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Pilot circuit jetting has me confused

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I recently was able to rebuild my carb on a new-to-me 2007 WR450F. Stock exhaust, derestricted. Air box snorkle removed and opened up. AIS removed. Powerbowl 2 with heavier AP spring installed.

 

PO had installed:

MJ: 160

Needle: Unknown, middle clip position (not stock because stock was non adjustable)

PJ: 40

PAJ: 100

 

I just installed:

MJ: 168

Needle: JD red in the 4th clip

PJ: 48

PAJ: 100 (the 70 pilot air jet I had wouldn't thread in correctly and didn't want to strip anything)

Adjustable leak jet cover

Fuel mixture screw (R&D)

 

Results:

Bike runs great. I plugged the TPS back in and the low end feels great. I can adjust the bog which is totally gone at 1.5 turns on the leak jet. Top end feels strong and the bike runs a bit cooler on the thermostat. 

 

I tried to check my pilot circuit with the fuel screw and got a weird result. From 2 turns out to all the way in, no change in idle. Once I get to about 3 turns out then I notice a slight drop in RPM's. From all the reading on the forum, is this not the opposite of what I would expect? If I have more air going in to the pilot circuit (PAJ 100) wouldn't that make it a lean mixture and going in on the fuel screw should stall the bike?

 

Also, will going to a 70 PAJ help tune in the off idle to 1/2-full throttle response or will the adjustable leak jet make the difference unnoticeable? The only thing I want to tweak is the bottom end power. 

 

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1 minute ago, Krannie McKranface said:

You want a 45

You could not stall it because it's too rich

Any thing after 2.5 turns will start to leak air around the threads of the fuel screw....

Thanks. 

That was what the tuning guide recommended but my confusion was about the 100 PAJ. Would having a bigger PAJ already make the pilot circuit leaner? 

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1 minute ago, Nixinus said:

Thanks. 

That was what the tuning guide recommended but my confusion was about the 100 PAJ. Would having a bigger PAJ already make the pilot circuit leaner? 

Yes it would.

You should also block off / disable the ACV valve on the side of the carb, as it will give you greif during this fine tuning process.

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9 minutes ago, Krannie McKranface said:

Yes it would.

You should also block off / disable the ACV valve on the side of the carb, as it will give you greif during this fine tuning process.

Thanks. I will try to go down one on the pilot jet. Do you think I need to change my PAJ or MJ? One of the FCR tuning guides said that for this fuel screw behavior I should go down one on the main.

Edited by Nixinus

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1 hour ago, Nixinus said:

Thanks. I will try to go down one on the pilot jet. Do you think I need to change my PAJ or MJ? One of the FCR tuning guides said that for this fuel screw behavior I should go down one on the main.

Fuel screw is for the idle (pilot) circuit only. It is just a trim for the pilot jet. Has virtually nothing to do with the main jet.

The pilot air jet is also a tuning tool for the pilot circuit.

If you keep the ACV, you don't need to change the pilot air jet.

If you disable the ACV, you will be lean, so you go SMALLER on the pilot air jet.

That is the only reason to change the pilot air jet.

 

 

 

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59 minutes ago, Krannie McKranface said:

Fuel screw is for the idle (pilot) circuit only. It is just a trim for the pilot jet. Has virtually nothing to do with the main jet.

The pilot air jet is also a tuning tool for the pilot circuit.

If you keep the ACV, you don't need to change the pilot air jet.

If you disable the ACV, you will be lean, so you go SMALLER on the pilot air jet.

That is the only reason to change the pilot air jet.

 

 

 

So, if I were to disable the ACV in order to fine tune the pilot jetting, I would need to change the PAJ? Do you think I can ballpark it with keeping the ACV intact and leaving the 100 PAJ? I've read up on the ACV a bit but I am unsure exactly what effect it would have on idle with 0% throttle?

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The ACV automatically richens the pilot circuit at under 2000 rpm, in order to eliminate deceleration back firing from the Air Injection system.

That is is sole purpose.

If you elminate the air injection, the ACV has no purpose anymore, accept to be annoying in fine tuning the pilot circuit.

You do not have to remove it or change the PAJ, if you are getting good running results.

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4 hours ago, Krannie McKranface said:

The ACV automatically richens the pilot circuit at under 2000 rpm, in order to eliminate deceleration back firing from the Air Injection system.

That is is sole purpose.

If you elminate the air injection, the ACV has no purpose anymore, accept to be annoying in fine tuning the pilot circuit.

You do not have to remove it or change the PAJ, if you are getting good running results.

How can I temporarily disable the ACV to test my tunning. I read you can disable it "open" and "closed", non permanently. Since I already have the 100 PAJ I figure I can disable it and see the results. I have no idea how to go about doing this. All the threads seem to point to epoxy or do not go into detail about changes to keep it open/closed.

 

Thanks for all your help. 

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3 minutes ago, Krannie McKranface said:

Lots of info if you search.

You remove the white plunger, and solid gasket off the entire area and put the cover back on

Yes, I really tried to spend a lot of time searching. I have so many different things turned up. Some people say cut the plunger, some say epoxy, some say hold it open some say keep it closed. No step by step tutorial so I just took mine apart. I decided to leave it in because the 45 pilot jet seemed to work alright. Still have popping and some low end issues. Might look into disabling this and unplugging the TPS and then rejetting.

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Just now, highmarker said:

have used a hunk of inner tube to make that gasket for testing

Should I just make one the size of the diaphragm, or the entire cover (covering the small hole on the lower right?

 

Thoughts on disabling this open vs closed? I already have a 100 PAJ and a few PJ's to choose from.

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Covering the hole, my carb was on a 650 and benefited from having it hooked up.  Some off throttle light burble is normal, big bangs and pops is not. 

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Went into the ACV yesterday and the diaphragm was kinked/not sitting flush. Looks like the PO was in there as well. I took everything apart and cleaned it up. The diaphragm was still in good shape and I was able to seat it better. Test ride felt good (also adjusted the leak jet and pilot jet) with much less popping on decel. I only get the occasional pop when going full throttle to nothing. Now its time to take a look at the main jetting and needle.

 

Thank you Krannie and Highmarker for your help.

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4 hours ago, Nixinus said:

Went into the ACV yesterday and the diaphragm was kinked/not sitting flush. Looks like the PO was in there as well. I took everything apart and cleaned it up. The diaphragm was still in good shape and I was able to seat it better. Test ride felt good (also adjusted the leak jet and pilot jet) with much less popping on decel. I only get the occasional pop when going full throttle to nothing. Now its time to take a look at the main jetting and needle.

 

Thank you Krannie and Highmarker for your help.

NCVS needle 3rd from top for a fully uncorked bike

2006 YZ standard needle for altitudes above 6000

160 main for stock header

165 for YZ header (larger diameter)

168 for YZ header and full race pipe

Don't worry about the main jet. You will get very strong symptoms if it is too rich or too lean (gurgling / bogging)

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3 minutes ago, Krannie McKranface said:

NCVS needle 3rd from top for a fully uncorked bike

2006 YZ standard needle for altitudes above 6000

160 main for stock header

165 for YZ header (larger diameter)

168 for YZ header and full race pipe

Don't worry about the main jet. You will get very strong symptoms if it is too rich or too lean (gurgling / bogging )

Ive got the JD red needle and a 168 in there. I had a 160 but it was too lean. Bike runs much better with a 168 but might be a bit rich. I am going to go down to a 165 and then see if I need to move the neddle up or down.

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