MasterGuns Posted March 2, 2012 Share #1 Posted March 2, 2012 When syncing the carbs on my 86 lst Ed, I can get all four carbs to be perfectly level at about 24 bars onmy Carbtune but at higher rpms, up around 3500 or 4000 or so, they are no longer anywhere being level. I have no vacuum leaks. Even when riding at 65/70 mph it feels like they aren't balanced. I hook up the Carbtune and at idle they are still perfect. Run the r's up while sitting there and same result.......not balanced at higher rpms. Otherthan than this, it seems to runs strong. Compression on all cylinders is about even 165 to 175. Just would like some comments regarding if this sort of thing is normal. I do have a second set of "just gone through" carbs and may try mounting those to see what happens. But that is a lot of work just to see "what happens". Thanks Link to comment Share on other sites More sharing options...
Pegasus1300 Posted March 2, 2012 Share #2 Posted March 2, 2012 (Do I have a Problem) Man I wouldn't touch that line with a ten foot pole:rotf:. But if you haven't done it yet you might want to look at the diaphrams for pin holes.Hold up to the light and you can see them.It is best to replace them if there are holes but I have repaired them with black RTV and had it work for a long time. Link to comment Share on other sites More sharing options...
Yammer Dan Posted March 2, 2012 Share #3 Posted March 2, 2012 (Do I have a Problem) Man I wouldn't touch that line with a ten foot pole:rotf:. But if you haven't done it yet you might want to look at the diaphrams for pin holes.Hold up to the light and you can see them.It is best to replace them if there are holes but I have repaired them with black RTV and had it work for a long time. Thats what I was thinking but I' ain't touching that one either!!! Light behind them in a dark room and you can spot holes you didn't think were there. When they start around the edges you can have pretty good luck sealing them. THIN COATS!!! And let them dry good. The black RTV is good. Several others work. I can't remember what I used. Link to comment Share on other sites More sharing options...
BuddyRich Posted March 2, 2012 Share #4 Posted March 2, 2012 Mines the same way. They are only balanced at idle. Once I run up the rpm's they are all different. I always thought they were suppose to do that. At idle you have plenty of room for even exhaust flow. As RPM's go up exhaust flow changes which is going to effect how much is sucked in to replace the burnt gases... Sounds good anyway don't it.... Link to comment Share on other sites More sharing options...
Yammer Dan Posted March 2, 2012 Share #5 Posted March 2, 2012 Mines the same way. They are only balanced at idle. Once I run up the rpm's they are all different. I always thought they were suppose to do that. At idle you have plenty of room for even exhaust flow. As RPM's go up exhaust flow changes which is going to effect how much is sucked in to replace the burnt gases... Sounds good anyway don't it.... And the "New" improved Yamaha's are faster than the old ones. Sounds good but...... That does sound good Buddy. Ever check it with pipes off? Or would exhaust with less restriction help? I don't know it raining and I got to go to the gym...... Link to comment Share on other sites More sharing options...
MasterGuns Posted March 2, 2012 Author Share #6 Posted March 2, 2012 Nope, diaphrams are new. (Do I have a Problem) Man I wouldn't touch that line with a ten foot pole:rotf:. But if you haven't done it yet you might want to look at the diaphrams for pin holes.Hold up to the light and you can see them.It is best to replace them if there are holes but I have repaired them with black RTV and had it work for a long time. Link to comment Share on other sites More sharing options...
MasterGuns Posted March 2, 2012 Author Share #7 Posted March 2, 2012 When I had an almost brand new 86 back in the day, she was pretty much balanced (synced) even at higher rpms. But I did like your answer. Still chucklin. Mines the same way. They are only balanced at idle. Once I run up the rpm's they are all different. I always thought they were suppose to do that. At idle you have plenty of room for even exhaust flow. As RPM's go up exhaust flow changes which is going to effect how much is sucked in to replace the burnt gases... Sounds good anyway don't it.... Link to comment Share on other sites More sharing options...
GaryZ Posted March 2, 2012 Share #8 Posted March 2, 2012 When syncing the carbs on my 86 lst Ed, I can get all four carbs to be perfectly level at about 24 bars onmy Carbtune but at higher rpms, up around 3500 or 4000 or so, they are no longer anywhere being level. Every bike that I have sync'd carbs has done that same thing . . . Link to comment Share on other sites More sharing options...
