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2018 KLX250 camo ; former owner of 2006 TW (retired at 23k); 19' S3, 09' F-250, 97' Cherokee
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Discussion Starter · #1 ·
Hi all,

I don't remember that my old TW (sold a few years ago) had this hesitation. I purchased an '03 with 420ish miles on it last October. Upon initial throttle twist while moving in any gear, there's a split second hesitation before it surges forward. It's pretty consistent, so I've just adjusted my riding and throttle use by more frequent "blips" to lessen the effect.

Is this normal? I replaced the prior TW with a fuel injected dual sport, so perhaps my familiarity is based upon the newer F.I. throttle response? I sort of seem to remember blipping the throttle a lot with the prior TW and I do remember when I was breaking in the fuel injected one, I realized I no longer need to do this.

Other than that, the '03 fires right up without choke and keeps running very well. It does have a fuel filter, and I've since ran new gas (with seafoam) in it for about 100 miles since owning it.

Thoughts?
 

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2021 TW
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Smells like the carb may be the culprit. Does it still have the stock idle jet and mixture screw setting?
Its got low miles but does have a few years on it. So its had some time just sitting.Pulling the float bowl and having a look around couldnt hurt. Easy to do and you have access to the jets and mixture screw at the same time.
The tdubs seem to have a reputation for coming with lean carb settings.
 

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Hi all,

I don't remember that my old TW (sold a few years ago) had this hesitation. I purchased an '03 with 420ish miles on it last October. Upon initial throttle twist while moving in any gear, there's a split second hesitation before it surges forward. It's pretty consistent, so I've just adjusted my riding and throttle use by more frequent "blips" to lessen the effect.

Is this normal? I replaced the prior TW with a fuel injected dual sport, so perhaps my familiarity is based upon the newer F.I. throttle response? I sort of seem to remember blipping the throttle a lot with the prior TW and I do remember when I was breaking in the fuel injected one, I realized I no longer need to do this.

Other than that, the '03 fires right up without choke and keeps running very well. It does have a fuel filter, and I've since ran new gas (with seafoam) in it for about 100 miles since owning it.

Thoughts?
I had this exact problem; just barely off idle, slow or fast throttle movement, but slow you can really sense it, try 2 shims on the needle. The issue is when the pilot starts to overlap the needle and there's a bit of 'dead zone' where the pilot jet runs out of fuel and the needle hasn't moved enough to provide enough fuel. It's a lean bog you are feeling. No amount of pilot screw adjustment will fix this. In fact, it's likely you can not feel much, if any effect adjusting the pilot screw other than fully shut off, when the bike won't idle at all.
Since you don't have a cold starting bike, not needing choke when it's warm out, most likely the shims will work without changing the pilot jet, but I also installed a #34 pilot. Here's a link to shims. (Amazon link says it's no longer available) If you want 2, I can mail to you in an envelope. I think I still have a bunch in my stash. Here's the specs on the shims;
18-8 Stainless Steel Round Shim, Unpolished (Mill) Finish, Annealed, Hard Temper, ASTM A666, 0.010" Thickness, 0.125" ID, 0.187" OD (Pack of 25)

 

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2018 KLX250 camo ; former owner of 2006 TW (retired at 23k); 19' S3, 09' F-250, 97' Cherokee
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Discussion Starter · #5 · (Edited)
I had this exact problem; just barely off idle, slow or fast throttle movement, but slow you can really sense it, try 2 shims on the needle. The issue is when the pilot starts to overlap the needle and there's a bit of 'dead zone' where the pilot jet runs out of fuel and the needle hasn't moved enough to provide enough fuel. It's a lean bog you are feeling. No amount of pilot screw adjustment will fix this. In fact, it's likely you can not feel much, if any effect adjusting the pilot screw other than fully shut off, when the bike won't idle at all.
Since you don't have a cold starting bike, not needing choke when it's warm out, most likely the shims will work without changing the pilot jet, but I also installed a #34 pilot. Here's a link to shims. (Amazon link says it's no longer available) If you want 2, I can mail to you in an envelope. I think I still have a bunch in my stash. Here's the specs on the shims;
18-8 Stainless Steel Round Shim, Unpolished (Mill) Finish, Annealed, Hard Temper, ASTM A666, 0.010" Thickness, 0.125" ID, 0.187" OD (Pack of 25)

Thanks, Ski. When you say, "since you don't have a cold starting bike...." what are you referring to?

