Holes in airbox door?

I am going home to fine tune my new FCR and have a feeling that i am a little too rich. I have seen some drill a few 1" holes in the airbox cover. Can i do this instead of changing the jet

Nope. You need to jet.

Nope. You need to jet.

ya i figured that. just looking for the easy way out. Just curious though as to why some people do that?

Just to get even more air to the engine once they've done all the mods.

But jetting is pretty important. Really no way around that.

It's worth it, trust me!

Steve

Just to get even more air to the engine once they've done all the mods.

But jetting is pretty important. Really no way around that.

It's worth it, trust me!

Steve

Will do. Thanks:cheers:

The current rage of all the holes in air box doors is a bling thing. No performance gain, in fact, there is the potential for performnce loss due to the passing air potnetially causing a vacuum.

The 3X3 is plenty for all but the wildest engines. Those that need it can open the top easily to 4X4 and that is more than enough.

The current rage of all the holes in air box doors is a bling thing. No performance gain, in fact, there is the potential for performnce loss due to the passing air potnetially causing a vacuum.

The 3X3 is plenty for all but the wildest engines. Those that need it can open the top easily to 4X4 and that is more than enough.

I'll be honest, I disagree. I had to run some errands so I decided to take the cover off and see if I noticed anything. I immediately noticed a difference. Low end throttle response is increased and it pulls harder. It wheelies in 2nd so much easier with the cover removed.

I'm a pretty realistic guy, and I'm telling you, there is a difference. I honestly am very surprised myself.

Steve

I am going home to fine tune my new FCR and have a feeling that i am a little too rich. I have seen some drill a few 1" holes in the airbox cover. Can i do this instead of changing the jet

So what jetting are you running now?..Altitude?

Any other mods...What pipe?

Done 3x3 hole?

On a stock engine with an fcr and free flow filter like K&N, the 3x3 should be enough air...

What makes you think its running rich?

I had my bike dynoed and when I removed the air box cover, there was an increase of 1.55 hp. Granted, it was running very rich.

I'll be honest, I disagree. I had to run some errands so I decided to take the cover off and see if I noticed anything. I immediately noticed a difference. Low end throttle response is increased and it pulls harder. It wheelies in 2nd so much easier with the cover removed.

I'm a pretty realistic guy, and I'm telling you, there is a difference. I honestly am very surprised myself.

Steve

If you noticed an improvement with the door removed, you are jetted too rich. My 470 did not gain anything with the airbox door removed.
If you noticed an improvement with the door removed, you are jetted too rich. My 470 did not gain anything with the airbox door removed.

:thumbsup:

That was my scenario, running too rich.

Well, I'm running a 165 main, but that's with my E with a full Muzzy.

So, let's say I am running rich, if removing the cover makes it run better, that proves that removing the cover allows the engine to breath.

If it didn't make a difference, then it would run rich with or without the cover.

Again, I don't think I'm running rich.

Steve

Well, I'm running a 165 main, but that's with my E with a full Muzzy.

So, let's say I am running rich, if removing the cover makes it run better, that proves that removing the cover allows the engine to breath.

If it didn't make a difference, then it would run rich with or without the cover.

Again, I don't think I'm running rich.

Steve

If you let more air in ( and it runs better)........:thumbsup:

think about it.

Well, I'm running a 165 main, but that's with my E with a full Muzzy.

So, let's say I am running rich, if removing the cover makes it run better, that proves that removing the cover allows the engine to breath.

If it didn't make a difference, then it would run rich with or without the cover.

Again, I don't think I'm running rich.

Steve

So, you don't think you're running rich yet readily recognize that allowing more air into the intract tract makes it run better. For a given amount of fuel in a given situation there is a perfect quantity of air for best combustion. In your situation, by removing the side cover you're allowing the engine to get closer to that perfect ration of fuel/air. So, if it needs more air to run better what does that mean in terms of how your engine is currently jetted? No way can you say it's correct with a straight face. If it was correct then removing the side cover would make it run worse.

OK, what are the symptoms of running rich then?

And the point of this thread was whether or not removing the side cover, or cutting holes makes a difference. That, I proved to be correct. It does. The stock set up is more restrictive.

OK, what are the symptoms of running rich then?

If the jetting stays the same (ie no changes between a bigger and smaller airbox opening):

More air moving through makes it run better = running rich

Less air moving through makes it run better = running lean

As stated before a 3x3 opening supplies plenty of air for a properly jetted carb, if you open the air box bigger you will end up putting in a bigger jet to get it properly jetted but you will not gain any power over the 3x3 opening with the smaller (proper) jet. The size of the opening will matter if you have one of Eddie's mega motors or similar. Almost all jetting advice given here assumes a 3x3 opening.

Well, I'm running a 165 main, but that's with my E with a full Muzzy.

So, let's say I am running rich, if removing the cover makes it run better, that proves that removing the cover allows the engine to breath.

If it didn't make a difference, then it would run rich with or without the cover.

Again, I don't think I'm running rich.

Steve

No, it means the main jet is to large for the vacuum signal. With the airbox door removed, the vacuum signal at the venturi is weaker, so less energy is available to suck up fuel and therefore it leans the bike out. If your jetting were correct, the bike would go lean with the airbox door removed.

I bet even a 158 would be too rich for you. This is the accepted method for testing a main without a dyno and A/F tool (both of which I use).

Main Jet

Starting with the recommended main, remove the airbox door and go for a ride (bike fully warmed up, 3rd or fourth gear, up a slight hill). Is it better or worse?

If it is better, you need a smaller main.

Go down one size, replace the airbox door, ride. Remove the airbox door and test again. Better or worse? If better, go down a size again. Keep repeating this till the test with the airbox door is worse.

If it was worse with the airbox door removed, tape over 1/3 of your airbox opening, test (airbox door on, of course).

If it is worse now with the tape and was worse with the airbox door off, your main is just right. You are done!

If it seems better, you need to go up a size in main jet. Then test it again (remove the tape). Replace the tape, test again. If with the tape on it is better, go up another size in main. Keep repeating this till having the tape on is worse than with it off.

To finish up and ensure you are set accurately, retest the bike with the tape off (airbox door on), ride it, then remove the airbox door (tape off, of course). Best performance should be with the airbox untapped, airbox door on.

If the jetting stays the same (ie no changes between a bigger and smaller airbox opening):

More air moving through makes it run better = running rich

Less air moving through makes it run better = running lean

As stated before a 3x3 opening supplies plenty of air for a properly jetted carb, if you open the air box bigger you will end up putting in a bigger jet to get it properly jetted but you will not gain any power over the 3x3 opening with the smaller (proper) jet. The size of the opening will matter if you have one of Eddie's mega motors or similar. Almost all jetting advice given here assumes a 3x3 opening.

+2 on this

With a mega motor, a 4X4 is more than enough (that is a 77% increase in size)

I agree with William. A 4x4 is way big enough. Most big v8 engines have a carb not much bigger than that, and how much air do they require?

Wow, I had no idea answering the OP's question would turn into this.

I went back and found a dyno I did a year and a half ago. I said the it was pig rich until about 5000 RPM, then it was steady at 13:1. This was with the stock exhaust.

I figured if I dropped the main jet size that it would probably be OK below 5000 RPM, but then lean up high.

Looks like I'm going to be taking the bike apart and look for that jet kit that I have laying around to put a smaller jet in.

I really appreciate the help everyone.

Steve

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