Timing question ...

[thewiz]

I have been having a problem developing power on my SF after about 5000 rpm. The engine doesn't wanna' rev much past 5500 or 6000 rpm. A few things I have done ...Carbs gone through, sync'd, new plugs, good big spark, plenty o fuel .... compression checked cold (wouldn't run at the time) cyls all even.

Had been having trouble with my timing light so I finally bought another one, and true to form for me today, soon after I began to use it, it also failed. Nice, eh? But it did work long enough to see that, when the pointer and the timing plate are set in the middle of their respective slots, my timing seems to be about 30 degrees advance at idle. It also cranks like an engine that's too far advanced ... a labored first revolution or two, then the cranking speeds up and it fires. In order to get the timing to read 10 degrees at idle, I would have to shift the pointer most of the way in one direction and the timing plate most of the way toward the stops in the direction of the pointer. I realize that shifting the pointer is not setting the timing . ... it almost looks as though I'd have to remove the screws in the advance plate to swing it far enough to get it into time??? I know I can't do this either .... sooooo ..

Could the pick ups be placed wrong? ... does the pointer need to be zeroed ? Something else altogether?? This is makin' me a bit crazy ..... any ideas would be appreciated ....

[The Lorax]

There's a procedure for getting TDC, once set, you can ensure your pointer is correct. If your timing is off significantly, I would guess it would have to be adjusted in some fashion. consult your service manual, it should tell you whether the pick up coils are in the right place(s) or not. is it possible someone (a P.O. perhaps) was fooling around with engine timing and made errors? I am merely throwing out suggestions, I certainly do not want to impune someone else's work. I would guess the best course of action would be to ensure the pointer is accurate and then determine wheather or not your components are assembled / adjusted correctly. I do hope that my inane ramblings will be of at least some help. have a nice day and ride safe

[79XS11F]

Your going to have to start by confirming TDC on #1 cylinder and set the pointer to it's correct location. If you don't have a dial gage to determine TDC you can get very close by removing the valve cover and rotating the crank until the cam timing dots are lined up with the arrows on the middle caps. When both the intake and exhaust cam dots on top and lined up with the cap arrows, # 1 is at TDC or darn close. This is if the valve timing is not messed up. A dial gage would however, be best. Once that is set up you will have no problem getting the timing set up.
Rob

[AlanB]

Hi wiz,

Did you remember to disconnect the vac advance pipe?(and to block the inlet on the carb body!)

XS is almost the only bike which has vac advance, so it is not always in the instructions.

Timing is always checked with the vac disconnected.

AlanB

[TopCatGr58]

Hey Wiz,

One thing you didn't mention was did you do any intake mods, like Indy Filters vs. the OEM airbox?

IF Indy Filters, the cheaper EMGO brand has a prominent mounting lip that can interfere with the air intake flows on the carb inlets, that can severely richen things and cause bogging at the 5-6K rpm range! JAT?
T.C.

[thewiz]

Thx, everyone

Guess I will have to pull the cam cover to 'zero' out that pointer ... thx Rob and Lorax.

And yup, Alan, I did forget to disconnect the vac advance thank you. Been so long since I used a timing light on a vehicle, I just forgot !! I'm sure that'll help.

Stock airbox, TC

I have been wanting to check the valve clearances and the cam timing. A third party, that literally screwed up everything else they did, set them .... Would the motor run if the cam timing were just a fraction off? Could that cause the performance loss I'm experiencing?

[79XS11F]

Yes the engine would run but depending on how much the cam times was out you could do top end damage. The cam sprockets are FIXED to the cams so the only way the cam timing could go out would be if they were installed out of position or the cam chain was so loose that it jumped a tooth. That sort of thing would likely damage the top end.
SO .. confirm that you can get both cam dots to line up with the middle cam cap arrows and if you can the cams are in the correct position UNLESS # 1 is not at TDC. That's not likely the case if the engine runs but you can confirm that the piston of #1 is at the top of its cycle with the careful use of a screw driver through the plug hole.
With the cams lines up check the pointer to the timing wheel and see that it is at the "T" mark. This will put you very close to the pointers original position.
Rob

[AlanB]

Hi Wiz,

Cam timing can only be out by a tooth, or a number of teeth; there is no "adjustment".

Cam timing will vary slightly as the chain stretches, so on a higher mileage motor, the marks on the cams will not line up 100%....... It just had to be to the nearest tooth. when you check it, remember theat the XS engine runs the "wrong" way round, and that the chain can never be "shortened"....... only "Stretched".