Perhaps I should clarify, the bike starts and immediately runs at any temp - without the choke. My '06 (purchased new) always needed the choke. I ran the '06 for 12 year/22k miles and never opened the carb, or adjusted anything.

I have no clue what's in the carb, as far as I know it hasn't been opened. The previous owner only added the cycle rack, handguards, and fuel filter. Prior to that it was a government-owned motorcycle.

EDIT: NEW INFORMATION
I just got back from a quick zoom up to the inland empire paper forest with a focus on when this hesitation occurs. It actually occurs after decelerating in gear - like going down hill - then, applying the throttle.
 

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I had this exact problem; just barely off idle, slow or fast throttle movement, but slow you can really sense it, try 2 shims on the needle. The issue is when the pilot starts to overlap the needle and there's a bit of 'dead zone' where the pilot jet runs out of fuel and the needle hasn't moved enough to provide enough fuel. It's a lean bog you are feeling. No amount of pilot screw adjustment will fix this. In fact, it's likely you can not feel much, if any effect adjusting the pilot screw other than fully shut off, when the bike won't idle at all.
Since you don't have a cold starting bike, not needing choke when it's warm out, most likely the shims will work without changing the pilot jet, but I also installed a #34 pilot. Here's a link to shims. (Amazon link says it's no longer available) If you want 2, I can mail to you in an envelope. I think I still have a bunch in my stash. Here's the specs on the shims;
18-8 Stainless Steel Round Shim, Unpolished (Mill) Finish, Annealed, Hard Temper, ASTM A666, 0.010" Thickness, 0.125" ID, 0.187" OD (Pack of 25)

Hey Ski Pro I have the exact same issue on my stock jetted '21.
It is very noticeable and irritating when you are putting around at slow speeds. I haven't found shims around here.
Any chance that same offer would extend to me ?
 

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Thanks, Ski. When you say, "since you don't have a cold starting bike...." what are you referring to?

Perhaps I should clarify, the bike starts and immediately runs at any temp - without the choke. My '06 (purchased new) always needed the choke. I ran the '06 for 12 year/22k miles and never opened the carb, or adjusted anything.

I have no clue what's in the carb, as far as I know it hasn't been opened. The previous owner only added the cycle rack, handguards, and fuel filter. Prior to that it was a government-owned motorcycle.

EDIT: NEW INFORMATION
I just got back from a quick zoom up to the inland empire paper forest with a focus on when this hesitation occurs. It actually occurs after decelerating in gear - like going down hill - then, applying the throttle.
I mean you don't need the choke to start a cold engine when it's warm out. If true, then likely the pilot jet is sized well. If you need to choke no matter the outdoor ambient air temperature, then going larger on the pilot will help. My bike was so cold, I'd have to run the choke for 10 minutes before it would idle without. After changing the pilot from #31 to #35, the bike would start easy without choke down to 55 degrees outside.

Regarding your edit. If it only occurs after a chopped throttle decel, then applying throttle, it could be the small side diaphragm on the carb. I think that is for keeping the bike from stalling on a throttle chop by slowly allowing revs to fall off. It's easy to open and check out anyway. There's a plunger and diaphragm. The cylinder plunger sometimes hangs up. It's brass in an aluminum carb body. Try burnishing the brass and using a little assembly lube putting back together. It should now slide easy when you chop and open throttle.
If it occurs when you are slowly rolling on the throttle from a stop, it's the needle position and shims should resolve. Start with one shim and work your way up. 2 was what I found worked, 3 was too much.
 

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2018 KLX250 camo ; former owner of 2006 TW (retired at 23k); 19' S3, 09' F-250, 97' Cherokee
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Discussion Starter · #8 ·
I mean you don't need the choke to start a cold engine when it's warm out. If true, then likely the pilot jet is sized well. If you need to choke no matter the outdoor ambient air temperature, then going larger on the pilot will help. My bike was so cold, I'd have to run the choke for 10 minutes before it would idle without. After changing the pilot from #31 to #35, the bike would start easy without choke down to 55 degrees outside.

