Hello everyone
I have a 1998 GS500 that I've owned for about two months and I'm having some specific Carb issues. I have just rebuilt and synced the carbs and checked the valve clearances. When i rebuilt the carbs I rejetted the pilot to 40 and the main to 125. I set the float height correctly(14.6mm) with the new float needles, put in new needles(not the float needle, the other ones), one new spring that sets above the needle(not the float needle, the other ones), two new intake boots and one new emulsion tube. The mixture screws are set to 3.5 turns out. Ok, here is the problem. From idle to 5000rpm it runs and pulls great and from 8000rpm to redline it runs and pulls good, but from 5000rpm to 8000rpm it stumbles and has very little power at any throttle position over 1/2 . I have no idea what the problem is :cookoo: It's worth noting that it did the same thing before i did all this work to it. Any help would be greatly appreciated.
Thanks,
Brown
Hey Brown. Did you verify your float height with a clear tube from the drain? Did you replace the needle valve seats or orings as well as just the float needles?
Quote from: bombsquad83 on July 11, 2014, 03:13:13 PM
Hey Brown. Did you verify your float height with a clear tube from the drain? Did you replace the needle valve seats or orings as well as just the float needles?
Yes, I have verified the float height and I replaced the needle valve seats and o-rings
Interestingly, you and solaratov are both having somewhat similar issues right now with your carbs. However, he has a modified intake and exhaust. Anyway, I know your jetting should be right becuase I have the same set up. 5000-8000 is squarely in the range of the needle jet. I asked solaratov about the condition of his diaphragms, so I guess I'll ask you the same. Do they feel stiff at all? Are the edges of the diaphragm nice and round and clean to make a good seal? I replace my old diaphragms and my bike smoothed out greatly.
Other than this, did you damage the one emulsion tube that you didn't replace, or not clean it completely?
I have this exact same problem, literally identical. Ever figure out what it was or fix it?
Quote from: straxcla on August 07, 2014, 07:50:46 AM
I have this exact same problem, literally identical. Ever figure out what it was or fix it?
Yes, I did. It was the aftermarket "stock" replacement air filter. The "HiFlo Filtro" one http://wiki.gstwins.com/index.php?n=Upgrades.AirFilter (http://wiki.gstwins.com/index.php?n=Upgrades.AirFilter).
I replaced it with an OEM air filter and now it runs just fine. I feel like the HiFlo Filtro filter was choking the engine for air.
Quote from: brownh7 on August 07, 2014, 09:25:19 AM
It was the aftermarket "stock" replacement air filter. The "HiFlo Filtro" one http://wiki.gstwins.com/index.php?n=Upgrades.AirFilter (http://wiki.gstwins.com/index.php?n=Upgrades.AirFilter).
I replaced it with an OEM air filter and now it runs just fine. I feel like the HiFlo Filtro filter was choking the engine for air.
It was just the opposite. Much less restriction, leaning out the engine. You have to up size the jets for a HiFlow, hence the name!
From reading other folks symptoms with the filter, contrary to the name 'Hi Flo'... many members have found it is more restrictive in general than the OEM filter, or other conflicting mixture symptoms. It is strange it doesn't affect the same over all of the range, some cases it seemed be lean for one range, and rich at another position :dunno_black: One member a few months ago contacted Hi Flo about the issue and they were actually able to suggest another filter part number and swapped him out with no charge, and it worked well... it looked about the same, but longer. I meant to take a note of the part number and bike it was originally recommended for, but it seems I cannot find it... I'm thinking it may have been for an SV650, but I'm just not certain - a part number would be best to avoid confusion anyway.
- Bboy
Quote from: ace50 on August 07, 2014, 09:29:07 AM
Quote from: brownh7 on August 07, 2014, 09:25:19 AM
It was the aftermarket "stock" replacement air filter. The "HiFlo Filtro" one http://wiki.gstwins.com/index.php?n=Upgrades.AirFilter (http://wiki.gstwins.com/index.php?n=Upgrades.AirFilter).
I replaced it with an OEM air filter and now it runs just fine. I feel like the HiFlo Filtro filter was choking the engine for air.
It was just the opposite. Much less restriction, leaning out the engine. You have to up size the jets for a HiFlow, hence the name!
Are you sure? I took the hi flo out and ran the bike with no filter before I put the OEM fiter in. With no air filter the bike ran good with no heaitation from 5k to redline at WOT, but I could tell it was a little lean as expected. If the hi flo had less restriction than OEM wouldn't running the bike with no filter make it run worse at the problem area?
