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xr650l bum

xr 650l slow jet,needle, main ?

6 posts in this topic

I am trying to fine tune my carb on my xr650l. It was running way to rich. I have since down sized all jets, and have slowly been bringing jet size up and backing out the needle. I have been checking my plug every couple hundred miles, and adjusting accordingly. It runs great, but does have minor pop in the 2-3 gear decel. Plug is not browning enough, so its needs a little more gas. I have two clicks left to back out the needle. How far is to far? What is the relation of the needle to the jets? I believe I have it now at 158 slow and 160 Main so we can forgo those questions. Thank you for your help!

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What worked for me was 58 slow and 160 main with the stock needle shimmed .025. and thats with the air box snorkle removed and a full aftermarket exaust. (XRs only)

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What worked for me was 58 slow and 160 main with the stock needle shimmed .025. and thats with the air box snorkle removed and a full aftermarket exaust. (XRs only)

Thank you for replying! What you are running does not answer my question! I to have all dave mods, de snorkle, and full exhaust. Every time someone asks a carb question it seems that everyone wants to say what there running. Yes its nice to know that we are all close, but there is fine tunning for different machines even though they have the same mods!

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Bum, if you are running the DJ needle its hard for folks to relate their experience because more folks run the stock needle shimmed.

Just for grins, is that a 160 DJ main or a 160 keihin?

Are you happy with the full-throttle jetting?

Dave

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I figured you would take on the task of answering my question! Thanks Dave. I was going to go the short route and just PM you. Lets answer this in public so that everyone can help to understand. I dont remember who the maker of the jets are. I have purchased many so I am not sure which are in right now. I am running the DJ needle, because I like the adjustable clip!

Let me ask my question another way! When you back out the needle to give the carb more fuel, does this give the carb more gas over the hole spectrum of performance? Or is it just confined helping slow jet, Idle, or full throttle performance?

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I figured you would take on the task of answering my question! Thanks Dave. I was going to go the short route and just PM you. Lets answer this in public so that everyone can help to understand. I dont remember who the maker of the jets are. I have purchased many so I am not sure which are in right now. I am running the DJ needle, because I like the adjustable clip!

Let me ask my question another way! When you back out the needle to give the carb more fuel, does this give the carb more gas over the hole spectrum of performance? Or is it just confined helping slow jet, Idle, or full throttle performance?

As I understand it, at full throttle (on the XRL this will be whenever the slide happens to be full-open, if that can happen at part-throttle on the butterfly) the needle is just about all the way out of the needle seat, and is supposed to have no effect on the jetting.

The needle is tapered, so by rasing the needle relative to the slide (backing it out) you richen the jetting for the main circuit, at all throttle settings where the main jet is feeding fuel and its less than full throttle.. The pilot circuit is supposed to be 'out of the loop' fairly early (at low throttle settings).

idle- pilot circuit only (needle does nothing)

small amount of throttle- pilot and main circuit (needle has some influence, a lot? a little?)

more throttle- pilot circuit has little to no influence, its all the main jet and the needle.

even more throttle- def. no influence from the pilot circuit

full throttle- main jet only influences the mixture.

I've seen diagrams where the throttle settings above are described as 0, 1/4, 1/2, 3/4, full throttle. With this dang CV carb, who knows? I usually figure the pilot is out of the picture somewhere between 1/4 and 1/2 throttle.

I have speculated in the past that if you use the DJ needle, you need to use a DJ jet, and if you use a keihin needle, you have to use a keihin jet. I know the DJ jets are shaped diff. than a keihin jet. Some funky stuff may happen if you mix-n-match.

Dave

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