This Carb is driving me Crazy!

I am really confused. I would appreciate any feed back or advice. Basically I have done all the free mods, installed Dr. D full exhaust, AIS Removed. I am at sea level, 80-90 degree avg. temp and my 07 450 was previously jetted as follows:

MJ: 170

PJ: 48

Needle: JD red 4th position

Everything else stock

Results: No sputtering, no backfiring on deceleration but i did have an off idle bog in 4th.

After much review of the jetting database and research in general i decided to do the following:

1. Changed main jet to 168. this resulted in crisper throttle, exhaust sound.

2. installed GYTR fuel screw set at 1.5 turns out.

3. installed NGK cr9eix iridium spark plug. seems to wake the bike up a little.

4. installed R&D Power Pump with ALJ set at 40. installed stiffer spring on AP linkage and also did O Ring AP linkage mod.

Here are my concerns:

1. Bike doesnt run smooth at mid rpm, it kinda sputters.

2. Although not significant, i do have some backfiring on deceleration.

3. When i checked the plug it was kinda black. The plug has been in for a few months and i was adjusting the fuel screw during this time so i had been running at 2 turns out for a period of time that could have caused this.

4. with the bike running at idle, standing still, i adjust the fuel screw all the way in (closed) and the bike continues to run???

I am thinking, if the plug is dark, i am running rich so i dont need to go back to a main jet of 170. I have messed with the ALJ but i really dont feel anything significant so i keep it at the suggested 40 position. Should i go higher on the needle... to the 5th clip position? What about the bike running at idle with the fuel screw closed? do i need to change to a 45 pilot? Please help, i am beginning to go crazy trying to get everything dialed in. Thanx.

Fuel screw all the way in and still running is a sign that your pilot is rich, this only affects the bike at 0-1/4 throttle but can contribute to a bog if you're going from no throttle to throttle in 4th (or any gear) due to too much fuel being delivered prior to the AP squirt on throttle, possibly resulting in just a little too much fuel.

I would definitely drop to a 45 and readjust the fuel screw to optimum.

The only real way to see how your main jet is performing is to do a plug chop, anything else will skew the visual plug results, being rich on the pilot can certainly do this.

matt4x4 Could you give a rundown on the plug chop ?

Your pilot is too big I think. Try a 42.

You'll have a bog off of idle but you can get that out with adjustable leak jet.

With unleaded fuel a plug chop won't tell you all that much. It takes alot to color the plug.

Chop = get the bike on the road in to third gear (properly warmed up), then keep the throttle 1/2 to 3/4 open for about .3 miles - grab the clutch and hit the kill button. Check plug.

sounds like you've got a rich pilot jet. try one step down from the 48. since you're in the bahamas, the humidity may be a bit of a factor. maybe someone that lives in a humid place can help you out.

In case you'd like to know how to do a plug chop, (and yes, you can get pretty good results even without leaded fuel contrary to popular belief)

Use a clean or new plug.

Completely warm up the bike - ride for 10 minutes to do so.

Find an open stretch where you can open it up some under load - a gentle uphill is nice.

Accelerate aggressively through the gears until you get in a higher gear (4th or 5th) with your throttle wide open for 20 seconds, then pull clutch and hold the kill switch while chopping the throttle - doing this simultaneously stops the plug from firing (holding kill) and stops the tranny from turning engine over sucking more fuel in (pulling clutch). Now - probably in the middle of some field - you have to pull the plug (hope you brought tools and gloves) - the color of the plug insulator will tell you whether you're lean/rich/just right at that particular throttle opening - in this case full throttle - meaning only the main jet is being tested.

If you perform this at varying throttle intervals (easiest if marked on your throttle/handle grip) you can map where on the throttle your bike does what - essentially giving you a profile of your needle, thus allowing you to determine which needle profile may be more appropriate for your setup by using your current needle as a baseline.

The OP's plug is showing signs of being rich, because this likely was read after shutting it down from idle and not a WOT chop - it will indicate the pilot circuit's current state, NOT the main jet. Many make the mistake of thinking they have to adjust the main jet based on this reading.

Do you know how hard it is to get at the plug on a aluminum WR450?

The pilot and main jet are fun too.

Plug readings worked when there was leaded fuel. Now it only works if your really way off.

yeah I know how hard it is, leave your shrouds at home, take a ratchet to loosen seat and the bolts that hold gastank, once you pop it off the plug is easily accessible - 5 minutes at most - probably want to let the plug cool that long anyways.

Sure - It's a bit of a pain, but once you're dialed in it's not exactly something you have to do every second week.

As for your main and pilot - yes the aluminum bikes leave a lot to be desired in the way of access, at least on mine (steel frame) I can get to them in 2 minutes.

You know, I think everyone here including the OP knows how hard it is to access stuff on these bikes, if he could wave a magic wand at it and fix it, I'm sure he would.

If I could tell him to wave a magic wand TO fix it, I'm sure I'd suggest it!

He's been at this for a while now, it's obvious he's trying to dial it in right, and although you may have a problem with pulling your tank, I haven't heard him complain about it.

TribalBC asked me to explain what a plug chop is - I did - including mentioning running uphill since this helps get a better reading with unleaded fuel.

Then there's always lead additives available at stores if you still have problems.

OK I've just always called the plug chop a plug check. I thought maybe there was an actual cutting of the plug :thumbsup:

Yeah with the pain it is on a 07 I pretty much rely on seat of the pants jetting.

Thanks guys for all your advice. I changed my pilot from a 48 to 45 and what a difference!!!! The bike runs prefetctly smooth in low and mid range. No hesitation, bog or sputtering at all. I did notice, on a few occassions, some very minor sputtering at constant throttle in 5th and some very mild backfiring when i let off the throttle in 5th but I am hoping i can reslove this by adjusting my fuel screw and/or adjustable leak jet. Is there anything else that i should consider?

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