Regarding your edit. If it only occurs after a chopped throttle decel, then applying throttle, it could be the small side diaphragm on the carb. I think that is for keeping the bike from stalling on a throttle chop by slowly allowing revs to fall off. It's easy to open and check out anyway. There's a plunger and diaphragm. The cylinder plunger sometimes hangs up. It's brass in an aluminum carb body. Try burnishing the brass and using a little assembly lube putting back together. It should now slide easy when you chop and open throttle.
If it occurs when you are slowly rolling on the throttle from a stop, it's the needle position and shims should resolve. Start with one shim and work your way up. 2 was what I found worked, 3 was too much.
That's very helpful. Thank you.
 

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On a perfectly jetted TW carb you can still blip the throttle faster than the RPMs will climb. That's the nature of a CV carb and is the result of it working to maintain proper stoichometry of air/gas. Notice there is no mechanical connection between the throttle & needle? The throttle is merely a polite request. The real gatekeeper is the slide and it only responds to vacuum not your hand. Another tuning parameter available is the slide spring. You can go lighter or clip windings to get the slide to respond quicker, right up until it unfavorably effects the air/gas ratio. But make sure your slide isn't sticking first.
 

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Well stated, vhortykho. If the slide spring is clipped, it is not expensive to replace when the result is undesirable.
However, drilling the slide with undesirable results is much more expensive. See 6) in link.


I am not in favor of either.

Balking/hesitation/stumbling is generally from a lean mixture. As opposed to "burbling" from overrich. Difficult to explain the difference, although "burbling" likely to produce a puff of black smoke.

Lean off idle is the result of:
1. Mixture screw too lean, probably less than 2 to 2 1/2 turns out from gentle seat.
2. Pilot jet too lean or partially obstructed (gentle probing with safety pin may help)
3. Needle too lean / not raised enough
4. Vacuum leak, possibly

Although not too lean, the slide diaphragm not operating to spec will slow transfer from pilot range to mid-range.
This occurs when:
a. diaphragm is not properly seated (placing used diaphragm in freezer for 15-30 minutes before installation can help)
b. diaphragm has pin hole leak
c. diaphragm is cracked (age)

Just my 3 cents for a Saturday morning.
 
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When I bought my 2003 XLH883 in December 2002, the dealer advised a 48 pilot to prevent hesitation.
It was not the best advice.
It worked well up to at least 5,000 feet elevation, but at 8,000 feet it was too rich to idle without throttle.
Proper advice would have been to replace the stock 42 pilot with a 45, ensure mixture ~2 1/2 turns out and then, if necessary, use a richer needle.

The moral of this story is that going overly rich on the pilot jet may work fine below ~5,000 feet, but not do well at higher altitudes.
 
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Any one who has chased carb issues knows that SportsterDoc's advice is worth A LOT more than 3 cents!
Very kind of you. Four cents?
 
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Well stated, vhortykho. If the slide spring is clipped, it is not expensive to replace when the result is undesirable.
However, drilling the slide with undesirable results is much more expensive. See 6) in link.


I am not in favor of either.

Balking/hesitation/stumbling is generally from a lean mixture. As opposed to "burbling" from overrich. Difficult to explain the difference, although "burbling" likely to produce a puff of black smoke.

Lean off idle is the result of:
1. Mixture screw too lean, probably less than 2 to 2 1/2 turns out from gentle seat.
2. Pilot jet too lean or partially obstructed (gentle probing with safety pin may help)
3. Needle too lean / not raised enough
4. Vacuum leak, possibly

Although not too lean, the slide diaphragm not operating to spec will slow transfer from pilot range to mid-range.
This occurs when:
a. diaphragm is not properly seated (placing used diaphragm in freezer for 15-30 minutes before installation can help)
b. diaphragm has pin hole leak
c. diaphragm is cracked (age)

Just my 3 cents for a Saturday morning.
Yes, this is it!

Drilling the slide to fix an issue isn't a fix, it's a bandaid imo. I'd go after that diaphram first, it's easy to get at and inspect and reinstall with a tiny bit of vaseline around the gasket side.
 
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