MasterGuns Posted March 2, 2012 Author Share #9 Posted March 2, 2012 Guess I'll stop worrying bout this. Every bike that I have sync'd carbs has done that same thing . . . Link to comment Share on other sites More sharing options...
mbrood Posted March 2, 2012 Share #10 Posted March 2, 2012 Wouldn't this be an indication that one (or more) of the needles was worn causing the imbalance at the higher revs? Maybe a slight shim adjustment would help ? Link to comment Share on other sites More sharing options...
MasterGuns Posted March 2, 2012 Author Share #11 Posted March 2, 2012 Thanks for the reply. But the more I think about this issue, the more I am convincing myself that the more an engine wears, relative to compression, even the slightest difference between cylinders, compression wise anyway, has a direct effect on the amount of fuel in. Cylinders with higher compression mean more exhaust being discharged from that cylinder. More out means more in, thus the difference readings on the Carbtune at higher rpms. Is this a possible explanation or am I out in left field somewhere. Wouldn't this be an indication that one (or more) of the needles was worn causing the imbalance at the higher revs? Maybe a slight shim adjustment would help ? Link to comment Share on other sites More sharing options...
Venturous Randy Posted March 2, 2012 Share #12 Posted March 2, 2012 I don't think some people actually realize that all you are doing is measuring vacuum in the chamber between the throttle plate and the valves and comparing the vacuum from one carb to another or to three other carbs. This is because an engine on the intake side is nothing more than a big vacuum pump. By adjusting the amount the throttle plate is open, you are adjusting the amount of vacuum by adjusting the amount of leakage you are allowing around the throttle plate. Given this, if you have even a small vacuum leak, when you are balancing the carbs, you have to adjust for that leak. The more you open the throttle plates, the less that small vacuum leak will effect the amount of vacuum you are reading on your meter for that cylinder. With a small leak, you are having to close the throttle plate to bring that vacuum up to the point it matches the other carbs. As you open the throttle, that small leak will cause the levels on the meter to become uneven compared to the other carbs. If you have a larger leak, you can completely close that throttle plate and the meter may still show you that you do not have enough vacuum, making you think you need to close it even more. Another thing that can have an effect on vacuum reading is having an intake valve that has a small leak. At idle with very little air flow, a small leak can cause a small spit back of air that disrupts flow into the intake manifold and appear to decrease vacuum. As RPM"s increase, that small leak becomes less of a factor as the valves are opening and closing much quicker and there is more air flow going through the manifold which somewhat neutralizes that small spit back. The first thing you need to do is to try to identify any vacuum leaks. I usually spray some starter fluid around the manifolds under each carb and around the YICS system if you have it still hooked up, which I suggest you remove and plug. If you do not detect any leaks, you can adjust each carb to be more balanced in the RPM range that you normally operate, even though theoretically, you would have to be under a load to truly be balanced. RandyA Link to comment Share on other sites More sharing options...
Mel Posted March 2, 2012 Share #13 Posted March 2, 2012 Had my '84 Royale until 2004, never balanced the carbs, had it done in a shop once when carbs needed cleaned/overhauled. HOWEVER--- I did extensive 4 cylinder tuning in the early 70's when drag racing a modified Honda CB 750, as well as having a 2nd one for street riding. Balancining the carbs at idle had absolutely nothing to do with having them balanced when running at partial throttle. The carb actuators were individually adjustable, therefor they could become individually mis-adjusted. The carbs had to be balanced at, say 3,500 RPM's by adjusting the individual actuators until all four were drawing the same amount of vacuum. When they are being balanced at idle, the carb actuators (cables or linkages) are all slack and you are adjusting the idle speed of each carb. At higher speeds (RPM's) each individual carb is reacting to how far it is being opened. If the actuators are not all lifting the same amount (maybe from stretch/wear), then there will be an imbalance. They must be adjusted at speed! Link to comment Share on other sites More sharing options...
skydoc_17 Posted March 2, 2012 Share #14 Posted March 2, 2012 Hey Herb, I too do not Sync. my Carbs. at idle. Since I spend most of my riding time somewhat above idle, this is where I set them. As long as the bike doesn't stall at a light, I could care less what vacuum it pulls at idle. A good place to set your Carbs would be the RPM's that you would be at, going 65 MPH in 5th gear. (3600 I think, mine is a lot different with the FJR final drive, and VMAX rear wheel) try setting the Sync level there, and see how it idles after the adjustment. Costs nothing but time, my friend. Earl Link to comment Share on other sites More sharing options...
