250 EX Pilot jet ?

[ULTRAVIOLET70]

I know there's alot of threads out there asking jetting questions but I'm a new member and apoligize for asking a couple more. I recently bought my girlfriend an "05 250EX and can't quite get it right. It has a UNI filter, intake duct to air box modified, dynojet kit ( I konw waste of money but I'd already bought and installed it before finding this forum), and the spark arrester tip from my 400EX ( 400ex tip higher flow than 250EX and it was just lying around anyway). oh yeah needle 3rd position 102 main jet.
My problem is when you hit the throttle hard at idle it has a bad
hesitation just off idle then it runs fine all the wat to redline (plug does look good). It gets better if I adjust the pilot screw but can't
completely eliminate. From what I've read in the other threads it sounds like I possibly need to install a larger pilot jet but that's just me guessing, if that is what I need can someone tell me what is stock, what I should put in and where to get it (my local Honda dealer sucks and doesn't stock s#*t). Sorry I ran on so long any help would be great thanks.

[White_Knuckles]

This may sound insane but make sure your gas tank is full or roll over to reserve. The "on" position is a pipe up into the tank and can be level or slightly below fuel level. Looking in the tank it looks like lots of gas but the pickup tube is dry. Carb float bowl is getting gas time to time but engine will act lean.

Shouldn't have to move the needle clip at all. Put it back to stock position.

[ULTRAVIOLET70]

Thanks for the reply, but I know the tank is full (93 octane) and as far as the needle it's the one that came with the dynojet kit (not the stock needle) I've tried in various positions as per dynojet techline all made a difference but none that helped with problem. The needle is now in spot 3 where the dynojet instructions orig. instructed. Spot 3 is where bike ran the best over all except for right off idle. Thanks anyway I appreciate the help. Please someone give me a hand.

[ULTRAVIOLET70]

:confused: Anyone??

[MIKE400EX]

Our 250EX has the exact same mods as yours, including the end cap, but w/o the airbox lid, and I found that a 40 pilot/slow jet solved the stumble off idle. At first I tried a 42, which also got rid of the stumble, but then tried a 40 which worked so I left that in. Removing the air box lid seemed to help the most on ours. Got to find a pipe now, the bottom of the muffler rusted through.

[White_Knuckles]

There was an issue with DynoJet needles included in the kit. Look in past posts they may never have solved the problem with a replacement. It only takes a few minutes to try the stock needle which works fine with Dynojet mains. Something about the taper.

Our 250EX has the snorkle end opened up, 4 1" holes in the airbox, Uni round insert filters pushed in the holes, a Uni filter and T-4 slip-on pipe. At 2500 ft. 105 main, stock pilot and stock needle.

No off idle lag.

[MIKE400EX]

Not trying to hijack the thread, but how do you like the T-4 slip-on? Noisey?
Thanks

[White_Knuckles]

The Pro-Circuit T4 is the older style turn down tip with spark arrestor and US forest labeled.

Slip on is a good solution as the factory head pipe is stainless. The smaller dia. head pipe vs. "full" system $$ is also a better choice for me. A larger dia. pipe is for top end, smaller, low end torque.

Well made product, easy to service and repack (no rivets to drill out). Had to enlarge one mount hole to fit properly. Most powerfull? - hate to say it, but in 4 stroke world big gun vs. HMF vs. XXX ... they are all about the same free flow pipes. Loud? not really, it's a small bore motor. Performance? Yes, you can feel the difference combined with airbox, filter and main jet mods.

Me Likey :D

[ULTRAVIOLET70]

Thanks for the help. ONe question though. With the stock needle do I leave the clip in the stock position? Thanks again I'm going to try to get it this evening.

[MIKE400EX]

Thanks for the writeup WhiteNuckles!

I tried ours with the stock needle and it worked better in the stock position (2nd or middle, it only had 3 grooves). The DynoJet needle seemed to work better - marginally.

[WheelerBob]

Just adding my .02, I had a 04 250ex with an hmf full system, uni filter, and the snorkle opened up to full size. I used keihin jet's not dynojet. winter i ran a 125 main 3 turn's on the fuel screw, summer a 118 main 2 1/2 on the fuel screw, both with stock pilot and needle, and it ran like a raped ape, the mod's added a good 20% overall. Hope this help's:D :D

[ULTRAVIOLET70]

Hey Mike400ex what do you mean that the stock needle worked better, but then you state the dynojet needle worked better-marginally? Which is better stock or Dynojet?

[MIKE400EX]

LOL, I don't know either! Actually I meant to say that the OEM needle worked best in the middle groove, not up/down one - if that's the only needle you have. The Dynojet needle does seem to work better overall (again in the middle/3rd groove). The OEM in the middle groove worked OK but seemed a little fat. These were done at between 0 and 2000' @ ~85F. I'm going to get a HMF (full sys.) for it, I'll let you know how that works.

