New 600, Erratic, Hanging, Stalling, Etc.

[brealytrent]

Hey all!

I just purchased a 1995 Suzuki GSX-600F, and am having some major issues with getting it to run right:


First off, if you blip the throttle it will hang the revs for a bit and eventually return to a (rough) idle. Sometimes giving it a very little bit of throttle while idling will cause it to stall. Sometimes the bike will raise its idle by 1-2k rpms all on its own for 30 seconds to a minute and drop back down.

What's been done:

The carb was cleaned by the person I purchased it from and look good. I have checked for vacuum leaks with brake clean multiple times and found zero. I balanced the carbs, and still have a rough idle. The carbs almost seem to unbalance themselves at times as well... The pilot screws have all been adjusted to 3 turns, which seemed to help somewhat.

This bike looks stock, however it does have have an aftermarket exhaust with a yoshimura muffler. The carburetors have been tampered with, but I don't know what has been done if anything. It's looking like the problem lies within the carbs, but I was just hoping someone with more direct experience with these bikes would have a better idea as to where the problem lies before I start throwing money at it, hoping I get lucky and fix the problem.

[Seft]

Hey all!

I just purchased a 1995 Suzuki GSX-600F, and am having some major issues with getting it to run right:


First off, if you blip the throttle it will hang the revs for a bit and eventually return to a (rough) idle. Sometimes giving it a very little bit of throttle while idling will cause it to stall. Sometimes the bike will raise its idle by 1-2k rpms all on its own for 30 seconds to a minute and drop back down.

What's been done:

The carb was cleaned by the person I purchased it from and look good. I have checked for vacuum leaks with brake clean multiple times and found zero. I balanced the carbs, and still have a rough idle. The carbs almost seem to unbalance themselves at times as well... The pilot screws have all been adjusted to 3 turns, which seemed to help somewhat.

This bike looks stock, however it does have have an aftermarket exhaust with a yoshimura muffler. The carburetors have been tampered with, but I don't know what has been done if anything. It's looking like the problem lies within the carbs, but I was just hoping someone with more direct experience with these bikes would have a better idea as to where the problem lies before I start throwing money at it, hoping I get lucky and fix the problem.

The hanging could be a dirty throttle cable too, have you checked, lubricated and adjusted them?

Have you checked the size of the jets that are installed in the carbs are they the stock size? I'm presuming as you say the carbs look clean you're talking about the inside and that you know there is nothing clogging any jets!?

The carbs101 guide here http://katriders.com/vb/showthread.php?t=63344 suggests 1.5 to 2 turns out too not 3, that's a lot more air in the mix. Is the air filter stock too?

Based on what I've seen on this site in the past and my own issues I'm gonna take a punt that you should tear down the carbs yourself, properly clean them following the carbs101 guide replacing the o-rings bowl gaskets and probably the needle valve and its seat too. BUT, I'm a relative newbie to this so don't just take my word for it

[Kreylyn]

The carbs are not clean. The person before did not do a good job. A full cleaning (IE that means complete disassembly and dip / ultra sonic cleaning on the bodies too, not just the jets.)

Hanging idle tells me it's lean. Idle creeping up = lean. Bouncy idle = air/vacuum leaks. Turning the screws out to 3 turns and that didn't overly rich the mix tells me that your carb bodies are not utilizing the jets to limit the fuel flow, but the fuel flow is limited by dirty ports inside the carbs.

Think of it this way... if you have a nozzle on the water hose, but the hose is kinked... your not going to get the flow you need for the nozzle to really do anything for you, right? So... clean the carb bodies.

Carbs 101 is old, with current fuel mixes start the a/f screws at 2.5 turns on US models. NON US models would be closer to 1.5. (different jets in those.)

While you are cleaning the carbs, pull the jet needles and count the number of slots on the Eclip for it. 1 = stock US. Multiples mean US has a Jetkit installed, non US is OEM to have multiples. I'm guessing your in wisconsin (truck tag in the pic) so I'm gonna go with US model.

5 slots = Factory Pro jet kit = Good!
6 slots = Dynojet (or a DJ knock off like sigma ) = I personally think they do not work as well, but it's something you can work from if you don't want to change it.

Check the air filter is OEM style (paper filter) and not a K&N reusable. K&N really mess with the tuning, so if you have one it needs to be factored into the equation.

