Pilot jet vs. K&N filter?

[simi_ed]

OK, I'm looking for opinions:  I have a K&N replacement for the air stock filter.  My FJ seems a touch lean at low rpm/low throttle.  I'm talking 1,300-1,500 RPM and 0-1/8 throttle.  Low speed trolling, IOTW.  It seems kinds lean right there, but by 2K, all is right.  I went through several cans of spray cleaner, compressed air, ultrasonic cleaning of jets, several vacuum leaks, etc to get where I'm at.
Engine is all stock, carbs all stock, exhaust stock (except for flat-spot on end of left muffler ).  I have Dyna green coils, but they've been there for a while too. 

Any thoughts about changing pilot jet to 40 from 37.5?  I'm concerned about killing fuel mileage, so I don't want to go willy-nilly changing, and besides, it's a PITA to do.
Again, looking for opinions.

[thuber3040]

Its been so long for me I cant recall if a 40 is one up, but if not then I would only go one up, the fun doesn't start until you goto pods, but its about 1000 times easier to take the carbs off and on, but you need a lot of jetting to debug that setup, but with stock exhaust and just the inside filter you should need very little adjustment if any, and if you pull the carbs for the pilots you might have them slightly clogged anyway, so either way its worth the efforts.

Oh and since you have the k&n, could you take a pic of how it goes in there and where that rod goes? my filter was not installed when I got this new bike. mines a 85, don't think that changes too much on newer ones I hope

My pods are waiting when I get ready for the big project,

[threejagsteve]

Ed,

What does it do on the fully-warm blip test?

Cheers, and Kookaloo!

[SlowOldGuy]

Ed,
If you want to experiment without pulling the carbs, then try shimming the needles about 0.020 to 0.040 inches.  In the 0 to 1/8 throttle range, that should be the idle jet and mixture screw setting, but shimming the needles "may" help.  Besides, that K&N will lean out the midrange, so you'll need to shim the needles anyway.

It probably wouldn't hurt the bump the idle jet to a 40.  That's the stock size on my '85, but I'm also running the richer 144 air pilot jet.  My '85 definitely has better off-idle throttle response than my '93 with the leaner 37.5 idle jet and 155 air pilot jet combination.  I've been meaning to richen it up to see if I can make it as good as the '85.  

The idle jet probably won't hurt your mileage, but shimming the needles will.

Finally, trash the K&N and get a UNI replacement filter instead.

Thuber:
The K&N holder rod fit into the same slots as the stock filter holder wedges.  The ends of the bar go in first so the long part of the bar supports the edge of the filter.

DavidR.

[RichBaker]

I put 40s in my '90, it works great.... mixture screws are all around 1 turn. I also have the DJ 144 air correcter jets, installed long before I put in the 40s.
Back when our bikes were new, the normal method for meeting emissions standards with the big-bore engines was to run lean jetting at idle and off-idle carb circuits because thats where they run for the EPA testing..... I was very surprised that the DJ kit did NOT include larger pilots.

As an aside, if you live in a dusty region, I would recommend NOT using K&N air filters, they pass way too much silt for my tastes. I ruined an XR600 cylinder running K&Ns in it. Sanded the cylinder, basically..... all I use anymore are UNI filters, but any dual-density foam filter is good. The UNI dual pods are a popular choice around this Owners group. I'm running a UNI in-airbox filter...

[simi_ed]

Steve got me thinking, so yesterday I noticed two things.  My mileage seems much higher than normal (46.4 mpg) and the blip test pointed out that she's so lean that she won't take the throttle in a blip test.  Big flat spot, then catches up.  If I roll throttle open, all's OK. 

I think I'm gonna take another look at the mixture screws, then maybe try 0.020 of shims under the needles if the screws don't help.  Pilot jets may not be required after all.

[LA Mike]

I have the same flat spot/ hesitation problem just off idle. Only mods are dual Yoshi cans and Uni's. I have played with the air/fuel mix and I can't seem to fix it. The carbs have 37.5 pilot do you think going to a 40 will fix it???

[simi_ed]

Mike, have you tried to adjust out the flat spot w/mix screws?  If you have & it didn't work, I guess you're candidate for the pilot jets.  Get them from Gary McCoy or Mike K.  I got a few sets from Mike K a few years ago, they were ~$2 ea, instead of $10+ at the stealer.

[racerrad8]

Don't forget...

I have all of those carb parts in stock.

Randy - RPM
randy@rpmracingca.com

http://www.fjowners.com/index.php?topic=69.0

[cadmanmadman]

I went through the same procedure at the beginning of the summer.....same EXACT procedure as a matter of fact. Low restriction air filter with stock exhaust.

I am an absolute fanatic about jetting. I used to race MX fairly seriously and a small MX engine will SING when you nail it. By most people standards I 100% solved the problem. By my standards, I solved 97-99% of the problem. There was still an ever so slight stumble in precisely the region you are talking about....I refer to that as 'just off of idle'.

Previous owner had one of those dynojet carb jet kits so everything I needed was right there. Otherwise, like your situation, it would have driven me out of my mind. Pay $40 for a set of jets by mail, wait, install, not quite right, buy another set of jets, wait, etc.....

Let me take a look at the jets I ended up using and I will e-mail to you what I did.....BTW: I am in Boston at sea level so if you are at elevation your jet setting will need to be different. But you can use what I did as a guide anyway.

[cadmanmadman]

Oh, one other thing. When you are going through all the iterations of jetting, if I remember, you can poke a stub of a 2X4 or 2X6 under the rear end of the tank and everything will still run OK. That way you can get to alot of stuff while its running. I believe it has a fuel pump so I think the line can even go uphill if you have to. Fishing that throttle cable off and on was the biggest pain if I remember.

Don't forget to re-synch when you are all done too. The balance may change.

[cadmanmadman]

I went 1 step richer all across the board.

Next size up main jet, moved 1 clip UP on the needle (same jet), and 1 size up on the pilot jet. In addition, I squeezed the pilot air screw IN by 1/4 turn.

Mine gets 42 maybe 44 mpg. Not the greatest but it seems to be what it needs to run nice.

[andyb]

You can often take the tank off, turn it 180 degrees, and lay it on the tailsection.  This makes working on the carbs super easy. 

That being said, it's the wrong answer.  The right answer is to get a dedicated gas can, hang it off the ceiling, and put a 15' line to it.  Now you can't knock your gas tank off while you're working.  Don't ask, k?


As far as pilots, the fuel screws control about a quarter of the mixture at idle.  They're really meant to do fine tuning, and if you're off by too much they don't really feel like they've got much effect at all.  Buy yourself a set of bigger pilots, possibly a couple sizes worth depending on your mods, and you'll be in heaven.  Jets are around $12 per set, and it's money well spent even if you don't use some.