required changes for air box mods?

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nick5oh

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Mar 10, 2015
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Location
Hunstville, Ontario
Well.....just found out that my air box is gutted....never even realized it before and noticed it by fluke today. Sled is a 99srx...rest of the air box is stock. Carbs have bigger jets. I remember from previous cleanings. Gonna be taking them apart tonight for cleaning...I remember the jets are bigger than stock though. I will post what they are in a bit.
Clutching is stock. The whole sled is stock as far as I know.

Just need to know if I do need to jet bigger for a gutted air box? I assume I do but not sure.
Is there a benefit of holes drilled in the top shelf above the tubes in the lower shelf?

Thanks boys
 
nick5oh said:
By that you mean the shelf with the round holes has additional holes in it and that the bottom half of the box still has the separators/walls in it?
Click to expand...

Sorry I meant the cold air kit mod. By not gutted I mean it's the way it came from factory, they did away with the walls later in the model years.
 

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Yes, normally gutting or modding an air box will result in leaning out your sled a bit.
By your saying that the carbs have bigger jets "I remember from previous cleanings", I assume you've had this sled a while? How does the jetting look on the plugs when you check? I wouldn't worry about noticing that the air box has been modded and then start worrying that you need richer jetting if you've had the sled a while already and it hasn't burned down. I would also assume that if you've had it a while you have certainly checked how the jetting looks. I'm not trying to be rude, but it is a super important thing to check jetting when acquiring a used sled with carbs. Many people have bought a used sled from someone and then burnt it down. Buying my sled would be a perfect example. I average riding at 5000' and up and have my sled jetted accordingly. If someone bought it and then did all of their riding at 1000', well they're going to burn it down if they don't richen it up. If you know that the carbs have bigger mains, then one would assume that the previous owner richened it up when he modded the air box...but other factors come into play too, like elevation and temperature. And we all know how the word assume breaks down.

My opinion is to do some low range, mid range, and full throttle runs if you haven't already, read the plugs, and jet/adjust it accordingly. If you ride a fairly wide range of elevations, be sure to do these checks at the lowest elevation area you ride.
Remember, fuel always stays the same unless you change jetting, but air is more dense the lower you go in elevation. So, if you jet it at 5000' and it is spot on perfect, but then go ride at 2000', then there is more air and you will be leaner. Warmer temps are richer and colder temps are leaner as well, but this is less touchy as elevation unless pretty drastic.
 
mod-it said:
Yes, normally gutting or modding an air box will result in leaning out your sled a bit.
By your saying that the carbs have bigger jets "I remember from previous cleanings", I assume you've had this sled a while? How does the jetting look on the plugs when you check? I wouldn't worry about noticing that the air box has been modded and then start worrying that you need richer jetting if you've had the sled a while already and it hasn't burned down. I would also assume that if you've had it a while you have certainly checked how the jetting looks. I'm not trying to be rude, but it is a super important thing to check jetting when acquiring a used sled with carbs. Many people have bought a used sled from someone and then burnt it down. Buying my sled would be a perfect example. I average riding at 5000' and up and have my sled jetted accordingly. If someone bought it and then did all of their riding at 1000', well they're going to burn it down if they don't richen it up. If you know that the carbs have bigger mains, then one would assume that the previous owner richened it up when he modded the air box...but other factors come into play too, like elevation and temperature. And we all know how the word assume breaks down.

My opinion is to do some low range, mid range, and full throttle runs if you haven't already, read the plugs, and jet/adjust it accordingly. If you ride a fairly wide range of elevations, be sure to do these checks at the lowest elevation area you ride.
Remember, fuel always stays the same unless you change jetting, but air is more dense the lower you go in elevation. So, if you jet it at 5000' and it is spot on perfect, but then go ride at 2000', then there is more air and you will be leaner. Warmer temps are richer and colder temps are leaner as well, but this is less touchy as elevation unless pretty drastic.
Click to expand...

You are correct I have had the sled a few years now. I have rode it 3 winters and about 4500 Kms now.

I hear you on the jetting. According to Yamaha jetting charts I think it is jetted properly for where I ride elevation/temperature wise. I drag race cars so I am familiar with carbs and jetting for mods I’m just not too familiar with reading 2 stroke plugs. Only what I’ve learned on this forum.

There is 148.8 jets in 1 and 2 and a 150 jet on the mag side. The piston tops are covered in carbon and don’t have any wash it appears although like I said I’m not very familiar with plug readings on a 2 stroke and I am not familiar with reading piston wash either. When I get it out for a rip I will take a look at the fresh plugs to see what colour they are and report back.
 
So your piston tops are just black? If so then it was plenty rich the last time it was shut down.
New plugs are tough to read and take a while to show a proper color for your jetting. It will be easier to read used plugs when doing the checks. Lots of folks like to read the pistons, but I've always just used the plugs. Like maim said, hold throttle steady in the range you want to check and then hit kill switch. I like to see the plugs around a cardboard brown color, which I'm sure you've heard before. The mid range is where most burn down a sled, so don't get too crazy if you drop the needles/raise the clips a bit.
Take pics and post them here if you want some confirmation from everyone on what your seeing.

What elevation do you ride? 3000'-5000' or so? Your mains are about where my cousin used to run his SRX. His had a modded air box too.
 
mod-it said:
So your piston tops are just black? If so then it was plenty rich the last time it was shut down.
New plugs are tough to read and take a while to show a proper color for your jetting. It will be easier to read used plugs when doing the checks. Lots of folks like to read the pistons, but I've always just used the plugs. Like maim said, hold throttle steady in the range you want to check and then hit kill switch. I like to see the plugs around a cardboard brown color, which I'm sure you've heard before. The mid range is where most burn down a sled, so don't get too crazy if you drop the needles/raise the clips a bit.
Take pics and post them here if you want some confirmation from everyone on what your seeing.

What elevation do you ride? 3000'-5000' or so? Your mains are about where my cousin used to run his SRX. His had a modded air box too.
Click to expand...

I will post pics of plugs after I go for a rip. Thanks for all the info. I usually ride central ontario. Looks like elevation is anywhere from 500’-probably 1200’ at most. Ride usually -7c - -29c so basically stock jetting to + 1 on each hole should be good I guess. Sleds runs good and pulls hard, I may be a tad rich but better than being lean.
 
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