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Discussion Starter · #1 ·
I just spent about 3 weeks trying to sort out a modified 660 raptor. In a way, this raptor helped me figure out a lot of problems with the different carb setup options we have available.

So, before is start, let's just clear up a few things. I am not here to promote any specific product. I am going to try and stick to the facts of what my A/F ratio probe and dyno was telling me.

Even though I have used a modified 660 (stock compression, stage 1 cam, ported head, dual exhaust system) it also applies to stock 660's running open air boxes and aftermarket exhaust systems. If you are running with the lid on, this might not be applicable to you.

Ok, so let's get started.

A lot of people seem to ask which jet kit is better and then you get people who believe jet kits are overrated and you only need to change the main jets. I never had the opportunity to test all of this until now.

For now, let's forget about the main jets. Frankly, I don't believe the main jet design actually have a big affect on the performance. As long as it supplies the right amount of fuel the motor needs, then you’re fine. You can use either DJ or Mikuni main jets. I personally like to use DJ jets, because I got use to their sizes or numbering.

The biggest and most important piece of hardware is the needles. The needle will affect fuel delivery across the whole RPM and throttle range. I know some people say the needle has nothing to do at top RPM, but I found it does.

The right needle can make the difference between a bad, good and excellent running engine. The reason all this has come about is the fact that a lot of people out there believe the 660's are slow and can easily be beat. Well they are not wrong and it comes down to how riders have their 660's set up. Those carbs, and especially the needles hold the key to release a serious amount of power.

I made a post to explain on how to set up the float levels correctly and what other little mods to do to get more power out of these carbs. Doing those mods will get you half way, but here is the rest.

Stock needles.

As mentioned earlier, a lot of people believe that stock needles are fine and jet kits are overrated. After hours and hours on the dyno testing all possible settings on the stock needles, the only conclusion I can come up with is.... TROUGH THEM AWAY!!!!

The stock needles are actually very nice for low RPM power, but as soon as you get over 4500 RPM, those thick tips on the needles prevent enough fuel to come up through the emulation tube and it causes massive lean conditions. I was running massive main jets with these needles and even then, I could not get them even close to supplying the right amount of fuel for top end RPM. The tips of the needles are just too thick

GYT-R needles.

I never used them before now, and the only reason I used them was because the client provided them to me and said I need to fit them.

So, after testing all possible settings here is my conclusion on the GYT-R needles.... They are average, and I would not use them, ever again. These needles cost me weeks of sweat and tears to sort out this modified raptor.

With these needles, even in clip1 and the metal spacer removed, it was supplying way to much fuel at low RPM. (2000 to 4500 RPM) Even in the leanest possible setting, these needles produces a A/F ratio of between 11:1 to 12:1. That is very rich. Also, when you accelerate from low RPM with full throttle, those needles dump so much fuel into the motor, that my A/F ratio meter read off the scale and the engine started to splutter. The fuel actually kills the spark on the plug. From 4500 to top RPM these needles are fine, they work good, so for guys spending most of their riding at high RPM, these needles are not bad, but overall, they are not the best.

Lastly, Dynojet needles.

These are the only needles that I could get to supply the right A/F ratio. For cruising or normal riding, they supply the perfect A/F ratio of 13:1 across the RPM range. From 2000 to 9000 RPM, assuming you have the right main jets obviously.

So, when it comes to needles, don't waste your money on anything else except the DJ needles. The DJ needles will allow you to adjust for basically any type of mod, from stock to modified, so they are the best choice to purchase.

With the needles sorted out, it leaves me with the last problem I am working on to resolve.

Even if the needles are perfect for normal riding conditions, they all have one major drawback. It is actually not the needles fault, but the slide and the way it reacts.