I would suggest a Jet Kit if you don't have one with that exhaust. One size up from OEM, 2.5 turns on the A/F screws, 3rd clip on the jet needle with a Factory Pro kit installed (what I would recommend.) Use OEM intake/air filter. From that baseline, follow the FP jet kit tuning instructions. A jet kit will not only allow you to better tune for the exhaust changes, but will improve over all rpm range fuel mix for smoother and less vibration on a stock bike.

Krey

[brealytrent]

Thanks for the suggestions so far guys! Update:

Carbs were taken apart a couple days ago and again, everything was spotless, for the most part. Checked and cleaned everything once more and found no dirt. The needles have six notches, and they were set to the second to richest setting. We moved the clips up one on the needles. A couple of the needles had a few black marks/pitting. We did not check jet sizes unfortunately, as they did not look removable...Will check that later. The previous owner did put on a K&N air filter on the bike, and I've ordered an OEM paper one.

After all of this, still no change in performance. For a second, while cold, the bike seemed a lot better. You could rev it and came right back down to idle. But as it warmed up the problems started to come back. Adjusting the idle down to a little over 1k leads to a lot of lumpiness, and a touch of the throttle leads to it going up to and sitting at 4k for 5 to 10 seconds before slowly coming back down. And again, sometimes it rises a few thousand rpm on its own.

Another thing I've noticed is a lot of soot. The exhaust pipe and spark plugs are really dark, darker than I think they should be. There's no black smoke however.

It just doesn't make sense to me! It's rich, but it's lean? Is it possible the choke is leaking?

EDIT: Also, the throttle is free and not sticking.

[Seft]

If you didn't remove the jets then safe to say you can't have properly cleaned them. If you look in the manual at section 3.8 it shows which jet is which, all quite removable!

http://katriders.com/vb/showthread.php?t=138096

[Kreylyn]

Yeah, I don't think our idea of "properly cleaned" is matching up. It's not the areas you can see that I'm concerned about at this point. It's the several ports internally you can't see, located on the other sides of those jets you didn't remove, that have me concerned. Someone cleaned the exposed area. That's good. Just not good enough.

A possible reason for the mix to change from rich to lean would be fuel in the oil. If the oil smells of fuel at all, any little bit... it needs to be changed. Then make sure the carbs are not leaking fuel into the engine.

On your model carbs for a proper cleaning, the main jet, pilot jet, air/fuel screws (and hardware of spring, washer, o-ring) should all be removed. Pull the diaphragm and slide so you can access the emulsion tube. Remove the choke plungers, separate the rubber/plastic form the brass. Then use a dip for 24 hours, or an ultrasonic cleaner on the bodies and jets. Make sure you check the air jets on the side of the carb intake are clean. I many times end up replacing the pilot air jets because they never come out with out damaging them, yet are notorious for being really difficult to clean. Check them closely.

Aerosol spray is a rinse, not a deep cleaner.

The OEM air filter will help things. Even with dirty carbs, because the back pressure will increase the pull on fuel through the ports.

Krey

[brealytrent]

I'd like to issue a correction - I thought my father did not remove the jets, however he did, and checked/cleaned them all. Again, EVERYTHING was clean. The carburetors are not dirty! The only thing we haven't checked were the choke plungers, however while running the bike we applied pressure to them to see if there was any difference in performance, and did not see a change.

Presuming the factory air filter will be more restrictive than the K&N, since we are still waiting the OEM filter to arrive, we've tried covering the air inlet with our hand, and still not seen any change in performance. Perhaps something magical will happen with the stock filter, idk.

Another correction is that the jet needle only has 5 notches. We moved the circlip from the second to richest setting to the leanest setting (the top notch) to see if this would help. While the idle was smoother, once warmed up a little, touching the throttle even the minutest amount would cause it to jump back up to 4k rpm like before, sit there for maybe fifteen to twenty seconds, and finally come back down. It's definitely too lean now, but I think the jump in rpms is not related to the adjustment to the needle as this was happening when the engine was way rich.

On another note, I also did a compression test, which showed the cylinders seem healthy. All readings came back between 130 and 135 PSI.

