Possible Problem or Just a FJ Quirk

[GeorgeF]

I've had my 1992 FJ1200 for a couple of days now and have several questions that I have not seen (or I've missed) being mentioned elsewhere in the forum.

1) I have noticed that the negative pressure builds up quite a bit in the gas tank.  I've had no problems with fuel starvation but I've never experienced build up to this extent in any of my prior bikes and,

2) when I apply my brakes the lights go dim.

I don't want to come off as a doting new owner but I know that most bikes have some quirks common to their particular model.

Are these common traits to the FJ?  If not, what are the most common causes?

Thanks in advance!

[Harvy]

George....... its not uncommon for the headlight to dim at low revs, when the alternator is not supply enough current to charge and supply at the same time.......my FJ is generally reading below 12V until the revs reach about 1300....... and lighting the brake lights will dim the headlight.
But it should not dim under general riding......if it is you may have a charging problem.
The cure for the rather poor FJ headlight brightness is to by-pass the factory wiring to the headlight by installing relays for both high and low beam which are controlled by the factory wiring but supply 12v direct from the battery...... or just recently Mr Bean posted about some HID replacement bulbs.

As for the tank........ there are small rubber flapper type valves in the gas cap, which over time fail for one reason or other.
One valve to relieve pressure in the tank and one to allow air in to replace used fuel.
Its a common complaint and is easily fixed by removing the flappers.......there is a story about it in the files section of this forum somewhere..... with pictures and all.....posted I think originally by Klavdy..... try a search.

Enjoy mate.
Harvy

[GeorgeF]

George....... its not uncommon for the headlight to dim at low revs, when the alternator is not supply enough current to charge and supply at the same time.......my FJ is generally reading below 12V until the revs reach about 1300....... and lighting the brake lights will dim the headlight.
But it should not dim under general riding......if it is you may have a charging problem.
The cure for the rather poor FJ headlight brightness is to by-pass the factory wiring to the headlight by installing relays for both high and low beam which are controlled by the factory wiring but supply 12v direct from the battery...... or just recently Mr Bean posted about some HID replacement bulbs.

As for the tank........ there are small rubber flapper type valves in the gas cap, which over time fail for one reason or other.
One valve to relieve pressure in the tank and one to allow air in to replace used fuel.
Its a common complaint and is easily fixed by removing the flappers.......there is a story about it in the files section of this forum somewhere..... with pictures and all.....posted I think originally by Klavdy..... try a search.

Enjoy mate.
Harvy

Thank you very much Harvy!  I'll check those posts.

I'm very happy that I finally got my FJ and look forward to putting many miles on her.
Cheers!

[jack02]

Harvy - sorry can't find the flapper valve stuff so I'll ask here! In the eight years I've had my FJ the filler cap has always whistled and wheezed,but I've never had fuel-starvation problems. Anyway,after a long time off the road and the subsequent fettling to get it back on,I decided to take the filler cap apart one wet afternoon. Lots of white-fur corrosion in there so I removed it,cleaned and greased everything and put it back together. Result: a silent filler cap ever since. You say the flapper valves can be discarded,so what is their reason for being there? Does their removal have no consequences at all?? I ask for future reference...!

[Harvy]

Jack..... my 91 FJ thus far (touch wood) has not stopped whistling as designed, so I have not had to do the filler cap surgery.

I will leave it to others who have experienced the problem to comment, but it should whistle.

As far as removing them is concerned...... I think the only problem will occur if you are unfortunate enough to drop the bike........gas will leak out the cap.

Harvy

[andyb]

This is the post you were looking for.

[Dan Filetti]

You say the flapper valves can be discarded,so what is their reason for being there? Does their removal have no consequences at all?? I ask for future reference...!

Not 100% sure, but I'd guess it's there to prevent spillage if a) there is sloshing, although it's not an actual issue that I've heard of or b) leakage if the bike is upside down -in which case you've got bigger problems.  Again, just guessing.  

As an aside, I was somewhat surprised at how many little hard-to-loose-spring-loaded parts there were in that cap, when I did mine.

Dan

[Dan Filetti]

I was somewhat surprised at how many little hard-to-loose-spring-loaded parts there were in that cap, when I did mine.

Make that; 'easy-to-loose hard-to-loose-spring-loaded-parts' or '[not-so-]hard-to-loose-spring-loaded-parts'

4:00am...

[jack02]

 

As an aside, I was somewhat surprised at how many little hard-to-loose-spring-loaded parts there were in that cap, when I did mine.

Dan

Thanks everyone. Andy I did dismantle mine to the extent of the pics in your link! Just how complicated does the lid on a hole for putting fuel in have to be?? On mine,I broke the very fine spring which keeps the flap over the keyhole shut,but thanks to my boundless ingenuity (ha!) I made a new one out of....... a piece of guitar string wound around a cocktail stick (as a former). To my amazement it worked just fine!

[andyb]

Nicely done.

My guess is the flapper valves are to minimize vapor losses from the fuel (read:  less evaporation), but still allow the tank to vent so that it doesn't bulge out or dent in when the pressures change.  Really a rather complicated system for a simple task.

[Klavdy]

I was somewhat surprised at how many little hard-to-loose-spring-loaded parts there were in that cap, when I did mine.

Make that; 'easy-to-loose hard-to-loose-spring-loaded-parts' or '[not-so-]hard-to-loose-spring-loaded-parts'

4:00am...

4:00 am?
Did you loose track of time?
When you loost your spring, was the cap lose?

Loose cap,lose spring.

[Dan Filetti]

Ever the vigilant speller Klavdy.  Did the nuns beat you when you miss-spelled something?

Just asking.

Dan

[Klavdy]

Nuns?
(note the capital "N")

[racerman_27410]

there was a picture posted in another thread of a fella who had the unfortunate luck to have his gas tank collapse from lack of negative venting..... IMO its worth it to remove the flappers.... starve for fuel or collapse the tank.... either one is not good.



Kookaloo!


Frank

[cherrylog gypsy]

my 90 fj started dimming the lights when the brakes were applied recentlty-turned out to be a broken tailight bulb (glass globe came off and knocked the filament against the metal housing causing a short).