Carb Balancing

[Passx]

Hey Guy's,



I tried something tonight that I've been thinking about for a while and thought that I'd throw it out and see if anyone else has done this or had any good results.



What I did was started with all 6 idle mix screws set to the same and then used a laser thermometer to measure the header (6-2-1) pipe temps at the head to register temperature as it relates to the air/fuel ratio for each cylinder and must say the results surprised me, the motor is much smoother and rev's better. with all the same I had a 50-70 degree difference with both outer cylinders being the same and coldest and the 2 center ones being quite a bit hotter and then cyl's 2 + 5 being only slightly warmer than 1 + 6, so I adjusted the screws to balance the temps to something close to each other and ended up with about 1 1/2 turns difference between the inner and outer cylinder pairs and a 10- 15 degree variation. The motor seems to carburete much better and has better response, what does this all mean ? Damn if I know for sure but it seems to make the cyl-cyl variation less, At this point I don't see a down side but that's part of why I'm posting this to see if I'm missing something here. I still need to look at the balance because the idle screws seem to have a fair effect on that so I need to take a look. Need to ride it for a while and see if anything negative jumps out if it does I'll post it. By the way I haven't tried this on the double walled pipes which may not work as well plus the Laser Thermometer that I have doesn't like real shiny surfaces like chrome but I also checked the head surface temp right above the pipe and it was real close to the pipe temps so that might be an option for the double walled pipes :twisted: , more later



Steve P. #5220

[Dave Ditner]

Steve, was the engine at operating temperature? How long had it been ridden? How long was it idling? The base cylinder temperatures for the inside cylinders may well have been differentially warmer than the outer cylinders to cause the result you saw. Did you have a fan blowing on the engine at the time you measured?

If I remember right, the original dyno test on the motor would flash 100 hp, but not hold it due to the excess heat in the center two cylinders. If you have a good sized box fan set it up in front of the wheel so it gets the block and head pretty good, check the temps again as the carbs are now set, then go back to all the same and see what happens.

[Passx]

Hi Dave, Hope its nice in Florida, we have cold and snow flurries here. Anyway I have since done this on both CBX's and my Wing and can say that it does seem to work quite well, the X's typically run hotter on the 2 center cylinders but you can add some fuel with the idle screws and the idle and throttle response smooths out. The cyl-cyl variation can be adjusted to within a small amount and you really don't have that big of a difference in the screw adjustments, you have to play with it a bit but I have tried it with the motors just warm enough to idle on their own to hot and idling with a fan on it and it seems that no matter what it ends up very close to the same. The only thing is that I think you need to rebalance the carbs once this is done because the idle screws do affect the balance but I have not rechecked mine but will to verify it probably not until spring unless I can get the 81 up to the shop with some time to work on it.



By the way I found that using the area of the cylinder head right above the header pipes about 1/4in in from the joint is most consistant and a small adjustment of the idle screws brings immediate change in temperature, you will be surprised at how quick the temps adjust.



Has anyone else tried this yet ?



Hope everyone had a good turkey day and has a good holiday season.



Steve P. #5220

[Rick Angles #3328]

My questions is this:Is the temp way a better way to balance the carbs then to use a sync gauge?When I took the carbs off of my 82 to clean them,I set the mixture screws to about 1 1/2 turns(or was it 2 turns?Was a couple of years).They have never been sync'ed and still it runs better then before.I understand what Dave was saying in that the center of the engine to be hotter,due to the fact it has less air around it compared to the outer cylinders.A fan may even the temp,but would that make the outer ones even cooler? Maybe it is something to do a comparison on.A future tech article maybe

[Dave Ditner]

He's not talking about syncing, he's talking about mixture adjustment. Carb syncing is setting the throttle plates so the cylinders pull equally at idle. Here the number 4 carb is the base carb with no adjustment to it. It's vacuum is measured by a column of mercury, and all others are set to it. Having this vacuum equal in all cylinders is what makes for a smooth idle

[ChrisCBX]

Hi Steve,



After you adjusted the mixture and ran the bike for a while, did you pull out the plugs to see if the center cyls were running lean or rich? I would be interested in hearing if those cylinders are getting the correct mix, also, I wonder why Honda wouldn't have done this at the factory.



best wishes,



Chris.

