Need carb help please

[Bonz]

Float height in reality is the main control of rich or lean when you come on the throttle in big handfuls.

I'm not going to budge on that one because I developed a full carb set up using ZZR1200/ZX11 40mm downdraft carbs on a side draft head for my ZRX 1200 and higher fuel level made it rich on the initial throttle application and lower fuel level leaned it out. Going around corners with too high of a float height which equates to low fuel level would starve the engine and had a lean hit when accelerating at more than a smooth roll on.

Lower the floats and raise the fuel level and it would bog rich. Sorry, I know what I'm talking about on this one.

[mack]

Did

I miss the mention of cylinders dropping out? I don't recall reading that? Anyway it would seem the PO had experienced the rich condition before and tried to remedy the situation by drilling out the air jets. So I'm inclined to think that the pre-existing condition may not be carb related at all (other than to correct what the PO did to them) set the fuel levels back to level with the bowl washers using clear hoses.
For some reason the fuel isn't getting fully burned in the cylinders. That's why I mentioned the advances. For some reason your not getting full spark and the fact that it is across all cylinders makes me believe that it's an electrical issue between the coils and the TCI.

[3Phase]

Mack,

The dropping cylinders and a fairly comprehensive check of the coils and ignition circuit current, voltages, and resistance was in another thread. I think DaVinci gave him some help with troubleshooting the TCI.

The upshot was that the ignition system voltage was good; ballast resistor was bypassed and the new Dyna coils were good. I don't remember if the TCI was shotgunned with a known-good TCI to see if it was working cold --> warm, then failing after it got hot.

[motoman]

Float height in reality is the main control of rich or lean when you come on the throttle in big handfuls.

I'm not going to budge on that one because I developed a full carb set up using ZZR1200/ZX11 40mm downdraft carbs on a side draft head for my ZRX 1200 and higher fuel level made it rich on the initial throttle application and lower fuel level leaned it out. Going around corners with too high of a float height which equates to low fuel level would starve the engine and had a lean hit when accelerating at more than a smooth roll on.

Lower the floats and raise the fuel level and it would bog rich. Sorry, I know what I'm talking about on this one.

Was and proved out to be the situation.....normally.

In reference to my post of proof.........running extremely rich to, at and back from rally. Got home and 'hosed' all four carbs with engine idleing....my suspicion proved out, with all four fuel levels being way low at 6-6.5mm instead of the recommended 3mm.
Had set floats just prior going to rally and no time to check levels let alone pull carbs a few times to get all four fuel levels spot-on the same, so some 9-1200mi. it smelled if following, and struggled up Pikes Peak. Started and idled fine, even at 14100ft......just don't come up on rpms or rev. the motor, cept slowly or cough,cough.
Changed fuel levels, re-tuned and rode 4-lane hiway south and back some 120mi.........way smooth off idle and up thru any and all rpm ranges.

[mack]

Thanx

Scott. Where the electrical checks done before riding the 20 miles or after, when the condition manifests itself?
He stated that his idle mixtures screws are at 1/4 turn out. On the 80/81 carbs this should result in a very lean condition as normally 3 turns is the starting point for tuning.Given the profile of the mixture screw itself, it's very rare to have broken tips and having to distort the orifice to remove them. Very odd that it is across the all cylinders unless the same mistake is repeated on each carb. Maybe something simple like not installing the little o rings but I find it hard to believe both owners would make the same mistake.
The only way I know for carbs being responsible for dropped cylinders is if NO fuel is getting to them , but wouldn't explain the plug fouling. I'm waiting on Jets R Us right now for some stuff or id send him down a known set of carbs to try. Maybe someone in his area could take a known set to him for diagnostics.

[3Phase]

I agree, the carbs don't usually cause dropped cylinders unless they're too lean and the air just won't stay lit all by itself or too rich and fouling spark plugs.

Here's the thread where we walked through testing the electrical system. The TCI is supposed to shut off when the engine isn't running but I don't think we tested it:-

I think these carbs are having an ignition problem ....

I'm not trying to bail on y'all but I'm finishing my XJ, trying to get out on the road and I keep losing large blocks of time. I had to degrease, clean, and re-paint part of the frame and let it dry overnight because the PO had a battery problem at some point and it pewqued acid all over the swing arm and frame. I just hope the paint will stay on at least until I get back home from XSSE and I can do a better job.

