1986 xt 600 backfires

10 replies to this topic
  • f1ford48

Posted March 30, 2012 - 05:22 PM


just got a [build date 12 85] xt 600 running. first thing I did was a carb overhaul. the bike started up on first kick with carbs redone but pops at idle and all the time. it will stay running when warmed up. but has intermittent back fires. the 2 inlet manifolds on head are brand new as well as o rings. bike seems to have full power but pops all the time. also smells like its running lean- gets hot fast.there do not seem to be any adjust screws outside of carb except the idle wheel. any help would be appreciated. bike has 16 k miles on odo.

  • pd350

Posted March 30, 2012 - 06:21 PM


All the time ... does that mean through the complete RPM range , under load or free revving , both ?

Are you running stock jets ? stock exhaust ? Any other modifications ?

On the primary carb , there is a pilot screw located just in front of the bowl . There is a cap covering the screw . Try resetting the screw to 2.5 - 3 turns out from lightly seated .

That might help the idle and very low end . What are you running for an air filter ? stock filtration set up ? Any at all ?

  • f1ford48

Posted March 31, 2012 - 02:35 AM


Thanks for your reply- the bike appears totally stock as far as muffler and filter box. I doubt the carbs have had any thing changed. it pops at idle -when you rev it the high rpm tries to cover the pops- under load bike has lots of power but not running smoothly.letting off throttle popping comes back. if I touch side of carb I can feel the popping in sync with the noise.
I will adjust pilot screw and get back to you and thanks again

  • f1ford48

Posted April 03, 2012 - 04:10 PM


there is no pilot jet adjustment- in front of the float bowl is a pencil sized drop in the casting -it has a brass plug-looks permanent-has a pin hole in it. bike still runs crappy- somebody help! this bike is in great shape and its got to run right!!!

  • pd350

Posted April 03, 2012 - 08:00 PM


The pilot screw is covered by that brass plug . The plug is not very thick . Carefully drill a hole in it and pop it out . Then you'll be able to adjust the screw .

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  • f1ford48

Posted April 04, 2012 - 07:43 AM


I figured it was something like that .bike has gone back to its owner so it will take me a week to do it and get back with the results. after more cleaning of the tank and petcock it ran some what better . are there any other causes as to why its not idling smooth- should the valves be adjusted? obviously this is a total stocker and has had no mods whatsoever THANX

  • pd350

Posted April 04, 2012 - 11:38 AM


It sure wouldn't hurt to check the valve lash .
The specs for my 350 are :
Intake : .003" - .005"
Exhaust : .005" - .007"
I would think they would be very similar if not the same for the 600 .
I suppose it's possible that the idle circuit is still a bit dirty . Is there an in line paper fuel filter ?

Edited by pd350, April 04, 2012 - 11:42 AM.

  • rzxt350

Posted April 04, 2012 - 02:07 PM


I just rebuilt my 1993 xt350 about a month ago and after the rebuild mine was doing the same exact thing that you are describing . I took pd350's advise on the pilot screw adjustment and now it runs the way it's supposed to. Do the valve clearance checks as that is very important. Good luck and keep us posted on the results.

  • f1ford48

Posted June 03, 2012 - 09:46 PM


Thank You everyone- yes that was the problem-someone had also taken off the smog equipment-dont know if that had anything to do with it. bike runs excellent now. it takes a bit to idle down [probably sticky cables] again thanks for a great site!!! :cry:

  • f1ford48

Posted June 03, 2012 - 09:49 PM


Thanks PD350!!!!!

  • pd350

Posted June 04, 2012 - 04:05 AM


Good , you got it sussed . :cry:


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