XS1100 ignition misfire, jumping tach and possible vacuum advance issues

[old_chopper]

Last night I checked and cleaned my grounds. I took the 4 Spark plug caps that had resistance closest to 5K ohms and cleaned them up. I cut off 1/4" off the wires and resecured the caps. Spark is much more consistent now. I believe my weak spark issue is resolved. However my vacuum advance is not functioning properly. I took it off last night and cleaned it. It seems to move properly. It goes to full advance with 6" of vacuum and holds. When the engine is running, it still rocks back and forth with the fluctuating vacuum off-idle.
Can someone put a vacuum gauge on your #2 carb ported vacuum and tell me what the readings are at idle and off-idle? Mine are so erratic I think I might have a hanging valve on that cylinder. Compression/CLT tested good. Is there something in the carb that smooths out ported vacuum? Something I forgot to put back in when I rebuilt them?

I'm working on the same thing. Looking forward to replies!

[James England]

The vacuum advance does precisely that on my bike. It's supposed to. The vaccuum fluctuates as the piston goes through its ycle. I was looking at mine only yesterday, in order to lubricate everything in there and to do the cam chain tension.

Since most spark plugs have a built-in 5k ohm resistor, I removed the resistors from all 4 of my HT caps. Less resistance must surely = more power at plug...

[James England]

The jumping tach suggests a voltage regultor issue.

Thanks for your help!

Or it just suggests a typical tachometer and nothing wrong with the VR. Loads of them jump and often it's the tachometer itself......

[GMGalambos]

The vacuum advance does precisley that on my bike. It's supposed to. The vaccuum fluctuates as the piston goes through its cycle. I was looking at mine only yesterday, in order to lubricate everything in there and to do the cam chain tension.

Since most spark plugs have a built-in 5k ohm resistor, I removed the resistors from all 4 of my HT caps. Less resistance must surely = more power at plug...

Check out this video of a vacuum advance in action. It operates smoothly and the vacuum reading is smooth too.

http://www.youtube.com/watch?v=ycofJRPfVZY

[James England]

Tickover is high in the video though. When my perfectly running bike ticks over at 900rpm, the auto-advance pulses just like what you've said yours does. It can't do anything else because the vacuum going down the pipe is pulsed

As in previous posts, I'd clean and lube everything to do with the auto advance.

Why keep something like coils standard? The 1.5ohm coils+ ballast resistor is so daft that Yamaha got rid of it. I've put 3 ohm Dyna coils on and got rid of the resistor. It's one less thing to go wrong and you get a huge fat spark instead of a weedy straw coloured one.....

[crazy steve]

...Since most spark plugs have a built-in 5k ohm resistor, I removed the resistors from all 4 of my HT caps. Less resistance must surely = more power at plug...

James, the stock NGK BP6ES plugs are non-resistor, so if you're running those without the resistor caps, the ignition usually generates radio interference. I don't know about 'over there', but that can get you in trouble here. The FCC has rules about this...

If the caps have excessive resistance, new ones are cheap; I just bought two for the princely sum of $6 from the local dealer. Ask for a NGK LB05...

[DiverRay]

Did you take the mechanical advance apart and clean it? That is what motorman was talking about. I've had a few bikes give me problems until I cleaned and lubed the mechanical advance that is BEHIND the timing plate. Do take care to keep the plate/advance unit lined up!

[James England]

James, the stock NGK BP6ES plugs are non-resistor, so if you're running those without the resistor caps, the ignition usually generates radio interference. I don't know about 'over there', but that can get you in trouble here. The FCC has rules about this...

If the caps have excessive resistance, new ones are cheap; I just bought two for the princely sum of $6 from the local dealer. Ask for a NGK LB05...

Sorry, I should have said...I put iridium plugs in mine and they have a built-in resistor. Yes, you're not allowed to run non-resisted circuits here either. It doesn;t make you popular with the neighbours either!

[motoman]

GM, that port for the advace has a restrictor in the base of the brass tube, unless someone thought it was plugged and punched it out. Find something that fits the I.D. and run it down in the brass fitting. If it stops part way down, the restrictor is likely still there as it should be. If what you run in there goes all the way and hits the other side of intake, then it's gone. If that's the case you can put a restrictor in the hose like a pilot jet or better yet a Kiehn jet or the small diamater Mikuni for a restrictor. When advancing it will flutter ever so lightly anyways, but diaphram should move the advance right off idle. If not, that advance mechanism HAS to be TOTALLY free able to just flip-flop with the vacuum diaphram removed. If it's even just rotates with ANY reistance, it won't advance properly initially off idle and won't advance far enough in the lower cruising rpm range, which leaves timing a bit retarded causing bike to not be smooth. This will also cause a drop in vacuum with timing a bit retarded.......which in turn won't allow carb slide to work properly too..........."one bad apple ruins the the whole basket".....and snowballs into causing an array of issues as a result of one bad function.

[TopCatGr58]

If it's even just rotates with ANY reistance, it won't advance properly initially off idle and won't advance far enough in the lower cruising rpm range, which leaves timing a bit retarded causing bike to not be smooth. This will also cause a drop in vacuum with timing a bit retarded.......which in turn won't allow carb slide to work properly too..........."one bad apple ruins the the whole basket".....and snowballs into causing an array of issues as a result of one bad function.

Hey Motoman,

I'm having a little trouble agreeing with the last part of your last post?

