Bandit Alley
MODEL SPECIFIC => SUZUKI BANDIT 250 & 400 => Topic started by: AlanDog on September 29, 2012, 01:44:18 PM
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I have seen a few threads here on detecting carb problems by checking the exhaust pipe temps, but my searches to find what you need to do to even them out have not found any advice.
So my cylinder #4 exhaust is much colder than others when just idling for a minute, is just a minute of start-up idle a fair test?
Okay, so now what do I adjust? Idle mixture screw? Float height? Carb sync? Which first?
Also, the bike is hesitating a fraction of a second when I twist the throttle at idle. But my fuel leak problem was solved, thanks! :beers:
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Before gauging the air/fuel ratio off the exhaust pipes you need to make sure that all four pots are firing perfectly, and that you're no.4 cylinder isn't intermittant, which could cause the throttle lag and a cooler exhaust pipe.
If you are testing the bike while it is idling then you should only adjust the idle mixture screws. If you play around with the other settings you'll mess up the mixture for the rest of the rev range.
I would start by pulling the plugs, and making sure they are all a similar colour. If they are then move onto a carb sync (preferably after you've checked and adjusted the valves). After you've done the sync and reset the idle rpms to the correct levels it would then be time to begin playing with the mixtures. :thumb:
Generally you'd leave the idle mixture screws as standard (which on a B6 is 1 7/8 turns) but I can't remember the B4's off the top of my head. If you have a slip on exhaust (not a full system) it is suggested to turn the screw out another 1/8 of a turn.
All the best,
Bullet5.
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So did a carb sync and that helped, but it still idles high (2-4k) without the idle screw engaged and without the choke,
and then dies after about 5-10 minutes and won't start. And now cyl 3+4 are hot, 1+2 are cooler.
I was playing around with my idle mixture screws, but if 1/8 of a turn is significant, this may take
a while to dial them all in... how different will the different carbs be--should I be adjusting all of them in sync, or
should the carbs running cool get more turns out? Or in?
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They should all be set to exactly the same amount, and yes 1/8 of a turn really make a fair bit of difference. I found the best way to guage the turns is to put some tape around your screwdriver, so you can clearly see how much you've moved it. :thumb:
If the valves weren't done recently, they may be out a bit.
Here's a quote from a fellow banditforum member I think's rather helpful...
My question: "Now my question is; is it really necessary to check the valve clearances before I balance the carbs?"
Answer:
Yes, and here's why - when you balance the carbs you're adjusting them so the engine's suction through each is the same, making all pots & carbs work evenly. If the valve clearances are off you can have each pot sucking differently (wide valve clearance=more suction, tight valve=less), so you have to open/close up the carbs more to compensate.
Get the valves all the same (you only need worry about the inlets at this stage, but while you're in there anyway ...) and you know the cylinders are drawing the same amount, so balancing the carbs should be quicker and the engine will be in much better balance. Any imbalance after this will be down to differences in the rings/bore, which you ain't gonna sort easily.
Summary - balancing the carbs without sorting the valves first is like trying to get three opera singers and an asthmatic to breathe in harmony.
Edit:
Oh and as for the screws you have to turn them in all the way until they won't go any more, then pull them out "x" number of turns.
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Bullet, Thanks for the quick reply. I did adjust my valves recently when I installed a manual cam tensioner--I actually adjusted them twice, so
pretty sure they are dialed in. I also have new ignition wires.
Well after feeling pretty beat last night, I'm all ready for another round of fiddling today, will try your method with the mixture screws. :thanks:
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Okay, a couple more days of work, and still not idling correctly. Just to clarify, this is a completely stock bike.
Today, the bike did fire up a few times, but most the time I was turning it over and it just wasn't catching. When
it did start, it idled high without the choke and without the idle screw engaged. This is with all the idle mixture
screws 3 1/2 turns out, which was what was working the best last weekend when the engine was hot.
When it did fire up, it shows the same symptoms, exhaust pipes for cylinders 3 and 4 are hot, 1 and 2 are cold.
I did vacuum sync the carbs again and it is still good.
