vacuum advance question ?

[BA80]

you are right but i think not totally, looking at my number 2 old XS11 carb i can see with a light down the vacuum tube that the hole isn't totally closed off when at idle. their is also a small cut out on the butterfly which will let a small amount of air past the vacuum hole. if you turn the idle screw back off where the bike no longer idles the butterfly will cover the hole. but the vacuum will increase as the butterfly opens.
you can see the light in this pic.

Test it with a vacuum gauge. If there is vacuum there at idle the carbs aren't set up right.

[DEEBS11]

Tony, I think from what Greg says, as long as the hole is behind the throttle plate it should work. No or very low vacuum there at idle.

[Tonyxs11]

Tony, I think from what Greg says, as long as the hole is behind the throttle plate it should work. No or very low vacuum there at idle.

yes i totally agree Deebs, and the way to go is drill the carb body. but saying that I spoke to a guy I know who has an XS11 thats fitted with kawasaki carbs, he put a small pilot jet in the hose many years ago and he's had no issues with many many miles on it, he says it runs good and he mechanics for a drag racer. he also put me on to a video on youtube from a guy called Andys motorcycle obsessions who did the same thing ive done. so maybe not the end of the world ?????

[DEEBS11]

Andy is great. I have watched all his videos and learned alot about XS11s. I think this is the video you are talking about. In it he is installing RS36 flat slide carbs with no port available similar to your set up. If you fast forward to 16:35 he talks about the vacuum advance hook up. He did it like you did. To adjust he closed the valve just until the advance unit did not move then opened it slightly until he saw advance movement. The advance unit should be as close to closed as possible then advance as the RPMs build.

https://www.youtube.com/watch?v=5eUn...MuTl2&index=39

[Tonyxs11]

Andy is great. I have watched all his videos and learned alot about XS11s. I think this is the video you are talking about. In it he is installing RS36 flat slide carbs with no port available similar to your set up. If you fast forward to 16:35 he talks about the vacuum advance hook up. He did it like you did. To adjust he closed the valve just until the advance unit did not move then opened it slightly until he saw advance movement. The advance unit should be as close to closed as possible then advance as the RPMs build.

https://www.youtube.com/watch?v=5eUn...MuTl2&index=39

yep thats the one

[Tonyxs11]

done a bit of a better mod today, got some 5mm aluminium rod and drilled a 0.4mm hole down it and pushed it into the vacuum pipe so i could get rid of the air valve I fitted.
the bike sounds and rev's sweet as and rides good. but whats confusing me is, when i fire the bike up the advance unit rotates anti clock wise and sits their steady and when I rev it, it rotates clockwise and corresponds perfectly with engine rev's. if I plug the vacuum it runs like crap and lumpy. the only video ive found on the net (googled it) the vacuum works in the opposite way ?????? can someone pull their timing cover off and tell me how theirs works please ? mines a 79SF by the way, cheers.

[LAB3]

Do you have access to a timing light? "To measure is to know"

[Tonyxs11]

Do you have access to a timing light? "To measure is to know"

i do and ive had it for years, i plugged it in and it flashed once and then died gona have to buy a new one

ordered a new one.

[DiverRay]

These bikes run with a vacuum advance/RETARD from the engine. So yes, you may see it rotate one direction, and then back the other direction. I've not fired up my '79SF this year, so I can't help at the moment. I will be taking it out in a few more weeks, I hope. Just need to wait until no more snow and salt on the roads.

[Tonyxs11]

These bikes run with a vacuum advance/RETARD from the engine. So yes, you may see it rotate one direction, and then back the other direction. I've not fired up my '79SF this year, so I can't help at the moment. I will be taking it out in a few more weeks, I hope. Just need to wait until no more snow and salt on the roads.

cheers Ray the way it works ATM seems right because of the way it responds to the throttle, its never run so good since the day i bought it !!!! but my last 3 XS11's always ran spot on so never had the need to check the timing or the vacuum advance. even when i worked for a Yamaha dealer we never had one in for work !!!!

[pete_s]

I think you are not understanding what the advance is doing while running. As load increases, vacuum goes down and that is why you are not seeing a change at idle or revving, it is already at high vacuum with manifold hookup. Ported will retard advance at idle only mostly for emissions and used on autos with automatic transmissions to control idle speed.
My 78E has stock carbs and jets, xs850 rear drive and gets 45mpg @70+ with a Vetter fairing, Krauser bags.
Sounds like your bike is working perfect and the only thing to check is mechanical advance timing (vacuum advance disconnected)
Baby the vacuum advance as I can't find them!

[bikerphil]

Tony, make sure the advance plate bearing is operating smoothly, lube it up if it doesn't. Not smooth can cause a stumble.

[Tonyxs11]

Tony, make sure the advance plate bearing is operating smoothly, lube it up if it doesn't. Not smooth can cause a stumble.

when i first got the bike running i knew the carbs where a mess but i also stripped the advance unit down to check everything, it was all cleaned up and working good. ive ordered a new timing light so when that turns up i will check the timing and report back.

[Tonyxs11]

I think you are not understanding what the advance is doing while running. As load increases, vacuum goes down and that is why you are not seeing a change at idle or revving, it is already at high vacuum with manifold hookup. Ported will retard advance at idle only mostly for emissions and used on autos with automatic transmissions to control idle speed.
My 78E has stock carbs and jets, xs850 rear drive and gets 45mpg @70+ with a Vetter fairing, Krauser bags.
Sounds like your bike is working perfect and the only thing to check is mechanical advance timing (vacuum advance disconnected)
Baby the vacuum advance as I can't find them!

I am seeing a change though !!! when at idle the advance unit rotates anti-clockwise but not as far as it can go, then when you open the throttle is rotates clockwise. throttle response it very good and rides well.