The cruising rpm/vac. adv. is just a higher amount of timing advance to take advantage of the lean fuel/air ratio at that speed. But if the vac. adv. doesn't move as far, then it just isn't advanced as far...ie +36 degrees...max level spec is 52degrees ....but the engine will still be running just as smoothly at cruising rpm, same level of vacuum to the carbs, but due to the less advance it would possibly need a little more fuel to maintain same rpm. So then the throttle would need to be opened just a little more sending more vacuum signal to carbs raising slides a little more to provide that little bit more fuel for the less advanced timing. Perhaps this is what you meant?

I'm not trying to make any arguement, just trying to be sure I'm following and understanding your statement. I'm not a pro mech or engineer so I may be totally off base, not sure, but just wanted to open and invite a discussion to help me and others understand the workings and affects.

T.C.

[motoman]

If the timing is slightly retarded, will NOT have a complete burn before exhausting. Therefore plugs Will show a rich condition. This happening CAN cause one to think jetting is too rich.......see where this is going? Retarded timing changes vacuum(less) in this case. Less vacuum changes where slide location from where it SHOULD be at any given rpm range, up until it is full in the main circuit, then it's a mood point when full in main circuit anyways and vacuum loss is at a max and slides lift fully anyways. This attributes to the reason several are having issues in the idle circuit, but "pulls like a freight train" above 5K at WOT. The thing one MUST remember, and is no different than relating to our old naturally aspirated muscle car motors, even having electronic ignition......Problems suddenly appear with poor running.........Primary ignition and secondary ignition source is ALWAYS the place to check functions before ever considering fuel supply or carb issues, and in our scoots case, unless for some reason you suspect restricted fuel supply(petcocks,pinched fuel line,etc.) which if you have done your proper checks prior should have already resolved those issues, or at least checked all that for proper operation before ever starting anyways. Pri.ignition= from ignition switch to pos. side of coils. Sec. ignition= neg. side of coils to and including plugs. This is why I've been harping so much about the advance assembly and some here suggesting checking those wires attached to unit......by seriously pullin on each wire with two fingers using both hands and trying to pull apart every little bit while going down the wire. A break somewhere as you know will cause you to stretch the sheaving like a rubber band when broken wire part is found....again, part of secondary ignition. Hope that helps. BTW, timing has NO idea what the fuel is doing........remember, not modern and has no sensors.

[GMGalambos]

update

I looked for a restrictor on carb #2 port vacuum. I did not see one. So I put one inline with the vacuum hose. It made no difference. The vacuum is still fluctuating all over the place.

I also noticed that after the RPM's are high (5-6K) and it comes back down to idle, the vacuum advance actuator stays advanced, idle is at 1800 RPM and after 3-5 seconds it returns to rest position and the idle drops back to the normal 1100 RPM. If I push the actuator to the rest position while the idle is at 1800 RPM, the vacuum pulls it right back to advanced position.

I decided to take it for a test ride to see how it behaved on the road. Right of idle it has a medium buck and surge. While at cruising speed, it surges. When I come to a stop, either the idle is at 1800 RPM or it tries to stall and I have to rev it to keep it running. I'm starting to think I have a carb issue even though I just rebuilt them. There may be some fuel circuits still blocked.

I'm starting to get pretty frustrated. Any more thoughts?

[cywelchjr]

That sounds like there is a problem causing the throttle plates to be open too far causing you to get vacuum at idle which you should NOT get enough to keep the vacuum advance moving at all. It also shouldn't be hanging high like that and that points to a problem with the carbs or the carb sync which can cause the issues you describe (part of syncing is idle mixture adjustment and lean mixture will require higher throttle setting and hanging idle when hot). One of the mistakes often made is to think that idle mixture is set by just setting the mixture screws to a set number of turns out, and those turns out are just a starting point, you from there adjust them for the highest idle speed with each carb THEN sync the carbs.

[GMGalambos]

That sounds like there is a problem causing the throttle plates to be open too far causing you to get vacuum at idle which you should NOT get enough to keep the vacuum advance moving at all. It also shouldn't be hanging high like that and that points to a problem with the carbs or the carb sync which can cause the issues you describe (part of syncing is idle mixture adjustment and lean mixture will require higher throttle setting and hanging idle when hot). One of the mistakes often made is to think that idle mixture is set by just setting the mixture screws to a set number of turns out, and those turns out are just a starting point, you from there adjust them for the highest idle speed with each carb THEN sync the carbs.

I'm sure the carbs are synched but not sure about the idle mixture. I researched that a bunch and most people were of the opinion that 1.5 turns out was good. Where would you start with the idle mixture screws and what is typical for newly rebuilt carbs?

Btw, thanks to everyone for the input and advice. It is all greatly appreciated.

[cywelchjr]

I'm sure the carbs are synched but not sure about the idle mixture. I researched that a bunch and most people were of the opinion that 1.5 turns out was good. Where would you start with the idle mixture screws and what is typical for newly rebuilt carbs?

Btw, thanks to everyone for the input and advice. It is all greatly appreciated.

That was the starting point 30 years ago for the gas back then. Again, that's the starting point, and you need to adjust either by ear or with a colortune to actually get the right mixture for YOUR engine and setup. If this has not been done, the carbs are not really synced as this is the first step of the sync process. It's one of the common misconceptions that 1.5 turns is THE setting, it's not and almost NEVER is it where you end up by the time it's right, frankly your more likely to get out something like 2.5 or 3, but you can't do it blind, you MUST do it properly or you would just make it worse. I'm guessing you get popping and such on deceleration as well, which can be another sign of lean idle mixture. Unfortunately, plug color is not usually much use for idle mixture, it's mainly for the mains.