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Husqvarna TXC 450

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The bike,

Stock Needle 3rd clip from bottom

Aftermarket fuel mixture screw, Ziptie from memory

180 main

42 pilot

leak jet was drilled to 30 from memory

o'ring fitted

Stock Exhaust

spark arresting mesh removed from air box and all other emision restrictors removed

Mild Temperature 2-300m above sea lev.

The performance of the bike I cannot fault however there is a couple of things I would like answers too.

The bike idles nicely and always starts first or second kick when cold. 1st kick when hot. 1/4 to WOT performance is more than satisfactory for my riding, I can't fault it. Cracking the throttle during this range is very responsive bordering abrupt.

My issue is with off idle, when the throttle is very slowly taken off the idle position the engine start to run poorly and the revs drop off and maintain a constant speed. I'm only talking about a very small amount of rotation of the throttle 0-3%. If I hold the throttle in this position the bike holds a stready but poor sound. if the throttle is slowly rotated futher 3-5% the engine revs pick up substantially, up to where you would expect them to be. I can only assume there is a problem with the pilot circuit which is why I bought the fuel mixture screw to try and tune it better.

What I have discovered is the screw is having minimal effect on the idle. I can screw it all the way in and the bike continues to idle. Opeing the throttle with the screw fully in does result in a major bog. turning the screw out barely changes the engine note at idle but does allow the throttle to be cracked without the bog.

The bike has a large amount of decel popping unless the screw is turned a long way out.

I'm tempted to take the pilot out to a 45 but thought I would canvas the pro's first.

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Fuel screw and pilot is for idle only. Set it for a perfect idle and then leave it alone.

If you can close the fuel screw and the bike still idles, the pilot is too big. Do not select a pilot and adjust the fuel screw to resolve decel pops. If decel pops are a problem, consider checking for exhaust leaks or a better muffler.

Your issue is with the needle straight diameter. Being the problem is on initial throttle application and once the bike is able to pick up speed, it runs fine, I suspect it is slightly lean.

I would try a size richer on the last letter of the needle code, possibly two sizes.

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Thanks William,

I always thought the pilot had an impact on idle and just off idle.

In terms of going for a richer needle, would it be better off going with an aftermarket needle kit, ie JD or if the cause of my is known would it be easier and cheaper to simply by the needle I need?

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Well it sort of does. The pilot/fuels screw (there are actiually twe seperate circuits) flow all the time he bike is running. However, as the throttle opens, the percetage of fuel they add is less and less. Imagine a straw sized pipe always flowing (the pilot/fuel screw) and right next to it, a 12" pipe with a valve (the valve being the needle and the pipe diameter, the main jet). With the valve closed, the flow through the straw is 100% of the fuel flow, with the valve opened 1/4 of the way, the straw is maybe 2% of the total flow.

Now, first get your pilot and fuel screw correct:

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

Then... you can work on the needle choice. JD has done all the testing and his needles are good for 90+% of the situations. To tune use off the shelf needles, you'd probably have to buy 2 or 3 to get it right, minimum (unless you are lucky). If you are going to do it yourself, First get the pilot/fuel screw right and then test to see how bad the gentle roll on throttle response is (I assume you are aware the AP can be adjusted to provide extra fuel and the needle really is only for steady state). If the roll on is a lot worse, go two or three sizes richer on the straight diameter. If it is the same then only a size larger.

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