Which models have a boost control hose ?

[leatherskin]

Does anyone know which models have the boost control hose (vacuum advance) attached to no.2 carby ? My 1tx doesn't have the hose yet my brothers 1ux does. Both are 86 models,mine has no vacuum fitting from the TCI box his does have the fitting. Both bikes appear to have the original TCI units ( they have the sticker on the side identifying the model codes ).

[Firehawk068]

My '90 has a separate "boost control" box located forward of the engine, up in the fairing. The hose runs up over the top of the engine, and up to it...........
It is possible that yours has it up in the fairing, and someone did away with the hose at some point. or someone has replaced your TCI with a later one.
My TCI box doesn't have a vacuum fitting on it either.

[leatherskin]

My '90 has a separate "boost control" box located forward of the engine, up in the fairing. The hose runs up over the top of the engine, and up to it...........
It is possible that yours has it up in the fairing, and someone did away with the hose at some point. or someone has replaced your TCI with a later one.
My TCI box doesn't have a vacuum fitting on it either.

I'm pretty sure mine has the original TCI box in it ( it still has the sticker on the side saying 1TX) but I could be wrong. My 1TX seems to run fine without the boost control. Another FJ mystery I guess !

[FJmonkey]

My 86 (California model) has the box under the seat near the battery and the vacuum hose routed to #2 intake.

[Mark Olson]

My 86 (California model) has the box under the seat near the battery and the vacuum hose routed to #2 intake.

yeah mine too.

[fj11.5]

my 84 had the boost system , till I fitted an aftermarket ignition , with re,mapped timing, now dousnt need the 4deg advance mod, as it played up

[leatherskin]

My 86 (California model) has the box under the seat near the battery and the vacuum hose routed to #2 intake.

Does anyone else with a 1TX have a boost hose connected to the TCI box or to their carbs ? Mine only has the one vacuum line leading to the fuel tap. Is this normal ? I can find no traces of any fitting on the TCI.

[Pat Conlon]

I think both the 84/85 have the boost control in the TCI box.
My '84 has the vacuum hose off #2 go right to the TCI box.

[fjman]

what does the vacuum hose do? 

[FJmonkey]

what does the vacuum hose do? 

It helps you reach those hard to get places when you are cleaning out crap from the top of your engine. 

[Pat Conlon]

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.

[FJmonkey]

Sounds like one more piece of crap I can take off the bike. I love having the room under the seat with the air box out. Now just that little bit more can be free.

[Havoc]

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

[1tinindian]

  I love having the room under the seat with the air box out.

Agreed!
After putting the UNI pods on I had extra room to mount my airhorn!

Leon

[FJmonkey]

Agreed!
After putting the UNI pods on I had extra room to mount my airhorn!

Leon

With a loud enough horn it would give new meaning to the rumble seat.