If you had a 1991 GS500, and it had a miss on the highway over 65 mph but no where else, what would you do? I'm starting to get really frustrated hunting what appears to be a mild lean miss at 65-75ish mph. The bike will still slowly accelerate past 75 mph with the throttle wide open and this seems to be about right for a GS; the pull is steady until I let off at 80 (in a 60mph zone, this seems more than fast enough to get me in trouble). It's great on the street, stoplight to stoplight shows no real issues. The bike warms up fine with a little choke, that can come off after about a minute of riding.
I've thrown parts at the fuel system; I'm now running a Pingel (wish I hadn't bought the thing, it's a mother to reach up in to actually turn the valve) down to a sintered bronze 5/16'th filter from the bike shop. From there it's right to the carbs. The jets are 147.5 mains, idle's are 40 non-bleeds, and I've got 3 turns out on the mixture screws. The bike farts and pops on decel in gear at speed if I leave the throttle fully shut; this seems like a slightly rich condition then, right? The plugs read nicely, no tan, just solid gray.
The bike has 11,800 miles on it now. I've not adjusted the valves and I guess they should be done, but I can't see a bike that runs hard from a stop being affected like this by out of adjust valves. The plugs are new NGK's, factory heat rating, nothing fancy. K&N Lunchbox, and a V&H full system. This is temperature independant, it was doing this when it was 80 out, and tonight it was maybe 45 out and it's the same story.
I'm kind of at my wits end and I can't afford to replace the GS with something, well, new. I'm also not excited at the idea of handing this to a dealership, since no one is really an expert with GS's around here and I can see a good number of hours involved in tracking this down. So I guess I'm wanting an idea on where to go next on this thing, do I attack the ignition (which seems to be working fine) or do a valve adjustment when it seems like this isn't my issue at all?
If it's the stutter at 6000 rpms it's very common. I've been hanging out here for years and havn't heard a solution for it yet. :cry:
What about just downshifting? (assuming you're in 6th already)
That's what I do.
Quote from: annguyen1981 on November 02, 2006, 11:30:24 PM
What about just downshifting? (assuming you're in 6th already)
That's what I do.
Me 2.
Quote from: pres589 on November 02, 2006, 10:11:01 PM
The bike farts and pops on decel in gear at speed if I leave the throttle fully shut; this seems like a slightly rich condition then, right?
could also be a air leak somewhere in the exhaust system.
check your pipes connection for carbon-oxyde traces.
Do you have an after market exhaust with linked pipe (as opposed to welded like to stock) ?
Quote from: annguyen1981 on November 02, 2006, 11:30:24 PM
What about just downshifting? (assuming you're in 6th already)
That's what I do.
So I'm supposed to be in 5th gear when I want to run on a flat stretch of 70mph highway?
The bike has a slight stutter at 70-ish in a cruise mode. Flat road. When I come to a rise I open the throttle up and it seems to go away. I live in Wichita, currently, so no long hills to run up. If the thing was fuel injected I would think I had a TPS problem with a burned spot being hit by the wiper in the TPS itself, but obviously that's not the case.
Quote from: Dom on November 02, 2006, 10:48:03 PM
If it's the stutter at 6000 rpms it's very common. I've been hanging out here for years and havn't heard a solution for it yet. :cry:
Once again, I wish I had never bought this thing, and had saved for another few weeks for something else.
Quote from: zOU on November 03, 2006, 02:17:53 AM
could also be a air leak somewhere in the exhaust system.
check your pipes connection for carbon-oxyde traces.
Do you have an after market exhaust with linked pipe (as opposed to welded like to stock) ?
The pipes look fine. It's a full Vance & Hines system from ports to tail. I haven't seen any carbon streaking or anything else that would make me think the pipes are leaking. And there's no bad noises on steady rolling down the street in gear. The backfires mostly come in between 6k and then down to about 3500 RPM. Below that, or way up above 6k, I don't notice that kind of thing.
Were the needles adjusted as well when the carb was rejetted?
Have you checked the float height?
carb synch?
do a valve adjustment or at least a check
run 2-3 mph faster/slower to get away from it
Check and see if it has NGK Resistor Plug Caps.If so Ditch them and Get some without the resistors.Also Spray your Plug Wires down with WD40 and ake it for a Ride it's possible that you may have a Arc Jumping From the Primary Wire.
Also it is Possible thaat you may have some Moisture in your Gas.The Other day I was Fighting a Stumble in My truck due to Bad Gas.Stop by your Local Drug store and Pick up a Bottle of 90% Rubbing Alcohol and Dump 1/4 of a Bottle in your Tank.If it Doesn't Get rid of your Problem it will at least Raise your Octane rating a Tad. :thumb:
Quote from: pres589 on November 03, 2006, 05:46:31 AM
Quote from: annguyen1981 on November 02, 2006, 11:30:24 PM
What about just downshifting? (assuming you're in 6th already)
That's what I do.
So I'm supposed to be in 5th gear when I want to run on a flat stretch of 70mph highway?
The bike has a slight stutter at 70-ish in a cruise mode. Flat road. When I come to a rise I open the throttle up and it seems to go away. I live in Wichita, currently, so no long hills to run up. If the thing was fuel injected I would think I had a TPS problem with a burned spot being hit by the wiper in the TPS itself, but obviously that's not the case.
I mean downshift when you want to accelerate from your current speed at the dead spot. Definitely should be in 6th when cruising at that speed.
i found when i changed from the stock can to a free'r flowing one my little hesitation, went with it :D :thumb:
Quote from: Egaeus on November 03, 2006, 06:09:05 AM
Were the needles adjusted as well when the carb was rejetted?
