vapour lock issue's

[wheels]

Gday all i was having vapour lock issues some time ago and i was told it was the rubber flap beneath the petrol cap. if this is so do i remove the complete rubber base that sits under the cap or do remove something else. it's becoming a pain, your cruising along at 110ks and all of a sudden the carbs start starving and you know you have a full tank of juice .then she just stops  so i sit on the side of the road for five min's with the cap open then shut it and she starts . any suggestions?

[Harvy]

Mate, from what I understand there are 2 small rubber flaps, you have to dis-assemble the components under the cap....there is a/are spring/springs under there so be careful........1 flap is for venting tank pressure, the other for allowing for tank vacuum.

There are pics of the procedure somewhere ...... Klavdy took em, but someone else posted them if I recall correctly.......I'll hunt around.


Harvy

[wheels]

cheers harvy .thanks

[rktmanfj]

Maybe we can make a sticky out of this... or I should just remember where to find it a little quicker next time.     

http://www.fjrally.com/picgallery/gallery.asp?action=browse&categoryid=15&whichpage=3

Scroll to bottom of the page.

Randy T
Indy

[wheels]

so do i just remove the orange rubber or do i remove the whole plastic vent?

[FJSpringy]

I removed and binned both rubbers and drilled out the breather hole, Spanish Alf had some detailed instructions on his fast jota web site, but I think the site has gone. 

[jvb_ca]

I also have a question regarding the tank venting issue.
I have never had a fuel starvation problem, but my tank does whistle/hiss when its hot and near full of fuel. What annoys me is that fuel seeps out the key hole, and makes a mess of the underside of my tankbag. One time this summer it was almost pouring out, after topping it right up while it was very hot. I have not done the flapper mod, but am not sure if the previous owner has done it either.

Is there a way to tell if the flapper is still in there without disassembling the filler cap?
Is the fuel seepage an indication it has or has not been done?
Cheers...Jake

[wheels]

if it is hissing and squeeling like a pig like mine does i reckon there still in there. it's not a hard job to pull to bit's just watch out for the springs .

[FJmonkey]

I have never had a fuel starvation problem, but my tank does whistle/hiss when its hot and near full of fuel. What annoys me is that fuel seeps out the key hole, and makes a mess of the underside of my tankbag. One time this summer it was almost pouring out, after topping it right up while it was very hot. I have not done the flapper mod, but am not sure if the previous owner has done it either.

The flapper mod will not likely affect your problem with fuel under the tank bag. It was designed to vent fumes from the tank to a charcoal canister when heat causes increased pressure in the tank when fuel consumption cannot/does not compensate for the increased pressure/volume. Like when your bike is parked and not consuming fuel.

Your tank filler area has a drain line (not sure if it is on all years) that should spill excess fluid to ground. It must be plugged up. I noticed that some small amount of fuel would get trapped in the recessed cap area on my 86'. I saw the hole for drainage so I chased it out with a thin wire and some air pressure. It now drains and I no longer have a tank bag smelling like unleaded.

I had the starvation problem (years ago) when I commuted from SoCal to NorCal (900 miles round trip) every two weeks. It was not consistent but it drove me mad a few times, like when it was raining.  I have not done the MOD but I did take the cap apart and almost lost the tiny ball that was spring loaded. I plugged the spill hole and the filler hole before removal and was able to properly reassemble the cap. I now rarely use my tank bag that I think added to the problem. Once you remove one half of the tiny flapper part the venting control and the whiny/singing issue is gone. And possibly the starvation problem. let us know how it is working for you.

[jvb_ca]

The flapper mod will not likely affect your problem with fuel under the tank bag. It was designed to vent fumes from the tank to a charcoal canister when heat causes increased pressure in the tank when fuel consumption cannot/does not compensate for the increased pressure/volume. Like when your bike is parked and not consuming fuel.

Your tank filler area has a drain line (not sure if it is on all years) that should spill excess fluid to ground. It must be plugged up. I noticed that some small amount of fuel would get trapped in the recessed cap area on my 86'. I saw the hole for drainage so I chased it out with a thin wire and some air pressure. It now drains and I no longer have a tank bag smelling like unleaded.

I had the starvation problem (years ago) when I commuted from SoCal to NorCal (900 miles round trip) every two weeks. It was not consistent but it drove me mad a few times, like when it was raining.  I have not done the MOD but I did take the cap apart and almost lost the tiny ball that was spring loaded. I plugged the spill hole and the filler hole before removal and was able to properly reassemble the cap. I now rarely use my tank bag that I think added to the problem. Once you remove one half of the tiny flapper part the venting control and the whiny/singing issue is gone. And possibly the starvation problem. let us know how it is working for you.

Thanks for the info. I was not aware that there was a drain hole in the filler area. I thought that the spigot thing at the bottom front of the tank was a vent line and not a drain line. I will check to see if it is plugged. I know the rubber line itself is not plugged, but maybe inside the tank.  I will have to wait till spring to check this, as the bike is in storage in my neighbors shop. I might as well pull the filler cap apart at the same time and see if the flapper is still in there. Do some preventative maintenance. We have a ton of snow here now.

Cheers...Jake

[davehorton]

I had the same type of problem with my 86, starvation at speed then cutout, but starts up after 2 or 3 minutes of helmet scratching...

In my case it was not the tank vents, it was the petcock.

I never fully understood the mechanism of the failure, could be a mixture of all the problems I found when I dismantled the petcock.

The bottom line is I replaced the o-ring and spring inside the petcock (cos the damn thing lists for $250 replacement cost) and it has never given me a problem since...

I later dismantled and reassembled the fuel cap assembly just for grins, but there was nothing wrong with it before or after the effort.

I posted shots of both dismantling jobs on the yahoo fj group in the files section cos I also wrote a few words about how and why....

Merry Xmas!

[jvb_ca]

I posted shots of both dismantling jobs on the yahoo fj group in the files section cos I also wrote a few words about how and why....

Merry Xmas!

Good tech write up Dave. Maybe should post it up here in the files section. It will definitely come in handy when I tear mine apart next spring. Now I Know what I'm getting into.

Cheers...Jake

[56 CHEVY]

My 86 had the same problem but it would have to sit about 30 minutes before it would start. My problem also turned out to be the petcock. As much as it hurt, I bit the bullet, spent the 250 dollars for a new petcock, and all has been well since.

Dan