81 vacuum advance question

[GLoweVA]

How many degrees does the vac advance move on the 81 4R0 engine?
My manual on covers up tp 80 and those are about 15deg. Max.

Hugo's only spins about 5. ???

[TopCatGr58]

Hey George,

The max vac. adv. is supposed to be ~16 degrees. I'm on my laptop right now, so I don't have access to my service manuals to verify that exact number, but that's what they were supposed to do, 35/36 degrees max cent. adv., and then 16 vac. for total of max 52 degrees under cruising speed.

T.C.

[GLoweVA]

That's what i thought too. I'm trying to download the 81 manual from bug's site now.

[GLoweVA]

I've got another spare on it has about 7mm of travel while the one oon Hugo only moves about 3mm

[TopCatGr58]

Hey George,

I know you're trying to troubleshoot your loss of power, saw your other thread. However, the vac. adv. is really more for just cruising rpm/fuel economy, when power is needed and you crank the throttle, the vac. adv. actually retards to provide the more powerful amount of timing advance which is nearer the 35 degree range, not above it. So...I don't think that the malfunctioning of your vac. adv. is causing your loss of power condition. I did an experiment several weeks ago where I closed OFF the vac. adv. completely, and it started and ran with plenty of power up to 7.5 k rpm.

Just saying, I hope it helps, but I don't think it's going to be the magic bullet fix!

T.C.

[GLoweVA]

3 of the 4 slides were stuck good. Took alot of force with my finger to get them freed up. I think that was my issue, but I'm going thru everything that can mess with performance and making sure it's right.
I haven't been this deep into it since i got him. I assumed that Charles had got him running good.

[motoman]

Hi George,
May check the idle vacuum, since idle mixtures affect that overall vacuum and raise heck with that vacuum advance rotating slowly and very little. That was just an added issue with mine I saw from low idle vacuum brought on from lean idle mixtures Things snowball and compound the issues when the simplest things are out of whack .

[GLoweVA]

When I say it only moves 3mm, I mean THAT"S it. there's some mechanical stop preventing it from rotating more.
I took some pics showing the rotation that I got.
The piece of paper is approx. 12degrees to measure the amount of rotation.
But I only got about 3-5degrees.

[TopCatGr58]

Hey George,

PULL the vac. hose from the #2 carb, bike NOT running, and then apply a vacuum to the hose ANYWAY you want! And then watch the movement of the tiiming plate, if the vac. adv. arm and plate are freely moving you should see plenty of excursion. Also after applying the suction, HOLD IT, and ensure that the plate/actuating arm STAYS put, doesn't move or release. IF it slowly release....then you have a HOLE in the diaphragm of the vac. pot, and will need to be replaced....they are NOS type items on the Yamaha site.

I've meant to investigate into this to see what type of AUTOMOTIVE unit would be a close match replacement both in amount of travel as well as actually FIT onto the bike!? You may end up being the investigator!

The unit isn't supposed to provide much action until under LOAD as has been stated, like cruising speed where the throttle plate isn't open much which allows more vac to build, air/fuel mixture leaner and so more time/advance wanted to allow thorough burning for fuel economy.

T.C.

[MPittma100]

Vacuum Advance

The vacuum source to the vacuum advance is "ported" vacuum. It is only available when the throttle is opened. There will not be any vacuum at idle to the advance plate. To actually see it move, open the throttle and hold it. It will begin to rotate at this point.

MP

[GLoweVA]

I'm not asking how much vacuum is required or at what load, just how much rotation should i get.
Here's a video.
Advance rotation: http://youtu.be/R8W-7aknay8

[TopCatGr58]

Hey George,

If that's YOUR video, you need to make it PUBLIC or put it in a public folder, it comes up a PRIVATE with a sad face!

T.C.

[GLoweVA]

Finally figured out how to make it public

[MaximPhil]

Hi George,
Remeber Hugo is an 81H. We are just a little bit different
Sorry I can not answer you specific question. I am willing to bet ( a beer at IH) that the plate rotates a different amount on an 81 than any other year XS. How much movement does an XJ have ? may be an indicator.
Venturer the original Frankenbike from the factory
Phil

[IanDMacDonald]

With the 81 being the first year of having the TCI control the mechanical side of ignition advance, I don't know if it would change the amount of rotation on the vacuum side of things. Then again, if the reported 16° of rotation is correct, 16° is 16°, and should be seen on the plate as such.