08 Honda cr450r powercore 4 and megabomb header jetting advice
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Mon Nov 30, 2020 6:26 am

    Hey guys, used to ride once a week, but wife mortgage and kids has my bike sitting mostly for past 8 yrs. bike has 61 hours in mint condition. It always had premium fuel in it with Stabil.

    Bike was 100% stock and was running as expected prior to exhaust

    recently put an fmf powercore 4 and megabomb header. Fmf says it doesn’t need to be rejetted. After install, bike feel same as stock exhaust, it’s like I threw a grand down the drain. Although I had several bikes in my racing/riding career, none had exhaust except for a Yamaha raptor atv that I put yoshi slip on exhaust on. I remember the install felt no difference, but when I sent to mechanic for jetting and got it back, there was a major difference.... no placebo effect.

    Im thinking this bike needs to be jetted. I’m on Long Island NY so 0-1000 ft elevation is my riding area. Bike always rode like it was FI from factory.

    I tried reading all over the internet, but main, pilot and clip position are all over the place for altitude and temps and mods that should yield consistent carb adjustments.

    Any recommendations are greatly appreciated. I was planning on getting a jd jet kit or dyno jet or similar.

    It looks like a real pita to get to this carb, and looks like I’ll have to remove it to work on it, so would prefer to do this once and not experiment. Since it’s an 08, I gotta assume someone has dialed this in by now.

    Any suggestions are appreciated. Again, carb settings are currently stock, have a uni air filter and full exhaust. Bike doesn’t run any worse than it did with stock, but it surely doesn’t run noticeably better...not even slightly. Valves are in spec.
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Mon Nov 30, 2020 8:35 am

    Hello,
    You absolutely need to rejet. Even with the stock exhaust they are in dire need of jetting to run as it should.
    That said - to help you with the jetting we will need your elevation and even region will help.
    Here is a basic guide to be used as a reference for the pilot jet. I went one up on the pilot jet also but do not have my records to give you that size right now. Maybe someone will chime in and have that number for you.
    You should remove the seat & lift the tank. The carb boots loosened will allow you to rotate the carb CW position to get to the underside and remove the float bowl. Pretty straight forward but make sure you check the throttle & hot start cables are free to rotate and good after repositioning the carb. You might want to do the want is called the tie wrap mod also. That is basically hard wiring the accelerator cam to the index lever. Just gets rid of the gap/ slop in quick hard snaps of the throttle. If jetted spot on there will be zero bog on hitting the throttle.

    You are going to love that bike once you get it jetted right. They are like a different bike!
    One other nice item to add is an aftermarket adjustable air / fuel screw. Slight adjustments with temp. altitude and air density keep that bad boy running perfect. Get a brass one not aluminum.

    Jetting Guide for Main Jet:(pilot 45) CRF450R/X

    Sea level....165
    2000 ft.......162
    4000 ft.......160
    6000 ft.......158
    8000 ft.......155


    Temperature/Elevation:
    One main jet size (up/down) for every 2,000 feet or 25 degrees in temp.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Leardriver
    Posts: 462
    Joined: Wed May 05, 2010 10:33 am

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Leardriver » Mon Nov 30, 2020 3:36 pm

    Has the bike been ridden recently before the exhaust change? A carb that needs cleaning from sitting can keep the bike from running.

    I have dyno'd nearly every exhaust made, just about, and yes, your money has been flushed down the drain. If you pick up one HP at redline, then you lost 2 in the midrange where you actually ride it. The OEM engineers know all about exhaust flow, and in a very competitive market, they aren't about to plug the bike up to where it won't run. Maybe on the off road models a little, but not on the R.

