Bizzare running FJ

[SlowOldGuy]

I remember working all weekend on an FJ for a local owner.  It was kind of a basket case and he really wanted to get it running beofre investing much money into it.

I cleaned the carbs, reinstalled them.  Did an idle mixture adjustment, carb sync but it ran like crap.  I don't recall the exact symptom, but it would barely run when we tried to test it out with a run down the street.  I checked everything; re-checked carbs, fuel level, mixture, sync, coils, timing, cam timing.  Nothing made any difference.  I finally gave up for the weekend.

He called me a few days later to say he put in new plugs and it was now running great.  The plugs looked fine when I checked them, maybe a bit old looking but the color was fine. 

Like Frank always says:  Check the easy/cheap things FIRST!

DavidR.

[racerman_27410]

is the vacume line to the ignitor box actually connected to the box and carb joint?


Kookaloo!


Frank

[rhubarbray]

is the vacume line to the ignitor box actually connected to the box and carb joint?


Kookaloo!


Frank

I think the `88 was the first year that there was no vacuum connection to the box.

As for the plugs, maybe, they looked ok, but I can try new ones. Right now I`ve cleaned the filter and it`s drying. I`ll re-oil it and try it again tomorrow if it`s not raining.

I know it`s going to be one of those " Oh crap, it can`t be that simple!!!" situations.

Ray

[SlowOldGuy]

I think the `88 was the first year that there was no vacuum connection to the box.

All years used a "vacuum sensor" of some type.  On the early models, it went directly into the black box.  Later models has a separate device called a Boost Sensor that was in the front fairing area.

You should have atleast one vacuum line running from one of the carbs (typically #2) over the valve cover and into the fairing.  The line is insulated where it passes over the head.

However, one small vacuum  leak on a single cylinder shouldn't cause the drop in perofrmance you describe.

DavidR.

[Marsh White]

This my be a reach, but could it be bad gas or water in the gas?  You said it was sitting for a while.  Octane drops as gas ages...just a thought.

Klavdy's FJ had the EXACT same symptoms last December after sitting for only 6 months.  I cleaned the carbs and changed the gas out in the tank...problem solved!

[jack02]

I think the `88 was the first year that there was no vacuum connection to the box.

All years used a "vacuum sensor" of some type.  On the early models, it went directly into the black box.  Later models has a separate device called a Boost Sensor that was in the front fairing area.

You should have atleast one vacuum line running from one of the carbs (typically #2) over the valve cover and into the fairing.  The line is insulated where it passes over the head.

However, one small vacuum  leak on a single cylinder shouldn't cause the drop in perofrmance you describe.

DavidR.

I've never noticed any tubing going from the carbs and over the cam cover then into the fairing on my '89. When it "disappears into the fairing",where does it terminate? Each carb has a vent line which simply hangs down the back of the engine (or are they overflow tubes??). Think I could be missing something fundamental here,but I've never experienced rough running which begs the question of what is this vent line for and does it actually do anything useful? My manual never mentions a "Boost Sensor". Now I'm really puzzled. Having spent two hours at the weekend singlehandedly grappling with refitting the carbs and airbox to find where this mythical (to me!) tube goes and then rectifying it's absence is not an appealing prospect! Please elaborate..

[racerman_27410]

I've never noticed any tubing going from the carbs and over the cam cover then into the fairing on my '89. When it "disappears into the fairing",where does it terminate? Each carb has a vent line which simply hangs down the back of the engine (or are they overflow tubes??). Think I could be missing something fundamental here,but I've never experienced rough running which begs the question of what is this vent line for and does it actually do anything useful? My manual never mentions a "Boost Sensor". Now I'm really puzzled. Having spent two hours at the weekend singlehandedly grappling with refitting the carbs and airbox to find where this mythical (to me!) tube goes and then rectifying it's absence is not an appealing prospect! Please elaborate..

the vacume line comes off the carb joint (on top between the carbs and cylinder head.....same place as you connect to balance the carbs) not underneath where the float bowl drains are.

its an electro/mechanical ignition advancer. I know for a fact mine didnt run worth a crap on the bottom end with it disconnected.

