Newbie dumb questions

[red]

hi, y'all
more newbie questions, please... to see if it's "working as designed/expected" or a real bug:
1-at 4 000 rpm or above there's a very loud mechanical sound coming from the gas tank, which sounds like a pump - then below 4 000 rpm it stops (doesn't positively or negatively affect the bike, it's just the whinning sound) - would this be the vaccuum fuel pump (petcock?) working its magic? Is it normal?
2-reading the specs of my '84 FJ 1100 it states the gas tank holds 24.5 Litres/6.47 US gallons; but at the gas station (with what seemed to me an almost empty tank) the gas maxed out at the top with only around 15 Litres/3.96 US gallons - was I miscalculating and there was still plenty of gas in the tank; or is the gas going somewhere else other than the tank (no visible leaks); or are the specs wrong?
3-the fuel gauge appears to work fine when in straight lines, but after some corners, downhillls or uphills it begins to work like it's cursed, sometimes showing I've no more gas, other times that I'm ok at half tank, then magically some gas appeared in the tank so it shows the tank is almost full...
regards

vertigobike,

1. That sound is NOT normal.  Something is going wrong, there.  The vacuum petcock is just an On/Off valve, nothing more, and it is silent.

2. You may have an undersized or non-OEM tank, but siphon the tank dry one time, then fill the tank completely, and record the results for future reference.  Somebody at the gas station will want the little bit of gas that you siphoned from your tank, to start.

3. Flaky fuel gauges are almost always caused by bad ground connections at the sender, or (more likely) at the instrument panel.  Clean them all to bright shiny metal, use a touch of conductive silver grease if handy, and see what you have then.  The gas can not slosh around inside the tank very much.  The sender unit very seldom goes bad, but it is possible.  Bad grounds or bad wiring will be much more likely there.

Keep us posted.
.

[vitorino]

thanks, red for your feedback - much obliged

none of my 1,2,3 questions are really urgent (I think) but I was intrigued

nevertheless my attention will go to #1 first

I forgot saying the noise doesn't come up every time I'm at 4 000 rpm or higher - just some times

I don't have a recording of it, but it's a loud noise that for me appears to be coming from the tank or beneath it - more or less like this pool pump noise: https://www.youtube.com/watch?v=sbS3GVKSUFk&ab_channel=BravoFix but then after some moments later it stops completely

unfortunately it will be only next year until I get to my FJ 1100 again, which I'm hoping to get a mechanic to look into it; but would be nice to have some clues of what it may be... vacuum pump, oil pump (if it exists), bearings, gearbox, chain/sprockets, alternator, etc.

regards

[red]

thanks, red for your feedback - much obliged
nevertheless my attention will go to #1 first  I forgot saying the noise doesn't come up every time I'm at 4 000 rpm or higher - just some times  I don't have a recording of it, but it's a loud noise that for me appears to be coming from the tank or beneath it but then after some moments later it stops completely
would be nice to have some clues of what it may be... vacuum pump, oil pump (if it exists), bearings, gearbox, chain/sprockets, alternator, etc.
regards

vertigobike,

You do NOT have a vacuum pump; no bike does.  You do not have a fuel pump if the bike is stock.  A fuel pump can be added, sure, but you would hear that fuel pump running briefly before start-up, and never later..  It could be the wheel drive chain, but I think the sound would change as RPM went higher, and a slack wheel drive chain would be obvious.  Do you see any wear points where the chain may touch something?  Are the front and rear chain sprockets secured at the proper torque values? 

You do have an oil pump, but an oil pump is just gears immersed in oil, if the oil level in the engine is correct.  If it was the alternator, you should hear the sound when the bike parked and running, with an ear to the alternator cover.  I would doubt that the starter is trying to engage, at that high RPM. My suspicion centers on the cam drive chain.  The cam chain may be slack, stretched, or the cam chain tensioner may be going bad.  Still, I have no idea what a bad cam chain would sound like, so that is only a guess.  I believe it would be worthwhile to check the cylinder head valve clearances; doing so may show you the problem, even when the valve clearances are correct.  Whatever is causing the noise, I believe it can be dangerous to the engine, if you ignore it.  Best wishes.
.