[Passx]

Hi Chris,



I did run the 81 a fair amount after doing this, it's about 20 miles to work each way and I did take a look at the plugs and the variation is less than it was before but I would like to look at this again after a longer ride where I can ride it at 60-70 for 50 or more miles to clean things up and then just shut it off to see how it affected the overall mixture setting but and this is a very large but (not mine) you really can't read plugs all that effectively anymore due to the additives in the current fuels and any time spent on the idle circuit means that you definitely cannot read the plugs accurately. I suppose that Honda never did this as a matter of routine because the technology wasn't available when the X's were built, what I mean by that is that they could've done this using thermocouples in the exhaust pipes but then you would've of had holes in the header pipes and this is the method used by most race teams these days. The laser thermometer is easier and less expensive than the thermocouples but is probably also not quite as accurate, but compared to doing it any other way that I've seen (ear, tach, etc) other than measuring the a/f of each cylinder individually this is a good way to do this.



Rick,

Dave is absolutely correct in that this is only setting the idle mixture screws and different from sync'ing the carbs, which I highly recommend anytime you alter any of the carb settings because it's based purely on engine demand (vacuum) like Dave said and if you alter the carbs their demand is also changed so they need to be resync'd. Anyway that's my story and I'm sticking to it.



Has anybody else tried this since my original posting, I'm curious to see if you all had the same results or possibly something different.





Steve P. 5220

[Passx]

Hi Chris,



I did run the 81 a fair amount after doing this, it's about 20 miles to work each way and I did take a look at the plugs and the variation is less than it was before but I would like to look at this again after a longer ride where I can ride it at 60-70 for 50 or more miles to clean things up and then just shut it off to see how it affected the overall mixture setting but and this is a very large but (not mine) you really can't read plugs all that effectively anymore due to the additives in the current fuels and any time spent on the idle circuit means that you definitely cannot read the plugs accurately. I suppose that Honda never did this as a matter of routine because the technology wasn't available when the X's were built, what I mean by that is that they could've done this using thermocouples in the exhaust pipes but then you would've of had holes in the header pipes and this is the method used by most race teams these days. The laser thermometer is easier and less expensive than the thermocouples but is probably also not quite as accurate, but compared to doing it any other way that I've seen (ear, tach, etc) other than measuring the a/f of each cylinder individually this is a good way to do this.



Rick,

Dave is absolutely correct in that this is only setting the idle mixture screws and different from sync'ing the carbs, which I highly recommend anytime you alter any of the carb settings because it's based purely on engine demand (vacuum) like Dave said and if you alter the carbs their demand is also changed so they need to be resync'd. Anyway that's my story and I'm sticking to it.



Has anybody else tried this since my original posting, I'm curious to see if you all had the same results or possibly something different.





Steve P. 5220

[Passx]

Hi Chris,

I did run the 81 a fair amount after doing this, it's about 20 miles to work each way and I did take a look at the plugs and the variation is less than it was before but I would like to look at this again after a longer ride where I can ride it at 60-70 for 50 or more miles to clean things up and then just shut it off to see how it affected the overall mixture setting but and this is a very large but (not mine) you really can't read plugs all that effectively anymore due to the additives in the current fuels and any time spent on the idle circuit means that you definitely cannot read the plugs accurately. I suppose that Honda never did this as a matter of routine because the technology wasn't available when the X's were built, what I mean by that is that they could've done this using thermocouples in the exhaust pipes but then you would've of had holes in the header pipes and this is the method used by most race teams these days. The laser thermometer is easier and less expensive than the thermocouples but is probably also not quite as accurate, but compared to doing it any other way that I've seen (ear, tach, etc) other than measuring the a/f of each cylinder individually this is a good way to do this.