[Kreylyn]

I'd like to issue a correction - I thought my father did not remove the jets, however he did, and checked/cleaned them all. Again, EVERYTHING was clean. The carburetors are not dirty! The only thing we haven't checked were the choke plungers, however while running the bike we applied pressure to them to see if there was any difference in performance, and did not see a change.

How the bike runs pretty clearly points to the carbs being clean is not correct. It's not running rich. Rich would flatten out/bog out the rpms. A rich running engine would drop rpms like a rock and die. Raised/hanging rpms is because it's lean. Lean is a reduced fuel flow issue caused 95% of the time by restrictions inside the carb bodies. The other 5% is after market air filters, air/vacuum leaks, sync issues, blocked air jets, or just poor settings.

Please... feel free to explain why the idle would hang otherwise. I'm all ears.

Presuming the factory air filter will be more restrictive than the K&N, since we are still waiting the OEM filter to arrive, we've tried covering the air inlet with our hand, and still not seen any change in performance. Perhaps something magical will happen with the stock filter, idk.

With everything properly working, it will make a difference in performance. With something preventing fuel from flowing properly through the carbs, it probably won't fix the issue.

Another correction is that the jet needle only has 5 notches. We moved the circlip from the second to richest setting to the leanest setting (the top notch) to see if this would help. While the idle was smoother, once warmed up a little, touching the throttle even the minutest amount would cause it to jump back up to 4k rpm like before, sit there for maybe fifteen to twenty seconds, and finally come back down. It's definitely too lean now, but I think the jump in rpms is not related to the adjustment to the needle as this was happening when the engine was way rich.

On another note, I also did a compression test, which showed the cylinders seem healthy. All readings came back between 130 and 135 PSI.

5 slot is a factory pro jet kit. Good! Once you get past the commitment that the carbs are clean, you may get the bike to start running really well.

Not trying to be a dick, but seriously... There simply is NOT another answer. You synced the carbs and checked for vacuum leaks. If it still hangs... it's a dirty pilot circuit. That is the answer. This isn't the first time it's come up, nor the first time someone thought it was fully clean... but it was not.

Krey

[brealytrent]

Is it possible the light corrosion on the needles could be causing them to stick? We cleaned a little of it off but I was afraid of causing more problems.

[Kreylyn]

Is it possible the light corrosion on the needles could be causing them to stick? We cleaned a little of it off but I was afraid of causing more problems.

No. The needle isn't doing anything until over 3k rpms. A dirty needle may make a very slight reduction in atomization of the fuel, but that would make for different issues.

Personally, I polish all the metal parts when cleaning the carbs. So it would not only be fine, but I'd suggest... cleaning the needles fully.

Your question tells me your trying to figure out why the bike runs like it does. That's good. Your just lacking the information to better understand.

You have a Factory Pro Jet Kit installed, so relevant reading...

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Now, to the specific issues your having.

Raised or hanging idle - rpms under 4k. Lets start with some basic info.

The only thing that runs the bike at the under 3k range is the pilot system. The main system (main jet, slide, needle your asking about) has pretty much almost nothing to do with the idle at all. It's for over 3k rpms. 3-4k rpms is the transition point for the pilot system to the main system. So simplified... any running issue under 4k rpm, is primarily the pilot system.

The basic function of the CV carbs equipped on you bike sorta gives it a life of it's own. The bike WANTS to run. If you starve it, it will auto adjust a little find another source of fuel. That's where the hanging idle comes in. When running lean in the pilot system, the CV carbs move the idle up to pull more fuel. Eventually getting into the main jet system if need be (the 4k hang)



So lets look at the pilot system. Pilot system consists of air and fuel jets. Air flow for the pilot system starts at the pilot air jet at the front of the intake side of the carbs.



This tiny jet and the port that flows air behind it MUST be clean and clear. No air flow = nothing to pull fuel. Blocked or reduced flow = lean running idle. Typically this jet is very difficult to remove with out damaging the jet. It's also very hard to clean, but very important to clean it and the port behind it. Since it is the intake port, anything carried by the air can/will collect inside the port with the fuel deposits that naturally occur. Some of those deposits are not soluble, like dust or dirt. Pests/bugs also will find that port and decide to use it for a nesting point, and clog it up with whatever they decide to use as a nesting medium.



