fixing different exhaust temperature

[AlanDog]

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! 

[bullet5]

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.

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.

[AlanDog]

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?

[bullet5]

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.

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.

[AlanDog]

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. 

[AlanDog]

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?

[bullet5]

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

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.

[AlanDog]

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...

[bullet5]

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

[AlanDog]

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.

[Sean]

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. 

[AlanDog]

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.

[AlanDog]

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! 

[AlanDog]

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

[Sean]

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.