Crykie, need some advice Weird things afoot

[EvilScooby]

Well I surrender!!!

Capped off the vacum, ditched the frame petcock, adjusted floats again, adjutsted the mix screws, put a new throttle cable on...etc etc....

And still revs at 3-5k on her own when she wants. it sux at stops signs when she starts revving up like that, plus I almost killed myself pulling into my garage when she decided to reve up on me, almost crashed into the gas grill

Plus wife is gonna divorce me cause I spent my whole weekend working on it
Just going to throw her in the back of the garage and ride my Schwinn

:dunno:

[Flash]

I may be way off base here, but have you by chance checked the choke cable?

I had a problem with my RPMs jumping unexpectedly while idling, but mine were more prevelant when I would turn my handlebar right (conclusion: pinched choke cable). I re-routed it to give more play, but it was not 100%. I later discovered the outer protective sheath on the choke cable either melted or rubbed down to the point it would get stuck in the on position. I replaced the choke cable and it works like a charm.

[The Buddha]

Yes cable bind, choke and throttle, and valves. If you have a exhaust valve that;s too tight, it will act just like its sucking air in the intake... cos it is.
Cool.
Srinath.

[MarkusN]

I still haven't read if you did the WD-40 test somewhere down the line. That'll tell you if she draws false air. And your symptoms do somehow sound like that. (Not the "tank off fine, tank on bad" dealie, though. That one is very weird.)

[scratch]

Spark plugs tight?

[scratch]

They are acting the same on all positions,
With the tank off I can feel suction on the fuel lines wether its on, res or pri

If you can feel suction on these lines, than the diaphragm in the petcock has a hole and is sucking gas through the vacuum line!

[EvilScooby]

So your saying if when I remove the tank and start the bike. If I can feel suction on the fuel hoses that connect to the tank petcock then the frame petcock could be bad?

Hmmm

Anyone have a spare frame petcock lying around they want to part with?

[scratch]

Yes. What's happening is that the vacuum line draws in extra gas (through the hole in the diaphragm in the fuel selector/frame mounted petcock) and acts like a choke sending your rpm's up, drawing in more gas and then it floods and the rpm's go back down. With the tank on, the vacuum line has all the gas it can draw, flooding and bogging, but still drawing gas and acting like a choke, rpm's go up, it floods, bogs, cycles again, over and over.

[scratch]

Capped off the vacum, ditched the frame petcock, adjusted floats again, adjutsted the mix screws, put a new throttle cable on...etc etc....

And still revs at 3-5k on her own when she wants. it sux at stops signs when she starts revving up like that, plus I almost killed myself pulling into my garage when she decided to reve up on me, almost crashed into the gas grill

Now, here you stated that you capped off the vacuum. Did you cap off the spigot on the left carb? Or, just put a bolt in the end of the vacuum line?

Next, you stated that you ditched the frame petcock, this should have fixed your problem, if it was as I stated before, a tear in the diaphragm.

The rpm's cycling like that, up and down, means that something is opening and closing, dependent on vacuum and/or something like that.

[EvilScooby]

Ok

What i did was pull off the vacuum line from the frame petcock, put a bolt in the hose to block it, I did leave the petcock on the frame with the fuel hoses attached. Then I started her up and there was no difference.

Now here is my question, If you have the vacuum line connected to the petcock, wouldnt you feel some sort of suction on the hoses that connect to the tank? I would assume thats why its set up that way. I could be wrong, I'm no mechanic

[scratch]

No. The reason why is that the diaphragm seperates the vacuum line from the actual fuel delivery lines, so that fuel only flows when there is a vacuum being applied by a running motor. The floatbowls are vented to atmosphere and thus no direct vacuum should be acting on the fuel lines.

Now, if the diaphragm has a tear, such that it might be a flap, then the vacuum could draw gas through there making it rich, like a choke, but it is not metered in any fashion other than by the diameter of the hose (which is far larger than even the main jet).

Now you state that you put a bolt in the end of the vacuum hose. Did you inspect the other end of the hose to see if it wa cracked?

[Kerry]

Capped off the vacum, ditched the frame petcock, ...etc etc....And still revs at 3-5k on her own when she wants.

Oh.  I thought, when you said that you "ditched the frame petcock", that you had bypassed it entirely.  How about going the extra steps and seeing what you get?

1) Block off the hose from the ON outlet of the tank-mounted petcock.
2) Run the hose from the RES outlet straight to the lower T-connection between the carbs.

... OR ...

1) Hook the lower ends of both hoses from the tank-mounted petcock to a T-connector.  (This one is from Chaparral.)

2) Find the fuel hose that goes from the frame-mounted petcock to the carbs.  Detach the petcock end and hook it to the 3rd "arm" of the T-connector above.

EDIT: Changed link from sisna.com to bbburma.net

[Hi-T]

Wow Scratch- you're a pretty fart smeller...

Seriously,  I never thought about a problem with the diaphram- but it makes sense if he was sucking in extra gas through that vaccum port.

Cap the vaccum port on the right carb and run a straight line from the tank to the carb (remeber to plug one of the two fuel outlets from the tank).  In other words - Completely bypass the petcock.

[EvilScooby]

Sorry I did fib a little when I said I ditched the petcock. I was still using it but I unhooked the vacuum line and plugged it, thinking I could get by like that.

Going to try taking the entire petcock off tomorrow and give her a go.
I am working late tonight so I will nto be able to try it today

[Kerry]

Going to try taking the entire petcock off tomorrow and give her a go.

Go ahead and "give her a go", but don't take the petcock off yet -- just bypass it for now.  (See post above.)

If your problem disappears, THEN take it off.