[krusty]

hi, y'all

went down to Portugal for my yearly 2-week vacation and (finally!) rode the FJ 1100: 238 miles in all roads except dirt: town + back and coastal roads + freeways

had 2 snafus with it... maybe post it in another section; but after that the bike rode well, despite being a very "moody girl"

more newbie questions, please... to see if it's "working as designed/expected" or a real bug:

1-at 4 000 rpm or above there's a very loud mechanical sound coming from the gas tank, which sounds like a pump - then below 4 000 rpm it stops (doesn't positively or negatively affect the bike, it's just the whinning sound) - would this be the vaccuum fuel pump (petcock?) working its magic? Is it normal?

2-reading the specs of my '84 FJ 1100 it states the gas tank holds 24.5 Litres/6.47 US gallons; but at the gas station (with what seemed to me an almost empty tank) the gas maxed out at the top with only around 15 Litres/3.96 US gallons - was I miscalculating and there was still plenty of gas in the tank; or is the gas going somewhere else other than the tank (no visible leaks); or are the specs wrong?

3-the fuel gauge appears to work fine when in straight lines, but after some corners, downhillls or uphills it begins to work like it's cursed, sometimes showing I've no more gas, other times that I'm ok at half tank, then magically some gas appeared in the tank so it shows the tank is almost full... I think I know the answer to this one, which can be called "normal" as unlike cars, gas tanks in bikes get tossed around a lot so the internal mechanism will do its best with gas "waves" inside the tank... but I don't recall having this issue on my '86 BMW K100 RT... and the riding style is the same (pardon me!)

now the bike is stored for the coming winter :-( ... let's see if next year I can ride it again

regards

1. Is the sound kinda like a loud buzz. I am thinking a pressure relief valve in the fuel cap trying to keep pace at higher speeds = greater fuel flow. Unlock the fuel cap to see if that makes a difference. If the sound disappears you will now know the cause.
2. My FJs, when showing very empty on the fuel gauge usually take about 17 litres. From memory, without checking, I thought the tank holds 22 litres. 5 litres is a good safety margin.
3. Not something I would worry about so long as you don't run out of fuel with the gauge showing that there's still some in the tank.

[fj1289]

I was getting ready to post the same thing.  First thing would be to check the fuel cap vent.  Try riding with the cap unlatched (half tank or less prudent!) and see if the issue goes away.

I NEVER fully trust a fuel gauge on anything!  Always know how much I've put in, and have an approximate idea of how much I've used - served me well on motorcycles (most with no gauge anyway!), cars, trucks, boats, and planes.   

Man that sucks to wait so long to ride it again!

[oldktmdude]

   According to the Yamaha specs, the 1100 tank should hold 24 litres but I doubt this. The most that I have ever been able to fit into a dead empty 1100 tank
was just over 23 litres.
You didn't mention (unless I missed it) when the noise was being emitted, ie when moving or stationary. My guess, if it's when moving, the dreaded speedo howl. 
   Regards, Pete.

[Bill_Rockoff]

It is worth noting that these bikes vibrate a lot, especially if the carbs are out of synch. But even a properly synched early FJ is a symphony of rattling vibrating things.

The fuel tank mounts to the bike on rubber bushings and grommets. The tank slides on at the front over two rubber bushings, and then the rear of the tank bolts to the frame under the front of the seat with two bolts through rubber grommets. If the rubber has disintegrated or come loose and gotten lost, you'll have metal-to-metal contact and it won't be a tight fit, so it will vibrate and make a lot of noise.

The inner fairing panels on these bikes are also notable for making a lot of buzzing noise.