Have you checked the float height?
Took the needles out, cleaned and inspected them. That whole assembly seems fine, the rubber bellows at the top of the slides as well. And yes, the little rubber o-rings under the plastic top hats were replaced with new and are installed.
Float height seems good and the carbs do not belch fuel when the Pingel is left on for days between runnings.
Quote from: hmmmnz on November 03, 2006, 10:01:37 AM
i found when i changed from the stock can to a free'r flowing one my little hesitation, went with it :D :thumb:
Again, I've a full Vance & Hines exhaust on this thing, previous owner installed, I do not have the stock exhaust so I can't try swapping to something else.
Quote from: annguyen1981 on November 03, 2006, 09:12:26 AM
I mean downshift when you want to accelerate from your current speed at the dead spot. Definitely should be in 6th when cruising at that speed.
I don't *want* to accelerate out of the dead spot. This isn't a dead spot, it's a spot where the bike stumbles and acts like it's running out of fuel. What I'd like to do is run, with traffic, in 6th and not feel like I'm running out of gas. If I pin the throttle wide open the bike stops coughing and accelerates up to 80 and probably beyond just fine. If I drop down to 5th and pin the throttle I'm fine. shaZam!, I'd probably be away from the stumble if I *did* leave the bike in 5th gear to run around at 70mph.
Let's try this again. I have a stumble spot at 70mph at what I would call "cruising" with steady throttle. It accels fine. It runs fine on the street. This condition won't show up anywhere else but is annoying on the highway and I'm afraid I will damage the engine if I just ignore it. Which I don't want to do, I'm tired of feeling my head nod back and forth because of power surges/misses when trying to ride this thing on the road.
Sounds like it might be an arc jump to me. As you accelerate the current through the plug wires increases. Try some different plug wires and check your resistance.
Quote from: werase643 on November 03, 2006, 07:19:14 AM
run 2-3 mph faster/slower to get away from it
This confirms my suspicions that no solution has yet been found because if werase643 hasn't heard of a solution to this common occurance, there probably isn't one. He's been around here forever.
Hope this helps, I drilled the stock can @the outlet. Not all the way just the thin "dounut". The first 3 or 4 holes didn't do what I wanted, I drilled the rest out and it started to pop on decel... I'm putn a jetkut/wileyco/k and n. I didn't do it till I drilled the crape out of it. No real stumble, it need a rejet, but I can whip it right to to speed..hope that helos!
[4
Quote from: pres589 on November 03, 2006, 10:23:58 AM
Quote from: Egaeus on November 03, 2006, 06:09:05 AM
Were the needles adjusted as well when the carb was rejetted?
Have you checked the float height?
Took the needles out, cleaned and inspected them. That whole assembly seems fine, the rubber bellows at the top of the slides as well. And yes, the little rubber o-rings under the plastic top hats were replaced with new and are installed.
Float height seems good and the carbs do not belch fuel when the Pingel is left on for days between runnings.
I saw nothing about adjusting the needle height. That's probably your problem. I can send you appropriate #4 washers. Just PM me your address and total height you want to raise the needles. I think 1-1.5 mm would be appropriate for your setup, but I'm not sure.
Quote from: Egaeus on November 03, 2006, 05:54:27 PM
I saw nothing about adjusting the needle height. That's probably your problem. I can send you appropriate #4 washers. Just PM me your address and total height you want to raise the needles. I think 1-1.5 mm would be appropriate for your setup, but I'm not sure.
You're correct, I haven't changed height of the needles. This always seemed like hack at best. And I worried about the OD on the washers in play.
Can you explain exactly why I want to lift the needles? If there's some real science behind this one I'm all ears. If this is just another "Throw in more fuel, Suzuki was being overly protective of the petrol when they set these things up" bit then I think I'd rather throw jets at it. Also, a *good* diagram of how to install the washers would be great, I worry about putting them in the wrong place and botching thigns up. I *hate* pulling the carbs on this bike. Hate with a side of dispise.
The only reason that it's a "hack" is because Suzuki didn't supply adjustable needles in US bikes. European bikes have always had them.
As I understand it (and I'm an Electrical Engineer, not Mechanical) the needle-raising "hack" is necessary because you only have 2 jets. The pilot provides fuel for the lower end of the RPM range, main for the upper. The problem is that there is a spot about halfway through the RPM range where the pilot can't supply enough fuel, and the venturi effect isn't strong enough to pull sufficient fuel through the main when you crack the throttle open until the airflow catches up. This causes the bike to hesitate. This effect is exacerbated by the increased fuel requirements of your setup.
Raising the needle increases the venturi effect at a given throttle position as it provides relatively more surface area for the air to act on the main jet since the tapered needle is raised. This can not be compensated for by throwing jets at it. You need to raise the needle.
More knowledgeable people feel free to correct any mistakes.
Quote from: Egaeus on November 03, 2006, 06:50:37 PM
The only reason that it's a "hack" is because Suzuki didn't supply adjustable needles in US bikes. European bikes have always had them.
Makes sense, at least at this hour of the evening. Let me dwell on this and see what other people toss out on the subject.
dd4
Quote from: Wrecent_Wryder on November 04, 2006, 05:27:29 AM
Personally, I suggest 3mm /M3 washers as opposed to #4. I know a number of people have had no trouble with #4 washers, but a number have, and the M3 is an exact match (ID + OD) for the stock spacers on my '02.
I have #4 washers that are an appropriate OD. However, the package I got had washers that won't work as well (2 ODs, WTF?). I know that the washers I offered will absolutely work in his bike, since it's the same setup as mine. Money back guarantee. :icon_mrgreen: