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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Carb tuning help. /cgi-bin/YaBB.pl?num=1502812854 Message started by Quimrider on 08/15/17 at 09:00:54 |
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Title: Carb tuning help. Post by Quimrider on 08/15/17 at 09:00:54 I hate starting yet another carb related thread as the info already available is very thorough. I am a fairly competent mechanic and have experience tuning carbs on other bikes. I'm hoping someone can save me some time and lessen my learning curve with the LS650 carb by giving me some pointers to help me figure it out quicker. My bike is an '02 with the stock exhaust/intake and stock carb. When I got it a few years ago I thoroughly cleaned the carb and did a refresh on it replacing jets, float needle etc. all with stock parts. I adjusted the idle air screw properly or so I thought. It's been a while so I don't remember exactly what I set it at. Now onto the symptoms I am experiencing. FYI it has run this way since day 1 when I refreshed the carb so this isn't a recent problem. I just dealt with it by having a slightly higher idle speed and am now getting around to doing something about it. Off idle and up it runs SWEET! So no complaints there. 1) If I am coming up to an intersection and go from part throttle cruising (constant speed) to close the throttle (engine braking) I get a LOUD shotgun blast backfire. This doesn't seem like it should be normal. It's not really a problem since I usually pull in the clutch, close throttle and roll to the stop. Also if I slowly close the throttle, ie. gradually slow down I don't get a backfire either. 2) Choke (fuel enrichment) doesn't seem to work very well. The first stop out will keep the engine running but idle is still very low. 2nd stop out causes it to sputter and die. 3) Bike warmed up and idle set at 1100RPM. When rolling and I pull in the clutch idle drops to 900-950RPM range but comes back up to 1100RPM when stopped. When doing the same on a freeway exit ramp it drops as low as 800 and usually stalls. I'm assuming for #1 it's the increased engine vacuum pulling excess fuel thru the idle circuit that then pools/ignites in the hot exhaust. Not really sure what I could do about that other than hope it's not normal and goes away when I fix the other idling issues. For #2 I speculate that I'm not getting enough air from the idle circuit and the choke adding more fuel just smothers the engine. Possibly I didn't adjust it right when I rebuilt it? I'm at a loss for #3. The reason I let it go so long was a lack of time to deal with it and that turning the idle up to 1400-1500RPM yielded about a 1100RPM idle when cold and eliminated stalling issues. I plan to start by removing the carb and disassembling looking for any passageway blockage, Checking whether or not I shimmed the needle valve (I think I did to richen up the mid throttle), and then starting over with tuning the idle circuit. I am guessing that if there aren't any plugged passages, when tuning the idle circuit I may need to crack the butterfly with the idle screw to get more air at idle for proper choke (enrichment) function and proper idle function. If anyone has any experience with the symptoms above I'd greatly appreciate hearing how you corrected them. |
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Title: Re: Carb tuning help. Post by Dave on 08/15/17 at 10:04:12 When you let the throttle close fully while coasting to a stop - there is a very high engine vacuum.....but the slide needle has completely closed off the jet needle, and the only fuel to the engine is coming through the Pilot Jet circuit (and maybe some from the TEV valve). With a lot of vacuum and very little fuel - the mixture in the cylinder is going very lean, and the spark plug cannot ignite this lean mixture....so the unburned fuel/air mixture goes into the hot exhaust system, and when it gets hot enough the mix is ignited in the exhaust header and muffler. When you open up a bit of throttle as you coast you are reducing the vacuum and also opening up the jet needle...and the spark plug can ignite the fuel/air mixture. (This is the proper way to ride a big single.....don't fully close the throttle as you decelerate or shift gears). The engine rpm dropping as the engine approaches idle is also a symptom of the fuel/air mix being lean as the engine coasts down to idle (high engine vacuum and low fuel flow). As the engine drops below the set idle speed there is a small lag until the air and fuel flow equalizes and gets to a good fuel/air mix for the idle speed. You might try opening up the fuel mixture screw a 1/4 turn and see if things improve. If you have a #47.5 pilot jet....you might want to bump that up to a #50. In warm temperatures the choke may not be necessary...or even desirable. The choke is better suited for use when it is really cold....and the choke may not work all that well in the summer - you will just have to get used to holding the throttle open a little bit for the first few miles until the engine comes up to temperature. |
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Title: Re: Carb tuning help. Post by eau de sauvage on 08/16/17 at 02:27:36 As an aside I think this bike needs an idle when warm of not be less than 1300. |
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Title: Re: Carb tuning help. Post by Quimrider on 08/16/17 at 06:43:22 08333E2938342F29323A37285B0 wrote:
I think you misunderstood what is happening. Let me see if I can describe it better. let's say I'm on the freeway going 75. I slow down to 70 as I'm getting onto an exit ramp. As I hit 70 I pull in the clutch to coast to the end of the exit ramp. Engine hits idle at 65. As I am coasting to the stop at the end of the exit ramp the idle will dip so low it stalls. Even if I crack the throttle to get the idle back up and then close the throttle the idle drops to a stall. If I manage to keep it from stalling until I'm down to say 40ish it will just idle really low and when I come to a complete stop it will creep back up to 1100RPM after I stop. The drop in idle is almost directly proportional to the speed I'm rolling. |
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Title: Re: Carb tuning help. Post by Quimrider on 08/16/17 at 06:46:21 72607477606664010 wrote:
If that indeed is the case then maybe I don't have a problem. |
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Title: Re: Carb tuning help. Post by stewmills on 08/16/17 at 07:38:21 Quimrider, Just for giggles, read my recent thread here about a similar issue which I solved as being an issue with my needle position: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1497301269 May not be your issue, but it may enlighten you on some of the carb behavior. Sometimes what we think is a lean condition is a flooding condition and vice versa. Hope you get your issue solved. |
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Title: Re: Carb tuning help. Post by eau de sauvage on 08/18/17 at 00:28:21 1E3A26223D262B2A3D4F0 wrote:
If that indeed is the case then maybe I don't have a problem. [/quote] That's very possible. Maybe take a look through this thread... http://suzukisavage.com/cgi-bin/YaBB.pl?num=1496795234/0 |
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Title: Re: Carb tuning help. Post by piedmontbuckeye on 08/18/17 at 07:35:24 I certainly an not an expert on this situation, but I have always opted for a higher-than-recommended idle speed setting. Mainly because I want to be sure that the oil pump is pumping as much oil as possible to the upper end and none of the engine is starving for oil at idle. This may also have the effect of helping your situation, I don't know. I know that I don't have any of the symptoms that you describe except for the lower idling speed at startup when cold. I just am careful enough to "baby" the throttle until it warms up. |
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Title: Re: Carb tuning help. Post by justin_o_guy2 on 08/18/17 at 08:11:04 Adjusting the idle is so easy that I do it while riding. |
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Title: Re: Carb tuning help. Post by piedmontbuckeye on 08/18/17 at 08:15:27 2B343235282F1E2E1E26343873410 wrote:
Uh...maybe that may have something to do with your running off the road and hitting three trees???? ;D |
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Title: Re: Carb tuning help. Post by justin_o_guy2 on 08/18/17 at 08:32:48 Haven't done that yet. |
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Title: Re: Carb tuning help. Post by Quimrider on 08/21/17 at 05:28:24 273E32333A3839233522343C322E32570 wrote:
I may be wrong but it was my understanding that 1000+ RPM was sufficient for oil to the top end. So I only get worried when Idle drops below 1000. I added a tach. so this is easily monitored. |
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Title: Re: Carb tuning help. Post by IslandRoad on 08/21/17 at 05:31:42 I think 1000 rpm is absolute minimum. I run mine nearer to 1400. |
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Title: Re: Carb tuning help. Post by LANCER on 08/21/17 at 06:06:45 1100+ rpm for idle Set after engine is completely warm |
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Title: Re: Carb tuning help. Post by Gary_in_NJ on 08/21/17 at 07:16:12 6B4F535748535E5F483A0 wrote:
Why in the wide world of sports would you pull in the clutch at 70 mph to coast to a slower speed? This is just a bad technique. Oh, like others have said, an idle of 1,100 rpm is too low. |
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Title: Re: Carb tuning help. Post by justin_o_guy2 on 08/21/17 at 07:23:17 Close the throttle gently and roll.. |
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Title: Re: Carb tuning help. Post by IslandRoad on 08/21/17 at 08:27:03 FWIW, I think Suzuki recommend the idle speed so low (And the gear change speeds) for reasons like emission control and (here in Aus) for noise control. They can be ignored as far as I'm concerned. |
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Title: Re: Carb tuning help. Post by Quimrider on 08/21/17 at 13:33:46 313B3F353E37333A646266560 wrote:
Well it's probably from my decades of driving MTX cages. To drive most efficiently (use less fuel) I would push the clutch and roll when I know I will be slowing significantly or stopping soon. Engine braking puts more wear and tear on the engine as well as sucks more fuel into the engine than just letting it idle. That is why I would do this. Why wouldn't you? :-? Did you misunderstand what I was saying? I agree it would be silly to do this if you're just slowing down a little but when you are exiting the freeway to a stop sign or for that matter rolling up to any stop sign I don't understand why you wouldn't roll and idle to the stop sign. |
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Title: Re: Carb tuning help. Post by Gary_in_NJ on 08/21/17 at 16:33:14 3014080C1308050413610 wrote:
Because you never know why you'll have to power out of a situation, and dumping the clutch when sudden power is needed is a sure way to loose traction or control. It's for this reason that I rev-match down shift while slowing, this way I'm always in the power band. Car or bike, I do it the same. Oh, I've never replaced a clutch on any vehicle I've ever owned. That's over 17 cars with a manual transmission and over 20 bikes. Over 1,500,000 miles. My A4 has over 200,000 miles on the OEM clutch and I got 135,000 on the OEM brakes. |
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Title: Re: Carb tuning help. Post by LANCER on 08/21/17 at 18:37:26 Wow, that is impressive Gary ! |
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Title: Re: Carb tuning help. Post by Quimrider on 08/21/17 at 18:40:14 I guess we just have different strategies but agree on the need to always have power available to get out of a bad situation. I keep the clutch pulled in and down shift appropriate to the speed I'm rolling at so I always have power available. Thankfully I've only ever had to get out of harms way once. That was coming up to a traffic jam on the freeway. I heard screeching tires glanced in my mirror and saw the side of a car approaching me fast. I had already aligned myself with the shoulder as an escape route. I instantly was WOT and was 5 cars ahead on the shoulder in what seemed like .2 seconds before I let off the throttle. I had no problems using the clutch appropriately for the fastest possible acceleration in an emergency situation. |
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Title: Re: Carb tuning help. Post by batman on 08/21/17 at 20:32:21 I have to agree with Gary, I down shift and use engine braking ,I've only replaced my front brakes once in 30,000 miles and have never replaced the clutch.(clutch plates don't wear out on these bikes , 8000 members an only one recorded case) Are you really worried about gas mileage on a bike that should avg .about50 mpg? If you down shift an let the clutch out each time the bike will no longer stall,try it you'll see.If you need to evade you can do it by grabbing some throttle(faster) because the clutch is already out and your in the proper gear .when you pull in the clutch ,and close the throttle at 70 mph the motor turning 4700 rpm and the idle jet is only supplying enough fuel for 1100 rpm ,why wouldn't stall ? how long does it take for the motor to slow to 1100 rpm with no load on it (forever) and there is a super lean fuel /air mix that won't support combustion. |
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Title: Re: Carb tuning help. Post by Gary_in_NJ on 08/22/17 at 05:21:17 We will just have to agree to disagree then. Your technique is counter to what many experienced riders practice. Good luck. |
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Title: Re: Carb tuning help. Post by ohiomoto on 08/22/17 at 06:32:14 Haven't done this on a street bike, but it's not uncommon to downshift multiple gears when riding/racing MX. Not recommend on the street because you'll probably lose control if you dump the clutch. :) |
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