Venturous Randy Posted March 2, 2012 Share #15 Posted March 2, 2012 . When they are being balanced at idle, the cyou are adjusting whearb actuators (cables or linkages) are all slack and you are adjusting the idle speed of each carb. At higher speeds (RPM's) each individual carb is reacting to how far it is being opened. If the actuators are not all lifting the same amount (maybe from stretch/wear), then there will be an imbalance. They must be adjusted at speed! On our bikes, each carb linkage is spring loaded against a stop and the stop setting is what you are adjusting when balancing the carbs. There should be no slack in any of the linkage. There is only one carb that has an idle setting and from that point on, each carb is adjusted to load against the linkage from that first carb. The problem with adjusting to a particular RPM is it takes very little throttle to maintain 4,000 RPM's in neutral, but to maintain 4,000 RPM's on flat ground in 5th gear takes a lot more throttle. RandyA Link to comment Share on other sites More sharing options...
BuddyRich Posted March 3, 2012 Share #16 Posted March 3, 2012 If I was gonna do that it would be between 3500 and 4000. That's where my tach is whenever I'm cruising. Taking off it's always going to nearly 6 or higher before shifting. Its more fun than saving gas....... Link to comment Share on other sites More sharing options...
Yammer Dan Posted March 4, 2012 Share #17 Posted March 4, 2012 Might be a little hard to balance them at redline:whistling: Link to comment Share on other sites More sharing options...
mbrood Posted March 4, 2012 Share #18 Posted March 4, 2012 Unless you install a "T" for carb 2's connection to the boost sensor, you don't have the vacuum advance making the timing at higher RPM appropriate. Link to comment Share on other sites More sharing options...
jasonm. Posted March 4, 2012 Share #19 Posted March 4, 2012 Jeeez...people have to stop saying "use RTV" for repairs to diaphragms. ALL RTVs warn against using it in gasoline environments. Gas is a solvent that causes the RTV to just fall off. Always set my sync as stated below. This takes into the fact of the wear on the linkages. As for the uneven sync issue... First, who here rides at idle all day? 1st- you sync at idle, then raise the rpm to 3000...,check the sync ...has it changed some ?= normal, Change a lot?...there is something amiss. FYI, the vacuum levels will drop the more you open the throttle. Link to comment Share on other sites More sharing options...
GaryZ Posted March 5, 2012 Share #20 Posted March 5, 2012 I did some reading about tuning CV carbs yesterday. Each of the articles seems to follow a similar pattern for stock bikes; When wanted or needed the wide open throttle is adjusted by altering the height of the main jet needle (jet kit or spacers). Idle is set using the low-speed screw. And the middle takes care of itself. On modified bikes there is an excellent discussion on the rich/lean symptoms for the three carb circuits. No one suggested sync'g the carbs above idle. Just sayin' . . . Link to comment Share on other sites More sharing options...
MasterGuns Posted March 5, 2012 Author Share #21 Posted March 5, 2012 Gary, Being that I am pullin the 86 apart for the Marks collector install, I thought I go ahead and sync the carbs "again". So, with all the plastic off, before I started with the exhaust I did just that. What I found that if properly synced at idle, the vacuum pull remains pretty darn close to being even all the way up to 5000. Of course, the bike is not under load. I also installed a "tee" in the #2 vacuum line so the vacuum sensor could affect whatever and however it was going to effect the process and it made no difference. At 4000 rpm the four carbs are darn near even. But in the process of the rpms increasing from idle to 4000 is another story. But I am satisfied with the way this 86 reads. Before I did all this, I used starting fluid to check for leaks and there were none at all. Also changed the plugs and the colors on all four is just right. Now all I need is the marks collector to arrive. Think I'll also reinstall the Jardines with the Marks collecter and wear earplugs. I did some reading about tuning CV carbs yesterday. Each of the articles seems to follow a similar pattern for stock bikes; When wanted or needed the wide open throttle is adjusted by altering the height of the main jet needle (jet kit or spacers). Idle is set using the low-speed screw. And the middle takes care of itself. On modified bikes there is an excellent discussion on the rich/lean symptoms for the three carb circuits. No one suggested sync'g the carbs above idle. Just sayin' . . . Link to comment Share on other sites More sharing options...
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