Fuel pump change -> hunting idle?

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by bloc, Feb 17, 2013.

  1. bloc

    bloc Been here awhile

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    2004 950 S, cannisterectomy, SAS blocked off, recent valve adjustment, FMF pipes, new air filter, etc.

    Recently the fuel pump slowly quit and was replaced. Until finally giving up the ghost, for the ~5 thousand miles I've owned the bike, it ran perfectly. Mixture seemed good, idle rock solid 1400rpm (not withstanding needing the choke when cold), acted exactly as it should. Some would complain that the exhaust popped a lot under decel, but I have read that these bikes do that a lot anyway.

    ALL I DID was change the fuel pump from old OEM to a new OEM unit.

    Now the bike seems to run more rich (exhaust smell) and the idle is all over the place. It'll often sit at 2k when pulling up to red lights, some times blipping the throttle brings it down to 1.4k, sometimes 1k, sometimes it stalls, others it doesnt do anything aside from blip.

    Any thoughts as to why the new pump would cause this?

    The pump seems to stroke more when I first turn on the key than the old one.. but the pressure regulation should be the same right?

    Thanks for any insight
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  2. DeepInIt

    DeepInIt Long timer

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    It probably isn't the pump, you knocked something else loose. Go back in and look around. Take a look at the vacuum lines coming off the carbs.
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  3. bloc

    bloc Been here awhile

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    Thanks for the advice, but I didn't go anywhere near the carbs. Just removed the 2 front bolts on the bash guard, swung it down, and did all of the work down there. What could I have possibly knocked loose?

    Could dirt getting into a fuel line make a float stick, and if so, would that cause my problems? I actively tried to avoid that, but it seems like one possibility.
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  4. Xmoto

    Xmoto Death Race

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    Do you want to get rid of the old pump?
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  5. gefr

    gefr Life is a trip

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    Did you by any chance remone crash bars and on the process pinch a cable? sounds like tps problem... or carb vents
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  6. bloc

    bloc Been here awhile

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    Bike is probably going up for sale soon, and it will be going to the buyer. Sorry.

    And no, no crash bars. I literally didn't touch anything aside from the engine guard, pump, fuel lines, wire harness plug, and petcock.

    I guess I'll pull the carbs and make sure they are at factory settings.

    Maybe if the old pump was SLLLOOOWWWLLLYYY dying the previous owner tuned the bike to the reduced fuel pressure? This pump cycles at least 3-4 times more than the old one, every single time I've turned on the ignition and the bike has sat for a little while.

    Could it be a bad pump? it came with the bike.. but was OEM, brand new, shiny, in the packaging. How do these things regulate pressure?
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  7. gefr

    gefr Life is a trip

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    The one side of the chamber is a membrane. The rod, driven by the coil, pulls the membrane so the chamber fills with fuel through the intake valve. Then the points lose contact and the coil stops pulling. A spring that was loaded from the rod movement, pushes the membrane and fuel. Fuel exits from the outlet valve towards the carbs. The spring regulates fuel pressure. Maybe you could use the points from the new pump on the old one?
    You could also check battery poles getting loose. They could cause all sorts of crazy problems.
    Cheers.
    #7
  8. bloc

    bloc Been here awhile

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    Thanks a ton for that info. If the carbs check out I'll look into what you suggest with the points.

    From your description it would seem the spring is what controls fuel pressure.. or has the biggest effect on it. At least if that is what is responsible for pushing on the diaphragm, forcing fuel into the carb bowls.
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  9. gefr

    gefr Life is a trip

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    Exactly.
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  10. KEELAYMONSTER

    KEELAYMONSTER BRRAAAAPPP!!!

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    What I experienced as my pump when out was similar. As the points in the OEM pump wear out the stroke of the actuating rod becomes longer. Effectively the pressure, and float bowl level, drops lower before the pump kicks on. At freeway speeds this can produce a surging "lean" effect. Basically your float level drops further as the pump wears out and changes your operating (while riding) float height. You can raise the float to "bandaid" the lean issue.

    If the previous owner had it tuned with a worn out pump then your float level may be too high when a new pump is installed. This is assuming the previous owner, or whoever he took it to, was savvy enough to raise the floats in the first place.

    Its pretty difficult to mess up installing the oem pump. The only issue I could see is swapping the fuel lines, in which case you would have a bubbler in your fuel tank.

    I replaced my OEM pump with a Facet 40171 and had a similar issue. Pulled the carbs and found impropper float height and mixture screw adjustment.

    I would start there. Also since you are pulling the carbs I would make a record of the current jetting if that hasnt been done already. Its always nice to know those things to prevent having to pull the carbs again.
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  11. bloc

    bloc Been here awhile

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    Exactly the kind of experience I was looking for. Thanks for the help.
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  12. bloc

    bloc Been here awhile

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    Where is the emoticon for pulling my hair out?

    Got the carbs off and checked everything.
    All jets factory stock.
    Needles at stock 2nd-clip setting (though I moved them to the third since I had them out.)
    No needle wear as per ktm950.info.
    Floats at stock 3mm.
    Idle screws at .75 & 1.5 turns.. which kinda makes sense considering this bike came from a much higher altitude than sea level. Turned them back to 2.25.
    Synced carbs.

    Some progress, but not much. Idle still hunts, occasionally backfires & stalls, usually hangs around 2k on decel. I've confirmed it isn't anything funky going on with the choke or throttle cable linkages.

    BTW it has had a recent valve adjustment, but that was done thousands of miles before all this popped up.