[White_Knuckles]

Altitude is huge variable dialing in your jetting. The "best" jet or needle is an unknown without some experiments.

Clip set to center is a starting point that seems to work for most as a permanent choice. Try going down in main sizes 1 step at a time if still lags. You may be introducing too much fuel at that range and not realizing you're still rich at WOT.

[ULTRAVIOLET70]

Alt is about 1000' . Maint jet is not an issue I've tried the dynojet
jets 88,92,96,98,100,102, and 104 ran best with 102 and switched back. But the stumble off idle has been there the entire
time regardless of main jet. Tried dynojet needle in spots 3 and
4 now back in 3 where it was better. Have tried adjusting the mixture/pilot screw in every possible position with every change and could not get rid of the stumble. I haven't yet tried a 40 slow/pilot jet as suggested by Mike400ex as I don't know where to find one. And haven't had a chance to try the stock needle
as you suggested earlier. Thanks again

[ULTRAVIOLET70]

Hey guys where can I get individual pilot jets for my 250EX and 400EX. Thanks

[White_Knuckles]

It seems you're on the right track with the last detailed post.

400EX owners seem to get results with larger pilots so it may work for you, but most 250's don't require the change. 102-104 sounds right for 1000'.

To see if it's mixture not timing or something else, try the air box lid on then off. What is the difference? Pull up 1/4 choke and test. Simulate a larger pilot forcing it rich.

Describe the off idle lag better. Is it under load (riding the machine)? Does it duplicate in any gear? Can you "roll" the throttle on and it's okay or is when you slam it?

Kehien Jets are easy to order through the dealer even if you hate 'em. Internet sites like Sudco are great, but shipping usually hurts for a couple jets.

[ULTRAVIOLET70]

Definitely seems to be mixture I've tried it with the choke before and it does eliminate the stumble. As far as when it occurs load doesn't seem to be a factor it's happens in neutral or gear (any gear if you let completely off throttle then stab it to WOT). And as you describe "roll" the throttle it is'nt noticeable only when I stab WOT from closed throttle. Oh yeah as far as my local dealer goes they can only get jets in lots of 5 @ 5 bucks a piece and they want me to buy all 5. See why I have a slight distaste for them.
Thanks White_Knuckles you've been really helpful.

[White_Knuckles]

That 5 lot policy is criminal! Never heard of that trick! Are there other brand dealers near? Yamaha and others use Keihin carbs.

What you are describing may not be throttle lag. Partially closing the choke would make a richer mix off idle and up if it cures the stumble, one step larger pilot may be the trick.

These little guys do not have a throttle pump to help lag by "injecting" a stream of raw gas. As push rod driven engines, the timing curve is gradual with the dreaded limiter. How much "snap" you're looking for may be out of reach.

Ours requires little coaching to bring up the front end but a full slam from idle to WOT makes some degree of lag.

If the bike's a girlfriend loaner, install a twist grip and call her done. It will run forever. Good luck.

[ULTRAVIOLET70]

Guys I give up I've tried everything suggested, and I'm just not satisfied. I understand White_Nuckles piont about the accelerator pump but,

These little guys do not have a throttle pump to help lag by "injecting" a stream of raw gas. As push rod driven engines, the timing curve is gradual with the dreaded limiter. How much "snap" you're looking for may be out of reach.

it doesn't mean I like it. Does anyone know if a 300EX/250X carb will work on my 250EX ? And if so what modifications are required to do so? Or does anyone have any other suggestions?
:confused: Why's the throttle response better in reverse?

[ULTRAVIOLET70]

:( Anyone?!?!?

[White_Knuckles]

You're right you shouldn't like it if indeed it's severe, noticieable lag.

Reverse acting different is odd. I wouldn't recommend testing WOT in reverse without a helmet!!

There may be a CDI or timing issue not identified. Study up on "plug chop" testing, proper plug reading and perform some field tests to eliminate the mixture.

Retarded timing will definitly duplicte your issue. Reverse sets a different timing curve noticed as the Rev Limiter kicks in sooner. Reverse testing is not a method to rule out timing.

My best advise would be A/B testing with another 250EX. Without a "benchmark" of how a stock 250 behaves, you can't establish if yours is really broken.

Poweroll makes a larger piston/cylinder kit for these and doesn't change out the stock carb, just jetting. So, some other model's carb is not the path to go. Their "bigbore" pulls fine without lag as so did the stocker.

[ULTRAVIOLET70]

Hey Guys I think I'm getting closer the bike seems to be running better. Once I'm satisfied I'll post what I did, but for now I've just got a quick question. Is a lean decel pop caused by the slow/pilot fuel circuit? Thanks