AlanB

[thewiz]

Here's a photo

taken of my timing disc. This was shot with the cam dots in perfect position, chain tight. This was s'posed to be a 7k motor and it looks to have virtually no wear up top.



Note that the pointer is moved to the limit of it's slot and still short of the 'T' mark by a few degrees. The disc itself has some wear on it from being installed backwards in the past. Was on correctly just now. Something doesn't look right to me here .... what do you people think?

[79XS11F]

Has the pointer been bent. so that it is not 90 degrees straight up from the base? I can see that the factory original position indicator paint is missing so that pointer has been moved or removed in the past.

Is the timing wheel properly and fully seated on the end of the crank. It should only go on one way without needing to be forced and once in place there should be minimal free play. Check the back side of the timing wheel for previous force fit damage that might affect it position.

If the # 1 piston is truly at TDC and the timing wheel is not damaged I would be inclined to bend the pointer to the correct position.
Rob

[thewiz]

Thx Rob

The pointer doesn't seem to be bent. I actually slid it into it's position at the end of the slot for the photo. Now the wheel ... that's a different story. It was installed correctly BUT at some point during it's roughly 30 or so odd years of life, it HAS been run backwards because it'll fit on the snout easily EITHER way, so it's worn. I do know the difference though. Once the crank snout bolt is cinched up, there is no noticable play. It was a used timing wheel when I put it on there, IIRC. The motor's original timing wheel was bent ... evidently in the same accident that cracked off a small piece of the case there on the timing side. You can see my little repair in the prior photo.

I'm also tempted to make the adjustment too .... BUT ... what I'm really wondering is: Could both cams be out of time with the crank and have the engine still run and do no top-end damage? There isn't any. I am chasing a power and rpm loss .....

It looks like there are at least a couple of links on the chain where the valves on #1 hole would still be closed and the cam dots could be lined up with the marks ??? I think I need to figure out where the piston is when the dots come up ....[IMG][/IMG] [IMG][/IMG]

[79XS11F]

I agree .. you need to confirm your TDC for #1 and get those dots lined up. If in the photo the piston is in deed at TDC the only way the dots could be out that "little" bit would be if the cam chain were stretched that much. How much free play do you have left at the cam chain adjuster?
Rob

[thewiz]

Yeah .... I'll check on the amount of tensioner adjustment left, but IIRC, there's plenty left. I just fixed the tensioner plug last month .... and ... this motor looks pretty new in there anyway. Was s'posed to have only 7K on it ... so I don't expect much chain slack.

I'm thinkin about grindin' down a 14mm bolt and makin' a piston stop out of it. Then using the timing wheel itself to find true top dead or maybe just stick a dial indicator down the plug hole and find it thataway. Once I'm sure where true top dead on the crank is, then I can check where those cam dots line up. It really looks to me like if I retarded the crank a tooth or two, the pointer would be somewhere near the middle of the slot. That seems like the way the factory woulda' made it.

[Miti-Babe]

Wiz

As you're already aware that this bike has had a fall on the ignition side, "some pre-set up" checks would be appropriate...

1. Check that the vacuum advance unit is actually advancing the pickup coil plate and that the plate is returning fully to its' stop. You could check by simply sucking on the the vacuum line after it's unplugged from #2 carb... It should move freely back to its' stop...

2. Unscrew the centre bolt & timing wheel and check that the rotor behind it is moving freely on its' pivot... A bent centre bolt can cause problems and you should be 100% confident that the wear on your timing wheel isn't causing that rotor to stick in an advanced position... The rotor and the mechanical advance mechanism behind it don't need much in the way of routine maintenance, but a little light oil on the pivots can work wonders.

When you're sure that all is OK with the two advance mechs, then set to with checking the position of the pointer and then the timing...

Could be worse... The '81 models have electronic advance..!!

Miti

[Deni]

AlanB or others,
I cannot find in either the Clymer manual or the Yamaha shop manual that the vacuum advance must be disconnected to set the idle timing. Both manuals say to disconnect it afterwards to check advance at higher rpm. Therefore, according to them, it should be connected when setting idle timing. But, I think that at that low idle rpm (1,100 for F) it wouldn't make any difference whether you did on not (I will check this). Why do you say that the vacuum advance unit must be disconnected when setting idle timing? Just curious. Thanks.