81 xs650 difficult tuning

[TDodge7]

I guess I'll leave it where it is for a few days worth of putting around and see how the plugs color . I didn't think about the non epa screws changing the amount of turns out . But I am of course open to second third and fourth opinions. Once I have this mixture issue out of the way all that's left to do is figure out why the battery keeps dying , it puts out 14volts running across the battery and there's no parasitic drains when the ignition is off , it seems to randomly kill the battery for fun.

 

[littlebill31]

LoL, it sounds good to me. I'm a little weary about the 1.5 turns out, but it sounds ok. Put some miles on it and see how it goes.

 

[Classic]

Correct idle for a 1981 XS650 is 1200RPM.

Sounds good, though.

Nice XS!

 

[5twins]

Actually, I think 1200 is the spec for all years.

 

[Classic]

You are right.

Anyways, TDodge can bump up the idle a bit.

 

[TDodge7]

I was using it more as a reference point since many of the how to's I had read said a lot of the time people will crank the idle up too high opening up those 3 little holes which can screw with your mixture settings . I can always bump it up , though it sounds pretty nice where it is , the tach doesn't seem to be very accurate either . Hopefully all is well on the tuning front , but the plugs haven't colored yet so time will tell .


On a side note I set my nighthawk s to 2 turns out and it seems to be almost dead on right from the get go which is refreshing to say the least . I get a slight pop on decel but the idle goes right down to where it should be right away and I can crack it wide open as fast as I want ....might let that one eat after I see how the plugs look.

 

[retiredgentleman]

TDodge7;

"I was using it more as a reference point since many of the how to's I had read said a lot of the time people will crank the idle up too high opening up those 3 little holes which can screw with your mixture settings"

I think you are a little confused about the relationship between the 3 bypass holes and the idle rpm. You can set your idle speed (with the idle speed screw) to 1000 or to 1200 or to 1400 or any rpm you wish. The carb is designed to work with the pilot jet feeding to the 3 bypass holes and to mixture screw (with its single hole outlet). You can't screw up your mixture by adjusting the idle too high.

The reason these bikes are best at around 1200 rpm for idle, is to keep the voltage up to 13 volts or better. If waiting at an intersection with the blinkers on and the right foot on the brake, the voltage can drop enough that the blinkers stop flashing. That is a safety hazard................so 1200 or better is safer.

Maybe you are referring to my earlier post. The "Dead Cylinder" method is where its important to have the butterflys almost fully closed, which closes off the 3 bypass holes.That's the only way that I've found to adjust the mixture screw and the engine rpm needs to be down around 300 or 400 rpm (just barely above a stall).

 

[TDodge7]

That may be it , none of my bikes idle over 1100 so 1200 and 1300 sound crazy high to me , but the battery does keep dying so maybe it's time to bump it up . The flashers never blink at stops though .


Took the xs on a little ride lastnight and checked the plugs today , they're not great , but they also don't have many miles on this new setting . The left plug is still pretty dark , it was pretty black before I did the adjustments and now it's chocolate brown . The right plug was super lean before , now it's just slightly lean looking , like a cigarette ash grey , still pretty close to white though . They're the plugs that came in the bike though and when we got it one cylinder was stupid rich and the other was lean because of the mixture screw o ring . Despite constantly screwing with the mixture over the past month they never seem to change colors much even though the engine obviously runs differently at different mixtures . I'd like to see what new plugs look like in it after a good ride , but I'm just doing all the work for free , I'm not funding this project ha ha . I'll see if I can't get my friend to grab some plugs for it today .

 

[retiredgentleman]

That's not a safe thing, if the turn signals don't flash waiting at intersections.

Have you measured the battery voltage when idling at 1200 rpm? Have you measured it at 3000 rpm?

 

[TDodge7]

Well I guess I wasn't at the best spot , now that I've taken the bike on a decently long ride it's popping on decel , pretty obviously too , I guess the long stretch in my neighborhood wasn't enough . So I guess I get to start over again , I'm so tired of setting mixture , I've been playing with it for weeks now and I can tell my friend is getting tired of waiting for his bike . I just don't understand what's going on . It would seem that there is a spot between 1 turn and 2 turns that should be correct , but once you go past 2 turns where it should be rich the idle hangs which it totally should only be doing if it's lean . When it's in the sweet spot between 1 and 2 turns the rpm is the highest yet it pops on decel and the idle drops to where it should quickly after a rev which it shouldn't do if it's lean . Also the right cylinder seems to always be leaner than the left despite having no leaks and the carbs being clean for sure . I just don't understand how it can be close enough to tuned to not let the idle hang after you rev it , but still be lean enough for the exhaust to pop on decel (and no the pipes don't have any leaks , brand new gaskets and everything) There's no way on earth it should be this hard for someone to dial in idle mixture , no way , either I'm a moron , I'm doing it wrong , or every bike I touch just hates me because I have this problem on everything . And even when I'm sure I got it I'll call my friend over and then an hour later he'll warm it up and it'll run like crap again . Tuning obviously isn't one of my talents .


ps. Just incase I'm doing it wrong feel welcome to tell me how you set your idle . I've been scrounging all over the internet to see different ways people set theirs . Everyone just always seems to be able to do this quick and easily , my inability to do it has me seriously doubting my backyard mechanic creds .

 

[5twins]

It may be those new mix screws. Maybe they're just not compatible with the carbs. The originals had a stepped tip. I don't know for sure but maybe the bottom of the mix screw hole is stepped as well. A tapered screw tip may not fit into and meter correctly through that. If there's any way you could try the original stepped screws again, I would give that a shot.

