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Mike Coe Jetting Interview - What You Need to Know

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I emailed Mike Coe a while back before jetting my 230 and thought that the email exchange could help anyone who's looking to jet the 230 properly. In my opinion, everyone should follow his instructions and tell the Power Up kit to go screw off. So, here we go.

Me: I'm going to be doing a series of mods to the 230, and wanted to start with jetting. I have a Pro Circuit full system waiting to go on, but here's the carb setup I intend on using based on all of the rave reviews:

120 main

45 pilot

03-05 needle, 4th notch from top

Mixture screw 1.5 turns out

Does this sound right for being in the Northeast at sea level? I also plan on modding the airbox by removing the snorkel and installing a Twin Air. Is that worth it?

I'm brand new to the 230 world, and from what I've read, you are the grand wizard when it comes to this bike. In other words, screw the Power Up needle :bonk:

Mike Coe:

Your data is correct, but I suggest going to a 48 pilot jet in most instances. No two bikes are ever exactly the same, so some fine tuning may be required, as with the fuel screw.

I did airflow and airbox/filter tests when doing my development years ago. Don't waste your time with the airbox. The stock box and air filter will flow more than required for my full race 250cc engines. Many claim to experience significant gains by removing the screens and making changes. IMO, its not necessary to mod the airbox in any way.

Good luck with your project! Once you get the thing uncorked and jetted, it will run much stronger. I feel confident you'll be impressed with the difference.

Me: Mike, thank you so much! I will go with the 48 pilot and play around with the mixture screw if there's popping on decel. What's the science behind the 120 main vs. the 132/135 in the Power Up kit? And why on earth are they selling the Power Up kit when your settings are much better?

Mike Coe: I'm not certain where Keihin missed the boat on the "Full Power" settings for the jet needle sold from Honda. Like most, I purchased the needle and installed the recommended 45 pilot and 132 main jet, after removing the inlet and exhaust baffles.

The bike exhibited improved performance over stock, but it was clear to me that the settings weren't optimum.

A short time later while performing some dyno testing on one of my 250cc race engines, I decided to perform some dyno runs on a stock bike. First with jetting as delivered and then with "power-up" jetting. Our dyno was equipped with an A/F analyzer. They really come in handy during testing!

To make a long story short, the OEM needle exhibited closer to optimum characteristics than the "power-up" needle, and the 132 main jet was too rich by a substantial margin. In fact, the 120 is still a little on the rich side.

These changes were immediately noticeable during seat of the pants testing directly afterwards!

So again, I can't say if the needle sold for "power-up" was ever fully tested. Maybe it was designed or extrapolated from proposed flow data provided when the baffles were removed. I don't know.

I do know from my own testing and from others that have gone to my settings after using the "power-up" settings also find improved performance.

Me: Thanks, Mike. You've been a huge help. I will certainly contact you when I'm ready to take the next steps with my 230. Out of curiosity, what work do you do on the 230 to make it a stronger machine?

As for the mains, I was thinking about my ZRX1200 and the jetting I did to it. Rather than keep the airbox, I installed individual K&N pods. Main jets for those were about 142s while the airbox kits were somewhere around the high 120's. I think the fact that the airbox is maintained on the 230 is huge in determining main jet size. I wonder what would happen if I installed a pod filter and got rid of the airbox?

Mike Coe: We went that far during our testing in order to see if the air-box was in any way restrictive, going as far as running the carb open on the dyno. Personally, if your planning to run an open K&N like a lot of flat trackers do, I feel certain you won't see much if any need for larger jets like you did on your street machine. As long as the engine remains otherwise stock. The addition of an aftermarket pipe may require some minute changes.

My development work consisted mainly of achieving a goal of producing 30 RWHP out of a modified CRF150/230. I achieved it that goal with a lot of hard work and many testing hours! I have made hundreds of dyno runs (chassis) with these engines/bikes and know what works and what doesn't.

Of course dyno runs aren't the only testing I've done. Like many, I truly enjoy these bikes and have owned a number of them since late 2002. They are the ONLY engines I work with/on. Throttle response and crisp carburetion is a key element to my satisfaction. What good is a powerful engine if it runs like crap except at wide open throttle positions?

