cenrifugal advance

[Bigleo]

The other day I was adjusting the ignition timing on my 1980 XS1100 from 5 degrees BTDC to 10 degrees BTDC, as I no longer have the vacuum advance hooked up. I was kind of shocked at the lazy way the centrifugal advance worked. Very little advance prior to 3000 rpm, and not full in until almost 5000 rpm. This is definitely not a performance advance curve. When I used to play with fast cars, we had all the advance in by 2800 rpm, 3000 rpm at the latest. Has anyone played with a more performance oriented advance curve on these bikes? I'm thinking that we are losing a lot of torque in the 3 to 5000 rpm range. Perhaps this is also the cause of the power dip and rich mixture indication we see at this rpm range on all the dyno charts posted on this site? Anybody have thoughts on this?
Leo

[81xsproject]

If you can find an advance off of a '78 (2H7-81653-10-00), it has 5 more degrees of advance than the '79 (2H7-81653-11-00)which is also a different advance unit than the '80 (3H5-81653-10-00) Which probably has even less advance (but I don't know).

[81xsproject]

Soon I will be trying out my '81 with a '78 advance unit and iggy.

[Bigleo]

Hi XS Project,
At this stage I am not looking for more advance, I now have 10 degrees initial timing, with 36 degrees total advance at around 4800 rpm. I want the advance to come in sooner, advancing all the way by about 3000 rpm. In cars it involves putting in weaker springs in the advance unit, I haven't had a chance to look at the XS advance unit yet, but I'm sure it's a spring system as well.
Leo

[Bigleo]

Hi XS project,
So I guess what I'm saying is I have 26 degrees of advance available with my 1980 unit. Does the 1978 unit have more than 26 degrees? I'm still looking for a bit of a solution for not having a vacuum advance anymore. I think the motor should be able to handle 38 or 40 degrees total centrifugal advance above 5000 rpm.
Leo

[81xsproject]

YES. I think the '78 has more like 35 (but again, not sure).

[81xsproject]

The reason for my swap is that I tryed my bigger valve 80's head with '70's cams and loved the top end. However, the bottom end left something to be desired. I went back to the 80's cams. So, now I want to try going with the 78 timing curve. Then, the the 81 curve with 70's cams (again). And THEN, '78 curve with 70's cams. What can I say, I went to school to be a scientist (geologist) for a reason, I like to experiment.

[Bigleo]

I have the 1980 head with 1978 cams as well. I haven't done much experimenting yet with the timing, but I can say that going from 5 degrees initial (the stock 1980 Special setting) to 10 degrees initial (the XS Standard model stock setting) made a big difference in low end throttle response. Much much better. Once I get my bike running again i will try 15 degrees initial which will give me 41 degrees total advance at 4800 rpm. If it still starts well and has no pre ignition problems, i'll start to fiddle with getting the advance to come in quicker.
Leo

[Bigleo]

Hi XS project
I was also comcerned with the drop in low end torque the 1978 cams might cause, but the 1197cc kit and the 10.25 compression ratio made up for any loss. If any thing the bike had more bottom end torque than before. But then I had also installed some Keihin CR33 carbs as well, which I think helped a lot. They don't have a vacuum port though, so no vacuum advance, which is why I have embarked on getting the centrifugal advance optimized.
Leo

[TADracer]

If you have removed your vacuum advance because of your carb upgrade then you must make another upgrade to the advance curve elsewhere. You have just taken away about 16 degrees of quick acting, variable timing that occurs at certain throtle positions. Also, the total of the centrifugal advance is the same since the specials static timing is 5 degrees and the standards are at 10 degrees. The total centrigugal advance is 26 degrees which gives your 31 degrees for the special and 36 degrees for the standards when added to the static timing. Granted, the advance CURVE may be different between the years in that some may come on sooner but the amount is the same. The aforementioned 16 degrees of vacuum advance is layered on top of the centrifugal and static timing for a total of 52 degrees at part throtle positions and when needed for a quick timing adjustment that is not dependent on crank speed.

