Vacuum Advance and detonation

[GtrMn]

Actually surprised I've never seen this addressed in a post here....Both of my MNS's did the same thing....And I put this in another post.

Sometimes sounds like the engine is coming apart...depending on load and RPM. But it's always between 3k + 4k. If you can't see the TB..right click the image and save it...then open it and Zoom in

[bikenutt1980]

Man i can hardly read it even saving it to the puter. Looks like something I really need. Is there anyway you can fax me or email it to me?

jason

[GtrMn]

I actually downloaded it from the Yamaha parts site (There was 8 TB's)....what you see is all there is that I know of....If you zoom in you can read it though.

[GtrMn]

I just tried something...not too bad. Right click and save it to your computer. Open the file and then print it...Still a bit grainy but readable.

[TopCatGr58]

Here it is zoomed in a bit!
BTW, already checked the part #, DISCONTINUED!!

[GtrMn]

Dang T.C. you're a 'puter wiz too! Thanks!

[GtrMn]

Hmmm interesting it's only the 80 and 81 models too...just saw that.

[GtrMn]

Sure would like to find a "fix" for this...cause it does sound nasty...even if it doesn't hurt anything. And it's right in the 55 to 60 MPH speed range. Maybe just going faster?

[slibno]

I have the vacuum advance, and still have the noise, and it is bad! My next step is to check my timing.

[slibno]

Was the vacuum advance standard equip in 1980 AND 1981? Maybe the VA is what's causing the noise?

[GtrMn]

Standard all years. Do you have the VA that Yamaha had as a replacement unit? The one T.C. said is no longer available?

[slibno]

The service bulletin does not describe the noise as something that a REPLACEMENT (different than original) VA will address. It makes it sound like something that the OPTIONAL VA will address, if added, meaning that it did not come standard on all bikes, but was a factory option. I don't conclude from the way it is written that Yamaha produced a different CORRECTED version of the VA. So, if I have it, I must have the optional VA, and I still have the noise.

Am I interpreting that correctly?

[GtrMn]

it did not come standard on all bikes

It was standard on all years. From what the TB said there was a optional VA that they say would help the problem. It's a discontinued part though.

[TopCatGr58]

Well, almost all years,! Again, that pesky XJ messed things up. I has a vacuum sensor/boost sensor instead of the vacuum advance pot on the timing plate! So...the vacuum diaphragm device was on all of the XS's! As has been mentioned, the OEM one as well as the replacement one mentioned in the TB are no longer available!

I plan on getting an OEM one, measuring the travel under full vacuum....IIRC rated at 150mm/5.9 in Hg and see what AUTO unit might be able to substitute for it....just one of many projects on my list!
T.C.

[Dragon Tamer]

I have limited (read almost none) experience on the the XJ models but the Dragon used to do the same thing until I saw a post here somewhere that said to retard the timing about 2 degrees. IT WORKED. And it seemed to have absolutely no effect on the performance.