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JD Jetting fail - WR250F 2002

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I may have done something silly. I didn't think my bike was that snappy, or powerful, or anything like other people's descriptions of a WR250F. So I bought a JD Jetting kit.

I was on the fence, then I was told about the triple taper, and not having to think for myself, so I bought it.

So on receiving this kit I threw all the ideas about changing one thing at a time out the window and installed it. Now can I start my bike in under 1000 kicks. Actually that's probably not true, but I wasn't counting. Seriously, I got it started but only after some serious effort. I had another go today and gave up in no time. 

I have to admit I was leery about changing things so wildly after looking at what was already in there, but I made the cautionary move of recording all the changes. 

There's a question in all this.. I want to know if I should just change the pilot jet back to what I had, or change all the jets back and then introduce the JD ones one at a time? 

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A cold bike should start in just a couple of kicks. 99% of the time when that is not the case, the owner messed with something.

Does the hot start fully seat?

Cold engine always should be choked.

What pilot jet was in it and what number did you change it to?

What fuel screw is in the bike? Did you adjust it for a smooth idle with a hot bike?

When you kick, are you pressing the lever or jumping on it?

No throttle!!!

The needle and main have no effect of starting and idle

 

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The FCR carburetor has many wear items, when was your's last serviced ? 

Throwing in a 'jet kit' won't improve anything if others parts are worn out.

 

-vacuum plate seal

-accelerator pump diaphragm 

-fuel screw o-ring

-emulsion tube

-slop in accelerator pump assy from wear 

etc.

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13 hours ago, William1 said:

A cold bike should start in just a couple of kicks. 99% of the time when that is not the case, the owner messed with something.

Does the hot start fully seat?

Cold engine always should be choked.

What pilot jet was in it and what number did you change it to?

What fuel screw is in the bike? Did you adjust it for a smooth idle with a hot bike?

When you kick, are you pressing the lever or jumping on it?

No throttle!!!

The needle and main have no effect of starting and idle

 

Oh yes! I have little doubt that the owner is the cause of this problem! :blush:

Hot start is a beautiful new shiny one that works perfectly. Fresh carb boot too. 

Fuel screw is stock (fresh o-ring), set to 2 turns out per instructions in JD kit. 

Haven't been touching the throttle.

Also fresh fuel, clean air filter (but not freshly oiled), timing checked, clearances in spec, good compression, fresh spark plug, hot white spark. Fuel is getting through, I can smell it in the end of the tail pipe after some unsuccessful kicking. 

Here is the thing, pretty sure the choke made things worse. Engine wasn't even trying when the choke was open. Ended up giving it a good blowing out with the decomp lever pulled, fuel off and hot start. Then it started. But then would not start with the hot start in (although by that time the engine was up to operating temp). 

So I'm thinking too much fuel in the pilot. Because yeah, it should need choke.

Coming back the next day I tried to start it with no choke. It was doing a little bit of almost starting but just not. Choke killed it. 

I found a 48 pilot in there. That got replaced with the 42 in the JD kit. The reason that I was ok with trying that is because I realize that the main and needle have no effect on the starting, but my thinking is that the pilot has an effect on the choice of main and needle clip. That's why I'm thinking I need to change everything back to what I had in there before and start again. 

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7 hours ago, Wait-A-While said:

Oh yes! I have little doubt that the owner is the cause of this problem! :blush:

Hot start is a beautiful new shiny one that works perfectly. Fresh carb boot too. 

Fuel screw is stock (fresh o-ring), set to 2 turns out per instructions in JD kit. 

Haven't been touching the throttle.

Also fresh fuel, clean air filter (but not freshly oiled), timing checked, clearances in spec, good compression, fresh spark plug, hot white spark. Fuel is getting through, I can smell it in the end of the tail pipe after some unsuccessful kicking. 

Here is the thing, pretty sure the choke made things worse. Engine wasn't even trying when the choke was open. Ended up giving it a good blowing out with the decomp lever pulled, fuel off and hot start. Then it started. But then would not start with the hot start in (although by that time the engine was up to operating temp). 

So I'm thinking too much fuel in the pilot. Because yeah, it should need choke.

Coming back the next day I tried to start it with no choke. It was doing a little bit of almost starting but just not. Choke killed it. 

I found a 48 pilot in there. That got replaced with the 42 in the JD kit. The reason that I was ok with trying that is because I realize that the main and needle have no effect on the starting, but my thinking is that the pilot has an effect on the choice of main and needle clip. That's why I'm thinking I need to change everything back to what I had in there before and start again. 

Yeah, 48 was way too big. 42 should solve your issue. Check float height as well. Then install a new spark plug.

While the pilot has an effect on the needle and main (they all build upon one another) the amount is pretty insignificant. Get the idle/fuel screw right before you worry about the needle and finally the main.

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31 minutes ago, William1 said:

Yeah, 48 was way too big. 42 should solve your issue. Check float height as well. Then install a new spark plug.

While the pilot has an effect on the needle and main (they all build upon one another) the amount is pretty insignificant. Get the idle/fuel screw right before you worry about the needle and finally the main.

Ok, I'll just worry about the pilot circuit for now.

I read somewhere a post from you that says to adjust the idle speed knob so that about 1/16" of the slide cutaway is showing. Is that the default position I should be using? 

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1 hour ago, Wait-A-While said:

Ok, I'll just worry about the pilot circuit for now.

I read somewhere a post from you that says to adjust the idle speed knob so that about 1/16" of the slide cutaway is showing. Is that the default position I should be using? 

When doing a full carb disassembly and reassembly, you need to have the slide slightly up to enable running, 3/32" is nothing more than a starting point for idle speed. Once the bike is running, you immediately rest the idle speed (Black knob on the side of the carb) to a normal idle. Ride the bike for 15 minutes or so, and do the fuel screw fine adjustment.

To see what I mean, next time you have the airboot off the carb, look inside and see the small gap at the bottom of the slide? All you want to do when doing a full reassembly is get it in the ball park.

Fuel Screw/Pilot Jet
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 fuel 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 knob 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 speed (knob) 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 fuel 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 1,850 rpm, but go by the spec in your manual.

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Ok, so I think I can officially rule out any jetting issues as being a cause of any problem, because I switched all the jets back to what was working before, and still no go. 

So my bike was running fine on the original jets. Then I installed the JD kit and the bike was near impossible to start. Now I've switched back to all the jets I had and cleaned the carb (again!) and I still can't get it to start. 

When I finally got it started with the JD Jets in it ran fine. Throttle response, everything. The idle was a little low, but I might have had the slide a little to closed up. It's just the starting that isn't happening. 

So I'm at a loss as to what this co-incident problem might be. 

Question - Since I got it to start eventually, and it ran fine, does that rule out electrical stuff... or not necessarily? 

I've done the obvious electrical things - checked the spark, unplugged the kill switch. 

Edited by Wait-A-While

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