So the green line shows where the air goes. Port all the way through the carb, and a great spot for deposits to collect and form.

The blue line shows where the fuel flow comes from that feeds the pilot fuel jet. This is often overlooked, and can be easily blocked to prevent full fuel flow. The pilot jets should be covered by a rubber plug to not only force fuel to flow only from the port the blue line depicts, but it also has been suggested that the pressures when running could force flow the wrong way due to turbulence with out the plug or if the plug does not properly seal. The rubber plug has to be tight and will hold in on it's own. The float rail will many times keep it from falling out if it's loose, but that won't properly make it seal and will cause running issues.

The air flow (green line) causes a void that pulls fuel from the pilot jet (red line). The transition ports reduce that pull as the butterfly opens. If you look in the bore where the butterfly touches near the bottom, you will see the 3 port holes and that they are covered by the butterfly. Part of the bench sync process is to adjust all 4 butterflies so they cover those holes near equally.

So... hanging idle, or an idle that wants to raise when warm (warm engine runs better when lean) = pilot system is not functioning correctly. You need to go back to investigate that specific system. The pilot air jet, the entire port behind it for flow through, the pilot fuel jet, the plug that covers it, the port the fuel transitions from the main jet area, the port the fuel flows from the pilot fuel jet to mix with the pilot air flow, and the transition ports. Check the all, make sure they are clear.

This is where I use aerosol spray the most to be honest. It allows me to simulate a flow through the ports, and compare. If I have all 4 bodies tore down side by side, I can pick up each one and spray through a port and compare. It will many times be obvious one or more does not match up. What should happen is a strong flow through and heavy atomization or misting of the spray out of the other end. If you find it's limited, or wants to pool up and dribble out, that's a clear sign of a blockage.

Now to be clear, I use the aerosol spray to simulate fuel flow so I can visually see how things are reacting. I know it's a cleaner, but it's not going to remove a hardened deposit or especially issues where part of the deposit is not dissolvable (like dust, dirt, rust). If it's showing it's blocked or reduced flow, I'll try a blast with a high PSI air hose to see if the blockage will blow out. If that doesn't remove it, the carb body goes back into a dip to dissolve what ever is binding the clog together and or loosen up hardened deposits so that the next time I put aerosol or air through it, it will blow out.

Krey

[92xjunker]

No. The needle isn't doing anything until over 3k rpms. A dirty needle may make a very slight reduction in atomization of the fuel, but that would make for different issues.

Personally, I polish all the metal parts when cleaning the carbs. So it would not only be fine, but I'd suggest... cleaning the needles fully.

Your question tells me your trying to figure out why the bike runs like it does. That's good. Your just lacking the information to better understand.

You have a Factory Pro Jet Kit installed, so relevant reading...

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Now, to the specific issues your having.

Raised or hanging idle - rpms under 4k. Lets start with some basic info.

The only thing that runs the bike at the under 3k range is the pilot system. The main system (main jet, slide, needle your asking about) has pretty much almost nothing to do with the idle at all. It's for over 3k rpms. 3-4k rpms is the transition point for the pilot system to the main system. So simplified... any running issue under 4k rpm, is primarily the pilot system.

The basic function of the CV carbs equipped on you bike sorta gives it a life of it's own. The bike WANTS to run. If you starve it, it will auto adjust a little find another source of fuel. That's where the hanging idle comes in. When running lean in the pilot system, the CV carbs move the idle up to pull more fuel. Eventually getting into the main jet system if need be (the 4k hang)



So lets look at the pilot system. Pilot system consists of air and fuel jets. Air flow for the pilot system starts at the pilot air jet at the front of the intake side of the carbs.



This tiny jet and the port that flows air behind it MUST be clean and clear. No air flow = nothing to pull fuel. Blocked or reduced flow = lean running idle. Typically this jet is very difficult to remove with out damaging the jet. It's also very hard to clean, but very important to clean it and the port behind it. Since it is the intake port, anything carried by the air can/will collect inside the port with the fuel deposits that naturally occur. Some of those deposits are not soluble, like dust or dirt. Pests/bugs also will find that port and decide to use it for a nesting point, and clog it up with whatever they decide to use as a nesting medium.



So the green line shows where the air goes. Port all the way through the carb, and a great spot for deposits to collect and form.

