Author Topic: Low-RPM performance gap? Wavering idle and some lurching at <2,500 RPM...  (Read 1923 times)

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Offline ZX6Rob

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Hey, all,

In my 2001 Concours, I have the SISF 2-minute Mod Jet Kit, along with the Torque Cams, and had Mr. Steve himself perform a full carburetor disassembly and cleaning about 7 months ago.  The performance of the bike is great, and it runs like a champ any time the RPMs are above about 2,500.  I have noticed, however, that at idle, it kind of bounces around between 1,000 and 1,100 RPM, and that, when taking off slow, or just idling along in traffic at less than 2,500 RPM, the bike is VERY jumpy, lurching a bit under very light load.

My working theory is a clogged or partially-blocked idle jet, which would get all but overridden once the revs are up and the throttle's open.  I'm probably going to end up sending my carbs back to Steve later this year for another cleaning and inspection, but I'm curious if there's anything else that may be helping contribute to this problem.

Thanks for any help you guys can offer!
motorcycle, n. (mō'-dər-sīk-(ə)l) - 1. A large, leaky container of various dangerous, viscous, and difficult-to-clean fluids.

2001 ZG1000 Concours

Offline Daytona_Mike

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I can recommend a few simple things to look for but I do have one question. Did you get overflow tubes installed on those carbs? I am assuming you did but I want to be sure.

I would check for vacuum leaks. Sometimes those carb plug caps rot and fall apart from the heat. Sometimes the carb boots are loose. Recheck  and tighten the clamps.
Also you could check the spark plug wires and caps for issues.  That is another common failure point. While you have the spark plug  wires off do the   Free Power Mod and toss in a set of new spark plugs.

How old is the fuel?  I recently had my C10 sit for one month and the gas went bad. I had to toss the whole tank (of gas that is- not the tank), drain the bowls and new fresh gas fixed what seemed to me to be a clogged main jet.  It wasnt. It was old gas.
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Offline ZX6Rob

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I can recommend a few simple things to look for but I do have one question. Did you get overflow tubes installed on those carbs? I am assuming you did but I want to be sure.

I would check for vacuum leaks. Sometimes those carb plug caps rot and fall apart from the heat. Sometimes the carb boots are loose. Recheck  and tighten the clamps.
Also you could check the spark plug wires and caps for issues.  That is another common failure point. While you have the spark plug  wires off do the   Free Power Mod and toss in a set of new spark plugs.

How old is the fuel?  I recently had my C10 sit for one month and the gas went bad. I had to toss the whole tank (of gas that is- not the tank), drain the bowls and new fresh gas fixed what seemed to me to be a clogged main jet.  It wasnt. It was old gas.

Thanks for the suggestions.  Yeah, I do have the overflow tubes installed -- Steve performed that maintenance when I had my carbs out to him.  I replaced all of the plug caps on the carbs with new ones when I was reinstalling them, but I'll check things over once more and make sure there's no leaks.

The bike has sat for up to 10 or 12 days at a time, though I always try to have some variety of fuel-saver or Seafoam in the tank for that.  Could just be bad gas, too -- I'll try draining the tank and bowls before I strip the carbs off again.
motorcycle, n. (mō'-dər-sīk-(ə)l) - 1. A large, leaky container of various dangerous, viscous, and difficult-to-clean fluids.

2001 ZG1000 Concours

Online Ranger Jim

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Most bikes tend to be "jumpy" in first gear and low RPM. Part of it is due to the nature of the gearing. The C10 is geared pretty low in first gear (makes it easier to get going when you're loaded up for touring), combine that with the Torque cams and it doesn't take much throttle movement to result in a little "jump."  Try leaving it in second gear, that will smooth out the throttle response.

