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idling, fuel and other issues ? - Nearly fixed

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by klau, Oct 13, 2008.

  1. #1 klau, Oct 13, 2008
    Last edited by a moderator: Jul 13, 2015
    Hopefully someone can point me in the right direction...

    (Firstly, I know next to nothing about bikes. I've worked in software technical support, testing and as a programmer, so I have a bit of troubleshooting ability... expect stupid questions)

    Basically, the bike (srv250) just cuts out. I had the first proper ride last Sunday and within 7kms, the bike had cut out 4 times. Happens when slowing down and going into (I think) 2nd or (definitely) 1st. The time before that (2 weeks earlier), the bike cut out under 4kms. At that time, it looked like all electricals had gone (no head light, dash lights, etc). Bike did manage to start after sitting for a few minutes.

    Taco - Initially idles above 1000, but then drops after giving throttle and then rolling off. Towards the video end, idle is below 1000. I've tried setting the idle screw, but the bike will not idle consistently. I don't know if the following have anything to do with it...

    Fuel Filter - Left side goes to the petc0ck, right to carburettor. There is another inline fuel filter for the second carb, both filters show the same symptons. When idling, it looks like air is coming into the fuel filter from the carb end???

    Spark plugs - Bike came with old spark plugs the previous owner had changed out. They are sooty black (not shiny). Search suggests fuel/air mixture is rich. The previous owner had mentioned the bike is running rich. I suspect the plugs in the bike will be black also.

    Bike doesn't need choke to start - Previous owner never did, and I haven't either. However, if the engine is hot, the bike will only start with a bit of throttle.

    Lastly, there doesn't appear to be any hose leaks (but I will do a detail check using a torch). No leaking oil on the ground either.

    Things that I plan on doing:
    - Get some sort of fuel addititive to 'quick clean' the carbs
    - Replace the fuel filters as they are cruddy as... How do you get the air out of them?
    - Replace spark plugs

    Any/all ideas welcome.

  2. It's definately running rich by the sound of things. A correctly tuned engine should need choke and closed throttle for cold starts and closed throttle only for hot. If you need to open the throttle when hot starting then the engine obviously needs some extra oxygen to lean out the mixture.

    The stalling problem is most likely caused by excessive fuel flooding the idle circuit when the engine decelerates. It basically drowns in its own fuel and stops.

    Rich fuel mixtures can be caused by any number of things. The most common being ignorant but well-meaning tinkerers and dirty air-filters.

    A "quick-fix" in a bottle wont really have any positive or lasting affect on the problem and I'm often staggered that most of them are still on the market although most people will happily blow $15 on 200ml of toxic chemicals rather than actually strip the carburettor(s), thoroughly clean and reset then synchronize and adjust the idle/air-fuel ratio first.

    It sounds as though it may have one or more valves rattling as well which will also upset the starting and idling due to cylinder pressure losses.
  3.  Top
  4. Klau,

    Old thread found in a search

    I have a 1995 SRV and have had troubles with fouling plugs as well, I had it in for a service and got the valve clearances done, plugs changed and carbies tuned... However a few months down the track with not a whole lot of riding and I find my plugs are fouling quickly again before needing replacement....

    Did you have any luck fixing the problem??

    I could use a different approach.

  5. hi DeeTee,

    I haven't been looking at this thread. Apologies for the late reply, but no, poor bike is still having the same problems.

    - Did the valve clearances. I had the wrong TDC to start with, so cannot tell if they were correct to begin with
    - Cleaned the carbs. Looked fine, jets didn't seem to be blocked. Floats and diaphragms looked fine, no holes, etc
    - Synced the carbs with a redneck water manometer. Bike has more power now (when it goes)
    - Changed the plugs, which promptly got carbon fouled again
    - Tried idling without the air filter, no difference
    - Tried adjusting the air mixture screw, but I couldn't find the 'window' between too lean and too rich. Ended up buying one of those colortune plugs to see if I was even getting a blue flame...

    When I first tried the colortune two days ago (~6am) I managed to get a blue spark turning the air mixture screw in. I couldn't get a blue spark turning the screw out however. Set both carbs to be blue spark. No choke (bad sign) needed to start that night and the problem still persists.

    Tried the colortune again tonight (~7pm) and couldn't get a blue spark at all. All I got was the orange spark. Engine was hotter then when I tried the other morning so it could be heat related as well.

    Basically, I don't seem to be able to remove the richness. Could this be a float height issue (I'm going to check it on the weekend)? And would it be worth while going down one size in the idle jet (leaner)?

