I will order the 45, thank you for your know-how!

 

45 is the go to jet in all cases, unless you have other carb issues

 

Don't use cheap jets!!



  • RockerYZWR
1,394 posts
Location: Florida
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Posted July 27, 2016 - 06:52 PM


Somewhat related are these Chinese jets OK or should I be looking for something specific?

http://www.ebay.com/itm/321709420521

Those jets suck and you'll be sorry you bought them. Plus, you won't use nine of them and the one you do use will probably strip out or break at some point. Genuine Keihin jets are worth the extra few bucks - check out jetsrus.com.

  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted July 27, 2016 - 10:24 PM


How do i know which one to get?

http://www.jetsrus.c...n_selection.htm,

I guess it's the 99103-420, 99103-MA1 or the N424-26?

  • Krannie McKranface
36,164 posts
Location: California
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Posted July 28, 2016 - 04:47 AM


Jets by make and model



  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted July 29, 2016 - 07:27 AM


I bought a genuine Keihin 45, thanks for the help.

 

 

Now when I´m going in there again this winter, i will also do a port and polish job  :thumbsup:

 

I´m a lucky guy and I live very near a infamous enginebuilder, he turbo´d a xr650 back in 2003 (120hk) wich was written about in some magazines.

 

 

I feel like a kid wating for christmas, but it´s July  :banghead:



  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted October 08, 2016 - 05:30 AM


Ok now I have parked the bike and I'm ready for some jetting.

I'm going to ad a adjustable screw to.

I have removed the back and the shock. Can I do the rest with the carb on the bike?

Also the Squirt seems short

https://youtu.be/noXV2ECCw8c

The fps is 240

Any expert advice?

  • Krannie McKranface
36,164 posts
Location: California
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Posted October 08, 2016 - 06:59 AM


Ok now I have parked the bike and I'm ready for some jetting.

I'm going to ad a adjustable screw to.

I have removed the back and the shock. Can I do the rest with the carb on the bike?

Also the Squirt seems short



The fps is 240

Any expert advice?

 

It's a little weak. Not sure about the duration because of the film speed (awesome shots by the way).

This is typical. A corked up motor needs nothing more, but once uncorked, and 1 sec WOT stream that hits the left intake is desireable.

 

If you have the stock pump system, upgrade it to the 2008 Honda specs, and change the linkage spring for a massive improvement...

 

 

  http://tokyomods.com...arburetion.html

  http://www.crfsonly....roducts_id/3932

 

Installing the new linkage spring is tricky, but there are some tricks to it, when you are ready.


Edited by Krannie McKranface, October 08, 2016 - 07:00 AM.


  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
Garage View Garage

Posted October 08, 2016 - 10:39 AM


All done now, and it really runs great, thanks krannie for all the awesome guidance.

It's smooth, and I haven't adjusted it yet, only 1,5 turns out and a adjustment of idle. But it fired up really easy and it's a noticeable difference when driving, the engine is really smooth.

I'm a small guy and next thing will probably to do a sumo of this and get a beta 300rr or xtrainer for the enduro

  • jamesm113

    TT Bronze Member

167 posts
Location: California
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Posted October 08, 2016 - 07:02 PM


All done now, and it really runs great, thanks krannie for all the awesome guidance.

It's smooth, and I haven't adjusted it yet, only 1,5 turns out and a adjustment of idle. But it fired up really easy and it's a noticeable difference when driving, the engine is really smooth.

I'm a small guy and next thing will probably to do a sumo of this and get a beta 300rr or xtrainer for the enduro

 

Did you end up doing the AP mods?  Which leak jet did you end up with?  I had a pretty short squirt myself and was wondering what outcome you got out of it..



  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
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Posted October 08, 2016 - 11:37 PM


Did you end up doing the AP mods? Which leak jet did you end up with? I had a pretty short squirt myself and was wondering what outcome you got out of it..

No, i did not remove the carb from the bike because i want to do a complete bike tear down when i do it, i still have some riding in me before i try the tokyo mod (thanks krannie)

Probably when the snow starts falling and its the time in between usage of regular tires and icetires.

I tried doing a search but i don´t remember what leak jet i have, i have the JD jetting kit JDY006, but with a 45 pilot jet instead of a 48.

I think i have the washer on third, blue needle.

After some investigation my conclusion was that my friend, that twisted the throttle, did it relatively slowly.

When i did it, it was noticeably better, did not film it this time. Next tear down i will do some better videos and take some pictures people can use

Edited by Agazza, October 09, 2016 - 12:05 AM.


  • Agazza

    TT Bronze Member

124 posts
Location: Sweden
Garage View Garage

Posted October 09, 2016 - 02:39 AM


Tried setting the carburetor just now and it is still acting funny.

Same symptoms for the pilot jet, even with the 45.

I think the carb needs some real loving with a clean and rebuild.

When i do the 2 turns out on the mixture screw and set the low idle and start to screw the mixture screw in again i can turn it almost all the way in, and just 1/4 turn from bottom, the idle speed increases. But it bogs like hell.

If i just sett it about 2- 1,5 turns out with a nice idle its fine´ish, only bog when i really force it.

What could be the problem? I really dont think the Pilot jet is to big, i have a YZ exhaust and a opened up airbox.

Edited by Agazza, October 09, 2016 - 06:06 AM.


  • Krannie McKranface
36,164 posts
Location: California
Garage View Garage

Posted October 09, 2016 - 06:52 PM


Tried setting the carburetor just now and it is still acting funny.

Same symptoms for the pilot jet, even with the 45.

I think the carb needs some real loving with a clean and rebuild.

When i do the 2 turns out on the mixture screw and set the low idle and start to screw the mixture screw in again i can turn it almost all the way in, and just 1/4 turn from bottom, the idle speed increases. But it bogs like hell.

If i just sett it about 2- 1,5 turns out with a nice idle its fine´ish, only bog when i really force it.

What could be the problem? I really dont think the Pilot jet is to big, i have a YZ exhaust and a opened up airbox.

 

Wrong, backwards!

 

Start with a hot motor, fuel screw at 1 turn, and lower the idle as low as it will go.

Raise the idle with the fuel screw until it has no effect. If the idle is now too high, lower it, and start over with 1.25 turns out.

Raise the idle with the fuel screw to attempt to reach your desired idle using only the fuel screw.

 

Make a note of the turns as best you can and write it on the side of the float cover.

 

Now, for fine tuning.

 

Blip the thottle. Notice how fast the idle drops. 

Blip, wait, listen, adjust.

 

Your goal is to SLIGHTLY tweak the fuel screw in or out (1/16 - 1/8 turn) to get the idle to drop as quickly as possible.

 

Remember, the carb will only work as well as the quality of the parts inside, and how they are adjusted.



  • RockerYZWR
1,394 posts
Location: Florida
Garage View Garage

Posted October 10, 2016 - 05:31 PM


I'm dealing with a hanging idle problem right now - ended my ride pretty much right after I started today because it was dangerous in the woods. Came home, pulled the 45 pilot and put in a 48 thinking maybe a lean issue. Didn't get a chance to go back out, but in the garage, it still did it once. And when it hangs up, it hangs up at 6000 rpm, occassionally less, so that's not cool. A light blip will generally being it back down. Been intermittent since I had the carb off to clean in July. No air leaks that I can find and the slide is not hanging up visually with throttle movement. I'm guessing it's crappy fuel screw tuning on my part. I have zero bog, good All around power, and it starts perfectly cold or hot. Annoying. Why haven't I bought a 450FX yet...




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