    The same with cars. They were choked off on the 1970's, and giving them dual exhaust and letting them breathe could make a little more power, but modern engineers test every flow characteristic, and aren't going to leave much on the table. The same with cold air intakes.
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Mon Nov 30, 2020 5:34 pm

    Hello,
    You absolutely need to rejet. Even with the stock exhaust they are in dire need of jetting to run as it should.
    That said - to help you with the jetting we will need your elevation and even region will help.
    Here is a basic guide to be used as a reference for the pilot jet. I went one up on the pilot jet also but do not have my records to give you that size right now. Maybe someone will chime in and have that number for you.
    You should remove the seat & lift the tank. The carb boots loosened will allow you to rotate the carb CW position to get to the underside and remove the float bowl. Pretty straight forward but make sure you check the throttle & hot start cables are free to rotate and good after repositioning the carb. You might want to do the want is called the tie wrap mod also. That is basically hard wiring the accelerator cam to the index lever. Just gets rid of the gap/ slop in quick hard snaps of the throttle. If jetted spot on there will be zero bog on hitting the throttle.

    You are going to love that bike once you get it jetted right. They are like a different bike!
    One other nice item to add is an aftermarket adjustable air / fuel screw. Slight adjustments with temp. altitude and air density keep that bad boy running perfect. Get a brass one not aluminum.

    Jetting Guide for Main Jet:(pilot 45) CRF450R/X

    Sea level....165
    2000 ft.......162
    4000 ft.......160
    6000 ft.......158
    8000 ft.......155


    Temperature/Elevation:
    One main jet size (up/down) for every 2,000 feet or 25 degrees in temp.
    Thank you for the advice. I’m on Long Island so id say 0-500 feet elevation is what it should be jetted to. Riding in 50-85 degree temps.

    I did ride the bike prior to changing exhaust and no noticeable issues. There isn’t really an issue now, except for no improvement on a full exhaust system. Although the bike mainly sat for past 8 years, it was at least taken for a 10 min ride 3-4 times a year.

    I noticed the JD kit does not include pilot jet, why? Is it worth buying this jet kit?
    Also, is it worth running a high concentration of sea foam and hi octane through it, let it sit, to help clean any gum. I work a lot and really don’t wanna start a project with this carb, if I can avoid it.
    Thanks for all the help. This is a great forum !
  • Leardriver
    Posts: 462
    Joined: Wed May 05, 2010 10:33 am

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Leardriver » Mon Nov 30, 2020 5:46 pm

    A 165 main jet and a 45 pilot will get you very close. The problem with jetting is that every 25 degree temperature change equals one main jet size. If you start out in the morning at 65 degrees, and end up in the afternoon at 85, you were probably right on at one point in the ride. Luckily, these bikes are very forgiving of being a few sizes off.
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Mon Nov 30, 2020 6:16 pm

    Thanks for the reply. I guess if I had to chose an average temp, I would say 70 degrees.
    What is the factory pilot jet size? Should I change the needle jet?
    Debating whether to buy JD jet kit and one or two pilot jets or just buy everything a la carte.

    I’ll probably run some sea foam through it too
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Tue Dec 01, 2020 5:42 am

    Do not waste your money on a "Jet Kit". You need one pilot and one main. Easy to change and you will be golden.
    While I do not agree with Mr. lear. An aftermarket muffler and proper jetting will greatly increase the running and ride ability of your bike.
    The engineers, which I am one of are required to make the bike leave the factory with a specific amount of allowed emissions and sound levels. Both of which are at the expensive of performance.

    Edit - Here is the jetting on my '06 450X. mind you, I'm a little fanatical on carburetors and finding perfection.

    MJ = 168
    PJ 48
    Pilot Screw or as many refer, Air / Fuel Screw. 1 1/4 out. Brass adjustable type.
    Needle, NCVS w/clip 3rd pos. from the top.

    This was in AZ and 2700 ft elevation. Temps ranged from the mid 50F to 115F. Riding from the 2700 ft to 5200 ft with no changes required. I presently live at 4300 ft and the bike has needed no adjustments. I do adjust the A/F screw a 1/4 turn either direction as air temp and density changes with the temps running 50F to 85F for riding.

