Modifications - Performance Discuss aftermarket and DIY performance modifications

drilling main air jets

Old 07-12-2011, 08:49 AM
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drilling main air jets

I just got a jet kit from factory pro, the crb-h77-1.7-RK. They include two drill bits for drilling the main air jets. I've not been able to find a picture that shows the location of the MAJ and there seem to be no mention of them in the repair manual. Can anybody clarify the location of the MAJ for me or better yet a picture showing location.

I was also curious as to why the main air jets are enlarged? I heard that HRC's kit blocks them off. does anyone know what they are trying to achieve here?

I appreciate your help guys thanks
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Old 07-12-2011, 09:01 AM
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It is one of the three brass bits you can see on the top of the carb by where the stacks bolt on. I don't remember which one off the top of my head and don't have a pic right now.

Why they would do it, I have no idea.
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Old 07-12-2011, 09:07 AM
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Umm I have a factory pro kit (forget which one) and it doesn't have any drill bits IIRC.. I haven't installed it yet, so I can double check when I get home.
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Old 07-12-2011, 09:08 AM
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Main air jets, or slide lifter holes?

Because it does make a difference =)

Mike has done a pretty comprehensive carb over-view for our particular bike and why you shouldn't drill out the slides.

And when my FactoryPro kit was installed, they weren't drilled out!
I would say that should only be done when you have a dyno handy to really fine tune everything.
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Old 07-12-2011, 09:08 AM
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if the kit is talking about drilling another hole in the carb slides im pretty sure your not supposed to do that.. personally I have not done any drilling but there are multiple discussions about carb set ups and whether or not to drill the slides (search function)
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Old 07-12-2011, 09:36 AM
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I've read the post about drilling the slides but this is diffently talking about the main air jets and not the slides. Thanks that puts me in the ballpark, still alot to chose from. I would also like to know why I am altering somthing before I do it especial because I don't think there is any going back. From what I understand they are prat of the carb and can't be switched out.

Last edited by rich.m; 07-12-2011 at 09:38 AM.
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Old 07-12-2011, 11:09 AM
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found this on their website

"
Factory RaceKits are carb kits that require modifications to the carb body. That may include drilling, tapping, reaming or other mods. These operations should NOT be done by one who is not comfortable with modifying expensive carb bodies!
"
sounds like you're not comfortable!
why is this text centered idk!
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Old 07-12-2011, 11:37 AM
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Originally Posted by nothing View Post
found this on their website

"
Factory RaceKits are carb kits that require modifications to the carb body. That may include drilling, tapping, reaming or other mods. These operations should NOT be done by one who is not comfortable with modifying expensive carb bodies!
"
sounds like you're not comfortable!
why is this text centered idk!
+1 Except is there a difference between racekits and Jet kits? Because I know there's diff. stages of the DJ kits. If it's just the phrasing then no more for me to say =)

The main air tubes adjust the amount of air that is going to enter your engine with the fuel and will effect the overall atomization and emulsion of the fuel and air.

By adjusting it to be more open, you are hence allowing more air into the carburetor at any given RPM. This is going to be matched with having the larger jets, remember that there is a A/F (air/fuel) ratio that is best for the bikes and best for performance.

One thing to bear in mind is that by drilling any air passages, is that in all cases I've seen, it goes WAAAAAY lean. I tend to recommend running rich vs. lean (if anything) so it's difficult to judge on whether you should do this or not from a running standpoint. I'm planning on reverting mine close to stock because it gives you the best baseline for tuning properly.


If you're afraid of doing the work, then just don't drill the mains. It's not that big of a deal, just make sure to check your plugs frequently for fouling.
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Old 07-12-2011, 12:18 PM
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The Factory Pro crb-h77-1.7-RK kit is a very radical kit. Most of us use the 1.1 titanium needle kit instead and the information on this forum pertains to that kit. I don't recall reading about anyone using the crb-h77-1.7-RK unless their VTR is for track use only.
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Old 07-12-2011, 04:16 PM
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Well I was kind of busy this morning so here is a little more info for you.

Drilling the air bleed would also require you to run larger main jets, Kind of the reverse of the plugged air bleeds in the HRC lit with the small (140-150 range) main jets.

Why they would want to run a modified air bleed (unless the engine is heavily modified) doesn't make a lot of sense to me.

The HRC set up was for ram air or running no air filter (race applications) were the turbulence in the air box was causing problems and we all know how much this bike likes the airbox messed with.....)

So your best bet would be call (or you might be able to e-mail him) Marc at FactoryPro and ask him what exactly what you need to do to set your base line.
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Old 07-12-2011, 04:18 PM
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I would say return that kit and get the 1.1 or follow 8541Hawk's instructions to jet it on your own without a kit: https://www.superhawkforum.com/forum...-set-up-24769/
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Old 07-12-2011, 07:52 PM
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Originally Posted by lazn View Post
I would say return that kit and get the 1.1 or follow 8541Hawk's instructions to jet it on your own without a kit: https://www.superhawkforum.com/forum...-set-up-24769/
+1. the 1.1 Factory jet kit does not come with drill bits.
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Old 07-15-2011, 02:41 PM
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Thanks for the info guys I think I might try jetting with out drilling first. I am going to send an e-mail to factoy pro and see if they think I should drill the MAJ with my setup (which is stock except TBR exhaust and BMC street filter) I'll let you guys know what they say. thanks agian.
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Old 07-16-2011, 11:16 PM
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Originally Posted by rich.m View Post
Thanks for the info guys I think I might try jetting with out drilling first. I am going to send an e-mail to factoy pro and see if they think I should drill the MAJ with my setup (which is stock except TBR exhaust and BMC street filter) I'll let you guys know what they say. thanks agian.
do yourself a favor and have them exchange that racing jet kit with the 1.1.
unless you've been re-jetting carbs for a living that kit is only gonna give you headaches.
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