TourMax float needles

[78530i]

Trying to fix flooded carbs after rebuilds with K&L kits. Grrr. I lost one of my stock needles.
I see the K&L has a longer travel for the spring loaded button at the tab end of the float needle valve.
I'm not sure exactly what difference to expect from that; but I definitely have a wild idle. It likes to either float at 2500 or settle and die at 1200.
I replaced my intake boots but I'll check for loose when I have it apart.

Getting off-track here.
I am putting the old needle valve seats with new o-rings back in place with some TourMax needles from ebay because they are cheap.
The pictures look like the button is shorter like the originals; and since they are sold by TourMax as stock replacements...

I have seen other threads warn about K&L valves but no specific mention of TourMax.
Also, yes I am cheap.

 

[78530i]

http://www.ebay.com/itm/Set-of-2-Carburetor-Float-Needle-Valve-Suzuki-GS500E-1989-2000-13370-02D00-/302146248330?hash=item465951de8a:g:sVkAAOSwSzFZYKel&vxp=mtr

[mr72]

If it works, it works.

But it's probably not safe to assume that the idle problem is caused by the float needles. Many other potential causes. I think float needles are very low on the list of probables. Pilot jet, idle mixture setting, idle speed, those are much more likely. IMHO.

[78530i]

If it weren't such an extreme difference, I'd agree. With this much fluctuation, however, I think its a big vacuum leak or one carb flooding enough to kill a cylinder. I could be wrong. It wouldn't be the first time.

[mr72]

If it weren't such an extreme difference, I'd agree. With this much fluctuation, however, I think its a big vacuum leak or one carb flooding enough to kill a cylinder. I could be wrong. It wouldn't be the first time.

Well it certainly could be a vacuum leak but I think that is more likely to manifest as issues not at idle.

Think about the idle circuit for a minute. It's SUPPOSED to get air in through a tiny orifice in the throat of the carb outside of the butterfly. This air goes over the pilot jet. Idle speed, then, with the throttle butterfly closed completely, is set by the idle mixture. vacuum is not at all a part of this equation. In an ideal world, you set the idle mixture right and it'll idle with the throttle closed. As we know, nothing is ideal so we ordinarily wind up opening the throttle plate a tiny bit using the "idle speed" screw. Here's where things get really funky. Now you are adding a LOT of air by comparison to the amount coming in through the little pilot hole. To compensate for the extra air you have to set the pilot jet very, very rich, since the extra air coming in through the throttle plate doesn't hit the pilot jet at all. This is what you have to do to get to an idle speed very much above 1200 rpm. That air coming past the throttle plate goes over the main jet (in a 2-circuit carb) so it'll pick up fuel if the needle is up. So when you rev the engine, the slide comes up and pulls the needle up due to vacuum and then before the slide comes all the way down on return to idle, some air still is coming through the throttle plate and it can still pick up fuel from the main jet and if vacuum is high enough at that instant in time then the slide may not come all the way down and the "idle" is kept high because in reality the main jet is not fully closed and some air can still come in past the throttle plate. This is especially true if the pilot circuit is at all lean because that tiny bit of extra fuel coming in the main jet for that instant is enough to keep the revs up and that keeps the vacuum up which keeps the slide up, etc. So you really are not idling since you have the main jet slightly open. This is "hanging idle". And it can stay high like this for like 30 seconds or until you get tired of it and "blip" the throttle which has the effect of creating a very temporary change in vacuum which might allow the slide to finally seat and it returns to "idle".

The cause of all of this is the throttle plate is open too much at at idle. Or in other words, your "idle speed" is set too high, which may be because you have set the idle mixture too rich in effort to get the bike to idle at 1500 rpm, or maybe you tried to set the idle when the bike was not fully warmed up and you set it to 1200 or 1300 rpm but if you go ride a half hour then it suddenly idles at 2K because it's finally warmed up, and you have a hunting/hanging idle because often it doesn't close the slide and you get that behavior I just described.

The solution is to set the idle speed lower, and to be sure you are setting it when the bike is fully, and I mean FULLY, warmed up. It will then idle very low when it's cold (my bike like 900-1000 rpm) unless you keep it on part choke for a good long while. Put the mixture needle at 2.5 turns out to start, ride until the bike is really, really warmed up, THEN set the idle speed down to 1200, turn the idle mixture screws out a quarter turn at a time until the idle speed stops increasing, then turn the idle speed back down to 1200, you're done. You probably end up with 2.75 to 3.25 turns out on #40 pilot jets and the idle "speed" screw nearly all the way out.

Trying to get the bike to "idle" with the main jet partly open is basically impossible, unless you want to idle at 3K rpm. It's way too unstable. Tiny changes in needle position make big differences in fuel and the idle will be all over the map.

I think with some of these older GS500s people set the idle too high to compensate for some other problem. Carbs are out of sync so it doesn't want to idle or it stalls. Or maybe valves are tight so compression is low at idle and it stalls. Or the rings or valve seats are shot and there's poor compression so it won't idle low without stalling. So you set the idle at 1500+ and then run into this issue of hunting/hanging idle. IMHO. I'm no expert.

All this to say, go back and recheck your idle speed and mixture and get them dialed. Far more likely the cause of your problem. But before you can do that you must fix any vacuum leaks, since vacuum leaks put air into the carb without fuel metering and that will make it run really lean at idle.

[78530i]

I want to replace those needle valves anyway; because I think they are opening later and closing sooner due to that longer spring loaded button I already mentioned; so I'm going to do that; and I'm still looking for responses from anyone who has used the TourMax brand. 

Otherwise, I appreciate your detailed explanation. My takeaway...

1) While its apart, I'll check the valve clearances. It's high time for that anyway.
2) Rather than just turning 2.5 turns out as before, I'll adjust the mix as you described; and remember to do it hot and at low idle speed.

[Peter Tez]

mr72, thank you for your clear explenation of hanging idle! very good info


'05 GS500 / k&n lunchpod + open exhaust / 20-65-145