Vacuum Advance, XS Turbo Question

[LVTom]

I have a question for the experts. Several years ago, I bout an XS with a Rayjay Turbo by Mr. Turbo. I pulled it out of the garage to bring it back to life. Every one wants to ride it, so I am getting plenty of help. One guy asked some questions I couldn't answer. It was "If the XS11 has a Vacuum advance, which runs on vaccuum, then how can it operate after the Turbo spools up and produces boost?". So, then we checked the vaccuum advance. The test consisted of hooking up a mityvac to the vaccuum nozle on the advance unit. It builds no vacuum at all. So, we concluded the vacuum advance unit is bad. Do you guys agree. Well, that's it. I would apprciate any advice(well, any good advise) anyone cares to offer. Thanks Tom

[crazy steve]

If the vacuum advance was hooked to a boost source, it's probably bad. But you don't want (or need) vacuum advance with a turbo set-up as a rule anyway, so no big deal. But are you sure it's the stock advance unit? It may be a vacuum retard unit, test for this by applying pressure to it. If the timing plate then moves, that's what you have and it should be hooked to a boost signal source.

If the advance unit does neither of these things (hold a vacuum or apply retard) check to make sure that the non-functioning advance is holding the timing plate in one position. If the plate can move, so can your timing. You might give a thought to locking the plate down mechanically.

[LVTom]

Vacuum Advance

Hi Steve, Thanks for the advise. I guess my next question is, don't I want the timing to advance? Especially when the RPM's aren't high enough to spool the turbo for boost?

[natemoen]

Hi Steve, Thanks for the advise. I guess my next question is, don't I want the timing to advance? Especially when the RPM's aren't high enough to spool the turbo for boost?

The few turbo xs' that I have seen videos of, and from what I have read, had their idle set way up around 2-3 grand. So that would negate that anyways.

[LVTom]

Thanks Nathan, Turning the idle way up wouldn't work in my case. I plan to use it as a daily driver and then probably sell it. I bought this bike on ebay about 5 years ago. It was in Missoula Montana. Took a Greyhound bus from Vegas to Missoula, the PO picked me up at the Greyhound Depot(not a really big place). Took me to his house. Told me a little about the bike, I got on it, and rode it from Montana to Wisconsin in 2 days. Never a hitch. Except that I don't believe the Turbo ever kicked in. Rode it all around Wisconsin and Minesota for 3 weeks in all kinds of traffic. Idled fine ran great. Still no boost. So, now that I am getting back to it. I am finding that when spinning the turbo by hand it is very sluggish. So I am sending that back to Mr. Turbo to get rebuilt. But this vacuum thing has me confused. Just like our stock XS1100. There is a vacuum hose going from the vacuum advance to unit to a vacuum port on one of the rubber/steel intake manifolds. Anyway, sorry for the long explanation. I think I wll get another advance and see what happens. Thanks Tom

[crazy steve]

Hi Steve, Thanks for the advise. I guess my next question is, don't I want the timing to advance? Especially when the RPM's aren't high enough to spool the turbo for boost?

Remember, you still have the mechanical advance (if you have a '78-80 bike; if yours is a '81, the 'mechanical' advance is built into the TCI) that will advance the timing based on RPM. So you do have advance...

The vacuum advance only changes the timing under low-load, high vacuum conditions i.e. small throttle openings. In a properly operating turbo system, you won't see any high manifold vacuum as the turbo will produce boost at probably anything over 2000 rpm; not full boost, but some; any boost at all will eliminate a vacuum signal. I'll mention here that where you connect for the signal makes a difference, as well as the type of turbo system you have ('draw through' or 'blow through'). But on either system, if you're making the connection on the intake manifold, that will give you a boost signal. If you want to run a boost gauge, this is where you would connect it.

If your kit manufacturer is still around, ask them; generally on any forced-induction system (whether it's a turbo or supercharger), any sort of vacuum advance is a big no-no. Too much advance under boost is a fast way to kill the motor. You do see boost retard units however...

If it were me, lacking any additional info from the kit supplier, I'd leave the vacuum advance disconnected and lock the advance plate down.

[LVTom]

Thanks

Hi Nathan, Thanks for the quick response. I hear what your saying. Mine is a 78. Mr. Turbo is still in Business, so I will ask him. I will also check to see if the plate is locked down. I'll let you know what I find out. Thanks again. Tom

PS: I have been on this site for over 10 years. I seldom ask questions, but when I do, I have been helped every time. Thanks again.

[daveyg]

I am very interested in pics of your bike, especially focused on the turbo and intake setup. If working properly I can't even imagine the scary ride that thing would be. A stock 11 has way more power than the brakes and suspension should be able to handle, multiplying that power by 1.5 or more would scare the crazy right out of me!

[Mathh]

When I was running the ATP turbo set-up I still had the vacuum installed, no problem. Both ATP and Mr.Turbo were known for their "late"" boost applications, probably starting between 3500 and 4500 rpm and having very low torque figures at off boost situations (35-50% from stock figures). Idle should be between 1000 and 1500 rpm. As you can run without boost (when cruising) it should be ok to keep the stock vacuum operated ignition (taken from the intake manifold). Having no boost does not necessarily mean that the turbo is broken. Check if the blow-off valve is stuck open or screwed wide open. Remove the airfilter and check if the vanes are not broken , are turning freely and spin up with the rpm, then remove the exhaust and check the same. If they don't turn the bearing is gone.... and you can spend your hard earned cash.. Good luck

oh yeah: when the turbo kicks in there will be no doubt ...

[airborneXS]

Pictures please!