More Carb Problems
Close
    
    
Results 1 to 7 of 7
  1. #1
    Member Oldad's Avatar
    Join Date
    Apr 2013
    Location
    Shawnee National Forest (Harrisburg), IL
    Posts
    85
    After going into the carb on my "new" 05 TW for the fourth time I thought I had it made. I'd, by then, put in a dealer-supplied kit, got all the parts in the right places, checked and adjusted the float level, reset the idle air mixture. It started about right, ran about right. Now that I'm able to ride it some distance I've got another carb-related issue.



    After the engine is well warmed up when I engage the clutch and close the throttle the idle speed remains very very high. I've checked throttle cable slack and for anything that would keep the throttle from returning to the idle adjuster stop. I can crack the throttle and snap it back but the idle remains high. However, if I release the clutch, putting a slight load on the engine, then the idle drops back to and remains at a normal speed. I'm no expert, having owned the TW about three weeks now, but I'm wondering if something like the main jet needle is hanging up, or maybe the problem might be related to the diaphram. I don't know that either of these things are possible.



    Any ideas?

  2. #2
    Senior Member jbfla's Avatar
    Join Date
    Jul 2010
    Location
    FL. GA, NC
    Posts
    2,392
    Quote Originally Posted by Oldad View Post
    ...



    Any ideas?
    ...a few, but can't promise they will solve your problem.



    Try opening the pilot screw a half turn more and see if that makes a difference.



    Check for air leaks around the rubber boot from the air box to the carb.

    Spray WD40 around the connection while the engine is running, and see if the engine rpm increases.



    Check to see if the small spring at the top of the main fuel needle is still in place.

    Sometimes it will fall out during reassembly.



    Check the plastic spacer on the fuel needle. It should remain at the top of the needle, and not easily slide or move.











    Jb
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
    2008 SV 650..................................2007 DR 650..

  3. #3
    Member Oldad's Avatar
    Join Date
    Apr 2013
    Location
    Shawnee National Forest (Harrisburg), IL
    Posts
    85
    Thanks for the tips. I'll check on these tonight.



    When you refer to the air box, you're talking about the connection between the carb and the engine, right?



    BTW, I've never read on the forum about any problems with the diaphrams in these carbs. I was wondering if one would know if they fail, especially the little one on the side of the carb.



    Jeff

  4. Remove Advertisements
    TW200Forum.com
    Advertisements
     

  5. #4
    Senior Member jbfla's Avatar
    Join Date
    Jul 2010
    Location
    FL. GA, NC
    Posts
    2,392
    Quote Originally Posted by Oldad View Post
    When you refer to the air box, you're talking about the connection between the carb and the engine, right?



    BTW, I've never read on the forum about any problems with the diaphrams in these carbs. I was wondering if one would know if they fail, especially the little one on the side of the carb.



    Jeff
    The airbox is where the air filter is located, but it wouldn't hurt to check the connection on both sides of the carb.



    If the diaphragm on the slide fails, there would be no vacuum (or reduced vacuum) to lift the main fuel needle.



    The diaphragm should be soft and plyable. Hold it up to a light source and GENTLY stretch the rubber fabric. If you see any pinholes of light or tears, you should replace it.



    If the small diaphragm on the side of the carb fails (coaster circuit), there would be a slightly leaner ( edited, see below) fuel mixture.



    Jb
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
    2008 SV 650..................................2007 DR 650..

  6. #5
    Senior Member jbfla's Avatar
    Join Date
    Jul 2010
    Location
    FL. GA, NC
    Posts
    2,392
    Out of curiosity, I removed the coaster circuit diaphragm/plunger, and replaced the cover ( it wasn't an air tight seal). Then started the TW and let it idle.



    It idled a few hundred rpms faster than normal. I adjusted the throttle stop screw, and rode the bike to the end of the road and back.



    The engine ran fine. I then removed the cover completely.



    Again the engine idled high, but turning down the throttle stop screw some more returned the idle to normal.



    Repeated the ride. The engine accelerated through the gears and back with no discernible change from with the diaphragm and cover in place.



    My conclusions (subject to change):



    With the diaphragm removed, and without an airtight seal (the diaphragm serves as a gasket for the cover) no additional fuel is drawn into the intake manifold on deceleration.



    But there should be additional air drawn into the intake manifold from the unsealed coaster circuit passageway... Like a small air leak.



    So theoretically, the fuel mixture should be slightly leaner. (If the cover made an airtight seal, I believe the mixture would be richer).



    I also did not notice any popping or backfiring from the exhaust. The purpose of the coaster circuit is to lessen exhaust popping/ backfiring.



    Other than the increased engine rpm, I could discern no difference with or without the coaster circuit diaphragm.



    However, my TW is set to run rich, so maybe that's why I saw no effect from removing the diaphragm.



    As they say,your mileage may vary...



    Jb
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
    2008 SV 650..................................2007 DR 650..

  7. #6
    Member Oldad's Avatar
    Join Date
    Apr 2013
    Location
    Shawnee National Forest (Harrisburg), IL
    Posts
    85
    FINALLY. It's fixed. Hallelujah! After removing, dismantling, reassembling, installing the carb four more time last evening, I think I figured it out.



    Assuming I still had a passage still blocked on the carb somewhere, I was going to tear it down again for another cleaning and inspection, but at the last minute I thought I ought to recheck the float level. I'd checked it before with the clear plastic tube connected to the float drain, but had considered that my symptoms might be caused by low fuel level in the bowl. Hooked up the tube again. Opened the drain screw and low and behold the fuel level came up about 8mm lower than spec.



    It took four tries but finally got the float set right, or at least right enough. Each time I'd try to set the float height with a caliper, then install and check again with the clear tube method. It's not as easy as it seems it should be. I'm still a bit confused by the instructions regarding when the "float needle contacts the seat but does not compress the needle spring". You definitely cannot just turn the carb upside down and measure. The needle spring will compress for sure. I had to tilt the carb more than 45 degrees for the needle to contact the seat and still not compress the needle spring.



    Anyway, since then, she fires up, idles smooth and seems to have more power at all speeds.



    I know this account does not lend great insight into carb adjustment, thought I'd pass it on anyway, considering the number of carb tuning inquiries posted here.



    I guess my advice is: Be thorough. Check everything.



    Oh, and one more revelation. If you put in a new idle air adjuster, be sure to use the right size o-ring ahead of the steel washer in front of the spring.

  8. #7
    Member MTLHead's Avatar
    Join Date
    Apr 2013
    Location
    Fremont, CA
    Posts
    31
    So adjusting your float height fixed your hanging idle problem? I just ask because I have an 2005 also with the same issue.

Sponosred Links

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Similar Threads

  1. Horrible carb problems
    By illesg in forum Technical Help
    Replies: 45
    Last Post: 09-25-2012, 09:53 PM
  2. 95 t dub carb problems solved
    By jhow67 in forum Technical Help
    Replies: 3
    Last Post: 09-23-2012, 11:56 AM
  3. 87 carb problems!!!!
    By chevy_lifted_4x4 in forum Technical Help
    Replies: 23
    Last Post: 09-21-2012, 05:25 AM
  4. Carb problems....help please
    By bigblock390 in forum Technical Help
    Replies: 2
    Last Post: 05-14-2012, 07:51 PM
  5. Carb Problems
    By RisingSun in forum Technical Help
    Replies: 7
    Last Post: 03-06-2012, 07:23 AM