I installed new spark plugs and replaced the ignition wires (again!). Swapping ignition wires on the same coil
didn't help. I guess I'm a wimp, afraid to test my spark to the frame with all the fuel dripping around... I have
the bike with the tank off and a funnel into a line feeding the carbs, and it's dripping...
I guess I don't need fuel to the carbs to test the spark while turning it over.
I guess I can swap the coils and see if cylinders 1 and 2 are still the cold ones. But 1 and 2 are off different coils,
so it doesn't really follow. Maybe the idle circuit on carbs 1 and 2 are just plugged or not working right?
When I parked the bike to work on it (a couple months ago), it was running--badly, but running. The gas tank
was full of rust and the fuel I dumped out of the carbs was full of rust. I thought I gave the carbs a good cleaning,
but maybe needs an ultrasonic bath? Anyone have any good experiences with ultrasonic cleaners with these carbs?
I'm thinking there may be a combination of issues here, maybe some spark issues. One question: are the two
high voltage wires out of each coil equivalent and can be swapped?
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Hello again, I can't offer any advice on ultraconic cleaners as I've never had to use them. It sounds like you've the majority of the basics covered, however mentioning the coil wires could be where your problem lies. The coils have to be wired into the correct part of the loom, otherwise the timing will be off for the spark. This could be causing the starting issue, aswell as having dead pots if she's sparking at the wrong time.
Another thing to check now you've tried turning her over for a while is to put the battery on charge for a good few hours before attempting again. It was a low battery that had my cruiser off the road for days, as I couldn't find the fault, and when I did eventually find out it was the regulator which wasn't charging the battery, I was fuming :duh:
I don't think it will be your battery, but it's always best to be safe and minimize the potential gremlins.
All the best,
Bullet5. :thumb:
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So I have had the battery on a trickle charger, and did a full charge recently. The battery is the only thing that is working well.
Okay, a question: how critical is the seal between the air filter box and the carbs? In my many iterations removing it, I have been getting more lax with it. I have been figuring it shouldn't matter too much, right? Or wrong?
Other than that, and cleaning out the 'cold' carbs again and checking the pilot screw o-rings on them again, I'm out of ideas...
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Yup having an air leak on that side of the carbs is alright. It's still not really what you want, but it shouldn't affect the bike much at all, however if you have an air gap on the carb outlet rubbers then this will be causing some problems of it's own. It's worth giving them a once over anyway :grin:
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I can't tell from the diagrams as it is not clear what goes in first: does it go rubber o-ring, washer, spring, pilot screw, or washer, rubber o-ring, spring, pilot screw?
I have had it with the rubber o-ring first and then the metal washer, and then the spring. Is this the source of all my problems?
But it's a little confusing how this circuit is supposed to work. I see the fuel inlet, so will the rubber o-ring and washer always be below the inlet, allowing fuel to flow, and the fuel adjustment by the screw is just the seating of the nozzle against the body?
Is there a source for washers that will fit these carbs? I just lost one today.
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Definitely o ring first; o-ring washer pilot screw. Logical and I've pulled apart of 4 sets and that's how all of them were set up.
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Thanks for the reply. It's been a while since I worked on them, so I guess my uncertainty made me suspect maybe I had it wrong. Well, the carbs are soaking in PineSol now so I will see if I see any improvement soon.
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Soaked the carbs for a week in PineSol, rinsed in hot water, sprayed everything out with carb cleaner and also sprayed with WD-40 to prevent rust.
Well, it may be that the pilot jet screw washer was my problem. What I didn't understand before (when I was putting it together) was that the rubber o-ring and the washer actually go around the thick part of the pilot screw above the spring. I was jamming them down into the hole first, then screwing in the screw--maybe things weren't getting lined up? Today I carefully installed the o-ring and washer on the screw above the spring and then inserted the assembly into the hole. Maybe it's the same thing, I guess we'll see. If I have time tomorrow and it works, it certainly be a Merry Christmas! :beers:
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I was optimistic today, but after warming it up ten minutes, I am getting the same symptom, cyl 1+2 have cold exhaust pipes and the bike just dies and won't start warm. I pulled the spark plugs and the 1+2 plugs are wet. When I test the spark it is visible but seems weak. So right now I am thinking this is a temperature-sensitive electronic or connection issue. I don't think it's the coils because 1+2 are from different coils and swapping 1 for 4 and 2 for 3 (including plug, cap and wire) does not make a difference, cyls. 1 + 2 are still cold. I am delving into the ignitor connections and the harness. It seems the previous owners have done work on the harness...