By removing the vacuum advance what you have done is taken away some of the finesse that the ignition system can provide. You are left with is the initial advance which makes for a nice idle and the centrifugal advance which should be optimal for the power band. BUT, you have taken away alot of ridability that the vacuum advance provides because it does not have to wait for crank speed to get where it has to be for the best advance to suit the condition.

All this brings up the question, what is done on the later models that did not come with a vacuum mechanism? Is the timing curve set up in the TCI unit? That is where I think your answer is but, I do not know very much about the different TCI units.

[randy]

The later model XS's '81 and up, ditched the mechanical advance and had electronic advance built into the TCI. They maintained the vacuum canister for part-throttle response.

Even later, the vacuum canister was ditched in favor of a 'boost sensor' which varied the electronic advance in the TCI via vacuum signal. I beleive this was feature began with the XJ models.

[TopCatGr58]

Hey BigLeo,

Don't know if you've seen the posts where folks suggested putting a pilot jet in line inside a vacuum line that would go to the vac. adv. unit, when you don't have one due to newer styled carbs?! They have reported similar drivability with this mod vs. ditching the vac. adv. altogether. Might be easier to do that trying to mod the cent. adv.?

Randy is right, the curves were programmed into the TCI's, the Cent. in 81, and then both in 82 using the XJ's vac. sensor to send the variable signals to allow the TCI to adjust the timing accordingly!
T.C.

[Bigleo]

Hi TC,
I have seen the post regarding the pilot jet in the line. I may try that too. But the main issue I see, is than you are only getting suction for 90 degrees of crank rotation when hooked up to one manifold. This, in my opinion is the cause of vacuum advance canister rattle people have mentioned when hooked up this way. This intermitent vacuum, even when hooked up to the stock ported carb source, is in my opinion, the cause of the infamous pick up wire fracture. What I would like to do, is hook up all 4 manifold vacuum sources together. This way I would get vacuum for 360 degrees of crank rotation. In other words, a smooth, non intermittent vacuum source. The only problem I see with it is that the vaccuum signal would be to strong, as it would be non ported. That would probably cause a pre ignition rattle when starting from a standing start, possibly also when shifting gears. However, with the pilot jet in the line to slow down the vacuum signal, I think the momentary pre ignition would be taken care of. What do you guys think?
Leo

[oldnortonrider]

Bigleo, you may be onto something there. Evidently, Yamaha kept "re-configuring" the timing "methods" each year on these XS11s, cuz they themselves "knew" it wasn't really like "it should be"; i.e., "it should be different slash better". I, myself, can tell it's definitely not like it should be. The camchain itself, is gettin' a beating, being "yanked" around, with these different timing configuration setups~~half the time, the combustion pop being either too much, or not enough, at the right throttle technique, and/or the right rpm; and enter into that, these old 15,000 volt coils (for which, TopCat has a pictorial cure for). I've even thought of rigging up a dang manual timing set-up, like the old Harleys had with the left twist grip, like the right throttle control, that controlled the timing. A-model Fords had a timing lever on the steering column, for this. Worked super.

Maybe Yamaha got it right, with the XJs. (??) When, I time mine, to suit me, where I think it's got maximum torque, in the rpm range, I mostly use~~(?) 2000-5000~~it won't wind fast enough above that, and it's hard to start when it's warm.

[Bigleo]

Hi oldnorton rider
The same thing crossed my mind too, about setting up a manual advance like the old harleys nortons, BSAs etc, as the vacuum advance is is mainly for extended highway cruising fuel ecomomy. But at my advanced age, I'd probably forget and leave it on "advance" when I shouldn't. I saw your post on the cam chain issue. I too have the thinner pin chain in mine, and it has me worried. I have ordered a Tsubaki heavy duty chain from APE. The problem with it is that it is an endless chain. But Yamaha sells a rivetable link for the cam chain, part #94600-02001-00. It has the same size pins as the heavy duty chain and just so happens to be made by Tsubaki as well. About $4 from bike bandit or your yamaha dealer. APE sells the chain for $40.
Leo