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miguelitro

dynojet kits?

22 posts in this topic

my roomate, a technician, told me a dynojet kit would help me to get my jetting spot on and increase performance :naughty: sounds great but worth $70 :D

I know about the 68s(i could be wrong on the #) pilot and am wondering if I should just get that ? :naughty:

is the kit worth the $$$?

do i even need too replace my needle?

My jetting is pretty close right now but can it ever be too perfect... too much $$$ at stake with going too lean!!!

Thanks guys

Mike

jetting is such a :D

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Save your money and just buy the size jet you want and shim the needle.Works just as good for a lot less. :naughty:

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I don't think its worth the money even I got it in mine. It came with just a main jet, needle and spring. Probably the dynojet stickers were the expensive pieces in the kit, the rest sure couldn't account for that price :naughty::naughty::D

I was just too lazy to search for a right size shim and didn't like the idea to drill the slide.

You sure get the same result with the recommendation you find here plenty in the forum describing the jetting thing.

Det

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Don't confuse Mike! He's got an R!

But generally speaking, factory jets and needles do the same for much cheaper.

Dave

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yeah guys i'm easily confused.....

i think i'll go ewith the stock

Why do you have to drill the slide???

Mike

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my L runs perfect with the DynaJet kit, but it really is way overpriced ... just get Keihin jets , drill the slide, and spacer the needle as suggested in these forums

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yeah guys i'm easily confused.....

i think i'll go ewith the stock

Why do you have to drill the slide???

Mike

The diameter of the holes are metering the slide position in relation to the vacuum going through the carb. Instead of using the tapered DynoJet needle and spring you get the same result by shimming the needle and slightly opening up those holes (forgot the size) and that for changing the slide position at a certain vacuum.

If you look at your carb the slide/piston is attached to a diaphragm and held down by a spring. The bigger the holes in the slide the lower the slide will stay at a certain vacuum or the more vacuum you need to pull it up.

I think that applies to the XRL, well I used the overpriced DynoJet kit...

Det

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Mike, no holes in your slide to drill.

dave

What? That doesn't apply to the XRL?? You tell me now after I bought that Dynojet kit because I didn't want to drill holes??? :naughty::naughty::D

Det

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Yes drilling the slide does apply to the XR650L.

No drilling the slide does not apply to the XR650R.

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oops, now i get it - Mike has the "R", I should have read Dave's post earlier, I was thinking the entire time he had the "L" too... :naughty:

Det

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Mike, 68s for the pilot,172 to 175 main move the needle to the 3rd clip....

Don't drill the slide, Thats a L thing............ :naughty:

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Det, the softer spring makes almost no difference on the throttle response, I went that route.

I'm wondering if I'd make any $$ having people ship me their carbs for modding- there are a bunch of people out there that don't want to take a drill to their carbs themselves.

What I'd like to do is find a bowl that's fit that had a plug for pulling the jets.

Dave

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Det, the softer spring makes almost no difference on the throttle response, I went that route.

I'm wondering if I'd make any $$ having people ship me their carbs for modding- there are a bunch of people out there that don't want to take a drill to their carbs themselves.

What I'd like to do is find a bowl that's fit that had a plug for pulling the jets.

Dave

The DynoJet spring is softer? I didn't really compare it with the stock spring when I put it in but that would make the opposite effect to opening the holes, wouldn't it?

I thought it was a bit longer than the stock spring, that for I assumed it would give more tension but I am really not sure...

What I really need to do is to mount my XR style taillight and get my decals I ordered last week on the tank and fender :naughty: getting stylish now!!!

Det

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The DJ spring is a little softer. The piston gets sucked up by vacuum, the spring holds it down.

A softer spring, and the further the slide will travel for a given vacuum. The bigger the holes, the faster the air above the pston will be sucked out, so it'll open sooner.

Dave

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Dave,

I found this description below once on the net, but this one explains the opposite about the holes and spring. Made perfectly sense to me?

But maybe it works both ways, I mean letting the slide move up faster at higher loads because the bigger holes in the bottom help additionally to suck more air out and going back to no load (no big vacuum under the slide) letting the vacuum above the slide bleed of faster and that for let the slide come down faster.

Just trying to make sense out of this stuff :naughty:

Det

What are the Holes in the Bottom of the Slides for ?

If you've had your carb apart, you have seen the slide and slide return spring and know that the slide carries the needle as it moves. With that in mind, the chamber & diaphragm at the top of the slides gets a supply of intake vacuum, fed through the little hole at the lip of the cover. The vacuum pulls the slides up, exposing more of the needle. That vacuum is pulling against the return spring, and also being bled off by the vent hole at the other end of the the needle slide.

So why change the hole diameter? To change the ratio of vacuum to slide position.

There are three ways to alter the needle position vs. engine load (vacuum):

1.) Change the diameter of the vent holes. The larger holes will bleed the vacuum off quicker, smaller holes will bleed the vac off slower.

2.) Change the rate of the return spring. A heavier spring will have the same effect as a larger vent hole.

3.) Change the position and shape of the needle.

You can use any combination you wish, provided it produces the results that you (or should I say, the engine) wants.

All three ways are done by different shops and kits. Some race shops prefer to use the stock needle (straight taper) and slides and only change spring rate and jet sizes. Others, Dyno-Jet kits included, use custom needles (stepped taper/adjustable position) and larger vent holes in combination with stock spring rates. And some just alter the needle shape while leaving the vent and springs alone.

The result is usually a mid-range adjustment. Low range is still governed primarily by the pilot jets & float height, and top end by the main jet size.

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1) is correct, but misleading. The air above the piston bleeds off quicker with the bigger holes.

2) is backwards- 'heavier spring' means stiffer = more resistant to moving.

3) is correct, but will affect only the mixture, not the 'throttle opening".

When the slide moves up, it increases the effective throttle opening, not just the needle position.

Dave

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one thing I found out some time after installing my DynaJet kit ... the DynaJet main jet numbering differs from the KEIHIN sizes usually mentioned ... evidently, a 165 DynaJet main is about the same as a Keihin 162 ... I would have thought jets were standardized, but I guess not ... check it out

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