Which models have a boost control hose ?

[leatherskin]

In the UK only the 36Y 1100 had the vacuum controlled CDI, the 3CV, 1TX and the 3XW 1200's didn't.

Thanks for that valuable piece of insight Havoc, gives me a little piece of mind knowing my 1TX TCI is normal and not butchered as well. Just wish I had bought the bike new,the P.O. was obviously a wanker who shouldn't mess with bikes.

[leatherskin]

what does the vacuum hose do?  

The hose sends a vacuum signal to the boost control which, when vacuum level increases, controls the timing advance for emissions compliance.
Here's a discussion:

The stock FJ has a ignition which runs ~35 degrees advance (BTDC) starting ~ 4k rpm and above. The power boost feature senses higher vacuum levels when the throttle plates close and then advances the ignition to ~40 to 50 degrees to flash off excess fuel in the intake mix.
According to Randy @ RPM this is a emissions control feature.
As I painfully learned, racers don't use this "power boost" module, they just disconnect it and plug the vacuum port and run the stock ignition advance.
Here's a thread on this subject: http://www.fjowners.com/index.php?topic=6739.0
Look at the different timing maps. Look at the vacuum levels.
Remember that the vacuum signal is taken between the plates and the engine, so when the throttle plates close the vacuum goes up.
The "power boost" feature is of no use to you. It's a emissions thingy.

If you look at the timing charts, the "vac sensor" as they have labeled it, causes the ignition timing to spike at high vacuum (closed throttle). We found that the car would actually accelerate when the timing jumped at the point when the throttle was released. (not what you want when trying to slow for a corner)

If you look at the timing curve on the chart below, it shows the timing at 37* at 9000 rpms, but when vacuum is supplied to the "boost" sensor the timing jumps to 50*. This is done to burn the excess fuel in the cylinders when the throttle plates are slammed shut on decel.

Thanks for explaining what the boost hose is actually for Pat.

[Tapartacus]

OK, so what happens when it's removed? Does the timing need to be adjusted?
Andrew

[Pat Conlon]

No adjustment needed. Plug the now unused vacuum port at the #2 intake manifold.