Rick,
Dave is absolutely correct in that this is only setting the idle mixture screws and different from sync'ing the carbs, which I highly recommend anytime you alter any of the carb settings because it's based purely on engine demand (vacuum) like Dave said and if you alter the carbs their demand is also changed so they need to be resync'd. Anyway that's my story and I'm sticking to it.

Has anybody else tried this since my original posting, I'm curious to see if you all had the same results or possibly something different.


Steve P. 5220

[Guest]

It seems to me that this would be a good way to set the idle evenly with the thermometer. Would the idle change after resyncing the carbs?

[Passx]

I personally have not seen this happen unless they are way off and if they are you're going to want to set the mixture screws with the carb sticks/gauges on because you're going to go back & forth a couple of times until you hone it in. I don't know if some of the "older" (experience not age, maybe both) guy's can shed anything different but that's my experience. It seems that any adjustments that you make to a multi-carb'd motor affects the balance some because each cylinder is different. Sometimes it makes no difference but I personally like to check the balance after any other changes but most times it just helps me sleep better, hope this helps.



Steve P.

[Dave Ditner]

The whole intent of carb synching is to get all cylinders to pull evenly AT IDLE!!! AT IDLE!!! Once the throttle cable is pulled, the throttles are off the stops that were so carefully set. Synching is or should be the last thing done. First know the condition of the engine---a compression check. Then the condition of the ignition system. Plugs, wires, coils etc okay?? Carbs clean? No passages obstructed? Okay, now it's time to sync 'em, with the object being a clean smooth idle. That's all. If everything else checked okay, when the carbs are all pulling the same amount of vacuum, the idle ought to be slick as snot on a doorknob. Slight variations cylinder to cylinder (compression pressure) will have very little effect on idle due to the fact that the cylinders are hardly loaded during idle. Exhaust temperature measurements can be very misleading, I'd think. First and foremost would be mixture screw adjustment. A little rich,exhaust temperature drops, a little lean, exhaust temperature drops. Just right? Peak exhaust temp. Why? ??? Too lean leaves unburned oxygen which will absorb heat, lowering overall gas temperature. Too rich? Unburned fuel. Does the same thing. Additionally, in order to measure exhaust temp accurately, a gas thermocouple should be used and there aren't too many of us that want to drill a 1/8" hole in eash pipe to accept a shielded thermocouple. Using infrared can be deceiving, especially with stock exhaust systems since they're double walled, a pipe in a pipe. Might take one long time to know where you're at.

How'd the factory do it? Not on an engine I'll bet. Some kind of test stand that measured airflow, or throttle position damn quit and damn easy. we gotta do it the hard way and pray a lot more.

[Mike Nixon]

[quote="Dave Ditner"]The whole intent of carb synching is to get all cylinders to pull evenly AT IDLE!!! AT IDLE!!!



Yep. At idle. Ya finally drew me into this thing. Carb synch has one primary purpose -- to make that beast purr. (If you're anal about it, you can even make it quiet.) Once off idle, we hope the throttles stay in synch, but they really don't, at least not perfectly. In the really old days, the CB750 had cable topped carburetors. The professional method was to synch the throttles at idle, and then check them at 3000 rpm. But idle was the more important stage.

[Passx]

Dave, Mike,



I beg to differ, the most noticeable effect of carb balance is at idle BUT it affects the balance/smoothness throughout the entire power band. Think about it, you're adjusting the throttle blades, nothing else and they control the engines performance by dictating the range you operate in. That said, I balance my carbs at about 50% of the cruise RPM, this makes the engine much smoother over the entire rev range by making all the cylinders closer throughout that range, actually just a smaller variation over a broader band width. Now I will say that if you have a 79/80 rattler and if you balance at idle only for best results then yes it will be quieter but it will vibrate more at speed and the balance will be off more at speed as well. My 80 with an 81 basket assembly can be made pretty much quiet by doing the balance at idle only, but if I balance at 2k it is MUCH smoother at all speeds, BUT the clutch does rattle more at idle, it's all a compromise but you will get better response and smoothness overall, your choice.



