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Vacuum line fuel issue..

Started by dadofseven38, April 16, 2020, 09:29:06 PM

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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??
Jim Richardson
2019 Honda Goldwing Tour
2012 Honda VFR 1200f
1986 Yamaha FJ 1200 project
1981 Honda CT110 Playa Bike

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.
T Legg

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
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


1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

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. 
DavidR.

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
Jim Richardson
2019 Honda Goldwing Tour
2012 Honda VFR 1200f
1986 Yamaha FJ 1200 project
1981 Honda CT110 Playa Bike

dadofseven38

Quote from: racerrad8 on April 16, 2020, 10:12:21 PM
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!
Jim Richardson
2019 Honda Goldwing Tour
2012 Honda VFR 1200f
1986 Yamaha FJ 1200 project
1981 Honda CT110 Playa Bike

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.
life without a bike is just life

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?
Cheers!

XIS

Pat Conlon

No need, unless you want to....
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

balky1

Quote from: Alexis Wenzel on April 20, 2020, 07:57:28 PM
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.  :biggrin:


FJ 1100, 1985, sold
FJR 1300, 2009

Sparky84

Quote from: balky1 on April 21, 2020, 05:43:16 AM
Quote from: Alexis Wenzel on April 20, 2020, 07:57:28 PM
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.  :biggrin:
3 and 4 are for the Right Hand Drive models  :lol:
1984 FJ1100
1979 Kawasaki Z1300
1972 Honda CB750/4 K2

Alexis Wenzel

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

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

XIS