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2009 CRF150RB - New Hot Cam - Not running correctly

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Short story, timing chain broke on unicam engine.  Decided to replace crank and install hot cam (intake lift 8.70mm lobe center: 110.5, duration@1mm: 254 - exhaust lift: 7.75mm, Lobe center; 100.75, duration@1mm; 273.5) and new wiseco crank.  Rebuild went fine.  Engine starts and idles but has erratic throttle response.  Changed to larger slow jet and seemed to help.  When riding it appears to be starving for fuel (plug is white when removed) so we installed the largest main jet (158) which has not helped.  

 

Question; Does anyone know what should be the proper jets for this bike when going from a stock cam to this hot cam?

 

Thanks

Donald

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Slow jet is for idle only

Main jet is for 7/8ths and bove

You cannot read plug color with pump fuels, the additives always make a plug look whitish.

You need to work with the straight diameter (maybe...) and not the clip position either of the needle.

Big cams often foul up slow speed running. You wanted more high rpm, that came at the expense of driveability. Welcome to slowed down for racing.

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Ok thanks. Not sure I follow your comments. I am running AV fuel so I don't think there are many additives. Are you saying I need to get larger jets? I have the needle on the bottom notch. Just trying to get clarity on the advice.

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AV fuel, you mean aviation? If so, that will cause running issues as plane fuel is meant for high altitude, slow reving engines and probably has way more octane than you need.

 

 

I am not saying you need larger jets, not at all. The slow jet (pilot) is for idle, it and the fuel screw are selcted and set for a perfect idle. The main jet is for 7/8ths and above throttle, inbetween is the needle, comprimised of the striaght diameter, taper and length. Changing engine parts (like cams) fuels and jetting without knowing what you are doing is a recipie for a poort running engine.

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William1, thanks for the feedback. The Honda book I have for this bike gives a bit different information about which jet controls how much of the throttle, but similar to your comments.  It seems like this is an adjustment process with trying different jet and needle combinations until the engine is performing well.

 

Does anyone else have more specific advice on the process for tuning?

 

Donald

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You have made no mention of all you carb tunings, so it's impossbile to be specific until you are specific

 

Your symptoms sound like a clogged main air jet, or a needle that is way too lean.

 

There is no reason to change the pilot if it idles and the fuel screw is 1 to 2 turns out for highest idle

There is no reason to change the main, unless are getting the 'kill button' affect at WOT at 6k rpms and above

Most of your tuning is in the needle

 

If you want specifics, you should post in the 150R forum where there is specific tuning information

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