Vacuum line fuel issue..

[dadofseven38]

So....here is a problem...

Vacuum line coming off of intake on the #1 cylinder for the fuel petcock valve, seems to be either not working, or not working enough. Bike ran well for a couple trips around the block, then just started backfiring, and running rough.  The petcock opens when I suck on the end of the vacuum line, and when I use a vacuum tester.  I also attached attached the vacuum tester to the vacuum line itself and drew about 75 psi of constant vacuum and the bike ran fine. ....

Petcock is brand new from RPM.

I replaced the vacuum line with new stuff from Autozone.

The vacuum tester showed about 50 psi pulsing as the intake valve opened and closed....so the petcock is not open all the time, only when the intake is...

Should I move the vaccum line to intake #2, or can I bypass it altogether and have the petcock open all the time....

Thoughts??

[T Legg]

It sounds like your petcock is ok.you can turn it to prime to get gas flow without vacumn. Does your petcock hold a vacumn? I've accidently had the hose come off when I was putting the tank on more than once.

[racerrad8]

It stopped running with the new vacuum hose or before you replaced it?

The factory hose is moulded as to not kink.

The vacuum at cranking is a significant pulse, but once the engine starts, the vacuum pulse becomes much smoother.

Randy - RPM

[Pat Conlon]

Travis....only our 84/85's have a Prime function on our petcocks, Jim has a '86.

Jim, did you install the oem electric petcock used on the '86?
If yes, then..
1) How much fuel do you have in your tank?
2) Do you know that when you get down to ~1/2 gallon, the low fuel sensor in your tank signals that electric petcock to close?  
3) You open that petcock back up by moving the rocker switch on the left side fairing cowl from 'RUN' to 'RES'

If that's not the issue, another common mistake is a pinched fuel line from incorrect line routing.

http://www.fjowners.com/index.php?topic=18286.0

Please report back on what you find.

Cheers

[FJ_Hooligan]

Could also be tank vent.  Next time pull over, shut engine off and open the gas cap.  Listen for an inrush of air. 

[dadofseven38]

Update!!!

After talking to Randy at RPM, I
took the original vacuum hose from the #1 Carb and cut off about 1/4 inch to get rid of a small crack....sprayed some carb cleaner into the vacuum knub and then shot some compressed air in it to clean it out.  I reattached the hose to the #1, then hit the starter a couple times, and SHAZAAM, fuel!!  So I connected the main fuel line, buttoned down the taken and she started right up!!

Thanks to all for the help, and advice!

Thanks Randy, you are the man!!

Jim

[dadofseven38]

It stopped running with the new vacuum hose or before you replaced it?

The factory hose is moulded as to not kink.

The vacuum at cranking is a significant pulse, but once the engine starts, the vacuum pulse becomes much smoother.

Randy - RPM

See update below!!  And Thanks again!

[andyoutandabout]

Yep, just imagine similar symptoms experienced at the side of the 101, some ways from home. A phone call, a Randy roadside remedy, a limp to Frank's house, a part in the post and the trip was saved.
Robert and Randy Rock. That's official.

[Alexis Wenzel]

Hey guys,
I have a similar problem.

On my 85, for some reason, the petcock vacuum is connected to cylinder 02, and the ignitor on cylinder 01.

Should I swap the lines to 01 vacuum and 02 ignitor?

[Pat Conlon]

No need, unless you want to....

[balky1]

Hey guys,
I have a similar problem.

On my 85, for some reason, the petcock vacuum is connected to cylinder 02, and the ignitor on cylinder 01.

Should I swap the lines to 01 vacuum and 02 ignitor?

Put them on 3 and 4 if you like it better that way. 

[Sparky84]

Hey guys,
I have a similar problem.

On my 85, for some reason, the petcock vacuum is connected to cylinder 02, and the ignitor on cylinder 01.

Should I swap the lines to 01 vacuum and 02 ignitor?

Put them on 3 and 4 if you like it better that way.  

3 and 4 are for the Right Hand Drive models  

[Alexis Wenzel]

Hahahahaha....you almost got me there, balky1! LoL

But, problem solved! Bike is running like a dream now.