A number of places sell carb kits designed for 2 strokes and claim they are shipped "pre-jetted". I have re-worked so many of these kits for customers its ridiculous. Anyways, I advise you stick with the Keihin on the bike. It is a VERY good carb for your application.

Me: Thanks, Mike!

Edited by Professor XR

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Thank you for sharing that with the rest of us. I always thought removing the backfire screen and/or drilling a bunch of holes in the airbox on this bike would gain nothing. It's really nice to know what works and what doesn't and it's awfully nice of Mike to share the results of his hard work with the rest of us.

Thank you Mike!

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Thank you for sharing that with the rest of us. I always thought removing the backfire screen and/or drilling a bunch of holes in the airbox on this bike would gain nothing. It's really nice to know what works and what doesn't and it's awfully nice of Mike to share the results of his hard work with the rest of us.

Thank you Mike!

Totally! Mike is a really great guy. You were right about removing the intake restrictor--I rode with it out briefly and noticed a bit of a snappier throttle response. Thanks!

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Testimonial,

I took the bike out this weekend for a full day. First time out with the new pipe and jetting.

The bike ran like a bat out of hell compared to before the mods.

Still can't keep up with the 450's. Close though.. :lol: ha ha..

Highly recommend the set up. Thanks to the above mentioned my bike runs great without a bunch of testing and screwing around.

You guy's saved me alot of time and trouble and other people should follow. :bonk:

Tom.

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Glad to hear it worked out. It always makes us happy to help others avoid costly mistakes and/or avoid time-consuming trial-and-error setups.

Thanks for letting us know the results.

Edited by VortecCPI

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Totally! Mike is a really great guy. You were right about removing the intake restrictor--I rode with it out briefly and noticed a bit of a snappier throttle response. Thanks!

Interesting.

A while back, I too had read the post about Mike Coe saying that air box mods were not necessary and interpreted that to mean that it was not necessary to remove the snorkel . . . so I didn't when I rejetted an '04 230 I got about 6 months ago.

Guess I've got another no cost mod to do now. :bonk:

Edited by thumpnokie

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dead thread? today i installed a 48 pilot and a 120 main on a 04 crf230 stock needle clip in 4th slot restrictors removed it seems to bog a bit on the botom end, i tryed adjusting the fuel screw and i,m at about a turn and a half or5/8 and i,m thinking adjustments on the screw dont make mutch change in idle but the idle varies or walks so am i probably right assuming that i should try a 45 pilot? allso their is a whare mark high up on the needle so i suspect a whorn needle and nedle jet guide may be partaly responsable for my wondering idle? any segestions apreciated guys thanks

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dead thread? today i installed a 48 pilot and a 120 main on a 04 crf230 stock needle clip in 4th slot restrictors removed it seems to bog a bit on the botom end, i tryed adjusting the fuel screw and i,m at about a turn and a half or5/8 and i,m thinking adjustments on the screw dont make mutch change in idle but the idle varies or walks so am i probably right assuming that i should try a 45 pilot? allso their is a whare mark high up on the needle so i suspect a whorn needle and nedle jet guide may be partaly responsable for my wondering idle? any segestions apreciated guys thanks

dead thread? today i installed a 48 pilot and a 120 main on a 04 crf230 stock needle clip in 4th slot restrictors removed it seems to bog a bit on the botom end, i tryed adjusting the fuel screw and i,m at about a turn and a half or5/8 and i,m thinking adjustments on the screw dont make mutch change in idle but the idle varies or walks so am i probably right assuming that i should try a 45 pilot? allso their is a whare mark high up on the needle so i suspect a whorn needle and nedle jet guide may be partaly responsable for my wondering idle? any segestions apreciated guys thanks

Idle that varies or walks won't change from a 48 to a 45 pilot. Sounds like a air/vacuum leak somewhere.

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humm...motor didnt surge or had no wondering idle before being uncorked and re-jeted , it just wouldnt idle worth a crap and wouldnt rev up well. maybe tomorow i will reinstall carb in intake boot maybe spray around and try and find a air leak

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