    Hope that helps you.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Tue Dec 01, 2020 5:25 pm

    Thank you. Would it be worth changing the needle or adjusting the clip position?

    I’m not doubting your knowledge, i just don’t know carbs well enough to understand why a jd jet kit includes Maine’s and needles but no pilot, Other kits include main and pilot no needle, some say just adjust aF screw. Recommendations are all over the place. But since you are kind enough to respond, and I don’t have the time anymore to become a carb guru, I want to take your recommendation word for word so we know whether it works.

    Do you have a website you recommend where I can buy the pilot and main online? I used to shop at Motorsport a lot.

    Thanks again for the help.
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Wed Dec 02, 2020 6:13 am

    To answer the question fully, your altitude is the main factor. For me since I like things to be perfect the answer would be yes. I would do the complete job. I would buy the NCVS needle, a 48 pilot and a couple main jets in relation to your altitude. Not knowing your altitude I cannot give you that recommendation or the clip position. Don't waste your money on a jet kit.
    As for jets, I buy mine carb parts from rockymountainatv/mc. You can also buy them here from this site or many other online cycle parts shops.
    You may need to adjust the clip position a second time after the initial install to get dialed in perfect. its an easy from the top job.

    Dialed in you will not believe the difference in performance. Carb jetting does take patience and understanding. That is why you get tons of bad information - most people do not understand even how a carburetor works and the physics that are going on while you are missing fuel & air for combustion. Carbs get a bad reputation from misunderstanding and neglect.

    You'll get this set up. Just hand in there.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Wed Dec 02, 2020 8:02 am

    My bike has MAIN JET:178 PILOT JET:42. Not sure if this is accurate I haven’t checked my manual or pulled the jet yet, but if it is accurate, You are recommending to go down in size to 165 main. Wouldn’t that make the bike run leaner ?

    Also my altitude is 0-500ft
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Wed Dec 02, 2020 11:36 am

    I do not believe you will find your MJ to be a 178 from the factory.
    I was stating what I have for my altitude in my carb, which is a 168 which is one or two steps up from the OEM. That was before you stated that you are at 0-500 ft. Alt. You may need to be around a 170 or even a 172 if you do not go higher than the 500 ft. elevation.

    Why don't you pull your jets and verify what you have and we can go from there. If you did not buy the bike new they may have been already changed to run properly.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Wed Dec 02, 2020 2:52 pm

    Hello, I pulled it out.
    The main jet is 178
    The pilot is 42
    Needle is the middle clip 3 from top or 3 from bottom same thing. Needle says NJGR on it.

    Just to recap...Bike is 2008 crf450r with 61 hours on it that I bought new. Very well maintained, except for sitting factor... but I used high octane and stabil so that helps.
    Bike has a twin air filter (which it always had), fmf megabomb and powercore 4.
    Altitude is 0-400 ft or so.
    Temperature 70

    Thank you !
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Wed Dec 02, 2020 3:53 pm

    Ok - now that we are on the same page.

    With your current set up, I would go one size up one on the MJ & the PJ. You may also want to go one position down on the needle clip. But I would try the two jets before changing the needle pos.
    That will add more fuel through the entire range which is required with the higher flowing & lack of back pressure muffler.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Thu Dec 03, 2020 5:41 am

    Ok thanks.
    Also, do you have a recommended procedure for adjusting the air/fuel screw mixture?

    On another note, my wife has a 14 400ex with a slip on yoshomira. I bought it used and the guy told me he didn’t change jetting. Do you think I should go up one size in main and pilot with that too ?
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Thu Dec 03, 2020 7:34 am

    Yes, you will need to jet for the muffler. I will check my notes on my wife's 400EX. I added White Brothers muffler to it.

    As for your 450. Without doing some research I do not know what taper and diameters the needle is that you have in the carb. I do not know if you even need to change the needle for that model. It may have a taper that works fine with your set-up once you do the MJ & PJ.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200

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