Fuel Starvation

[homerfj1100]

All this is about a stutter under load and has turned worse.
Finally sorted everything airbox rubbers. New fuel lines
That's a fiddly tank to work on. Now I'm fuel starved. I used "prime" to prime carbs. Started first time. Good job I didn't go out. Engine splutter and stops. Re prime, starts no prob then stops. Repeat.There's enough petrol.
Something's not "sucking"? What do you think? Thanks. T

[FJmonkey]

Homer, with gravity feed fuel you have to have all the stars aligned to avoid problems. I too had starvation issues after years of flawless performance. The single most common issues are fuel line routing and fuel filter.

Use the search function, you will find pictures of proper and improper routing. The line that connects to the tank goes under the split lines after it winds around the top of carb #3. This looks wrong but it keeps the line from getting pinched.

Fuel filter, if you have one, take it off!!! The gravity feed system will work with a new filter most of the time, as the filter clogs the fuel flow is reduced and will cause what you describe.

Did you recently do any work on your filler cap? I had a problem after working on my fill cap, put a simple part in upside down. I should have tossed it.

Tells all recent work performed, it will help us help you.

[the fan]

FJ1100 has gravity feed and no fuel pump. From what I understand fuel line routing is pretty critical to avoid pinching or otherwise restricting flow. I am sure someone will be around shortly to explain the fix.

Another possibility is a plugged gas cap. Try running the bike with the cap open an dsee what happens. With a gravity feed system it does not take much to slow or stop the fuel flow.

[homerfj1100]

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.

[FjLee]

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.

For fuel to flow into and thru the system, with petcock in "normal/on" position, there hasta be gas in the tank.  There hasta be a correctly functioning petcock.  And, importantly, the engine hasta be running and supplying constant vacuum to the petcock.  It's vacuum supplied by running engine that "opens" the petcock when it's in on/normal position.


What the other guys have said is also applicable, especially abt. paying close attention to hose routing. 

FjLee            Lee Carkenord     84 FJ1100            Denver CO

[homerfj1100]

Thanks. So before I start playing with the petcock, sort out the lines. There may be no vacuum. There are so many tubes under there, some go nowhere, really, just to the outside. T.

[Bearly Flying]

Could be the vacuum diaphragm on the fuel valve, or possibly a build up of sludge on the internal screen of the fuel valve standpipe.
Pull the fuel valve out of the tank and check it.

[FJmonkey]

Perform the suck your petcock test.

http://www.fjowners.com/index.php?topic=9787.msg95549#msg95549

[homerfj1100]

That test sounds dreadful but if necessary I'm up to it Ta.

[FJmonkey]

That test sounds dreadful but if necessary I'm up to it Ta.

My '86 failed this test, replaced with an '84/'85, lost the reserve and gained the prime function.

[homerfj1100]

That's right. I have no reserve. I have a 'prime'. Could I simply run the bike on 'prime' ?. Would that be OK? It's obviously not correct. Interesting. T.

[FJmonkey]

That's right. I have no reserve. I have a 'prime'. Could I simply run the bike on 'prime' ?. Would that be OK? It's obviously not correct. Interesting. T.

The vacuum actuated petcock is an important safety feature. This stops the fuel from flowing when the engine is off. I would use prime if I had to to get home, but not all the time. Lets find the root cause(s) and fix them so your FJ runs as it should. Do the easy tests first. Verify your fuel line routing is correct.

I found the old thread that shows proper routing of fuel line.
http://www.fjowners.com/index.php?topic=9266.msg87760#msg87760

[homerfj1100]

Thank you so much. Of course there is a time difference. Here it's 11.40pm so it will be tomorrow when I check. Routing first, then other possibilities. I have to say, being English, in Spain, it's fascinating that someone from the US would make such valuable contributions. I was a teacher, not a mechanic. Thus, I know limited amounts of tech.
Why not try to keep my bike alive? I might as well.
There's an underlying simple answer to this. It's finding it that's difficult.
It's a fuelling problem. Got to be.
Let's give it until Saturday. If I fail, I blame myself. Thanks. T.

[Bearly Flying]

To check the fuel line routing, you have to lift your Tank. At that point, might as well take it off, drain it, pull the fuel petcock off the bottom of the tank and start from square one. There is a screen inside the tank on the Fuel Petcock outlets. It will have two different heights. The normal run outlet will be the higher one, the Prime, or Reserve is the lower one. Make sure the screen is clean.

In the Prime position the fuel valve is manually open all the time. In the normal run position, the vacuum diaphragm will shut the fuel off when the Bike is not running, otherwise you are depending on your floats and needles to seal completely in order to keep from flooding the engine with raw fuel. Causing a Hydrolock condition that can break shit, very nasty.....

If you have a Mitivac or even a chunk of hose and a good hard suck on the diaphragm to verify its function, could be a cracked diaphragm, or a pinched vacuum hose leading to it.

Then ensure the fuel hose is correctly routed and reinstall the tank.

[homerfj1100]

 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