Any idea on the cost of a complete carb rebuild?
Are you sure? I took the hi flo out and ran the bike with no filter before I put the OEM fiter in. With no air filter the bike ran good with no heaitation from 5k to redline at WOT, but I could tell it was a little lean as expected. If the hi flo had less restriction than OEM wouldn't running the bike with no filter make it run worse at the problem area?
[/quote]
That's curious. I've had to increase all the jet sizes to get mine to run properly with HiFlow. Wondering about air patterns in air box could cause some of it. Think I'll do some playing around.
Hmmm ok. What sizes do you run with the hiflo filtro? I am running 40/125 with one washer under needle.
Quote from: brownh7 on August 07, 2014, 12:28:46 PM
Hmmm ok. What sizes do you run with the hiflo filtro? I am running 40/125 with one washer under needle.
Your sizes indicate a pre-2001? Mine's a 2001 and still playing with it as it's my daughter bike and she wouldn't have a clue anyway.
I have 27.5 slows to go in as I'm 4 turns out on 22.5's and it needs a little more. 67.5 on mids. Haven't played with needles yet. Think I could go higher than my 135 mains. Just need to spend more time on it. Keep playing with my other bikes.
I've been thinking about putting a K&N fuel ratio gage on the exhaust I could try for free, from a friend.
Quote from: ace50 on August 07, 2014, 12:41:45 PM
Quote from: brownh7 on August 07, 2014, 12:28:46 PM
Hmmm ok. What sizes do you run with the hiflo filtro? I am running 40/125 with one washer under needle.
Your sizes indicate a pre-2001? Mine's a 2001 and still playing with it as it's my daughter bike and she wouldn't have a clue anyway.
I have 27.5 slows to go in as I'm 4 turns out on 22.5's and it needs a little more. 67.5 on mids. Haven't played with needles yet. Think I could go higher than my 135 mains. Just need to spend more time on it. Keep playing with my other bikes.
I've been thinking about putting a K&N fuel ratio gage on the exhaust I could try for free, from a friend.
Yes, '98
Glad that you got your problems sorted out brown. How's the bike run now?
Quote from: bombsquad83 on August 08, 2014, 05:46:00 AM
Glad that you got your problems sorted out brown. How's the bike run now?
Pretty good. The major hesitation is gone but there is a slight feeling of lag when rolling on the throttle between about 5k-7.5k. It feels like the engine if having to catch up with the throttle movement. It feels like turbo lag on a car almost.... a little power then a lot of power. If I roll on the throttle slow it doesn't seem to lag. It is worst when snapping the throttle open. This sounds like the same problem I had before but this one is very very minor, just annoying haha. Could this be due to my jetting? I'm running 40/125, and 3.25 turns out on the air screws 1000-1500 feet above sea level.
EDITI forgot to say that I have one washer under the needles.
That lag may be the slide rising too fast. Does it get better if you roll on throttle slowly ... if so then definitely yes - slide rising too fast. I'd practice rolling on gentler. The alternative is to close off 1 hole in the slide.
Cool.
buddha.
Never thought of playing around with the air filter to see if it has any effect on the problem, I'll have to try it. I've been thinking about upgrading to a pod filter/s anyway just because I despise removing and installing the stock air box. Also could I try putting in a washer for the needle jet? Anyone know the best place to get jets (if i need them) for an 02?
Quote from: brownh7 on August 08, 2014, 06:54:09 AM
Quote from: bombsquad83 on August 08, 2014, 05:46:00 AM
Glad that you got your problems sorted out brown. How's the bike run now?
Pretty good. The major hesitation is gone but there is a slight feeling of lag when rolling on the throttle between about 5k-7.5k. It feels like the engine if having to catch up with the throttle movement. It feels like turbo lag on a car almost.... a little power then a lot of power. If I roll on the throttle slow it doesn't seem to lag. It is worst when snapping the throttle open. This sounds like the same problem I had before but this one is very very minor, just annoying haha. Could this be due to my jetting? I'm running 40/125 and 3.25 turns out on the air screws 1000-1500 feet above sea level.
You have the same jetting as me. Part of it is just because of where the power band on the GS is. The torque really increases around 7k. I do have one small washer under my needle clip. You could try that to see what difference it makes.
Buddha, are there plugs available for temporarily plugging a hole in the slide that could be easily removed later?