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Discussion Starter · #1 ·
So I'm looking to make my bike have better throttle response on the low end. As of now my power really doesn't come on until 4000+ rpm. I thought about gearing it down but I need the top end for cruising. Right now my bike is apart but was set up as follows.

X4 cam
102mm 12.5:1 Piston (balanced HR stock stroke crank)
HV porting (stock size ferrea's) with KW springs
3 plug mod
39mm FCR's
barker dual exhaust

I run 93 octane with dynamic compression of 204PSI or 9.71:1 DCR (600ft asl)

Will going back to 35mm carbs gain me much as far as low throttle response?

When I started my build last time I remember reading that cam duration would put the power range will be ON AVERAGE at
240-250= 2500-6700rpm
250-260= 3000-7200rpm
260-270= 3500-7700rpm
270-280= 4000-8200rpm

My X4 is in the 276 range (or 4000-8200rpm) so I was thinking that maybe I should go back to a stage 2 hotcam which has a duration of 246 (or 2500-6700). However this would require me to switch to an 11:1 piston to run pump gas. (this would put my DCR at roughly 205psi or 9.77:1)

Another option would be to switch back to a stage 3 hc which would be approximately the same DCR as the X4 but has a 265 which in theory would drop the power to the 3500-7700 range. This is a slight gain but isn't quite as low as I would like.

Should I swap just the carbs? Carbs+ stage 2hc/piston? 2hc/piston? Carbs + 3hc? What would you do?
 

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Sounds like you were trying to put a race bike around in the trails. How much hp are you willing to give up to make it at that lower rpm? You should be in the mid to upper 60's with that setup, the kind of build that would better suit your needs is likely to make around 10 hp less.

I had a very similar setup, I needed to change the way I rode it and my gearing, but it was still a nice ride in the trails. If you're not willing to go that route then I'd chuck everything above the headgasket and start over.
 

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Discussion Starter · #3 · (Edited)
So you don't think that I would be able to use the head and just swap the cam/piston/carbs. Peak numbers don't mean a terrible amount to me anyway because once I get into the higher RPMs, the power probably isn't getting to the ground anyway.

Also, if I were to run a 102mm 12:1 piston with a stage 2 hotcam I would be around 222psi (or 10.4 DCR) This would also put my power down lower in the RPM. The though here is that the three plug head and custom timing brings the thing to life in the higher RPMS.
 

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I guess it depends on if the head was ported for the x4. I dont know how HV porting works for different cams but with traditional porting if you set it up for a high reving cam then it has larger ports, and valves. Wich isnt probably going to be good for a midrange cam.
 

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Discussion Starter · #5 ·
I bought the HV head used so I am not sure what exactly it was ported for. I do have the dimensions though. How could I find out? Use a flow bench? I think it may be a barker port job so I may have to swing over his way sometime and ask him.
 

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I bought the HV head used so I am not sure what exactly it was ported for. I do have the dimensions though. How could I find out? Use a flow bench? I think it may be a barker port job so I may have to swing over his way sometime and ask him.
Or just call him. Not very likely that the HV port job would be made for a stage 2 cam. Every HV port job I have seen has a x4 or a x14 cam in it. Would running a single give any more torque? I like how power comes on(well came on:lol:) just ride in the higher RPM's is what I do. I have not rode a stock raptor in a few years though and don't know what kind of low end they have.
 

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I bought the HV head used so I am not sure what exactly it was ported for. I do have the dimensions though. How could I find out? Use a flow bench? I think it may be a barker port job so I may have to swing over his way sometime and ask him.
If you have the stock carbs, give them a shot and see how it reacts........
 

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Stock carbs jetted properly with the 3 plug set up is very responsive down low, even a desent top but I now she is hungry for more. I love having a LOT of HP in the wood's + the way the power comes on with the 3 pluger is, for lack of a better word ...FUN...
 

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Discussion Starter · #9 ·
Yeah. Maybe I'll try it with stock carbs and see what she does. I'm thinking alot of it is in the carb size. If that doesn't work I'll change it up a little bit.
 

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Stock carbs jetted properly with the 3 plug set up is very responsive down low, even a desent top but I now she is hungry for more. I love having a LOT of HP in the wood's + the way the power comes on with the 3 pluger is, for lack of a better word ...FUN...
Awesome...............:D
 

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Discussion Starter · #11 ·
So I put my FCR's on it when it went together this time. I wanted to see how much (if any) my jetting would change after fixing the coolant leak. I was actually had drop a size on the mains, increase one size on the pilots and richen the needles one clip. It seemed to run really well and have better response and power came on alot smoother/crisper.

However, I have a new dilemma... while I was out testing it I was starting to do some good thrashing and the chain must have been getting loose. It unhooked from the back and even though I had a case saver on it punched a small hole in the stator cover (where the oil goes over to the tranny?) Either way now that is leaking and as expected the case saver mount ripped off.

Anyone know what type of aluminum the cases are made out of? I have some 4043 and 5356 that I can weld it back up with.
 

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So I put my FCR's on it when it went together this time. I wanted to see how much (if any) my jetting would change after fixing the coolant leak. I was actually had drop a size on the mains, increase one size on the pilots and richen the needles one clip. It seemed to run really well and have better response and power came on alot smoother/crisper.

However, I have a new dilemma... while I was out testing it I was starting to do some good thrashing and the chain must have been getting loose. It unhooked from the back and even though I had a case saver on it punched a small hole in the stator cover (where the oil goes over to the tranny?) Either way now that is leaking and as expected the case saver mount ripped off.

Anyone know what type of aluminum the cases are made out of? I have some 4043 and 5356 that I can weld it back up with.
4043 is fine. Give yourself a good bead. I make a dummy suport out of 1/8 inch flat stock steel that bolts to the cover and holds the broken piece of case saver mount. Grind a good 'v' in the break for the weld.
 

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Or you can just weld another piece of aluminum round stock to the area where the mount is missing and drill and tap it..............
 

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Discussion Starter · #15 ·
Well I took the stator cover off and I don't know why it was leaking. There was no hole in the stator-side cover Apparently the o-ring was bad because I simply replaced the two o-rings and gasket and no more leak. As far as the case-saver tab I JB welded that. Doing a temporary fix seemed good enough as if the chain comes off again I'd rather have the tab break than make it too rigid.
 

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Discussion Starter · #17 ·
So I checked with stock carbs and it seems to have a smoother power in the low end. I only took about 30min to rough the jetting in... with a 138/140 Dynojet main in it, it was still running rich. However, the power seemed much smoother and therefore I'm going to keep looking for a set of 35mm's.
 

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Im not up on DJ numbers, but try running the same jets in each stock carb, dont stagger them & see how that works..
 

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I run the same jets in each of my carbs for my HV head. I'm guessing you just used the jets you had from a leftover jet kit is you reason for not using the same.
 

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However, the power seemed much smoother and therefore I'm going to keep looking for a set of 35mm's.
That is because when you slame the throttle open the slides dont lift up right away. It takes Vaccuum and RPM to open the vaccuum slides. You can do the same thing with FCR's just dont slam them open.

I do agree that a pair of 35's are still better suited for general riding, vs. the 39's being used for drag racing.
 
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