1986 Dual carb XR600 idle problems


8 replies to this topic
  • StevensXR

Posted April 18, 2009 - 06:18 AM

#1

Hello-

I tried the 'jetting forum for this problem, with no luck, so hopefully someone here can help out.

My buddy has an '86 600r that seems in decent condition. It had been sitting for a while, and it supposedly ran before he got it, but not too well. It had a stock intake with a crappy, filthy K&N type filter, stock header with White Brothers "supertrapp" style exhaust with 12 discs installed and 45 pilot, 125 main 1.75 turns out on the air screw, needles @ 3rd slot.

I took the carbs apart, cleaned all passages with cleaner and compressed air. Removed the jets and cleaned and inspected them and found no issues. Assembled carbs, installed a new stock air cleaner and put in fresh fuel.

I could not get it to start. No spark. Traced the issue to what I thoght might be the stator, and my buddy just happened to get a free Ricky Stator with the bike, so I installed that, but still no spark. Put an Ohm meter on all electrical parts, and found the exciter not in spec. Replaced it with a new unit.

Full choke, TDC, kick and it fired first try! Great! I let it run for a bit, then knocked the choke down to mid point, it still ran okay. Pushed the choke off, and it immediately started to cough and pop until it died. Did the whole procedure again, with the same results. Sounded like a lean condition.

I took the carbs out, disassembled, cleaner, compressed air, etc. Installed everything back in and it fired and ran great on full and mid choke, but stumbles and dies when the choke is off.

So, we got a 48 pilot, 128 mains and I once again tore the carbs apart and THOROUGHLY cleaned them. I tore everything I could off the carbs and inspected each part for issues, slides, air valve, jets, etc. I replaced a couple of O-rings on the tubes that cross between the carbs, but everything else seems okay.

Fired and ran great on choke, but once again popped and died off choke. I had someone keep the bike running off choke with the throttle while I sprayed starting fluid and choke cleaner around the carb plates, expecting a vacuum leak, with no results.

I am deserate at this point. I checked timing, I have checked and set all the valve lash, I even removed 6 discs from the exhaust with no change. The bike runs great on full and mid choke- no hesitation, absolutely not 1 ounce of smoke, and the sparkplug shows almost black (but I cannot do a true plug chop because of the idle condition)

The 48 pilot is the largest made for the carbs that we can find, but I can't imagine this needs a bigger pilot- I feel I am missing something in my trouble shooting.

Any ideas other than removing the gas cap and parking a new bike under it?

Thanks!

  • Horri

Posted April 18, 2009 - 01:33 PM

#2

Hmm,,Sounds pretty similar to the way my XR600 runs or ran. If I start my bike I cannot really take the choke off for a least a couple of minutes or it will probably give a fart through the carb and die. Now before the carbs were reconditioned it did the same but worse. Internals of carbs wear out..needles,Jets etc. Their is an Air Cut off valve on the side of one of the XR carbs. Its behind a plate which is held on by three small Philips head screws. Take it off and inspect the Rubber manifold behind it for holes. Hard for me to tell you what other parts needed replacing in mine as I didn't personally do it and without looking in a manual I don't know their names. Start at the Air cut off valve anyway.

  • StevensXR

Posted April 18, 2009 - 05:29 PM

#3

Hmm,,Sounds pretty similar to the way my XR600 runs or ran. If I start my bike I cannot really take the choke off for a least a couple of minutes or it will probably give a fart through the carb and die. Now before the carbs were reconditioned it did the same but worse. Internals of carbs wear out..needles,Jets etc. Their is an Air Cut off valve on the side of one of the XR carbs. Its behind a plate which is held on by three small Philips head screws. Take it off and inspect the Rubber manifold behind it for holes. Hard for me to tell you what other parts needed replacing in mine as I didn't personally do it and without looking in a manual I don't know their names. Start at the Air cut off valve anyway.



I did take the air valve apart. Held it up to a light and checked for rips and tears, it is in excellent condition. The interior of the carbs looks good, not worn out at all.

Thanks for the idea.

  • applachin86xr600

Posted April 18, 2009 - 05:43 PM

#4

i just built a 86 xr 600 that was in five boxes completely disembled a basket case. the o rings on the two tubes that conect the carbs dry rot . the carb will suck air ,run lean and be impossible to tune.

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  • StevensXR

Posted April 18, 2009 - 06:31 PM

#5

i just built a 86 xr 600 that was in five boxes completely disembled a basket case. the o rings on the two tubes that conect the carbs dry rot . the carb will suck air ,run lean and be impossible to tune.


Yes, I replaced two of the o-rings that were questionable, no change. I spray carb cleaner, WD-40 and starting fluid all over the carbs trying to get a vacuum leak, with zero results.

I have been fighting it for a while, I can get it to run at a good idle with the choke at mid-point, it will have to stay that way.

Thanks!

  • Onederer

Posted April 18, 2009 - 06:44 PM

#6

Might cause a problem if someone set the carb linkage to open both carbs together. If the second cab opens at the same rate as the primary carb from completely closed, then the second carb could be slightly open as the idle is adjusted from the the primary carb, causeing a lean condition. The second carb slide should'nt move until at least past 1/4 throttle. Of course once off the idle circuit it might seem to run ok. Something to look at anyway.

If that year has the decompression chamber and the fifth valve, that vavle may not be seating properly or the cable to the kick start that works the valve could be out of adjustment, on the tight side.

  • Quadracrack

Posted August 14, 2013 - 05:19 AM

#7

Might cause a problem if someone set the carb linkage to open both carbs together. If the second cab opens at the same rate as the primary carb from completely closed, then the second carb could be slightly open as the idle is adjusted from the the primary carb, causeing a lean condition. The second carb slide should'nt move until at least past 1/4 throttle. Of course once off the idle circuit it might seem to run ok. Something to look at anyway.

If that year has the decompression chamber and the fifth valve, that vavle may not be seating properly or the cable to the kick start that works the valve could be out of adjustment, on the tight side.

Why would someone set the carbs that way?  Is there a power advantage?  Whats the trade off?  Reviving this thread from the dead...



  • Onederer

Posted August 15, 2013 - 09:17 AM

#8

Why would someone set the carbs that way?  Is there a power advantage?  Whats the trade off?  Reviving this thread from the dead...

 

If you talk to someone who has modified the carbs to open synchronously, ask them, your guess is as good as mine.

 

There is no power advantage and on anything other than a full race engine, which is actually being raced, it will cause ridability problems and lower fuel economy.

 

I am not aware of any aftermarket company selling carb kits for the XL600R, but I remember reading about someone who modified two newer carbs to work. Maybe it was here; search.

 

Sudco does sell a Keihin 31mm and 33mm  dual carb kit for the Yamaha XT600 which had a similar dual carb setup. Here is a post from a person who used the kit: http://www.thumperta...carburetor-kit/

 

I am not experienced with the XT600, a search should reveal if the Yamaha OEM setup was progressive, the Sudco kit isn't.


Edited by Onederer, August 15, 2013 - 09:18 AM.


  • Muzz67

Posted August 16, 2013 - 01:09 AM

#9

Have you set the pilot airscrew correctly? Or tried turning it out one complete turn ?







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