#2 carb dead at idle

[Guest]

Just did a top end rebuild on my '80 gs850. Problem im having now is while setting the idle mixtures on the carbs with a colortune I noticed that #2 is barely firing at idle. If I rev it up it kicks right in. Others seem to be running pretty decent. I pulled the bowl off the carb and seems to be pretty clean. Float isn't stuck, and screen is clear. Just seems like its starving for fuel because if I introduce a tiny bit of fuel mist into.the carb while its running (via spray bottle) it kicks right in. What should I be looking for in.the idle circuit that could be clogged?

[tkent02]

Have you synchronized the carburetors yet? Have you seated the rings yet?

[bikerdave]

Yes the carbs are synched.. its ran for about 20 min. How long do I need to run it to seat in the rings? I was afraid to run it too long with the cylinder not firing right. The carbs are relatively clean inside but there is a little evidence of varnish. Do you think it just needs more time to seat the rings?

Have you synchronized the carburetors yet? Have you seated the rings yet?

[hjfisk]

Yes the carbs are synched.. its ran for about 20 min. How long do I need to run it to seat in the rings? I was afraid to run it too long with the cylinder not firing right. The carbs are relatively clean inside but there is a little evidence of varnish. Do you think it just needs more time to seat the rings?

If there is varnish showing then you need to clean the carbs. Also you say the carbs are synced, is that a bench sync or while running?

[tkent02]

How long do I need to run it to seat in the rings?

It's not how long, it's how hard. Open the throttle.

[bikerdave]

Only very minor staining in the bowl. The working parts are clean. I only had it running at about 2-3k. If I bring it up to 4-5k it kicks right in. Maybe the rings aren't broke in yet. They were vacuum synched before i tore it down. It ran good before the teardown but the lower jug gasket was leaking terribly. The bike had been sitting awhile and is higher miles so I just refreshed everything in the top end. And yes the valve clearances were checked and adjusted. I'm thinking I just need to run it in more. Because it seems to get better the longer I run it. Was just afraid to run it on a misfiring cylinder for too long.

[tkent02]

Only very minor staining in the bowl. The working parts are clean. I only had it running at about 2-3k. If I bring it up to 4-5k it kicks right in. Maybe the rings aren't broke in yet. They were vacuum synched before i tore it down. It ran good before the teardown but the lower jug gasket was leaking terribly. The bike had been sitting awhile and is higher miles so I just refreshed everything in the top end. And yes the valve clearances were checked and adjusted. I'm thinking I just need to run it in more. Because it seems to get better the longer I run it. Was just afraid to run it on a misfiring cylinder for too long.

Take it for a good hard ride. Open and close the throttle. Once the rings have seated synch the carbs again. The previous synch is null and void once you put in new rings or even adjusted the valves.

[bikerdave]

Ah ok. i will try that thanks!

[Steve]

Yes the carbs are synched.. its ran for about 20 min.

How long the bike ran has very little to do with carb sync. As long as it is warm enough to not be running on "choke", you are OK.

The carbs are relatively clean inside but there is a little evidence of varnish.

"Relatively clean" does not cut it. They need to be PERFECTLY clean. The parts that NEED to be clean can not be seen for inspection, and they are the ones that affect idle and low-speed operation the most.

Only very minor staining in the bowl. The working parts are clean.

The bowl can be terribly "stained" and the bike can work perfectly, so that is NOT an indicator.
What are you calling "working parts"? As mentioned above, the parts that NEED to be clean can not be seen and can not be removed for cleaning. You need to do a full "strip-and-dip" cleaning, followed by a new set of o-rings.

I only had it running at about 2-3k. If I bring it up to 4-5k it kicks right in.

Sounds like a very BAD carb sync or clogged fuel passages inside the carb. 4-5k RPM in neutral is still pretty much on the idle (pilot) circuit.

They were vacuum synched before i tore it down.

And how many times do we see ads in the paper for a bike that "ran well before it was parked"?
The very fact that you have "refreshed" the upper end (rings? valves? carbs? whatever?) will change the amount of air that each cylinder can breathe in. The carb's throttle plate needs to be adjusted to match, so you need to re-sync the carbs. As tkent mentioned, even a valve adjustment requires a carb sync, and you have done so much more.

.

[Maddevill]

You need to remove the pilot jet and clean it and the passage it sits it. Unfortunately, you'll have to pull the carbs to get at that one.

[tkent02]

Pulling the carbs is super easy on an 850. May or may not need it. A poor idle is a minor inconvemnience. Much more important is to seat the rings while its still possible. Run the crap out of it, opening and closing the throttle. Worry about the idle problem later.

Poor compression forever because you didn't seat the rings when they were new is a much more serious problem than a little rough idling and running on three cylinders at low power

If you don't get it, read this:

http://www.mototuneusa.com/break_in_secrets.htm.

[bobgroger]

The pilot jet (the one under the rubber plug) has a VERY small hole in the end. With the ethanol crap gas we get now it takes only months to plug those up. I am trying Sta-bil in every tank to see if it helps...

[tkent02]

Do you park it for months on every tank?

[bikerdave]

Heres the whole story... Got the bike as a project. It was sitting almost 5 years. First thing I did was dismantle and rebuild the carbs, synched and tuned them and it ran OK. Then rode the bike for a season. Near the end of the season the lower jug gasket began leaking badly. The valve seals burnt oil a bit and it has some miles on it. First top end rebuild I've done. Messed with carbs plenty of times on my old gs550. Anyway, replaced the valve seals, cleaned and relapped the valves, had jugs checked for clearance and runout an honed. Installed new rings. New gaskets, had to order some smaller valve shims due to machining the valves a bit. Now that its all back together I'm having what seems to be fuel delivery issues. haven't done much with the carbs besides inspection since the first rebuild. But when I say relatively clean I mean all the brass workings are spotless only the bowl has some yellowing that won't come off even after hot dipping and scrubbing. I don't see it being my issue. the pilot jets are clean as a whistle. Though I wasn't aware that the ring breakin was done by running the bike hard. I've always done car engines and your taught to run them at cruising speed for about a half hour. Which I've done and #2 seems to lean out and die off when the bike gets down below 3k rpm. But the more I run it the better it seems so you may be onto something with the rings not being seated. I'll also recheck the synch. I wad just attempting to set the mixture first because it seemed like had no fuel. I pulled the carbs back apart and went back over them. Seem to be ok. But I may resoak #2 just to be sure.

[bobgroger]

Do you park it for months on every tank?

If you were responding to me, I thoroughly cleaned the carbs in May. The pilot jet was plugged again by September. There were multiple tanks run through it over the summer. On disassembly over the winter, there was an abundance of white chalky corrosion which I am assuming is from water after only 4 months. I am now adding Sta-bil to each tank to see if it makes a difference. Where I live we have to use ethanol added gas all year, 8.5% in Winter and 10% in the summer. Add the condensation from 8 months of rain a year in Seattle and at least for me it is annual carb cleaning. I pull the Vacuum line from the petcock and run the gas out if I am anticipating extended time without riding. Maybe different in other areas or fuel blends....