Poor Running - HELP

[MPittma100]

Out of nowhere my engine starts stumbling from idle and will not idle unless you are on first stage of choke. I read exhaust temps with gun. Three are 150-170, one is 320 degrees. It appears to be missing on more than one cylinder. It seems to clear up at a higher RPM. Have changed plugs and one coil pack - but no change. Tried all the voltage/ohm tests in the manual and found no problems there. Could it be the ignition box?

MP

[natemoen]

Have you cleaned the carbs? Sounds like your idle circuits are plugged up.

[MPittma100]

Poor Running

I had the carbs off and rebuilt earlier this year. I don't think they have had time to mess up yet. Thanks

[GLoweVA]

I hate to say it, but yes the carbs can clog up easily.
Got inline filters?

[natemoen]

Who did the carb work? Very few people have had good luck with MC mechanics because these bikes are older than the people working on them and you just end up paying for them to learn about the carbs. Most usually end up with the bike running worse after getting the bike back...

I say the idle circuit needs cleaning. Time to pull them and clean them up. Check out the "Carb Cleaning 101" tech tip for a step by step pictorial

[James England]

There's 'cleaning' and there's cleaning! How well were they done? Did you do it yourself? Did you remove all jets, clean everything, blast air through holes etc?

It sounds like a carb problem to me.

[natemoen]

Also if carbs kits were used often they have the wring style pilot jet in.them and that causes problems with the low end.

[DAVINCI]

Ditto on all of the above, sounds like carbs. Sometimes these problems can show up seemingly 'out of the blue', but think about it...have you recently used reserve after not using it for a looong time? Yep, all that gunk in the bottom gets sucked in.

Good idea to run the reserve once in a while while on the highway. Keeps the bottom clear of water and whatnot. Filters help alot.

Don't leave it on reserve, though. DAMHIKIJK

[James England]

DAMHIKIJK

What does this acronym stand for?

[GLoweVA]

Don't Ask Me How I Know, I Just Know

[MPittma100]

Is there anyone who specializes in rebuilding these carbs properly?

[TopCatGr58]

Is there anyone who specializes in rebuilding these carbs properly?

Yep, almost every member on this Forum! That's not meant to be a smartass remark, but really the truth. Even if you sent the carbs to someone to work on them, you would still need to peform a proper vac. synch and further fine tuning to your bike/engine!

SO....this is why you just need to learn how to work on them yourself, they are not as scary as they seem. There's a great thread/tech tip with photos and everything to help walk you thru the tear down and cleaning process!

Read the tech tips...ALL of them pertaining to the carbs, repairs, maintenance, etc., and then DIVE IN.

Edit your signature to include the year/model of your bike for more specific tech info. The 1 cylinder sounds like it's got a clogged pilot circuit, lean=hot, and poor off idle throttle response and poor idle. Even the wrong type of fuel line can contribute to particles in the fuel getting into the carbs, clogging the small holes in jets, passages, etc.!

T.C.

[JeffH]

There's a great thread/tech tip with photos and everything to help walk you thru the tear down and cleaning process!

Read the tech tips...ALL of them pertaining to the carbs, repairs, maintenance, etc., and then DIVE IN.

Edit your signature to include the year/model of your bike for more specific tech info.
T.C.

As T.C. pointed out, we are not sure which XS year / model, but if you get stuck send me a PM. I'm willing to help resolve the issue so you can get setup for doing it next time when zoom-zoom goes to putt-putt-pop-bang. Where in Atlanta??

Jeff

[MPittma100]

Yes, I did them myself several months ago. New floats, one diaphram, new jets/kits. Synced all and idled and ran perfectly afterwards. Put 200+ miles on it on one May weekend. Just been on short trips since.

It was running fine a month ago. I am not saying that there is nothing wrong with the carbs, but it does not seem that they have had time to mess up. Then again, I don't know the "characteristics" of these carbs other than they seem to be very sensitive. Been adding K100 fuel treatment and running premium unleaded.

If I end up taking them off and apart again, is there something that I will specifically be able to see that is clogged up? This is a 1979 XS11 Special (SF).

There was an interesting find when I first got the bike. No. 2 cylinder had 100% leakage (no compression) by the exhaust valve. I removed the head and found the no. 2 exhaust valve face cracked almost completely around the circumference. Would not have been long till it would have fallen off. Noticed the other ehaust valves were completely white. I thought TOO LEAN. Checked carb inards and found smaller than spec. main jets (about 10 numbers) and rods were set to one lean position rather than standard. I asked around to see where these jets and rod settings may have come from. No one could tell me anything, so I simply put everything back to Yamaha factory specs. And it ran fine until most recently.

MP

[MPittma100]

Poor Running - Problem Solved!

Ok Guys,

First of all, thanks to all of you for your input concerning my problem. You all knew exactly what was wrong with my "poor running" 79 XS11 Special.

Took carbs off and removed bowls and pilot jets. Found that three of the jets had some "foreign material" in them. Cleaned the jets and passages and installed some filters. Runs like a champ. Good throttle response and perfect idle. No more popping through the exhaust and shutting off.

Thanks much,

MP