Fuel Starvation

[FJmonkey]

I lifted the tank, all was well. Then I rested the back end of the tank on some cloths. Also found a tube on the right going nowhere ( not fuel) and stuck it on the right side of the end carb. Irrelevant as its been off b4.
Prime. Choke. Start first time.
Prime off, choke still on. Fine. Revs rising. Choke off. Blip throttle.
Fine. No pops no bangs strong tickover.
15 minutes later, still running. Smooth revvy throttle blips. So carefull lowered the tank . Still running, no prob. I thought I'll go around the block. Out of driveway. Bottom of road. Stops. No start.
Someone helped be push it back up the road. I've got it on charge now and will try to repeat the process. Does that provide more info? Ta. Tony

So you confirmed that the fuel line is routed properly, good. Did you perform the suck test? This will tell you if the petcock and or vacuum line has a leak.

[copper]

Why is it on the charger, is there enough power to keep it running or is battery going dead?

[homerfj1100]

Not sure where to write this, above on below
Anyhow, no not performed the suck test yet. I'm wondering, as it did so well, with the tank raised an inch on some rags, that I could try and repeat it.
The battery is a month old but because of this particular problem it has been hammered.
I thought it a good idea to give it a fresh charge for more attempts at starting. Thanks. T

Why is it on the charger, is there enough power to keep it running or is battery going dead?

[FJmonkey]

Anyhow, no not performed the suck test yet.

Turn the petcock to off, lift the tank high enough to pull the vacuum line off of the #2 intake boot (the other end connected to the petcock) and suck on it. If it vacuum locks then all is good, if you can keep sucking then you need to fix this first. It may be a cracked hose so test the hose as well if you fail the suck test. It is possible that all this hassle is over $0.50 of vacuum line. And you don't need the battery for this test so get after it dude.

[homerfj1100]

When you say turn the petcock to off, you mean "on" don't you? Only 2 positions (I think) on and prime. I shall try. It looks to be an awkward job as the tank won't lift too high without pulling the fuel line off the petcock. T.

[FJmonkey]

When you say turn the petcock to off, you mean "on" don't you? Only 2 positions (I think) on and prime. I shall try. It looks to be an awkward job as the tank won't lift too high without pulling the fuel line off the petcock. T.

Oops, you are correct "On" and "PRI". If you have to disconnect the line from the tank then have a safe place for fuel to drain to while doing this test (I used an empty water bottle). You will know in the first 2 to 5 seconds if it passes or fails. A pass takes 1 to 2 seconds to get a vacuum lock.

[homerfj1100]

Okeedokee. I took the tank off then removed the vacuum hose from the carb. I don't think it had ever moved. There was a tear or split near the end. I attached it to the petcock and sucked the end. Fuel flowed out of the petcock. So the vacuum works. I cut the split end andcre attached everything properly. My problem now is getting the bloody thing running for more than 20 seconds. There's fuel, the vacuum works (unless the carb isn't making a vacuum). How long can I leave it on "prime", or should I? Thanks T.

[FJmonkey]

Okeedokee. I took the tank off then removed the vacuum hose from the carb. I don't think it had ever moved. There was a tear or split near the end. I attached it to the petcock and sucked the end. Fuel flowed out of the petcock. So the vacuum works. I cut the split end andcre attached everything properly. My problem now is getting the bloody thing running for more than 20 seconds. There's fuel, the vacuum works (unless the carb isn't making a vacuum). How long can I leave it on "prime", or should I? Thanks T.

The test is not making fuel flow.

You will know in the first 2 to 5 seconds if it passes or fails. A pass takes 1 to 2 seconds to get a vacuum lock.

Did you feel the that you could not suck any more? Or did you keep sucking air to keep the fuel flowing?

I could keep fuel flowing on my '86 but I had to keep sucking, air kept leaking in. It should feel like sucking on a straw with the end completely pinched off.

[homerfj1100]

Believe it or not the bike acted like bikes do. It started. And ran for 15. So threw my helmet on and turned right out of the gate. Uphill. Then left. Uphill. All OK except for that stutter on load that I don't think will go without a carb clean.
However, top of hill turned around and was thinking of going down to the petrol station.
I thought... Nah, I'll go back up the hill. It's very windy and my leg felt cold (and wet). Stopped. Fuel everywhere. Kill switch and coasted back to the house.
Yep the fuel line had come off. So, at least I didn't have to push this time! I need to secure that line with something better than the wire clip Yamaha provided.
T

[Miker]

Er thank you for the very speedy replies. Yes I have been fiddling like Nero. What started as a stutter is now no go. The thing is, the carbs fill in seconds when I turn to "prime". Then I turn back to normal or " on" I can't read it. So yes I replaced the fuel line. If it was pinched is it still possible to prime but then not function in the normal position. I must admit its a pain tank off tank on. A strange design.Oh, no filter. And took the ball bearing out of the cap...yes I had that problem I used to ride with a spare key in the cap. Ta again.

Will removing the ball bearing from the gas cap prevent a disruption with the gas cap ventilation system and guarantee the tank will remain at atmospheric pressure?  I am getting the fuel starvation issue with my '85 after about a half hour of 'enthusiastic' highway riding.  Thanks!

[Pat Conlon]

Is your fuel line routed correctly?
https://fjowners.com/index.php?topic=18286.0

[Miker]

Is your fuel line routed correctly?
https://fjowners.com/index.php?topic=18286.0

Yessir.  I've checked all the fuel starvation related boxes in this thread including rebuilding the gas cap.  I get great power through the rev range as well.  I get the stutter and bog after burning about two gallons.  I am going to ride tonight and leave the spare key in the cap so I can crack it when the bogging occurs.  My bike is a Cali model.  I removed the canisters and did all the necessary alterations, except fiddle with the gas cap beyond rebuilding it. 

[melloncollie]

According to the info in the thread below the bearing provides detent for the keyhole cover.  I believe you'd want to remove the flapper (orange piece) if venting is an issue.

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

[Pat Conlon]

The early 84/85 gas caps didn't have the flapper valves. They had a small ball bearing that acted as a 1 way valve. I took mine out. The Calif. model FJ's have a special sealed tank system that vented any tank vapors back into the carbs when the engine was running, and when the engine was off, vented tank vapors thru charcoal canisters. When you take this system off the bike I found that I had to modify the cap so to equalize internal tank pressures with outside pressures.

Miker you could be experiencing a failing vacuum petcock...a common problem. One moment fine, next, bam...no gas...
I have not had good luck rebuilding the vacuum diaphragms...I suggest you buy a new petcock from RPM before they are no longer available.

Cheers.  Pat

[Miker]

The early 84/85 gas caps didn't have the flapper valves. They had a small ball bearing that acted as a 1 way valve. I took mine out. The Calif. model FJ's have a special sealed tank system that vented any tank vapors back into the carbs when the engine was running, and when the engine was off, vented tank vapors thru charcoal canisters. When you take this system off the bike I found that I had to modify the cap so to equalize internal tank pressures with outside pressures.

Miker you could be experiencing a failing vacuum petcock...a common problem. One moment fine, next, bam...no gas...
I have not had good luck rebuilding the vacuum diaphragms...I suggest you buy a new petcock from RPM before they are no longer available.

Cheers.  Pat

Thanks as always Pat!  I'll remove the ball bearing.
Opening the gas cap didn't work. I'll check out the petcock from RPM.