Does anyone have any experience with the ebay ignitors like this one?: http://www.ebay.com/itm/Suzuki-BANDIT400-GSF400-BANDIT-GSF-400-GK75A-Derestrict-CDI-for-Ignitor-Ignition-/261093347716?pt=Motorcycles_Parts_Accessories&hash=item3cca605184&vxp=mtr
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I'm not a pro but your swap tests leads me to rule out electrical issue. -> both sides "work when on the right side of the engine. I'm thinking super super rich. Stuck floats needles or something.
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I see your point. And dying hot is a sign of it being too rich. I have all the idle mixture screws out 2 1/2, I will try to reset them to 1 out and see if I can get it to idle hot turning the screw out from that point. Thanks for the input.
I found the threads here about converting to the Denso coil plugs and it was so cheap on ebay ($33 shipped) I couldn't resist. It will at least rule out everything except the ignitor itself. No shortage of totaled supersports, hmmm, why is that?
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I swapped the float needles between 1+2 and 3-4. Adjusted the idle mixture to 1 turn out, and everything is still the same--starts up, I can idle it at about 3k (adjusting the choke down as it warms up) but dies after about 5-10 minutes. Spraying the exhaust pipes with water, 3+4 cylinders are still the hot ones. I guess I could turn the idle screw all the way in, and if it still idles cold, would that suggest a fuel leak? Does the choke increase fuel at all or just change airflow? :banghead:
Well, my ignition swap can't hurt...
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Can't remember which one choke affects, but it only changes the flow of one, not both. :thumb:
Have you checked the carb boots for air leaks? (Between the carbs and the engine).
Before spending any more money on it, I'd pull the carbs back, give the boots a propper clean, then remout the carbs spending extra time to make sure all the boots are fitting flush with the carbs and not at angles. Get those C-clamps done up nice and tight, then once back together fire her up and spray carb cleaner fluid into the carbs.
After doing this for a minute or two on each cylinder put it back together with the airbox attached, fire her up again and spray the carb cleaner around the carb boots at idle. If the revs are affected in any way by this it will indicate a boot leak. :)
Sorry if I repeated myself, I'm rather tired and had completely forgot about this thread.
All the best,
Bullet5.
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I just found in the factory service manual, page 4-9, that the choke on this bike actually enriches the fuel mixture.
I did go out after reading the last post and checked my carb boots by spraying them with carb cleaner while idling and I didn't get any changes. Overall they seem to fit pretty tight and look to be in good condition. I had checked it a couple times before but that was many iterations ago.
But doing some web searches on vacuum leaks it does sound similar. Except my bike still idles high without the choke.
So it definitely is running less rich (no fuel smell in the exhaust) and now does not die hot with the mixture screws 1/2 turn out (although shutting it off and trying to start back up it doesn't catch immediately and I have to use the choke again). But blipping the throttle, the bike returns to high idle very slowly.
So now the weirdness is that it is idling high (3-4k) without the choke and without the idle speed screw engaged at all. I think maybe now I need to reduce my throttle valve position screws that I tweaked to balance the carbs. Will work on that now.
Thanks for the input, it has been helpful!
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Aye that's certainly a high idle. Is your throttle cable slack when at idle? If not that could be causing the higher than normal idle too. I'll mull over a few other possibilities after re-reading the entire thread later on :)
Bullet5
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My fuel leaks popped up again. I did a bunch of swapping of the float assemblies and found a leaky float needle. But all this stuff is intermittent, this is crazy. I've been doing this testing with the carbs off the bike by just connecting the fuel inlet to tubing to a funnel.
The metal tab that you adjust on the float assembly to adjust the float height... should it be completely flat, ie, should it be bent at a single point closest to the float. Or can you adjust the curve of the metal to adjust the response? I do have a digital micrometer to measure height and I'm setting them to 14.6.
