cutting out

[apolloant]

I just got this '79 sf (my second one, loved the first, sold it, kicked myself for 9 years, bought this one) from the first owner. Sat for 19 years in dry storage. He got it out and did all the required stuff, I assume. He put a set of Mac 4-2 turn out headers on it ,new intake boots, had the tank lined, carbs cleaned and rejetted. At 12,000 miles, this bike is a beaut. He rode 3000 miles last summer, and it started to cut out at 3000 rpm and up. If you turn the throttle slow, it's mostly o.k. If you twist it fast, puts and sputters. while messing around trying to figure this out, I tried advancing the timing, without a light, to see if it would mellow out. It did, revs smoothly up the tach. I know I need to get a timing light on this, but could this be the prob. or is it just masking it? Could a small slip joint leak cause this? Thanks.

[mro]

running outa time!!!

I'm a little new at this but setting the timing sounds right.

While you have the cover off I'd check that the diaphragm moves freely when vacuum applied to the hose going to #2 carb and that the hose is in good condition. Also look at the wires on the PULSER COIL ASS'Y, and see if there insulation is OK and not shorting out.


My 80G only had 12K on it when I got it. Think vac advance hose was the only one I didn't have to replace.


mro

[Ken Talbot]

Re: cutting out

Originally posted by apolloant
... carbs cleaned and rejetted. .....If you turn the throttle slow, it's mostly o.k. If you twist it fast, puts and sputters.....

My guess - carbs need to be cleaned properly i.e. thoroughly, and the after-market K&L jets that were probably installed need to be removed and the stock size put back in. Use the search tool at the top of the page to look for K&L jets and all the problems they cause. The K&L jets tend to be way larger diameter than the stock items, even with the same stamped number. This causes an overly rich condition through the mid-range. Chances are you'd find black sparkplugs because of this.

[apolloant]

Yes, black, black plugs. Carbs were gone thru , every jet possible tried. Wouldn't the stock jets run her too lean? Prev owner said mpg went south. I've read that headers get 2 sizes up, k&n get 1, so three up on the jets would be good. Heck I don't even know what's in there now. Also, the timing plate seems to be getting erratic pulse when accelerating, I can see it jiggle. Is this low vacuum due to pipes and air filter? Stopped when I advanced it.

[TopCatGr58]

Aha, Now I see, said the blind man!!

You just self diagnosed your problem!!

Check the vacuum advance hose and where it's located! Bet you'll find it connected to the # 2 Intake Manifold port!!! It's NOT supposed to be there, but IS to be connected to the #2 CARB BODY port. You're probably getting too strong a vacuum pulse from the wrong port being used! Not the first time this has happened. Especially after having new intakes mounted, and the carbs being done, other mechanics don't realize the difference in the ports, and think one port is as good as another. The carb port is specially sized to provide a more metered amount of vacuum!
T.C.

[apolloant]

Dang, it is connected to the carb body already. I called Yamaha here in Post Falls to ask about rejetting and the first thing he said, and I know I've read it here too... "Your pick-up wires are broken, that's why it smoothed out when you advanced the timing." So, I geuss I'll take it to the bench and do the duty. What's the easiest way? Braid new wire in, past both sides of the break. I saw a post about radio-shack tester wire being used. Do I leave all the old carbon-wirecrap as a guide, and do it one strand at a time?

[TopCatGr58]

P. U. that stinks, and so did my answer!

Follow this link, and all will be answered!
Pickup Coil repair tech tip
T.C.

[apolloant]

Well, I ran new wires on both set of pick-up coil wires, no difference. That's a real fun job, on the cold garage floor. I ran all new fuel lines, took out the inline filters someone had put on, no difference. I cleaned up the centrifigul advance (it was a bit sqeaky), seemed to smooth out the advance a teany bit. The only thing I do that seems to make any difference is to advance the timing a couple degrees, so that's what I'm going to go with until I can get some road tests under my belt. The only thing holding me back is a set of headlight ears. Mine were bent when prev. owner layed it down at stoplight. I don't want to reassemble the front end until I get those, had it apart for some new fork seals. P.S. Isn't there supposed to be an air gap adjustment between the pick-up coil and the stator. I can't find it in the book, and I swear my buddy adjusted it on my last XS.

[randy]

Isn't there supposed to be an air gap adjustment between the pick-up coil and the stator.

Yes, the gap is supposed to be .7mm

[TopCatGr58]

Hey there ApolloAnt,

Do you have a timing light? Your timing may be off after all? After it's warmed up and idling at ~1,000 rpm, connect to #1 plug, and shoot it at the timing plate, you should see the "F" hitting the indicator, but if not, then it's out, and you'll need to loosen the plate and rotate to change it's setting. The book states you need to shut the engine off to do this. I have an 81SH, and mine isn't adjustable, but the 78-80's are. I was wondering if anyone has left theirs running, and loosened the locknuts and adjusted the plate and then reshot with the light WITHOUT turning their bike off?

Once you've got it set at idle ~1,000 rpm, then disconnect and plug the vacuum advance, and rev to 5200, and reshoot, it should be around 31 degrees for the Special!
T.C.

[scalded dog]

Check your carburator diaphrams, if they are not sealed then your throttle body jets, can't work properly. Later 'Dog

[Shuriken]

On my bike, I've been trying to find the solution to what sounds like the same kind of problem you are having.

http://www.xs11.com/forum/showthread...&threadid=7501
http://www.xs11.com/forum/showthread...&threadid=7752

I will recheck timing when I get some time. Have to wait for weekends....

My bike runs better if you go slower on throttle advance and worse if you crack it faster. It seems to miss and sputter a bit through a part of the midrange and then from like 6-8500 it screams like a shreaking demon.

I want that scream through the entire range, or at least proper response.

Ben

[TopCatGr58]

What timing!

Hey Ben,

You,we, may have "stumbled" on to something here. Aside from the carbs being set right, if the timing is too retarded, it won't respond or accellerate properly. When you crack the throttle, the vacuum pulse to the vacuum advance actually drops, and it doesn't get as advanced, but when you roll the throttle on slower, then there is more vacuum and it is actually more advanced! This was described in that '78 MC mag review of the Xs11's ignition system.

When you get to 5000 rpm, you are now hitting the max centrifugal advance, and so it's then able to respond to the fuel flow much better. So, it'll be interesting to here what you find when you check it this weekend, nothing worse than a RETARDED Motorcycle!!
T.C.

[randy]

apolloant,

To set the timing statically (not running), look through the tiny window in the timing plate and rotate the crank to lineup the tip of the reluctor with the line on the pickup. BTW, this may be easier with the spark plugs loosened to bleed off compression.

Then you can loosen the screws holding the plate to the engine and rotate the plate to line up the 'F" mark with the pointer.

Tighten everything down and then it's best to re-check it with a timing light dynamically (running). While you've got the light on it you will be able to see the advance (and retard) work when you throttle up.

Remember, it's got a centifugal advance and a vacuum retard, so as TC said, when you crack the throttle wide open it will retard and if you smoothly throttle up it will advance.

[motoman]

check the two vacuum caps on the outer two carb to engine boots. If you can turn rotate them fairly easily, replace them with a couple new good, tight fitting rubber vacuum caps. Spraying WD-40 around them at idle won't always cause a rpm increase to determine if there is a vacuum leak at these points, but will be enough vacuum loss to cause diaphrams to not transition slide smootly from idle into main fuel circuit....Sure you can guess how I know that....Happy XS'en, Brant.