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Discussion Starter #1
Last year I had to do an engine rebuild on my 06 brute force 750i. I decided to go with the cylinder works 860cc big bore kit from Rocky Mountain ATV.
Since getting my quad back from my mechanic it seems like it actually has less power than my stock 750 had. Guessing it's not getting enough fuel for the extra 110cc. Any suggestions on solutions? Recommendations for different jets or changing the valve settings?
Also running really hot, to the point that the exhaust actually melted some of the plastic last winter while riding in below freezing weather clearing a frozen pond. Any suggestions to cool it down a bit too?
 

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My guess is that you need to rejet the carbs or clean the carbs if they were already jetted for the 860 .

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No, I don't have that answer. I would try at least # 40 or # 42 pilot jets, and go 3 - 4 sizes larger main jets. Buy Keihin only - They are the factory type jets.
If you don't have a a wide band O2 set up on your exhaust, jetting can take a lot of work.
 

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Is it stock other than the big bore kit? Why was it rebuilt?
You should have rejetted as soon as you noticed it was running hot.
 

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Discussion Starter #6
I'm a rookie when it comes to quad upgrades. Rebuild was done due to the crankshaft bearing going and the chaos that ensued. Everything in the carbs is stock. The engine was rebuilt with the cylinder works kit by at my neighbours HD mechanic shop, that being said they mostly work on tractors, combines and other large equipment. I know very little about changing jetting. Good to know that the jets could solve both issues. Recommendations on jet #'s? Both pilot and main jet # suggestions would be appreciate it. I believe the stock ones are 152 front and 158 rear but again, I'm just learning.
 

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My only concern (other than jetting) is if they got the front and rear cams in the right place, and if they got the cam timing correct.
 

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Discussion Starter #8 (Edited)
Used the Cylinder Works Big Bore kit and a Hot Rods complete crankshaft assembly kit. Had to get the case bored out to fit the cylinders (despite being sold as "no machining required"...)
It ran hot before the rebuild, just not this hot.
As far as the timing goes he said they set timing and valve clearances according to my service manual so again, stock settings.
 

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Used the Cylinder Works Big Bore kit and a Hot Rods complete crankshaft assembly kit. Had to get the case bored out to fit the cylinders (despite being sold as "no machining required"...)
It ran hot before the rebuild, just not this hot.
As far as the timing goes he said they set timing and valve clearances according to my service manual so again, stock settings.
Yup, and lots of shops/people have come here after using the manual, in order to figure out whats wrong when it doesn't turn out as planned.
You might need to go up one size on the pilots, a shim under each needle, and probably 3 sizes on the mains.
 

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Is it stock other than the big bore kit? Why was it rebuilt?
You should have rejetted as soon as you noticed it was running hot.
^^^^^^ ?
 

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Discussion Starter #11
Is it stock other than the big bore kit? Why was it rebuilt?
You should have rejetted as soon as you noticed it was running hot.
^^^^^^ ?
Crank case is stock, heads and cams and valves are stock but from a parts bike because mine were toast and the ones in the parts bike were good so he set them to Kawi manual reccomended settings and re-assembled.
Hot rods crankshaft kit and big bore kit had all the required rebuild components needed.
Replaced temp sensor, gaskets etc at the same time.
Will order some new jets and go from there I guess. Thanks for the advice.
 

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The stock exhaust is fairly restrictive, so you won't feel the full benefit of the extra cc's.
 

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Wonder if the pistons have enough valve relief to run bigger cams..

Back to the issue. If its a stock motor with just the 860 kit you will still need to jet up for it. Unless you did exhaust and cams then I would start with 3 sizes up on mains and shim the needles.
 

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Discussion Starter #14
Ok, so finally gave up trying to find time to work on the bike myself and took it back to the mechanic. Also it does have muzzy exhaust on it. Any thoughts on having two differs sized jets? Read about some guys switching to two of the same size jets. It currently has one #150 and one #144.
 

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You need bigger jets. Step up to around 160 Keihin front and rear. And Keihin #40 pilot jets.
 
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