You don't seem to be doing your adjustments any differently that we all do. Sometimes, I go for a ride and take a small screwdriver with me. I make 1/4 turn adjustments, ride for a while to test, pull over and adjust another 1/4 turn, etc. I watch for the tell-tale popping on decel, hanging idle, etc. while riding.

 

[retiredgentleman]

TDodge7;

With a high idle hovering problem, its important that the 2 carbs are synchronized. Have you sync'd the carbs?

If they are sync'd, I would follow that with mixture adjustment at about 400 rpm (dead cylinder method as I posted earlier)

 

[TDodge7]

I've synced , I have a morgan carbtune . I just went out there and did the dead cylinder method again , starting with the right cylinder , I pulled the plug wire off the left cylinder , and I pulled the petcock vacuum off the left cylinder and moved it to the right (since the right cylinder will be the one running) leaving the sync port cap off the left cylinder so it's not sucking in gas . Then I fired up the bike and adjusted the rpm down to between 400-600 rpm (the tach kind of bounces around a little) Then I started adjusting . The right cylinder will hiccup and pop below half a turn out , and runs it's fastest between 0.5 and 1.5 , anything more than 1.5 and the rpm drops and the idle sounds rougher . Not to say that between 0.5 and 1.5 that the idle sounds good , because it doesn't sound great , not smooth sounding . The right cylinder is the one that seems to like to pop a lot despite reacting to the pilot screws the same as the left cylinder . I just rechecked for leaks and there still aren't any , valves are adjusted , carbs synced , wits at end .

I don't know if this means anything but when it pops on decel it only seems to do it at lower rpm . Out on the main road I took it up to about 5 and then shut the throttle hard , I didn't get any popping until I was around 2k and below . The bike feels good everywhere else , mid and wot feel great , no flat spots or anything , just popping on decel and crappy idle .

 

[Wally]

Looks like my two into one system
Old pic attached

 

[TDodge7]

Ok , disregard the previous post , I have made a breakthrough . I decided it would be best to put the original mixture screws back in so that at least I'm working off the original stuff . As soon as I pull the mixture screw out of the right carb I instantly see why it's running leaner than the other . Somehow the o-ring and washer had slide between the bottom coil of the spring and worked their way up above the spring where the o-ring was proptly shredded . The one on the left side wasn't cut but was all caught up inside the spring . I knew these springs that mikes xs sent me looked iffy but I went ahead and used them anyway . Once I find a new o-ring I'm going to give it another try with the original mixture screws and see how it does .

Anyone else had a problem with migrating mixture o-rings ? and is there somewhere anyone knows of where I can pick up a handful of them without having to order oem yamaha o-rings at 6 bucks a pop ? And what caused it ? These were all brand new parts and while I know I've been giving that screw the ole back and fourth for weeks now but the o-ring for the right carb was pretty shredded and it was new a month ago . Doesn't appear to be any burrs or sharpness down there aside from the threads for the mixture screw .

 

[5twins]

Sounds like you assembled the mix screw and it's parts incorrectly. Starting from the bottom up, it should be o-ring, washer, spring, then screw. The washer needs to be between the spring and o-ring or else, well, you see what happens, lol .....

The o-ring is 1mm thick x 3mm I.D. If you have trouble finding them, shoot me a P.M. and I'll send you some. I buy them in quantity from McMaster Carr, only cost like 24 cent each. With good o-rings and assembled properly, maybe the new screws will work. If not then, yes, try the originals again.

 

[TDodge7]

I'm still surprised that I didn't pick up on any leaks with the propane , I literally tested for leaks half an hour before I found the dead o ring and there were none to be found .

 

[littlebill31]

It's amazing how, if missing or wrong, the o-ring affects the performance.

 

[TDodge7]

Ok , so all the parts are in , original epa screws are back in the carbs with new o rings in the proper order this time . So first I do the dead cylinder method entirely by ear , which gets me to 3.25 turns out on each side . Then I got out the dwell tach and tried again , again the highest rpm I can get comes between 3.0 and 3.5 turns out . Then just for over kill I got out the color tune to make sure , at 2.5 turns it's lean , at 3 it's nice and blue , same with 3.5 , and then by 4 it starts going yellow indicating that it's getting too rich . All of this sounds great , it idles well , throttle response is fairly crisp , and after a rev it quickly returns to idle . But , the right cylinder seems to pop on decel . The header nuts were a little loose so I tightened those up but it still seems to do it , the exhaust gaskets are new . As you're engine breaking it gets down to the 1500-2000rpm range and you can hear it crack in the right pipe a few times , always on the right side . Granted these pipes are pretty free flowing and some mild popping on decel is normal , but sometimes you can hear the difference between the normal decel and these pops . Both cylinders reacted the same way to the same number of mixture screw turns so I find it hard to believe that the right cylinder is lean and the left isn't . I can't find any exhaust leaks , carbs are synced , valves adjusted , cam chain tensioned , it's an 81 so the timing can't be off , I've even tried yelling at it , is there something I'm not thinking of or am I just being paranoid and trying to find a problem that isn't really there ?

 

[xjwmx]

I just being paranoid and trying to find a problem that isn't really there ?

I would say so. For the popping on decel, try this if you want; turn the synch screw 1/16 turn at a time in both directions until the popping goes away, regardless of how carefully you've synch'ed it. Shouldn't take more than 1/4 turn.