I haven't had the problem on my FJ, but I did on an earlier bike - if part of the exhaust is loose, it can rattle and vibrate at certain RPM.

You can probably stand next to the bike while it's in neutral on the center-stand and rev the engine up past 4,000 rpm and see if you can find the vibration. Something may need to be tightened or bent or shimmed or bolted down or replaced.

Good luck.

[fj-f3a]

As far as point 3 is concerned, I feel the problem would most likely be with a 30+ year old capacitor (capacitors) on the gauge itself.
I am assuming there would be a Resistor/Capacitor Analogue Sampling Circuit of some design and an old leaking capacitor would cause similar problems.

Gavin

[vitorino]

thanks red + krusty + fj1289 + oldktmdude + Bill_Rockoff + fj-f3a for all your tips

indeed, I'm 1 367 km/849 miles and 2h by plane apart from my FJ 1100, and in a different country; so unfortunately only next year I'll be able to ride it again God permitting... it's like a long-distance relationship with a lover which you only see in person from time to time... but oh boy, when you do, it's fireworks! ;-)

the sound is only when the bike is moving and only when I push it a little bit... the first time I heard it I was on a freeway doing 80 kph/50 mph in 5th gear and at around 4 000 rpm... it lasted a couple of seconds and then it stopped; the second and last time I was on a back road doing around 60 kph/37 mph in 3rd gear (I think) stretching it with the revs... it also lasted a couple of seconds only... this is like only 5% of all my riding... as in 95% of my riding there's no noise whatsoever

it doesn't appear to be coming from the engine itself, as it's not dependant on the engine rotation or speed, and it doesn't matter if I take off some throttle; also, like I stated before, it neither gives more power to the bike nor less power... the bike behavior is exactly the same... so I really hope it's some sort of device doing it's thing as designed rather than a bug/issue with the bike... it really does sound like some sort of a pump or a valve like you said... perhaps increasing the flow of gas into the engine due to the revs... or a "relief"output, letting some pressure off for safety reasons; either OEM or an aftermarket device that once someone installed

the sound is very similar to this one: https://www.youtube.com/watch?v=sbS3GVKSUFk&ab_channel=BravoFix

next time I'll try to replicate the issue while the bike is on its center stand, like you said, to see if it happens again

regarding the tank capacity and sometimes unreliable fuel gauge those are more of a curiosity of mine than anything else; I'm sure with time I'll get to the bottom of it

thanks all again
regards

[red]

thanks red + krusty + fj1289 + oldktmdude + Bill_Rockoff + fj-f3a for all your tips  thanks all again
regards

vertigobike,

If the sound you hear is the speedometer howling (that is possible), just disconnect the speedometer cable from the front wheel and secure the loose end up to the handlebars for a while.  If that fixes the problem, either slide out the cable core and apply a good quality thin grease, or replace the speedometer cable with a new one (they are not expensive).  If the sound persists, you can add lube to the speedometer itself; that job is not too difficult, but ask here first, to save time and trouble.
.

[FJ_Hooligan]

The '84 and '85 FJs have a double-walled exhaust pipe.  Sometimes the inner pipe can get corroded and start breaking apart.

This will cause a rattling noise that some have described as it sounds like something really bad is happening with the motor.  The noise comes and goes but typically occurs under fairly aggressive throttle.

For the fuel gauge, sounds like you've lost all the damping fluid.  With a full tank of fuel pay attention to the needle when you turn the key on.  If the needle quickly snaps to the full mark, then there's no damping fluid.  But, it never hurts to check the wiring and connectors.

[vitorino]

hi, y'all

thanks again for all your help

wow, I had never heard about that "howling" speedometer, lol :-) didn't know that was even a "thing" - had 5 bikes before and none "howled" to me

but it could be the root-cause... I'll let you know (next year)

regards

[krusty]

I have a quick fix for rattly FJ motors.













I switch my hearing aids off before riding.