On the idle mixture adjustment, this really does work to make all the cylinders closer to the same mixture and the changes you make will appear before you can put the screw driver down and check the exhaust port for temp, so the changes appear & stabilize very quickly (surprised me) , what this does is compensate for the various machining and casting differences. If you check the carbs and jets with some precision pin gages you will notice that there is some small differences in the diameters of the jets and the most overlooked thing is the differences in the lengths of the metering orifices, small differences of only .001in can make a big difference in the amount of fuel delivered to each carb. Also if the mixture is lean the temps will go up short of shutting the fuel completely off and if they are rich they will go down. Check with your local pro racer with thermocouples in the exhaust.



Then there is my personal pet peeve of the float setting and the float to float variations in float area and setting, these have huge effects on the fuel metering. I set all my floats with the carbs laying on their back, why you ask, because it's easier and it make the fuel level slightly lower, why you ask, because contrary to the popular belief the main jets on these bikes are flat out pig rich and need to be leaned out not richened but the idle and slow speed circuits are indeed lean for emissions. I have spent a lot of time & $$$ on the local dyno with a tailpipe sniffer and I am confident that this is a typical Honda trait after doing several Goldwings, Valkeries and my own 80 X around 10 times. They need to be in the high 13.8-1 to 14-1 range for the best power which coincidentally gives you really good gas mileage. In building many engines my philosophy has always been efficiency, efficiency, efficiency, if you use more than the typical 70-80% of the delivered fuel you'll always make more power and economy plus the motor will live longer by not washing the cylinders down. Wow was that a ranting tangent or what, good luck



Steve P.#5220

[Passx]

Dave, Mike,



I beg to differ, the most noticeable effect of carb balance is at idle BUT it affects the balance/smoothness throughout the entire power band. Think about it, you're adjusting the throttle blades, nothing else and they control the engines performance by dictating the range you operate in. That said, I balance my carbs at about 50% of the cruise RPM, this makes the engine much smoother over the entire rev range by making all the cylinders closer throughout that range, actually just a smaller variation over a broader band width. Now I will say that if you have a 79/80 rattler and if you balance at idle only for best results then yes it will be quieter but it will vibrate more at speed and the balance will be off more at speed as well. My 80 with an 81 basket assembly can be made pretty much quiet by doing the balance at idle only, but if I balance at 2k it is MUCH smoother at all speeds, BUT the clutch does rattle more at idle, it's all a compromise but you will get better response and smoothness overall, your choice.



On the idle mixture adjustment, this really does work to make all the cylinders closer to the same mixture and the changes you make will appear before you can put the screw driver down and check the exhaust port for temp, so the changes appear & stabilize very quickly (surprised me) , what this does is compensate for the various machining and casting differences. If you check the carbs and jets with some precision pin gages you will notice that there is some small differences in the diameters of the jets and the most overlooked thing is the differences in the lengths of the metering orifices, small differences of only .001in can make a big difference in the amount of fuel delivered to each carb. Also if the mixture is lean the temps will go up short of shutting the fuel completely off and if they are rich they will go down. Check with your local pro racer with thermocouples in the exhaust.



Then there is my personal pet peeve of the float setting and the float to float variations in float area and setting, these have huge effects on the fuel metering. I set all my floats with the carbs laying on their back, why you ask, because it's easier and it make the fuel level slightly lower, why you ask, because contrary to the popular belief the main jets on these bikes are flat out pig rich and need to be leaned out not richened but the idle and slow speed circuits are indeed lean for emissions. I have spent a lot of time & $$$ on the local dyno with a tailpipe sniffer and I am confident that this is a typical Honda trait after doing several Goldwings, Valkeries and my own 80 X around 10 times. They need to be in the high 13.8-1 to 14-1 range for the best power which coincidentally gives you really good gas mileage. In building many engines my philosophy has always been efficiency, efficiency, efficiency, if you use more than the typical 70-80% of the delivered fuel you'll always make more power and economy plus the motor will live longer by not washing the cylinders down. Wow was that a ranting tangent or what, good luck



Steve P.#5220