When I push down on the floats through their entire travel, the two leaky carbs have orange-colored float assemblies that do not seem to respond in the same way as the two good carbs, which have tan-colored float plastic. The leaky floats seem to offer much less resistance to downward force. Surprisingly, when I swap the needle, the light resistance follows the float assembly, not the needle, and just by testing the needles, the spring feels the same between them (they're all new). It's as if the 2 types of floats have a slightly different design, and the leaky float assemblies were on cyls 3+4, ie the hot exhaust cylinders in my idle tests. So I'm idling on leaking fuel in 3+4.
So maybe much of my current idle problem is just dialing in my floats, getting them to respond equally (maybe by bending the metal tabs differently between my two float types) and not leak. Or maybe I just need to get float assemblies that are identical...
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Okay, I've been staring at and playing with the float assembly and looking at the differences between my 4 carbs.
So the spec is to adjust the float height as it just touches the top of the float valve to 14.6. So this is without pushing down on the float valve spring at all. There will be some point as the fuel increases that the force from the float will depress the spring to a point where the fuel is completely shut off--but that's not the level that is set to 14.6 mm. 14.6 is just the beginning of engaging the valve. Or does the fuel get shut off when the spring touches the tab? The spring seems really soft, so wouldn't they just have it be solid if they wanted it to be an on-off switch? I assume it has the spring to smooth out the transition between on and off.
So my theory is that the curve of the float adjustment tab does make a difference, since it controls how much float travel will shut off the fuel completely. What I notice is that very slight changes in the curve of the metal tab seem to significantly change the fuel cut off point. So two carbs set at 14.6 can have completely different fuel delivery curves based on the shape of the metal tab. My two leaky carbs would bottom out (float touching the carb body) without pushing down on the float valve completely. So no matter how high the fuel level, the valve was not completely shut off.
It seems that putting a 'S' curve in the tab will allow you to set the height to the 14.6 spec but will engage the float valve to shut off fuel earlier in the float travel. I will experiment with this more. It just makes me wonder if this is one of the fine details of tuning these carbs.
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You are very much overthinking things.
If your float valves are that far out: replace them, they are not that expensive. Get new, viton tipped ones as the cone taper on the valve seals against fuel. The whole purpose of the system is on and off, not progressive. It's purpose is to either fill the bowls or shut off. That's it.
All you are doing when you bend the tab is adjusting the point that the valve shuts off fuel and it should be where the float "lightly touches" when gently turning the carbs. Float height affects almost everything in the carb as it is will richen or lean all of the circuits. The factory setting or jet kit settings are what you should stick with unless you're a full on ninja or tuning god.
If you have replaced these, ALL of the o-rings and rubber parts in the carbs (including diaphrams if they're holed), and still getting a leak: then you're doing something wrong and you should check your work. The youngest Bandit example in the US is 20 years old this year and I can assure you that the rubber has perished by now. You are merely pissing into the wind if you don't start with that step first. Also, repeated removal and reinstallation of parts wlill tear the o-rings if you're not gentle or if they're old. Ask me how I know.
Carb work here is WELL documented and alot of the folks on here, myself included, have lost YEARS of sleep working on these things. Start with the basics and go from there. These things are elegantly simple but can be made a nightmare by a little ring of viton.
Also: just read that your tank was gummed and rusty. Rust is the biggest PIA with these carbs as the orifices are absolutely tiny. Even a bad tank of gas is enough to make them run like poo. Get it running well off of a known good fuel source and make sure your tank is as clean as possible with fresh gas.
-Randy
Cliffs:
-Start with all new rubber
-Refer to your jet kit manufacturer or the database sticky here
-Test
-Go ride
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I was hoping I was overthinking it. Just to clarify:
- I have replaced all the o-rings (more than once) with new viton ones using sizes in the FAQ.
- My fuel tank has been cleaned and epoxy sealed.
- engine, intake and exhaust are totally stock.
Basically you're saying at 14.6 mm float height, the carbs shouldn't leak fuel, and if they do it is likely the o-rings or a bad float valve... I hope you're right! Thanks for the input.
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There is a caveat: make sure you use the correct float valves:
Someone on the board had used some other ones and they leaked. They swapped over to OEM Mikuni/Suzuki ones and the problem was solved.
