fixing different exhaust temperature

[AlanDog]

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?

[AlanDog]

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? 

Well, my ignition swap can't hurt...

[bullet5]

Can't remember which one choke affects, but it only changes the flow of one, not both.

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.

[AlanDog]

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!

[bullet5]

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

[AlanDog]

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...

[AlanDog]

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.

[tomacGTi]

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

[AlanDog]

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.

[tomacGTi]

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.

[AlanDog]

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.

[AlanDog]

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.

[tomacGTi]

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

[AlanDog]

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!

[AlanDog]

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.
 

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!