Also, IF you can only use NON-ethanol fuel in the bike. That ethanol crap will gunk up (technical term) your carbs quicker than you can imagine. SISF also recommends adding an ounce or so of TWO STOKE oil that contains TCW-3 to the gas. His experience is that it "coats" the inside of the carb and reduces the likelihood of carb issues due to ethanol gas.
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Offline ZX6Rob

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Most bikes tend to be "jumpy" in first gear and low RPM. Part of it is due to the nature of the gearing. The C10 is geared pretty low in first gear (makes it easier to get going when you're loaded up for touring), combine that with the Torque cams and it doesn't take much throttle movement to result in a little "jump."  Try leaving it in second gear, that will smooth out the throttle response.

Also, IF you can only use NON-ethanol fuel in the bike. That ethanol crap will gunk up (technical term) your carbs quicker than you can imagine. SISF also recommends adding an ounce or so of TWO STOKE oil that contains TCW-3 to the gas. His experience is that it "coats" the inside of the carb and reduces the likelihood of carb issues due to ethanol gas.

Yeah, I thought that might be it, and I'm just chasing ghosts...  Honestly, this is a minor annoyance at best, at any time where I'm not literally idling in 1st or 2nd in heavy traffic, the bike is smooth like silk.  The wavering idle got me a little concerned, but whatever the issue is, it's minor enough that I don't feel like tearing down the whole bike to find it.
motorcycle, n. (mō'-dər-sīk-(ə)l) - 1. A large, leaky container of various dangerous, viscous, and difficult-to-clean fluids.

2001 ZG1000 Concours

Offline Steve in Sunny Fla

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You should be able to have a rock solid idle, and be able to idle along in traffic with no throttle input at all. I just sent another bike out with that setup yesterday, it's stupid how strong it is at idle and coming off idle. So this makes me think there's a vacuum leak, or a valve clearance issue, or maybe the cams didn't get installed correctly. You should have about 1.5" foam in the airbox, and if you have the 90* screwdriver I've been seeing lately that I like the idle a little better with the TQ cams at 2.5 turn out rather than 2 turns out. Other obvious stuff is the free power mod, and checking for strong idle voltage. 14.3V is common when all is as it should be. If you haven't done it, I would also pull the plug wires out of the coils and check resistance, it should be about 5k. Not uncommon to find one or 2 open. If you watch my video "does your zg1000 do this" a properly set up set of carbs and cams WILL do that. The bike I just sent out would idle so low the needle was bouncing off the very bottom line on the tach. This is what to expect when everything is right, if you don't have it, start working down the list. Good luck - steve
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Offline DC Concours

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While Rob goes down the list I have a sidebar...

For the rest of us w/o your torque cams but with your jazzed up carbs, is it normal for the bike to jump between 1000-1100 rpms at idle?

Mine does.

Offline Steve in Sunny Fla

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While Rob goes down the list I have a sidebar...

For the rest of us w/o your torque cams but with your jazzed up carbs, is it normal for the bike to jump between 1000-1100 rpms at idle?

Mine does.

  Stock cams aren't going to give the same solid idle quality the torque cams give, so yes, you'll see some fluctiation. it comes from the overlap. That said, you get the same list too. Careful syncing, along with all the other stuff matters. I can send out a very nicely done set of carbs, but they still need the installer to put the cherry on the top.  ;) Steve
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Offline ZX6Rob

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Thanks for all the info, Steve!  That's quite a list.  I think I'll start by checking for vacuum leaks and go from there.
motorcycle, n. (mō'-dər-sīk-(ə)l) - 1. A large, leaky container of various dangerous, viscous, and difficult-to-clean fluids.

2001 ZG1000 Concours

Offline jettawreck

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.".....

Also, IF you can only use NON-ethanol fuel in the bike. That ethanol crap will gunk up (technical term) your carbs quicker than you can imagine. SISF also recommends adding an ounce or so of TWO STOKE oil that contains TCW-3 to the gas. His experience is that it "coats" the inside of the carb and reduces the likelihood of carb issues due to ethanol gas.