[Barbarosa]

Scott. Where the electrical checks done before riding the 20 miles or after, when the condition manifests itself?
He stated that his idle mixtures screws are at 1/4 turn out. On the 80/81 carbs this should result in a very lean condition as normally 3 turns is the starting point for tuning.Given the profile of the mixture screw itself, it's very rare to have broken tips and having to distort the orifice to remove them. Very odd that it is across the all cylinders unless the same mistake is repeated on each carb. Maybe something simple like not installing the little o rings but I find it hard to believe both owners would make the same mistake.
The only way I know for carbs being responsible for dropped cylinders is if NO fuel is getting to them , but wouldn't explain the plug fouling. I'm waiting on Jets R Us right now for some stuff or id send him down a known set of carbs to try. Maybe someone in his area could take a known set to him for diagnostics.

Was thinking the oversized pilot air jet was increasing the vacuum causing too much fuel to draw, but that would only be in the pilot circuit. Replacement 185's will be here soon and I have some bits I use to drill out jets (ARRRGGHHHH) that I can check the size of the main air jets with to see if they have been altered. The only other odd thing I have found is the ignition fuse gets really hot. Have been thinking there is a problem somewhere in the ignition circuit since I first started this project. While trying to find a voltage loss, whenever the field coil on the stator/alternator is unplugged the system stayed at over 12v with the key on.

[Barbarosa]

Mack,

The dropping cylinders and a fairly comprehensive check of the coils and ignition circuit current, voltages, and resistance was in another thread. I think DaVinci gave him some help with troubleshooting the TCI.

The upshot was that the ignition system voltage was good; ballast resistor was bypassed and the new Dyna coils were good. I don't remember if the TCI was shotgunned with a known-good TCI to see if it was working cold --> warm, then failing after it got hot.

Got a TCI from Greg but only ran it a short time.

[Barbarosa]

I miss the mention of cylinders dropping out? I don't recall reading that? Anyway it would seem the PO had experienced the rich condition before and tried to remedy the situation by drilling out the air jets. So I'm inclined to think that the pre-existing condition may not be carb related at all (other than to correct what the PO did to them) set the fuel levels back to level with the bowl washers using clear hoses.
For some reason the fuel isn't getting fully burned in the cylinders. That's why I mentioned the advances. For some reason your not getting full spark and the fact that it is across all cylinders makes me believe that it's an electrical issue between the coils and the TCI.

When it gets dark tonight I'm going to hook up my trusty old spark tester and eyeball what's happening. The plugs arc with a white spark when grounded to the head but it's not a big fat one like my HD puts out. The wires and caps ohmed out proper and the coils are new so I don't expect to find anything, but if I hook up the timing gun too it should be a good light show lol.

[MPittma100]

Was thinking the oversized pilot air jet was increasing the vacuum causing too much fuel to draw, but that would only be in the pilot circuit. Replacement 185's will be here soon and I have some bits I use to drill out jets (ARRRGGHHHH) that I can check the size of the main air jets with to see if they have been altered. The only other odd thing I have found is the ignition fuse gets really hot. Have been thinking there is a problem somewhere in the ignition circuit since I first started this project. While trying to find a voltage loss, whenever the field coil on the stator/alternator is unplugged the system stayed at over 12v with the key on.

Check for poor grounds. All factory grounds are chassis grounds. You can vastly improve that by improving all chassis grounds to direct battery grounds. Poor ground = too much resistance = hot wires.

[Bonz]

Pilot air jet??? The pilot jet is a fuel jet...

[3Phase]

Taking a short break

Pilot air jet??? The pilot jet is a fuel jet...

There are two air jets in the intake bell of the carburetors: Pilot and Main. The Pilot's removable; Main's pressed in.

[Bonz]

I don't understand the term oversized air jet. That implies it is something that is changeable.

[3Phase]

I think Barbarossa has the air jets confused with something else but that's beside the point. All of the jets are changeable, that's how people screw up their bikes and then sell them to someone else or part them out on eBay.

Changing the air jet changes the Air/Fuel ratio of the mixture delivered by that circuit but not the amount that's delivered.

An over/under size Main air jet would make the Air/Fuel ratio lean or rich when it was delivered by the nozzle/emulsion tube/needle jet. You can change the Main air jet but you have to drill it out and press in a new jet or be like Billy Big Bore and drill it out oversize.

An over/under sized Pilot air jet would make the Air/Fuel ratio lean or rich when it was delivered by the idle mixture screw and the intermediate trio/transition ports. You can change the Pilot air jet by unscrewing it and putting in another jet or you can be like Billy Big Bore and drill it out oversize.


The Start circuit enrichener doesn't have an air jet, it sucks.

[MPittma100]

The carbs in question should not need smaller than stock jets to fix this problem. Because stock jet size (if Mikuni, and not drilled) will not foul plugs. Problem, although yet identified, lies elsewhere even if the pilot and copilot aren't getting along - Just kidding.

Finding some loaner carbs may be the next step.