If the vacuum line is the one connected to the fuel tap, then this will not allow the tap to open properly/fully if it is leaking or has a hole in it. Modern fuel taps don't release fuel to the carbs until the engine is turning, causing a vacuum to the tap which then opens a diaphram, thereby releasing fuel to the carbs. Hope it is this simple a solution for you!

 

Me and Dad pulled the bike apart today, cleaned out all the carbs, jets, valves and that. Put it all back in and it was running very smooth Better throttle response, and no more flat spot when I give it all I can in neutral. Started the bike with choke, and it started up fine, took it for a test ride, so I set the fuel cap on, and went down the street, the bike seemed fine, but on the way back, the bike started stuttering again, and it sounded like the whole bike's noise was different.. Like it was fighting to stay alive. I managed to get back. I waited a bit, and told my Dad what had happened, and he said try putting the fuel cap on Reserve, I did so and went down the same street and further without any problems.
Any idea on what the problem is?
I told him it might be a R/R problem, but he said the starter motor wouldn't work if it was that.

 

Check the screen on the inside of the tank. If it is a single reservoir (probably, most are),
the petcock just uses two different height straws to draw gas from the tank. if the top straw is clogged, it might starve the bike, when you switch to the (rarely used) lower
straw it gets the fuel it needs. Based on your description, you might try, draining the tank, remove the petcock from the bottom and check the filter-screens.

Ern

 

Okay thank you. Will do so when me and Dad have some spare time. I noticed the bike idles on 2100 RPM's when the bike is warmed up and on Reserve, but when it is warmed up and on, the bike idles at 1500-1600 RPM's. Will check the straws and let you know if the problem is fixed

 

i had same kind of deal was riding and started jrking i new i was low on gas so put petcock to revs and when i open up the throttle its got no power and the revs creep up to 7-9k rpm then it starts to get faster but gose back when u change gears ne i deal wot it could be ne one ???

 

Hey guys, have been pretty busy lately, but thought I would update you on the bike.
When we cleaned out the Carb's it was still giving me problems, and it has been around 4-5 months with it still playing up.
I have cleaned out the air filter, changed the spark plugs, cleaned out the bowl area of the carbs I think it was.

But the bike is still cutting out. I rode with the fuel off once, and when it eventually dies it has the same symptoms as if I was riding with it on Reserve when it cuts out.
After it dies, I pull the choke cable up and try to crank it over until it starts, after about 2-4mins the bike starts up again, but has a very weird sound to it, and it is unable to achieve full power and tries to lose it's idle just like it is running out of fuel.
Any Suggestions?
Thanks!

 

Oh yeah also a note, the bike had been having some rough idle (it wasn't able to hold it's idle without me revving it) and then I ran some carby cleaner through my fuel, and the idle was perfect. The bike wasn't cutting out or anything, she was running perfect. But today I was riding and had lowish fuel and she cut out again.. I don't want to keep putting carby cleaner in my tank just so it runs fine..

 

You might try pulling the tank and then removing the petcock. There is a filter on it,
that sticks up into the tank. If it is dirty, it might be restricting flow when you get
near the bottom of the tank.

Drain the tank, pull the petcock. Clean it with an old tooth-brush and kerosene.
DO NOT use gasoline as a cleaner/solvent...that way lies madness and pain!

Kerosene is safer, due to it's low flash-point. After cleaning the filter,
pour about a quart of kerosene into the tank and swirl it (to remove any sediment).
Drain that through a painter's filter and save for re-use.
Re-install the petcock/tank re-fill with fresh gasoline.

Hope this fixes the problem, Ern

 

Mine is an older model so it's just the fuel ****, it doesn't have the diaphragm and all that other stuff. I did empty the tank though and found alot of dirt/rust in the bottom of my tank which is maybe blocking it up while I ride?
Am going to clean it tomorrow and will let you know how she runs!

 

Tank is all clean but still running bad. Have to use choke every single time to start up (maybe due to coldish weather). But everytime I start the bike up with choke, the idles do not go up to 4k anymore, they just stay around 2. And it makes a really strange sound like the carbs are flooded when i start it. I'm beginning to think it's my carby's again? Maybe something is wrong with them? I know they need a good tune, do you think this is the problem?