TCW-3 isn't an additive to the recommended cheap two stroke oil, it's a specification/rating. And a very basic one at that, which most any general purpose and/or marine spec two stroke oil will meet (or exceed).
Works well, too.
Snowmobiles, I have a bunch.
Motorcycles-I haven't had anything except dirtbikes 30 years ago, so this will be all new to me.
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Offline Jorge

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Re: Low-RPM performance gap? Wavering idle and some lurching at <2,500 RPM...
« Reply #10 on: January 13, 2016, 02:18:30 am »
Rob,
One question to help point... It sounds  like it was very smooth for a time, then started not running right; is this how it happened? If yes, the the cams are in right etc, and you should look for something that could happen "by itself" over time (ie: leaks, etc.).
I'll second Steve's comments... It's my bike he just did, and I told him I wasn't happy because the idle reminds me of my Accord, purrs too smoothly :rotflmao:
Haven't had a chance to ride it more than a couple of miles, but smooth idle, and very smooth from at all speeds, not lurching like it used to between 2200 and 3000.
Hope you find the culprit.
Jorge

Offline Mettler1

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Re: Low-RPM performance gap? Wavering idle and some lurching at <2,500 RPM...
« Reply #11 on: January 13, 2016, 03:20:59 am »
.".....

Also, IF you can only use NON-ethanol fuel in the bike. That ethanol crap will gunk up (technical term) your carbs quicker than you can imagine. SISF also recommends adding an ounce or so of TWO STOKE oil that contains TCW-3 to the gas. His experience is that it "coats" the inside of the carb and reduces the likelihood of carb issues due to ethanol gas.

TCW-3 isn't an additive to the recommended cheap two stroke oil, it's a specification/rating. And a very basic one at that, which most any general purpose and/or marine spec two stroke oil will meet (or exceed).
Works well, too.
  DITTO! I use it (TCW-3) on any 4 stroke that has a carburetor. Ethanol will plug up any carburetor that sits unused for awhile.
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Offline ZX6Rob

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Re: Low-RPM performance gap? Wavering idle and some lurching at <2,500 RPM...
« Reply #12 on: January 13, 2016, 03:30:18 pm »
Rob,
One question to help point... It sounds  like it was very smooth for a time, then started not running right; is this how it happened? If yes, the the cams are in right etc, and you should look for something that could happen "by itself" over time (ie: leaks, etc.).
I'll second Steve's comments... It's my bike he just did, and I told him I wasn't happy because the idle reminds me of my Accord, purrs too smoothly :rotflmao:
Haven't had a chance to ride it more than a couple of miles, but smooth idle, and very smooth from at all speeds, not lurching like it used to between 2200 and 3000.
Hope you find the culprit.
Jorge

Hey, Jorge,

Yeah, I'm inclined to believe that the cams are correctly set and that this is either a vacuum leak, a clogged or obstructed idle- or mid-cycle jet in the carburetors, or a faulty coil.  I figure that if the cams were that badly out-of-phase, it probably wouldn't quit above such a low RPM.  And you're right, this is something that seems to have creeped in over time -- I remember it being much less obvious right after I installed the cams and redone carbs.  I'm going to move forward assuming the cams are correct, and slowly isolate other issues one by one before I revisit those.

My current theory, based on what Steve and others have said here, is that either a) it's a carburetor issue, and there's a clogged or obstructed idle jet somewhere, or b) it's an electrical issue, with either inadequate grounding or incorrect resistance, which is partially overcome as the revs climb and the alternator starts producing a higher voltage.  We'll see if I'm at all correct!  It could very well be a vacuum leak, too, so I'm going to try to check over all the obvious spots.  Probably replace a lot of the vacuum hoses and caps just to be safe.
motorcycle, n. (mō'-dər-sīk-(ə)l) - 1. A large, leaky container of various dangerous, viscous, and difficult-to-clean fluids.

2001 ZG1000 Concours