Fuel Issues

[PaulG]

Last week - after finally having time to replace fork seals - went for a couple of short test runs and was getting (I think) fuel starvation above 4500 rpm.  Then this past weekend drove it to work for 3 days, and had no issues at all   

Got out for an all day cruise on Wed about 500km total. It seemed to run ok, except it emanates some fumes at a standstill. In the hot sun it gives off a squealing noise from the gas tank, and when I pop the lid it stops, so I think I may still have an issue with the breather.  The carbs were rebuilt and synched last month.

When I got up Thurs morning it had started to piss gas out of #4 carb when the sun  got on it.  Left a nice puddle in the driveway and ate the asphalt.

So I'm wondering.... If the breather is blocked, can pressure build up enough in the tank to force gas through the fuel pump into the carbs?  The bike was on the sidestand, so #4  carb would have been elevated above the level of #1.  I only have about a litre of gas in the tank which would give plenty of room for pressure to build up in the tank.

I checked the breather hose and it's ok.  So I was thinking of blowing out the breather pipe from the tank downwards with my air compressor.  Did I hear someone shout in slow motion, "Nnnnnooooooooo......"   

Any suggestions?   

[ribbert]

So I'm wondering.... If the breather is blocked, can pressure build up enough in the tank to force gas through the fuel pump into the carbs? 

Any suggestions?   

Yes, in principle. An un vented fuel tank, low on fuel in the sun will build enormous pressure, think of the metal lawn mower fuel can you left sitting in the sun that bulged at the sides and blew the cap out of your hand when you opened it. It will choose the component offering the least resistance to vent that pressure, and it will find somewhere.
In your case, that may well be the fuel pump, the most common place though I would expect to be the cap.

Noel

[FJmonkey]

In the hot sun it gives off a squealing noise from the gas tank, and when I pop the lid it stops, so I think I may still have an issue with the breather.

That squealing/singing sound is the flapper valve in the filler cap. It is designed to vent in one direction, keeping the tank from going into a vacuum. There are other directional valves to vent fuel vapor into 2 charcoal filled cans at the front of the engine. This prevents fuel vapor from venting to atmosphere. Once the engine is running, a solenoid actuates and allows other valves to pull the trapped vapor back into the combustion cycle and burn it.

Now that I have over explained this system, you could do what many have already done and remove the flapper valves in the filler cap. Look it up in the files section and try not to lose the (gnat's balls size) steel ball that shoots out.

And you might want to check that your fuel pump is not leaking when turned off, leaking fuel is a safety issue. I would disconnect the fuel line from the carbs and route it to an empty fuel safe container. If you have fuel leaking when parked then consider a new pump.

[PaulG]

... There are other directional valves to vent fuel vapor into 2 charcoal filled cans at the front of the engine....

... And you might want to check that your fuel pump is not leaking when turned off...

Sorry, I forgot to mention this is a '92 non-US model, so it doesn't have all the charcoal filters.     The fuel pump is a new replacement one from RPM, but I'll double check it anyhow.

The Clymer manual didn't say anything about the flapper valve in the cap.  I'll look it up in the files and check it out.  It'll be a few more days before I can work on it, so I'll post an update next week... hopefully a good one... 

Thanks a bunch

[ribbert]

........So I was thinking of blowing out the breather pipe from the tank downwards with my air compressor.  Did I hear someone shout in slow motion, "Nnnnnooooooooo......"   

Any suggestions?   

Paul, without the benefit of the forum wisdom at the time, I assumed that any blockage would enter from the top, so it made sense to blow it out from the bottom.
I opened the cap, stuffed a rag in the filler neck and blew it from the bottom of the vent. There was a great puff of dust, and evidence of dirt on the top of the tank. Certainly enough to block a pipe that size.

It's never sung to me since.

Noel

[PaulG]

... you could do what many have already done and remove the flapper valves in the filler cap. Look it up in the files section and try not to lose the (gnat's balls size) steel ball that shoots out....

So I disassembled the fuel cap as per the post in the Files section.  Cleaned all the bits, and started to reassemble.  That "gnat's balls sized" steel ball?  Well I didn't lose that.  But that fucking spring that holds it went p-tiiing off into the ether! 