When you start a dyno run at 2000 RPM, all open airbox raptors show a massive amount of fuel supply from 2000 to around 4500 RPM. It produces A/F ratio readings of around 10:1 and lower. Again after testing hundreds of different setups, it seems that the slide is reacting to quickly and opens up way to quickly and dumping a lot of fuel into the motor. With the airbox lid on and limiting airflow, you don’t have this problem, but them the airbox lid reduce top end power output.

So my mission is to sort out that rich low RPM acceleration condition. I also suspect that this is also the reason why the 660’s splutter when you pop a wheelie or crawl up steep hill in low RPM.

The following is not fact and only based on initial testing.

To limit the slide movement, it seems like running dual slide springs per carbs help with the rich low RPM condition. Yes dual springs, meaning I have installed both he DJ slide springs and the stock slide springs. You press them together, from the side, so to keep the total length the same as a single spring.

Initial testing seems to indicate that this leans out the very low RPM acceleration fuel delivery, but it might, note, might, limit top end power output slightly. I will need to test this further, but it might drop around 0.5 or 1 HP.

One last thing I want to try is to modify the slide vacuum holes. I will try and get some used slides and reduce the oval shaped hole at the bottom of the slide. In theory , with smaller holes in the slide it should react slower to throttle changes. I am hoping this will do the same job as the dual springs, but allow the slide to open fully and not limit top end RPM.

Anyway, that’s my findings, use it or don't. It might give some of you some ideas and also help most of you to set up your 660's better and whip some butt.
 

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good post man, thankx for letting us know !! :thumbsup:
 

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It's hard to make any decisions when each engine builder has his own view on how to modify the engine/carbs.

This is the first I've heard of problems with the GYTR needles. There are other highly respected engine builders that swear by them.
 

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Thanks for sharing your findings Freez, it'll give us all something to discuss/debate.

Just wondering if you recieved the CT needles when you purchased your CT pipe? If so, did you test them? I've heard that they are either close to or exactly the same as the dynojet needles but I have absolutely no reliable evidence to back up either claim. I do know they are significantly more tapered than stock.


I ended up going back to the stock needle after building my bike up a little without any porting. It may not have been the best choice for hp output but it turned out to be the only way to fix a horrible midrange stutter/stumble without restricting or changing the intake.
 

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Discussion Starter · #7 ·
I have had other raptors that used the GYT-R needles and they run fine. Although they seem to run fine, I never put them on the dyno to test if the A/F ratio was right. The 660 can handle quite a lot of fuel at low RPM before it will stutter, so most people never know it is there.

The base of the GYT-R needles are thinner than the stock and Dynojet needles. Thinner means it will allow more fuel thru and can cause a very rich running condition at low to mid RPM when the slide is stationary or just beginning to move.

As I said, I tested these needles on a stage 1 Hotcam and ported head 660, running dual pipes. It might be different on a stock 660 motor.

Also, be very careful about the way you dyno test these needles.

If you install any of the needles and you start a dyno run in 4th gear, the stock, DJ and GYT-R needles all cause a rich condition at low RPM. I constantly get readings of 10:1 till around 4000 RPM with any of these needles in their recommended clip positions. Depending on your mods, it can be ok and the motor will not stutter, but on some cases it does. You need to do more than just an acceleration run on the dyno to really see which needle is best. I put a bit of load on my dyno to hold the motor back a little and then you slowly up the revs from 2000 revs and hold it fixed every 500 RPM. This is to simulate normal riding conditions where you don't need acceleration all the time. If you do this testing and hold it every 500 RPM you will see that the GYT-R needles supply heaps more fuel below 4500 RPM than the DJ needles. In fact, in the leanest position the GYT-R needles supplied an A/F ratio between 12:1 and 11:1. The DJ needles in clip 1 supply a A/F ratio of 14.5:1 or slightly leaner. You cannot make the GYT-R needles leaner than 12:1, while with the DJ needles you can.

