Crazy Carbs

SRDESIGNER · Full Member Joined: Jun 05, 2008 Posts: 31

I've been around and around with these 1980 carbs trying to get the bike to run the same way twice. One day it runs the next day it won't. Sometimes I get it running ride it up the road seams fine and then a couple hours later it won't even idol.

One carb won't run on it's own unless I start with both and then pull the plug wire off the other, even then it doesn't run well. I've cleaned the idol jet and have them turned 3 out.

If I could keep it running for a little while I'd start my next phase of learning how to tune/sycronize & all that stuff. But I just can't seem to get that far...

What are the symptoms of a bad diaphram?

A couple times another phenominon has occured, where I get it running and while the choke is still on the motor races up to 4k and I shut it down quick as this scares the crap out of me. I have verified that the butterflies are not opening further and ther throttle cable is not the issue as it's occured with the cable off. The springs are intact and working good and I manually reached down and pressed with my figure to assure that they are in the idol position...this symptom really blows my mind. It's just so random.

I've read EVERY single post on this site in the last two days and I'm more confused that ever.

Thanks in advance for any help.

SrDesigner

killtrip · Posted: August 24, 2008, 3:46 pm Post subject: Re: Crazy Carbs

If you wanna give me a call, I've got a few hours to kill.. I could prolly come out to your place and look at your carbs if you want..

As for the symptoms of a bad diaphragm, I dunno... they should be easy to visually tell if they're bad though. just hold them up to the light.

did you ever take out the needle jets and clean them up?

mcaiki · Posted: August 24, 2008, 11:39 pm Post subject: Re: Crazy Carbs

"What are the symptoms of a bad diaphram?"
She's pregnant. (Sorry, I just couldn't resist.)

OK, so where did you start with this issue? Was this running well before and then something changed? Sounds like the carbs might need to be pulled and cleaned out at the very least. You may just see something in that process and it will all become clear.

Is the compression OK? Is the valve lash properly gapped? Is the timing close to where it should be? Are your advance timing weights seized up or are the springs too loose? All of this can contribute to the problem you describe.

The thing I like the most about my XS is that it is so easy to work on and it's pretty low maintenance. The carbs will come right off and out with very little fuss if you still need to do so after checking the other items.

tweedy64 · Posted: August 25, 2008, 5:19 am Post subject: Re: Crazy Carbs

Theres an easy way to check your diaphrams are ok while carbs are in situ. Lift the slide and on the intake put your thumb over the top hole now drop the slide she should drop real slow if not your diaphram is damaged but make sure your thumb covering the hole real good. one minute job. cheers tweedy

Joseph · Full Member Joined: May 22, 2007 Posts: 767 Location: NY

I have an 80 same thing with the choke if I leave it on the rpms climb. When they get nice and warm it changes the idol speed. I don't think that is a sign of something wrong.

weekendrider · Posted: August 25, 2008, 9:48 am Post subject: Re: Crazy Carbs

A symptom would no increase in rpm as throttle is increase. An easy way to check is remove air filters use a mirror to "look" back into the carbs as you increase the throttle(motor running) the slides/needles should raise.

SRDESIGNER · Full Member Joined: Jun 05, 2008 Posts: 31

Thanks for all the devine wisdom ya'll! I haven't had a real chance to try any of the suggestions due to a loss in the Family. As we get back on our feet I'll get back in the shop and try to apply all my new-found wisdom.

I'm expecting parts from Mikes XS on Thursday and should be able to play around a little by the weekend. I'll just keep plugging away till something/anything gets better.

Thanks again for all your assistance,

SrDesigner

mcaiki · Posted: August 27, 2008, 8:49 am Post subject: Re: Crazy Carbs

Sorry to hear of your loss. Sometimes having a bike to work on is a nice distraction. Obviously it can't change things, but it's something else to focus on.

Hopefully when you get back to it, you will find that it's not your diaphrams. They aren't cheap. You could try running some seafoam through the system in a tank of gas and see if that helps. It may be a cheap fix if it just needs a little cleanup.

God Bless.

killtrip · Posted: August 27, 2008, 6:40 pm Post subject: Re: Crazy Carbs

best wishes to you and your family..

for future reference, when I needed new diaphragms, I looked at mikesxs site, and they are $60 a pop there.. $120 for the pair of carbs. Not bad, considering local shops charge almost $100 each here.. that I checked out anyways.

I went on ebay and found a pair of used, but good condition carbs for $75. came with flawless diaphragms. as well as a bunch of other parts that I could use (jets come to mind)

What Happened to 650rider.com?

Yamaha xs650