So what now?  Is there any way of finding this part anywhere, or do I go to a flea market and buy some old watches to smash them open for one?

Can I reassemble it without ball & spring - Im guessing not.

Help   

[FJmonkey]

Wow!! You ruined the entire bike, might as well scrap it out now, total loss.... 

Can I reassemble it without ball & spring - Im guessing not.

Help   

The ball and spring has one simple job, to hold the little flap up. My '86 has had the ball and spring missing for many years, and the flap is always down unless the key is in the way.... No big deal. Reassemble and ride it...

[PaulG]

Wow!! You ruined the entire bike, might as well scrap it out now, total loss.... 

WHYYOUIOUGHTTA....!   


OOPS - Musta bin thinkin out loud agin 

Thanks for the prompt reply. I shall continue with the struggle. 

[PaulG]

Soooooo...... let's start again.....

Removed the diaphragm valve from the tank cap last week.  Took it for a short test run on the freeway for about a 20 km round trip.  Got it steady at 5500 rpm with the occasional blip to 6000 when traffic would allow it.  Everything seemed fine no hiccups or stuttering.

Drove it to work for my next 3x12 stint - 1st day fine, but on the 2nd & 3rd days the stuttering above 4500 rpm came back. 

Finally had a chance today to double check the fuel pump.  This is the replacement Airtex which I got from a fellow forum member, who bought it new but never used it.  I disconnected the outlet line and had it pump into a water bottle. 

The flow seemed rather slow and the pressure low.  So I thought if I hooked up my OEM one and videoed a comparison, maybe there would be some bigger foreheads than mine that could offer some more valuable advice. 

The background as to why I changed pumps had to due with my carb problems this spring/summer, (if you recall from the post that my carbs wrote denigrating my ham fisted attempts - but I digress).  I kept the OEM pump just in case.

You will see the Airtex pump continues to leak after being shut off, while the OEM one doesn't.  Also in the video you will hear a nasty screetchy/crackly sound when I turn on the ignition key.  It's seems to be coming from the didital ignitor box (gulp!  ) underneath the right front fairing.  This is also an intermittent issue over the last couple of years.  Any ideas/warnings regarding this?  Could the two be related?  The fuel stuttering has only appeared this summer after my carb debacle earlier, so I'm hoping not....

Anyhow, here is another award winning educational video....


http://vid839.photobucket.com/albums/zz315/pgirard005/92%20FJ%201200%20Fuel%20Pump_zpsf5xrieat.mp4

[FJmonkey]

The Airtex pump is not safe, as it allows fuel to flow when off. This can dump raw fuel on the ground (fire hazard) or fill your cylinders/crank case (possible hydro lock & mechanical damage) And it may be drawing too many amps or have some other electrical issue. The OEM pump sounded good and did not have that scratching noise. I would run with the OEM pump and see if your issues remain.

[PaulG]

So I ditched the new/broken Airtex pump and left my OEM one installed. drove it to work again, and again the stuttering began to occur upwards of 4000 rpm.

So I park it for a couple of days, realizing I may have to chase down an electrical gremlin  .  Considering I don't even have a working multimeter I thought that I was as prepared as usual to accomplish a task that I have little (succesful) experience with. 

Ok, check the plugs and leads.  Firstly #4 (cuz thats the side I'm standing on).  Oh look!     What's that stuck to the spark plug that's burnt all black?  Seems the electrode inside the cap has separated and was arcing against the plug head.

Case solved! 

New spark plugs, new caps, nip the cables back a tad and now she's running perfect again. Honest!  Put about 500 km on her since without a glitch.  No more fuel smell and much better mileage, idling, etc.

I had foolishly thought that the coils/cables/caps were a sealed unit, as the Clymer manual says nil about them.  Thanks again to fellow members Tiger and paulfj03 for setting me straight on that issue and more advice.   

What frustrates me the most, is that a few years ago I would have found this out a lot sooner.  Recently I've realized my brain likes to take a more circuitous path when trying to use logic or solve problems.     Maybe too many dents in the cranium has scrambled the wiring a bit.   

[FJmonkey]

Very happy you found your problem and solved it... Awesome dude. 

[Tiger]

Yippeeeeeeeee, success 

John.