Fuel cap question

[shayes9761]

Hey guys,

When I bought my used FK1200 the seller said that when the fuel level got down below 1/2 tank sometimes the motor would shut down.  He said it was a bad diaphragm in the fuel cap (in the smaller insert of the cap).  He said if he cracked the cap open the bike would restart and run normal until it happened again.  He said this would be fixed by replacing the cap.

The cheapest I could find them is about 120 buck so before I do it I want to make sure this makes sense to you guys that this could be the problem.  Also, do you think the new fuel cap will come with a key???

Thanks in advance,

[FJmonkey]

It could be the cap, but don't buy a new one, perform a flapectomy. You also should perform the SUCK test on your fuel petcock. It is an easy test, I posted it a while back when my 86' was having fuel delivery problems. Mine failed, meaning it was not allowing fuel to flow freely while the engine was on. I still have my original cap, but a new petcock.

[Capn Ron]

If you buy a new cap, it will come with a key.  You can swap out the lock cylinder from your old one so you can continue using just one key.

Hmmm...flapectomy.  An operation that is only needed on the gravity-fed models (yours included).  Basically, your fuel cap isn't venting and there's a modification that folks here refer to as a flapectomy to get the air flowing into your taink again.  Doing a search comes back with a lot of "Do the flapectomy!" references, but I'm not certain of what the exact modification is.  You can find a great tutorial on how to tear down your fuel cap in this thread:

http://www.fjowners.com/index.php?topic=2024.0

Perhaps someone could circle the part on one of the pictures with a notation of "make incision here------>"?  Maybe that's already been done and I just can't find that thread?

Cap'n Ron. . .

[FJmonkey]

Try this - http://www.fjowners.com/index.php?topic=2024.0

The orange/brown round thingies in the white plastic housing are the flaps. Remove the entire white plastic piece. Save it if you wish, reassemble and your tank will vent. However, if you still experience what feels like vapor lock, it could be a small number of things. The first suspect is fuel line routing, every owner seems to mess it up (including me), as it is not intuitive. What looks right will pinch the fuel line and when the tank is low will starve for fuel. This symptom can be masked by stopping on the side of road, opening the fuel cap, cranking the engine to get fuel to flow and fill the carb bowls. It seems like opening the cap did the trick, but all it did was allow time for the bowls to fill up when fuel demand was low (idling).

This might help - http://www.fjowners.com/index.php?topic=9266.msg87760#msg87760

[Capn Ron]

Ahhh, so you would just leave out this part during reassembly?



Seems simple enough!   

Cap'n Ron. . .

[ribbert]

To fix mine, I opened the lid, stuffed a rag in the opening and gave it a shot of compressed air into the vent at the lower LHR of the tank (where the hose fits)
There was a puff of fine dust like dried sediment that came out and it's been fine ever since.

Noel

[FJmonkey]

To fix mine, I opened the lid, stuffed a rag in the opening and gave it a shot of compressed air into the vent at the lower LHR of the tank (where the hose fits)
There was a puff of fine dust like dried sediment that came out and it's been fine ever since.

Noel

That is good for clearing out the over fill drain, if any fuel that spills over the fill opening, it drains to the ground under the bike. I do the same about once a year.

[shayes9761]

To fix mine, I opened the lid, stuffed a rag in the opening and gave it a shot of compressed air into the vent at the lower LHR of the tank (where the hose fits)
There was a puff of fine dust like dried sediment that came out and it's been fine ever since.

Noel

Can you post a picture of what vent line to blow it into?  What did you use, just one of the cans of air for cleaning keyboards or something?

[shayes9761]

That is good for clearing out the over fill drain, if any fuel that spills over the fill opening, it drains to the ground under the bike. I do the same about once a year.

Can you post a picture of what vent line to blow it into?  What did you use, just one of the cans of air for cleaning keyboards or something?

[ribbert]

That is good for clearing out the over fill drain, if any fuel that spills over the fill opening, it drains to the ground under the bike. I do the same about once a year.

Errr, where did that come from? I don't think I said that?? and without investigating, I think it's a vent not a filler drain anyway (which will vent fuel with the lid closed if overfilled when hot and on the side stand)

Noel

[FJmonkey]

That is good for clearing out the over fill drain, if any fuel that spills over the fill opening, it drains to the ground under the bike. I do the same about once a year.

Errr, where did that come from? I don't think I said that?? and without investigating, I think it's a vent not a filler drain anyway (which will vent fuel with the lid closed if overfilled when hot and on the side stand)

Noel

On my 86' there is a hole just outside the fill hole in the recessed area. Fuel cannot get to it with the cap closed. But I noticed that if I am not paying attention while filling up, and I over fill, the fuel runs down the hole. It runs out the back of my tank under the seat to a hose that dumps to the ground.

[ribbert]

That is good for clearing out the over fill drain, if any fuel that spills over the fill opening, it drains to the ground under the bike. I do the same about once a year.

Errr, where did that come from? I don't think I said that?? and without investigating, I think it's a vent not a filler drain anyway (which will vent fuel with the lid closed if overfilled when hot and on the side stand)


Noel

On my 86' there is a hole just outside the fill hole in the recessed area. Fuel cannot get to it with the cap closed. But I noticed that if I am not paying attention while filling up, and I over fill, the fuel runs down the hole. It runs out the back of my tank under the seat to a hose that dumps to the ground.

Fair enough, I am certainly no model difference expert and I've never had occasion to investigate it anyway.

Noel

[movenon]

"On my 86' there is a hole just outside the fill hole in the recessed area. Fuel cannot get to it with the cap closed. But I noticed that if I am not paying attention while filling up, and I over fill, the fuel runs down the hole. It runs out the back of my tank under the seat to a hose that dumps to the ground."

Yep , just what it will do.  Just an opinion here but I would clear the tube, disassemble the cap and clean everything and try to reuse the flapper valve.
Could just be some crap in there not letting the valve open.. Or someone put the valve in backwards...

Nice to keep a sealed system with ethanol gas if you can.

George

[ribbert]

"On my 86' there is a hole just outside the fill hole in the recessed area. Fuel cannot get to it with the cap closed.

George

It will if you fill the tank with the bike upright, then park it on the side stand with a hot motor or in the sun. That's what the whistling is after you turn them off hot. You open and close the cap and 5 minutes later it starts again. It's the pressure forcing it's way past the seal.

Anyone who had a Japanese bike in the 70's or 80's will remember the red fuel stain to the left of the fuel cap (the side stand side)

Noel

[movenon]

I have learned not to over fill the FJ.  On the side stand I try to just fill it up to where the fuel just touches the bottom of the fill tube.  At least that's in a perfect world....  When I cleaned out my "new to me" fuel tank I spent some time cleaning up the main rubber seal ring and neck area. Seal is nice now.  I am surprised that there hasn't been a source to replace that rubber seal as they get hard and take a set sometimes.

The flapper valve and vent area were clean so I lightly dressed everything up and reassembled.  So far no problem but due to the weather no long trips have been taken.
George