You may be running into the same issue.
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So the float valve I just got, K+L part number 18-8944 (http://www.ebay.com/itm/350436461439) are about 1.5 mm taller than the valves I got in my carb rebuild kit six months ago. With this taller float valve, the tab is almost horizontal. I just put the two leaky carbs back together with the new float needles, and right now at least, it's holding fuel in my test rig. Will try to fire it up tomorrow.
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Quick update: the carbs held fuel overnight. I put everything back together and it doesn't die idling hot! Yay! I rode it around the neighborhood but now I am getting the accelerator cable too tight and it's making it idle high. I should be able to figure that out and get that fixed tonight.
The interesting thing is that I moved the leaky floats to carbs 1+2, which previously had the cold exhaust pipe. And although now it idles, carbs 1 and 2 still have the cold exhaust. So it seems the fuel leak problem I just fixed (and any other problem related to the float assembly) is not related to cylinders 1+2 running cold.
I have the mixture screws 2 turns out now, so my idling problems may have just been being too rich. I double-checked for vacuum leaks again around my engine intakes with carb cleaner... still looks good.
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Glad to hear.
Only thing I can add to 1-2 being cold: check for spark and also look at the plugs/leads. A motor needs air, spark and fuel to fire. You've narrowed one down, to check air I'd say checking the valve lash would be next followed by a carb synch.
It wouldn't be the coils because 1-4 and 2-3 are shared IIRC. Do the cylinders come back when revving the bike or up higher on the tach?
Ah, the joy of 20 year old rare bikes...I can assure you though, when all runs well, all the hard work is payed off.
-Randy
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Do the cylinders come back when revving the bike or up higher on the tach?
Randy, yes, it does return back to idle at a lazy pace, it takes 2-3 seconds. This was today when it was idling correct and warmed up. What does that mean?
Thanks!
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So I pulled the carbs to get the mixture screws out 2 1/4 turns, and adjusted the floats down a tad (~14mm) on cyls 1+2 that were running cold. When I started it up I could immediately hear it was running stronger. Some sort of low frequency rumble that the engine made. Sure enough, all the pipes are hot now. It idles and runs fine.
:beers:
It is definitely flat in the mid-range and top end--when I bought it, it pulled much stronger. Maybe the fuel leaks were enriching the mixtures, maybe the mixture screws were out more (my one mistake is when I took it apart: I didn't check what the screws were set at).... right now I just want to enjoy riding it!
:thanks:
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Do the cylinders come back when revving the bike or up higher on the tach?
Randy, yes, it does return back to idle at a lazy pace, it takes 2-3 seconds. This was today when it was idling correct and warmed up. What does that mean?
Thanks!
Sync your carbs...
Also, usually means that you're a little lean if I remember correctly on idle. I would do 2 1/2-3 turns and see how it is. When you're happy, then sync the carbs.
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http://www.randakks.com/TechTip72.htm
Good page to read up on for the basics. Factory Pro has a good one as well.
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Mixture screws out to 3, carbs are synced, idles cold (with choke) and warms up nicely, but still weak acceleration in the mid-range and top-end. When I bought it, it was stronger, but the exhaust really smelled of gas when it idled, so maybe the mixture screws were way out and maybe the fuel leaks helped the WOT performance...
In any case, I'm wondering what the next step is. Should I invest in a Factory Pro kit? Play around with my main and pilot jet sizes? All the jets are stock... ps. the valves are adjusted and I did install a higher temp thermostat.
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Get the FP kit. Well documented and great customer service, you won't be disappointed.
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I never wanted to get this good at pulling the carbs and putting it all back together... I installed the kit in a little over 2 hours. I know there are guys here who do it in 20 minutes, but for me...
A definite improvement. I just went with the 97.5 main jets since the jetting thread here it seems to be popular with stock intake/exhaust. I went with the needle set 3 down... basically the bike runs stronger on the bottom and top end. It's probably stronger in the middle (4-7k) but the flat spot is still there. I've been studying the jetting thread here and I'm thinking of going to 2nd groove on my needle. Although most setups seem to be set to 3. I've tried running WOT in the middle rpms cold versus hot and it's hard to say--weak either way. Although it seems to be stronger with the choke on thru that range. I think I need to ride it more. It's a bit hard to test dead cold, as I have to ride out of the neighborhood and I'm not going to hit WOT at any rpm on the street where I live, it's just not safe.
