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.
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.
