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How To: Intake Crossover for Carbed Brutes

44K views 65 replies 11 participants last post by  NMKawierider 
#1 · (Edited)
THIS MOD WILL ONLY WORK ON PRAIRIE 650/700, VFORCE AND BRUTE 650 SRA MODELS.

Hi all, Thought I would post this up as I did a search on here for crossover intakes and nothing came up.

I got the info for this mod from Kawieriders and jetting help from vforce john, so thanks to all that helped out.

It's pretty easy mod to do and also very cheap with excellent power gains. The biggest gains are on a stock motor of about 5hp and modded motors around 2-3 hp(vforcejohn dyno tests). I also polished the carb slides while I was at it and I think this contributed to the excellent throttle responce I now have.

Tools and parts you will need are as follows,

Electric low psi(approx 3.5 psi) fuel pump. Mr. Gasket 42s I think is the one they suggested over on kawieriders.

Some earlier model brutes and prairies had the electric fuel pump from the factory so no need to get it if you already have an electric pump standard(mine is an 09 650 sra and I needed to buy the electric pump as mine was vacume operated).

3/4" or 1" copper pipe for the crossover tube.

Black silicon sealant.

Some nipple block off caps.

Asorted jets as you useualy need to fatten up the jetting after this mod. Stock jetting on mine was 40 pilot front, main 138. Rear 40 pilot and main 142. Fuel screw front 1.25 out, rear 2.25 out.

After the mod my jetting is front pilot 40, main 142 and rear pilot 40, main 145 fuel screw 3 turns out both front and back with 1 #4 washer as a spacer for the needles. I think I could have gone 42 on the pilots but I couldn't get any but mine runs real strong from top bottom to top, no hesitations or popping with the above jetting at sea level. Stock air box.

Dremel tool or similar for for smoothing crossover tube and polishing slides.

Hacksaw.

Various basic tools for removing the body plastic, airbox ect.

Soldering iron or crimps/conectors for wiring fuel pump.

The biggest PITA was disconecting and reconecting the choke cables lol.

Once you have the intake and carbs out mark where the crossover tube will go on the rubber intake boots, cut the holes out carefully a little smaller then your tube then cut your copper tube to length and insert into the holes you cut in the rubber intakes.

Smooth the copper tube so there are no lips ect when installed in the rubber intake boots. Make sure the rubber intake boots are clean so your sealant will stick. Add sealant on the outside of the copper tube transitioning onto the rubber boots and smooth out as best you can.

Now bolt the intake only back on the motor and let sealant set, you will have to do this a couple of times until you are happy with the build up and shape.

Remove your vacume fuel pump and wire in your new electric pump as per instructions in this link. http://www.kawieriders.com/forum/in...el-pump-mod-brute-650-s-vacuum-fuel-pump.html

Polish your slides as per this link. http://www.kawieriders.com/forum/kawasaki-brute-force-prairie-bayou/96424-polishing-carb-slides.html

Re-jet and bolt everything back up and enjoy your new found power and throtle responce for very little cost. My 650 sra can not get traction after doing this mod on stock tires! Once I get my new tires this thing is gunna want to hook up and wheelie all day! Very noticeable seat of pants gain from this mod, I highly recommend it.

Here are some pics of mine.

Old fuel pump and vac lines removed


New fuel pump installed.



You can see in this pic of the intake where I used the rubber block off nipples to block the vacume lines that are not needed anymore.



Pics of crossover installed.



Polished carb slide.
 
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#5 ·
I've moved this into the Kawaski how to's and renamed the thread
"How To: Intake Crossover for Carbed Brutes"
 
#6 ·
good write up! i've been meaning to do this for a while!
 
#10 ·
I would say do it.....cheap mod and good improvement to throttle responce and power.

If you dont mind spending the dollars you can order the crossover intakes from vforcejohn or UPPS but doing it yourself will save you cash and the only extra work is drilling your intake boots, installing the crossover tube & add sealant for virtually the same result as the bought ones.

No matter if you make your own or buy them you still have to remove air box, install pump ect.
 
#7 ·
can someone explain how this benefits airflow. it looks like it would cause turbulance
 
#8 ·
it allows any one cylinder, which may be short on air, to borrow from the other.
It makes the flow to each more even.

its proven to work. there's dyno charts to back it up.i saw them somewhere.
in fact we've had this thread come up before on MIMB.
 