Go richer or leaner for the needle setting? Any input? Would going lean on the mixture screws, say bringing them from 2.25 to 1.5 turns out and seeing if the midrange is better or worse be a good way of narrowing down which way to go? (I just tried to re-read the link to the Randakk page and it looks like he took that content down). It's totally rideable now, maybe I should just keep riding it more until I'm more sure... I really don't enjoy fiddling with the bike, I just want to ride it...
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Get the warmer thermostat as well. It will make the jetting much more consistent.
Do all of your tuning with the engine at operating temperature, you're wasting your time with it cold. Also, it is neigh impossible to jet out the dead spot. All you will manage to do is move it around and compromise everything else.
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As far as testing cold, I was just trying to follow the factory pro tuning instructions:
http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html
"If the engine pulls better or is smoother at full throttle/5k-7k in a full throttle roll-on starting at <3k when cool but soft and/or rough when at full operating temperature, it is too rich in the midrange and the needle should be lowered.
If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.
If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set."
I actually did upgrade my thermostat a couple weeks ago... so you're saying other changes (to intake and exhaust?) need to be made to get rid of the midrange flat-spot, or I'm just stuck with the way this particular bike is??? Certainly there are posts on the jetting thread of people who say the engine pulls strong throughout the rev range.
Thanks for your help Randy!
-Alan
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To go by factory pro's suggestions would be to warm up the bike and ride it till hot. This way you can accurately compare cold running and hot running and go from there.
Easiest way I've found really is to set the top end first with the main then idle when hot via the screws and then the midrange but the middle needle setting 98% of the time is perfect. You can also shim with a washer to get that 1/2 step if need be. Also remember that all circuits overlap so what may be good for one will affect the other. That's why I try to tune either end first, the middle usually follows with. Don't forget to synch the carbs after.
That flat spot is damn impossible to tune out. People that say that it has a clean pull usually pull right through it via gearing in the 1-3. Flat spots will manifest more when the engine is under load and cold so you should tune the motor for how you ride versus outright pull at high revs. Area under the curve is better than outright numbers.
As worked over as my bike is, that flat spot is still there but is certainly diminishes as it warms up. I've just learned to ride around it. Certain exhaust and airbox combos can also affect it as well: making it better or worse depending. Like I said, you compromise and move it around but it really never goes away.
Search the SV forums as well for tuning tips. Although a different bike there are more of them and the theory is the same. Just don't try their cam swap on the 400, ask me how I know...
Isn't tuning fun?
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Alan, the other thing I can tell you is that the factory pipes on this bike are restrictive. This may be your top end issue. Don't be afraid to call FP for advice as well.
When I swapped headers, my jetting went from a 105 main to a 120 with all other parameters remaining the same.
Even my ported/gutted stock headers with a Cobra F1S slip on didn't flow as well as the Vance and Hines pipe that I have now. There is a difference up top with these for sure. The Vance and Hines is also louder than hell but is no match for the growling airbox that you straddle.
These things have potential but you have to keep things in perspective: all this work will still not make it an R6 or GSXR. It'll be more fun but it's still not the same.
-Randy
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I brought the mixtures screws out 1/2 turn ( to about 2 3/4 ) and it's clearly rich at idle but that pretty much fixed the midrange problem, at least enough for me. I had to dial back the idle speed screw when it warmed up but hopefully that's it. I wonder how much that mixture screw position affects gas mileage. I guess I can measure it now and dial it back and see...
I'm not into crazy high performance, and I really don't want a loud bike. I really like the idea of a small inline 4 as a move up from the ninja 250. This bike had enough power for me. I was holding off on other mods because I wasn't sure if I'd ever get the carbs sorted out. Now I want to customize and raise the seat, get new brake pads and change the fluid, and get new tires. I'll be ready for my 2nd track day this spring!
Thanks again. I would of certainly given up without this forum. Hopefully this thread will help others!