KOokaloo!
Frank

[Marsh White]

I've never noticed any tubing going from the carbs and over the cam cover then into the fairing on my '89. When it "disappears into the fairing",where does it terminate? Each carb has a vent line which simply hangs down the back of the engine (or are they overflow tubes??). Think I could be missing something fundamental here,but I've never experienced rough running which begs the question of what is this vent line for and does it actually do anything useful? My manual never mentions a "Boost Sensor". Now I'm really puzzled. Having spent two hours at the weekend singlehandedly grappling with refitting the carbs and airbox to find where this mythical (to me!) tube goes and then rectifying it's absence is not an appealing prospect! Please elaborate..

Here is the vacuum line (wrapped in silver shielding):



Here is where it goes on the #2 Carb:



It snakes around a lot on it's way up to the control box which is mounted just below and to the right of the front headlight on your 88 FJ.  The box is in different locations on different years.

[Arnie]

All years used a "vacuum sensor" of some type.  On the early models, it went directly into the black box.  Later models has a separate device called a Boost Sensor that was in the front fairing area.

You should have atleast one vacuum line running from one of the carbs (typically #2) over the valve cover and into the fairing.  The line is insulated where it passes over the head.

However, one small vacuum  leak on a single cylinder shouldn't cause the drop in perofrmance you describe.

DavidR.

No vacuum line on my '91 B model FJ.  All the carb manifolds have a single vacuum tap for balancing, but that is capped for normal running.
I think even rocket scientists can err occasionally :-)

Cheers,
Arnie

[RichBaker]

Yamaha calls it a pressure sensor on the 'fiche.... #24 in Electrical 2 http://www.yamaha-motor.com/sport/parts/home.aspx

[SlowOldGuy]

But if Arnie doesn't have it and he doesn't have it on his '88, maybe it was just a US "feature."  I'm too lazy to look at the different wiring diagrams right now.

Sometimes I forget that there's a larger world out there.  Comes from 20+ years of working "behind the wall."

Besides, I'm from Texas, nowhere else really matters (unless you want to ride really great roads, or have good weather, or a nice beach, hmmmm, maybe I need to re-calibrate).

DavidR.

[Harvy]

All years used a "vacuum sensor" of some type.  On the early models, it went directly into the black box.  Later models has a separate device called a Boost Sensor that was in the front fairing area.

You should have atleast one vacuum line running from one of the carbs (typically #2) over the valve cover and into the fairing.  The line is insulated where it passes over the head.

However, one small vacuum  leak on a single cylinder shouldn't cause the drop in perofrmance you describe.

DavidR.

No vacuum line on my '91 B model FJ.  All the carb manifolds have a single vacuum tap for balancing, but that is capped for normal running.
I think even rocket scientists can err occasionally :-)

Cheers,
Arnie

Same for me Arnie......'91 Japanese domestic model.


Harvy

[jack02]

Seems that all is as should be then on my '89 here in the UK... all carb rubbers are fitted with a cap on the vacuum gauge take-off points and the one on carb#2 isn't suspiciously absent - as if it would run without it! So the vent line in question and the "Boost Sensor" can't have been in the UK model's specs. Reassured now,thanks all.

[Harvy]

Jack02...... I believe Euro spec and Jap domestic models were one in the same beast? Well at least in the way of colour schemes........my 91 has the grey colour on the bottom of the chin scoop, while US models were white.
So maybe the Euro bikes did not have the vac line either?

Harvy

[Scooterbob]

Besides, I'm from Texas, nowhere else really matters (unless you want to ride really great roads, or have good weather, or a nice beach, hmmmm, maybe I need to re-calibrate).

DavidR.

I couldn't agree more. 
May I quote that in my Sig?