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Tarheel34
  • Rank:XL Board Member
  • Posts:6
  • From:USA

Date Posted:05/11/2016 12:06 AMCopy HTML

Recently bought a 73 XL175 project.  Bike had been sitting for a long time.  Cleaned tank, took apart and completely cleaned and rebuilt the carb with Keyster kit, replaced petcock, new plug, charged battery.  The issue I am having is that when I start the bike up, with the choke open or closed, it immediately revs to high rpms and stays there.  If I hit the throttle it will rev a little higher but then returns to where it was. i never get anywhere close to what would be considered an idle.   I adjusted the position of the clip on the jet needle, adjusted the throttle cable, the slide seems to be functioning properly as far as I can tell.  I also adjusted the air and idle screw to different positions but it makes no difference since the bike is running at such high rpm's.  I'm not sure what to do next.  Everything I have tried has left me with the same result.  Any ideas would be appreciated. 
GB500guy #1
  • Rank:Gold Member
  • Posts:179
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/11/2016 1:27 AMCopy HTML

The problem has to be that the throttle slide is not closing. That can happen if there is no free play in the cable or of the slide is installed backwards - the long thin slot in the slide should be on the right, opposite the idle speed screw. To check free play, slide the rubber boot on the top of the carb up a bit, then make sure you can pull the throttle cable outer casing up at least 1/8" freely (without feeling the throttle slide spring). If there is no free play in the cable, run the cable adjuster on the carb top down and/or adjust at the handlebar end until there is free play. Also make sure there are no kinks or internal damage in the cable by disconnecting it at the carb end and making sure the inner cable moves freely with no hangups.
Then confirm that the throttle slide is hitting bottom in the carb body by twisting the throttle open, then snapping it closed quickly. You should hear a knock as the slide hits either the idle speed screw, or if the speed screw is backed way out, the slide will knock against the bottom of the carb body itself. You can also check visually by pulling the carb and looking in from the engine side. With the idle speed screw backed all the way out, the slide should rest against the bottom of the bore. If it is raised up at all then there is some mechanical hangup in the slide or carb bore, or no free play in the cable. 

One other thing, aftermarket carb kits do not always match original parts. Make sure the needle jet is installed right side up, and does not protrude too high into the carb bore. Hope this helps,

-Bill 
Tarheel34 #2
  • Rank:XL Board Member
  • Posts:6
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/12/2016 11:13 PMCopy HTML

Here's an update.  I tried what was suggested above and determined that the slide and throttle cable are working properly as far as I can tell.  I am now able to get the bike to idle with the choke all the way closed, however, as soon as I open it the littlest bit it immediately revs to the high rpms.  When the choke is closed and it's idling if I give it throttle I get nothing, just sounds like its about to choke out.  I tried putting some grease around the choke cable at the top of the cap and around the intake and gasket to seal it up and see if it was sucking air there but it changed nothing.  I sprayed some brake cleaner around the head gasket and intake while it was running to see if I could notice any change but again nothing.  I'm not sure where to go from here.  Any suggestions would be appreciated. 
GB500guy #3
  • Rank:Gold Member
  • Posts:179
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/12/2016 11:44 PMCopy HTML

 So you are saying that when you remove the carb and look in from the engine side, the throttle slide contacts the bottom of the carb throat? I still say that is not happening, if it were there would be no way for air/fuel to enter the engine.

-Bill
Tarheel34 #4
  • Rank:XL Board Member
  • Posts:6
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/12/2016 11:54 PMCopy HTML

nm
Tarheel34 #5
  • Rank:XL Board Member
  • Posts:6
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/12/2016 11:57 PMCopy HTML

In rereading your post I see you are suggesting I look in the carb from the engine side. I was looking in from the air cleaner end and trying to see if the "sides" of the slide were contacting bottom.  I have been looking at it wrong and need to go back and reevaluate.    I guess it would help if I read your advice correctly the first time.  So when I do look from the engine side I should see absolutely no gap at all between the slide and the bottom?  Even with the air screw in place? 
GB500guy #6
  • Rank:Gold Member
  • Posts:179
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/13/2016 12:25 AMCopy HTML

 The air screw is the one toward the air cleaner end and has nothing to do with slide movement. The idle speed screw acts as a stop for the slide, so if you back it clear out then yes, there should be no gap between the slide and the bottom. With the idle speed screw completely removed, then if there is a gap there is no free play in the cable or something is assembled wrong or damaged in the carb that is not letting the slide move all the way down. Could you post pictures looking into the carb from the engine side, one with the throttle closed and one with it open? That would help,

-Bill
Tarheel34 #7
  • Rank:XL Board Member
  • Posts:6
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/13/2016 12:54 AMCopy HTML

Right, that was just a mistype, I meant idle screw.  Yes I can take some pictures this evening and post them.  Sorry for not following the advice correctly initially.  I appreciate the help.  
GB500guy #8
  • Rank:Gold Member
  • Posts:179
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/13/2016 1:09 AMCopy HTML

 No worries!
Tarheel34 #9
  • Rank:XL Board Member
  • Posts:6
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/13/2016 10:25 AMCopy HTML

Went back over the carb tonight.  Actually doing what you suggested and you were correct, the slide isn't going all the way down.  Very close, maybe a 1/4 inch gap.  The problem is definitely the needle.  The slide goes all the way down without it, but with it, gets caught up at the very end.
It is a new needle jet set that is installed in the carb.  Put it in when I rebuilt it.  Any ideas?
GB500guy #10
  • Rank:Gold Member
  • Posts:179
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/13/2016 11:04 AMCopy HTML

Well that's strange, sounds like the needle is too thick or the needle jet opening is too small. That's the trouble with "carb kits", they have parts that you usually do not need, and the parts are sometimes the wrong dimensions. Change back to the old needle and needle jet and recheck tpo see that the slide seats all the way. Good luck,
-Bill 
GB500guy #11
  • Rank:Gold Member
  • Posts:179
  • From:USA

Re:1973 XL175 Idle Issue

Date Posted:05/14/2016 6:19 AMCopy HTML

Reply to Tarheel34 (05/13/2016 2:25 AM)

The problem is definitely the needle.  The slide goes all the way down without it, but with it, gets caught up at the very end.



Besides switching back to the original needle and needle jet, make sure that when you assemble things the ferrule on the end of the cable wire is not somehow getting hung up on the bottom of the slide, and failing to seat down into its recess in the bottom of the slide. When you see the slide held up 1/4", has the free play disappeared from the cable? If so then the cable is not seated properly someplace.
-Bill


Go soothingly on the grease mud ... as there lies the skid demon! ...





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