#9 ·
ah ok. so could this b aproved on by designing a crossflow section that borrows better
 
#12 ·
im not sure it could be improved on any more. the existence of a passageway between the two, of at least a minimum size or greater, will acheive the intended affect. any change in shape or size would would have litte effect.
 
#11 ·
One thing I would do different is the choke cable......I disconected mine down by the front cylinder where the single cable from the bars goes into a joiner and exits as 2 cables going to the carbs......this was a major PITA and to get barely enough slack to disconect it I had to remove the cable from the choke lever at the bars anyway.

So I would say just disconect at the bars and pull the cable through and remove as a whole unit connected to carbs.....if anyone has a better/easier way please chime in and let us know.
 
#13 ·
what is the best kind of sealer to use? black silicone? urethane glue/sealer?
 
#15 ·
do you have equal length header pipes on your bike? i wonder if that would make a difference on how the xover performs
 
#16 ·
No I dont have equal length headers.......I dont know what diff that would make to xover but should make a power/torque gain on its own.

I do know(according to vforcejohn)with the shorter rear header ie stock or slip-on that the rear cylinder needs to be jetted a bit fatter than than the front to keep it cooler as it does not get the air flow that the front does.

In theory the xover should sort of = out the jetting in front and rear as now each can draw the fuel/air mix from one another. From what I understand an = length exhaust system such as Muzzy should make more power but the xover mod will be an improvement no matter what.
 
#17 ·
sounds like i should get me some more jets and a fuel pump and do this thing already!
 
#19 ·
i've heard it does that :bigok:
 
#20 ·
does it matter what size copper pipe u use for the crossover tube
 
#22 ·
ok. i have to jet mine after the 3'' snork i jus did so i guess i should go ahead and do this b4 i start so i dont have to deal with the head aches of the jets
 
#23 ·
I see in your signiture that you have the BF 750...is this the bike you will do the mod on? I thought I read somewhere that this mod will only work on Prairies, sra and vforce but I will try and find out for sure and post back here.

If I confirm this I will make a note of it in the original post so there is no confusion.
 
#24 ·
ok do that if u will
 
#25 ·
Ok sorry for the confusion byrd......apparently the crossover mod will only work on Prairie 650/700, vforce and BF 650 sra models.

The 650i and 750 are supposed to have different intake runners and heads so the mod will NOT work on these models wether they are FI or carby.

I will edit the first post to include this information so there is no confusion....sorry.
 
#26 ·
Here is a quote from VFORCEJOHN on jetting for crossover intake.

"jetting will be lower than normal if you are using stock closed airbox even if piped CDI I use 145-150. with the crossover you can run stock jetting but need a 42 pilot.

open airbox. you will need 200+ main jets. so you have to drill them to 5/64's and te 42 pilot as well

but you make more power using closed airbox on the stock intermal setup on the prairie or bf 650."
 
#39 ·
Here is a quote from VFORCEJOHN on jetting for crossover intake.

"jetting will be lower than normal if you are using stock closed airbox even if piped CDI I use 145-150. with the crossover you can run stock jetting but need a 42 pilot.

open airbox. you will need 200+ main jets. so you have to drill them to 5/64's and te 42 pilot as well

but you make more power using closed airbox on the stock intermal setup on the prairie or bf 650."

So, let me make sure that I understand this correctly.
If I do this mod to my 2008 650 SRA, I would have to rejet my carbs and go to a 42 pilot jet, correct?

My current set-up is Dynatec CDI, Full Muzzy exhaust, Jetted 148F - 155R with both needles shimmed .040, K&N air filter wtih prefilter and 2" Snorkel.
 
#27 ·
Another quote from VFORCEJOHN regarding HP gains with crossover intakes.

"They actually gain more HP on a stock bike. I've seen +6 rwhp +8 rwhp on a stock internal machine.

Vforce I got to 50 rwhp
Prairie Twinpeaks 700 to 47 rwhp

They are an all over gain. top end gains are even better than the peak gains

On modded motors Like 730's I see 2-3 rwhp gain with the 32 crossovers."
 
#28 ·
well that blows. ill do a different mod then. maybe make me a custom dual exhaust
 
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