The stock needles in the leanest position is actually not bad for low RPM, but even with 180/185 DJ main jet in there, the A/F showed that the bike was running leaner than 18:1 at top end RPM and the power output was down by around 5 HP. It was also giving slight miss fires due to the lean condition. I would strongly recommend that people never run stock needles with full exhaust system, open airbox raptors. Even if you install size 210 DJ jet into those carbs, you will still be running lean, and that assumes the stock carbs can supply those massive jets with fuel, which I doubt very much.

I have been struggling with this problem for more than 3 years now, on my own personal 660 and also a lot of other 660's I have done.

Remember that the stock, GYT-R and DJ needles where never designed to run without the airbox lid on, so there are problems. If you run any 660, with open airbox and you pop a wheelie or ride up a very steep hill in low RPM, trying to crawl over steep obstacles, then you will feel the stutter. If you give it more throttle, the stutter goes away, so most of you that don't ride heavy technical stuff or so, might never know that there is a problem. That problem is made worse with the GYT-R needles

This modified 660 I did, arrived with the GYT-R needles installed and the owner has been riding with them on the stock 660 for a while, with no stutter problems.

The ported head seems to suck a lot more on the carbs and actually worsen the problem of running to rich at low RPM.

If you put the lid on and restrict the intake flow, there is hardly any rich condition, but the more the head flows and the harder they suck on the carbs the worse it gets.

I also have to run the DJ needles in clip 1 to stop the motor from stuttering and getting to much fuel, but the GYT-R needles are much richer, because they are thinner at the base.

Like I said in the beginning of this post, I am not here to shoot down any of the jet kits, but from my own testing, it seems the only decent needles that supply the right mix for low to top RPM are the DJ needles.

Also, note that this is not over and done with. I am still doing further testing on the slide to see if I can get rid of that low RPM rich condition.

I will come up with a mod to fix it, just give me time.
 

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Any idea about the CT needles? Do they make their own, or do they repackage them as their own?
 

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Figured I would bring this back to life. I'm curious about this as I'm about to get a full pipe and k&n filter setup for my raptor. So I want to be able to get the proper jets.
 

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Freez, I'd be willing to send you my CT needles if you wanted to test them.
 

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Can I buy just the DJ needles seperate, or do I have to buy the whole DJ kit?...cause I'm running the GYT-R needles.
 

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Freez said:
I am based in South Africa.

I will test them, but it's a long way to send something.
It would be a lot easier for someone here to just put them all on an optical comparator or something like that. Along that line, I have access to an inspection grade comparator and would be willing to do the comparison. And I have both the GYT-R and Dynojet needles already, I'd only need the CT needles for a full comparison.
 

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Why not just scan them on a hi res scanner, blow them up and superimpose the images in photoshop?
 

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Well, the optical comparator is actually a measuring instrument, so it would be very accurate and remove any human error. Plus it's pretty easy to put all three needles up there and compare them at once, no superimposing needed. But the scan and photoshop idea would probably work also. I'm just better with real instruments than I am with the computer in a case like this.
 

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I understand. I used to have access to an optical comparator, and it would be ideal. BUT, there are a lot of photoshop junkies out there, and i'd be surprised if at least a few didn't belong to this forum.
 

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Discussion Starter · #17 ·
Well, I did not check the whole needle, but I know the DJ needles are 0.01mm thicker than the GYT-R needles at the blunt end of the needle where you will find most of your low RPM fuel delivery. That small difference is the main problem of the over fuelling with the GYT-R needles.

Actually even the DJ needles over-fuel at that range, but not as bad as the GYT-R’s, and I would love to get a needle specially made up that is even thicker than the DJ needles at the base.

It will sort out a lot of problems.
 

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Have any idea how the Alba needles compare to the GYTR's or DJ's? I called Alba and a lady said they use their own now, but the gal didn't sound like she knew a lot or what needles they were including when I got my pipe. I got my Alba kit in the Winter of 2002/2003 and was wondering what people knew about the needles I have for A/F ratios.

Great post and thanks for any input.
 
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