    Lastly, not sure if this is important, but I started the bike once on the side stand and noticed the idle was highter than normal. I guess this is related to the float level position when the bike is on an angle so to be expected.

    Thanks for reading (it's a lot to read),
  6. Yes float level will effect everything. You should set it before buggering with mixture settings. You also need to be confident that the float needle is sealing properly.

    Either of these two things will cause your problems.

    Keep in mind, unless you change something, the mixture setting will change very little over the life of the bike. So why would you suddenly need to do an adjustment?

    Something has changed.
  7. Thanks for the reply ibast,

    I actually bought the bike knowing it was running rich, not really knowing what this meant... being new to bikes. The seller was kind enough to deliver the bike as I've only ever rode at the pre learners a few weeks earlier and didn't fancy riding in traffic. I guess, if I had test rode before buying, I might have a different bike now...

    But, it's been educational, and I've learnt much more than I would have otherwise :)

    Has something has changed?

    Probably, but bugger if I know what, as I don't have anything to compare against. All I know is that the bike doesn't idle properly and gives me grief if I have to stop, ie stall. I've googled/asked about the symptons, applied any possible fixes, so hopefully we are getting closer (thanks for the tip about the float needle!).

    Hopefully, I can post a follow up in the future saying the bike is working fantatic!

    Thanks for reading, and if anyone have any other ideas, I will definitely try them.

  8. Some notes stolen from the factory Pro website:

    " * NOTE: A rich problem gets worse as the engine heats up.
    o If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
    * NOTE: A lean problem gets better as the engine heats up.
    o If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!"

    But set you float level first and make sure the float needle is sealing.
  9. Why not take it to a good Mechanic?
  10. MVrog - A good mechanic would make sense, but I'm determined to fix it myself now. lol.

    ibast - Thanks, came across similar info in my travels. Turning the air screw in makes it richer in my case, turning it out seems to makes no difference however...

    Floats levels were basically correct. The front one was out by 1mm, so adjusted acordingly. Put in new plugs, synced the carbs, and the bike idled even worst, air screw seems to makes no difference...

    I'm going to pull the bike apart again and see about putting in leaner idle jets.

  11. I can understand why you want to fix it yourself now BUT in the end if you cant, it's going to cost you 5x more to get it fixed. As they then have to correct what ever you have done 1st then start from scratch again.

    A few years ago I had a customer bring his engine into our shop in 3 boxes, with the statement ' it wouldn't start so I pulled it apart and I couldn't see any problems, now its too hard for me'

    After a visual inspection I put it back to together, then started the usual trouble shooting....and found the CDI unit had packed up.

    His invoice :
    Oil / gaskets etc = $120
    CDI = $80
    Labour 9hrs @ $88 = $972

    Total $1072

    Or if he bought it in before he screwed it up

    CDI $80
    Labour $88

    Total $168
  12. Point taken :)

    I'm not at the stage where I'll be needing boxes, so there's hope yet.

  13. You lot sound a bit more technically minded than me. But I am following with interest.
    The blokes I took mine too, (on bondi rd...) have been really helpfull, One tip they gave me was to make sure you are not running on premium, (I hadn't been) but apparently that can foul plugs on smaller capacity bikes.

    Anyway It has been a couple of weeks now and still clean plugs with no idle trouble, but I'll report back here if it happens again

    Great thread.
  14. If its getting richer but wont lean out then its gettig fuel from somewhere else (shit Im a poet ) Its time to get a mechanic to rebuild your carbs ,You have learnt alot with what you have done, now find out what it really is ,This way you learn as you ride rather than spending all your time in the garage ...
  15. Update.

    Thought about the float levels a bit more, and purposely lower the levels by a few mm to lean out the fuel/air mixture. This resulted in a hanging idle ('corrected' mostly by lowering the idle below 1000 rpms, and blipping the throttle where necessary), and would you believe, the bike only stalled once or twice (in two 45min runs)... no trouble doing low speed u turns, etc.

    Since I appeared to be headed in the right direction, I've replaced the idle jets from #15 to #10 (2 sizes down) and have set the float levels back to the correct range. Idle rpms are still below 1000, and the hanging idle (now briefly at 2000 rpms) is still present, but the bike hasn't stall at all and there's no smell of petrol at the exhaust either.

    So things are looking really good. I will replace the pilot jets with #12.5, and hopefully my next post will be "Fixed!"

    btw, got the mikuni pilot jets from 'Ian Williams Tuning' in SA who express post the jets to me and I got them the next day. Happy with the price and service and will obviously be getting the #12.5 from him.

    Happy New Year!