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Can a petcock causing high idle ????

  • Thread starter Thread starter Jeepijee
  • Start date Start date
J

Jeepijee

Guest
hi all,

I did a rebuild on a gs 650 gl 1982 usa model
I cleaned the crabs have new intake boots O-ring
the O-rings from Robert Barr etc. etc.
I did all by the book and still I have a high idle :(
is did the spray test and i am pretty sure its no vacuum leak on the carbs
I guess its my petcock failing but before I replace this I want to know if it is possible that a bad petcock causes high idle :confused:
it runs on 4500 rpms
and i am on the end of my alphabet after 6 months working on it i wanna ride it before the summer ends
pls help ...
grtz Rider from Belgium
 
A few thoughts to check - does the idle drop as you unscrew the idle adjustment in the rear middle of the carbs? Have you checked your throttle cable to make sure it's not hanging up?
 
Also check to make sure your "choke" cable is fully disengaging at carb end- the plungers must retract fully or idle can go crazy. Make sure choke bracket at carb end is correctly positioned to let them fully retract. It's hard to tighten those clamps on old boots ,so recheck them.
 
Have you synced the carbs after the rebuild? I had nearly the same thing, a simple sync solved all woes.
 
After all of the above: A quick check to make sure the petcock is not your problem is to put it on prime and plug the vacuum line. That effectively removes the vacuum port on the petcock from being a factor.
 
Unplug the vacuum line at the carb and suck on it to see if it holds vacuum. You might get a little gas in your mouth if it doesn't. That would indicate a leaking diaphragm which will also fill the crankcase with fuel when the bike sits overnight. The cylinder the petcock draws vacuum from will also be running rich.
 
ty for all replies,

mb a bit more background..

the bike is being neglected for 4 years and it didn't started when I got it ..
after a rebuild of the carb still didn't started cus of a weak spark so I did a
full electrical system clean up with a relay mod started up right away after
that (imagine my happiness) with high idle speed thou ...
so I looked further
and though I would be the intake boots and O-rings so I replaced that with new ones
and started... it didn't make any difference so I ordered the o-rings from Mr Barr and then it started with 1050 rpm for 5 mins (woohoo)
but I turned it of switched the petcock to prime and there it was again 4500 rpms
so from there I posted this tread cus It had to be something with that ...
now after stand still al night it starts with 1050 rpm and goes up when it warms up ...
the throttle cable is working perfectly and I bench sync the carbs... also the choke goes in and out to the end ...
I will do that petcock vacuum check later today cus I got a shop and I can't smell as gasoline right now..
ty again for the replies...

if I may say I did all the changes mods improvements on the bike only reading this site and it got me a long way so far
and i'm pretty sure the answer to finish my project is here to .. keep up the good work !!!
 
Last edited:
Billy Ricks said:
Unplug the vacuum line at the carb and suck on it to see if it holds vacuum. You might get a little gas in your mouth if it doesn't. That would indicate a leaking diaphragm which will also fill the crankcase with fuel when the bike sits overnight. The cylinder the petcock draws vacuum from will also be running rich.
Click to expand...


did that and it still works fine I can hear it open and closing when I suck it
 
I disconnected the vacuum line and switched the petcock to prime and the idle fell down to where it should be. I smelled the crankcase oil too and noticed a strong fuel smell. Confirm the rich condition on the plugs as well.
 
Not sure if its still relative considering the petcock-to-prime thing but I'd definitely recommend a vacuum sync of the carbs. I bench synced mine and had a high idle after total carb rebuild with new rings and intake rings - that was remedied by the vacuum sync.

I used this set-up with great success.
 
ty guys;

i'm starting to have doubts about my vacuum line now..
I guess its old and a bit oversized.. i'll fix that and I'll do the bottle
sync too .. I saw vids on you tube about it too ..
i'll let you know how it turns out...
ty have a nice day :cool:
 
taaadaaa :)

high idle gone it just run for more than 25 mins on 1000 to 1100 rpms
I had to quit because it got scared it would get to warm and catch fire somehow... I changed the vacuum line and a new gas line and with my tank on my steering wheel
is could easily work on the carbs while it was running...
now a new question to sync the carbs is there a way to follow to vacuum sync ??
at start I saw carb #4 was way out of line with the others sucking the fluid all up :| never the less I could adjust it to the others (a bit)
but to fine tune and all get synced that is not easy ...
so if there is a guideline to follow I'd like to now ...

thx to all.. I see myself riding my bike in the nearby future :clap:
 
Be sure to use a big fan when you run your engine like that. Before I do a vacuum sync, I adjust all the pilot needles to best idle, then finish off with a vacuum sync. It does take a bit of practice and changing one carb sometimes changes another.

I would still investigate why you have gas smell in your oil. You might have a leaky fuel valve or float needles.

V
 
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