The blue line shows where the fuel flow comes from that feeds the pilot fuel jet. This is often overlooked, and can be easily blocked to prevent full fuel flow. The pilot jets should be covered by a rubber plug to not only force fuel to flow only from the port the blue line depicts, but it also has been suggested that the pressures when running could force flow the wrong way due to turbulence with out the plug or if the plug does not properly seal. The rubber plug has to be tight and will hold in on it's own. The float rail will many times keep it from falling out if it's loose, but that won't properly make it seal and will cause running issues.

The air flow (green line) causes a void that pulls fuel from the pilot jet (red line). The transition ports reduce that pull as the butterfly opens. If you look in the bore where the butterfly touches near the bottom, you will see the 3 port holes and that they are covered by the butterfly. Part of the bench sync process is to adjust all 4 butterflies so they cover those holes near equally.

So... hanging idle, or an idle that wants to raise when warm (warm engine runs better when lean) = pilot system is not functioning correctly. You need to go back to investigate that specific system. The pilot air jet, the entire port behind it for flow through, the pilot fuel jet, the plug that covers it, the port the fuel transitions from the main jet area, the port the fuel flows from the pilot fuel jet to mix with the pilot air flow, and the transition ports. Check the all, make sure they are clear.

This is where I use aerosol spray the most to be honest. It allows me to simulate a flow through the ports, and compare. If I have all 4 bodies tore down side by side, I can pick up each one and spray through a port and compare. It will many times be obvious one or more does not match up. What should happen is a strong flow through and heavy atomization or misting of the spray out of the other end. If you find it's limited, or wants to pool up and dribble out, that's a clear sign of a blockage.

Now to be clear, I use the aerosol spray to simulate fuel flow so I can visually see how things are reacting. I know it's a cleaner, but it's not going to remove a hardened deposit or especially issues where part of the deposit is not dissolvable (like dust, dirt, rust). If it's showing it's blocked or reduced flow, I'll try a blast with a high PSI air hose to see if the blockage will blow out. If that doesn't remove it, the carb body goes back into a dip to dissolve what ever is binding the clog together and or loosen up hardened deposits so that the next time I put aerosol or air through it, it will blow out.

Krey

Need to sticky this!!! Good info on carb function.

[brealytrent]

Update

Soooo, we pulled the carbs again. We removed all the jets again:






We flushed everything, we checked all ports for proper flow with an aerosol, we used our jet cleaning tools to check the jets and emulsion tube - a couple of the main air jets had a little crud in them, but that was it. Adjusted the air/fuel screws to 2.5 turns again. Moved the main jet needle to the middle setting. Put it back together anndddd....

Nothing changed. Still hesitant to return to idle at times, sometimes hanging around 4-5k rpm for a few seconds. Idle would be low, low enough to not register on the tachometer so using the idle adjuster we'd try to bring it up. But if you got it to about 1200 rpm it would just start to creep back up until it went to 4-5k. Then we couldn't get it to come back down without adjusting the idle way down again..... I just don't know anymore.



We also found this:





So add that to the list of mods done to this bike: a Factory Pro jet kit, ignition advancer, k&N air filter, and Yosh 4-1 exhaust. The only thing we can think to do at this point is start to return it all to stock.


If you're looking for specs on the jets in the carburetors:

Main jets say 120
Air jets say 32.5
Pilot air jet says 1.55
Main jet emulsion tube says 589 - P2

[92xjunker]

Ditch that shit filter...OEM style will most likely fix your problem.

[Kreylyn]

The main jets are way over sized. Stock would be 112. Generally 1 size up is all that is needed for the aftermarket exhaust. As the pilot jet system feeds from the mains, that could have an effect. Add to that the aftermarket filter, you have another issue that could add to combine an idle issue.

I'd drop the jets down to no more than 1-2 sizes larger.

Also... I'm looking at the pic with the float, and the plug for the pilot jet looks deformed. Like, in the pic it looks like I can see past it into the port, and that it's not sealing the hole. Is that seated in fully and will it stay seated when the float rail isn't holding it in place?

One last thought... have you checked the petcock for a vacuum leak too? That could cause some issues.

Krey

[92xjunker]

Agreed 115 should be the limit, you really don't need to but, it won't hurt. That filter is a problem that is difficult to overcome.