    I'm starting to burrow down on the possibility of some dirt having gotten into one of the float needles via the fuel line while changing the pump, and causing it to hang. I guess I should have checked for that when I confirmed float height yesterday. What bugs me is that even with the idle screws set so lean, it had a distinct rich smell to the exhaust very soon after changing the pump. Either the pump itself is causing this, or something that could be jacked up by the install. I'll try and drain the bowls today and measure the amount of fuel.. though I'm not sure if I can do that precisely enough. Either way, I'm getting really good at pulling the carbs now..

    Does that sound like a possible cause? It is about the only thing that would explain it acting so weird immediately after a fuel pump change where I'm confident I didn't mess anything else up..

    Edit: also gonna look at TPS adjustment.
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  13. KEELAYMONSTER

    KEELAYMONSTER BRRAAAAPPP!!!

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    very interesting. One thing I would note is the stock jetting. If you have pipes you should probably re jet.

    The next thing I would check is your new pump. Was it purchased brand new? If not I would pull the little plastic cover and check the points. Sometimes as the points wear they wear unevenly, causing one side to skew off center. Its worth checking. :deal

    If thats Ok then I would defintiely look at the needle and seat next. If the float needle has a groove on the tip at all then it needs to be replaced. Then check carb vents for propper routing and such.

    Sometimes when replacing a failed item with a new one, it unmasks a new problem. It sounds like you are at least looking in the right direction.

    :freaky
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  14. bloc

    bloc Been here awhile

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    I'm not sure where he got the new pump but it was absolutely brand new, never installed, still in a shipping-type zip-lock bag.

    Would uneven wearing points effect the operation of a brand-new pump? This all started about the first time the bike warmed up after the new pump.

    Carb vents seem routed appropriately.. this has the newer style where they are T'd then dump out the bottom. I'll make sure they aren't restricted.

    Edit: I'm also gonna unhook a fuel line at the carb and let the pump run wide open to see if any trash flushes out of the line. Not sure why it took so long for me to come up with that idea, but it seems like good info.
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  15. bloc

    bloc Been here awhile

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    Carbs back out. There was a TINY bit of sand in the bottom of each bowl.. but the grains were small enough that I'd have trouble seeing anything like that get lodged in the float needle and hanging it up.. and not easily getting flushed through by the fuel and vibration of WOT.. which has happened a few times since this started. I confirmed all of the jets in the fuel are clean and not obstructed. Floats seem to operate fine. No noticeable groove in the needle, and seats look fine.

    By the way, looking up into the float needle seat, above the press-fit brass seat there is what looks like some stainless mesh that keeps large particles from getting to the float. The closest thing these have to a fuel filter, I guess.

    I did notice what seems like a -tiny- bit of slack in the linkage connecting the front and rear throttle body butterfly shafts. It doesn't seem to be in the shafts or sync screw. It seems like the actual pivots on the linkage. Are these replaceable bushings? Even then, the spring tension on each plate should keep the linkage taught against the slack. And why crop up as a problem only when I change the fuel pump?

    I also noticed more black carbon lining the throttle body throat around the rear butterfly than the front. No idea what that means. Maybe each of the backfires is coming through the rear? The front is under the crank case vent so it stands to reason that one gets washed down with a bit more oil vapor.

    Open to any thoughts or observations.
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  16. ABuck99

    ABuck99 0.0

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    I feel your pain, & dont envy pulling the top end apart just to check the carbs over :cry.

    You mentioned that the new pump cycles on longer than the old one when you turn the ignition on, which means the pump is taking longer to build pressure ( old one was building pressure faster and shutting of sooner?) - So its possible there is a leak of some kind- air seeping in through a fuel line- a float sticking open- or maybe that "new" pump is not the right one or not so new?- Double check the pump by inspecting the points beneath the cover. You can pull the cover off the old one and check those points against your "new" pump.

    In a perfect world when you turn the ignition on the pump should only take a second or two build pressure and shut off. Also If your pump cycles on every time you switch the ignition on- say even after 15-30 minutes there is probably a leak somewhere.

    If the new pump is bad for some reason you can check it. If you want to experiment- take the points off the new pump and install them on the old pump re-install pump- test- what happens?

    here is a how to on that process

    "Dont replace your fuel pump- FIX IT.
    "
    http://www.advrider.com/forums/showthread.php?t=611799
    #16
  17. bloc

    bloc Been here awhile

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    Interesting.

    Found a few of the air jets partially clogged and cleaned.. cleaned the bowls, double checked slide diaphragms, etc. Idle hunted really bad. Couple spits through the rear carb while warming up.

    THEN,
    I gravity fed the carbs from a fuel container and the idle is rock solid, goes right back where it should after revving..

    Gonna try the new points on the old pump and see what happens. Or maybe a facet.

    Edit: side question.. should we be able to see fuel flowing out of the orifice around the slide needle at idle? It is idling awesome while gravity fed, but it sure seems like a ton of fuel. Needles on middle clip groove.

    Second edit: Yeah, the pump cycles more.. but I was assuming this one was operating at a higher pressure or something as opposed to the old one, thereby stroking more. It does only take a second or two.. but whereas the SOP for the old pump was one "click" upon turning the ignition on, maybe two.. this one goes 5 or 6.
    #17
  18. ABuck99

    ABuck99 0.0

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    Im hooked now so keep us posted what you find- good luck
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  19. bloc

    bloc Been here awhile

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    Well, I want to put more miles on it than the quick trip to get food that I just did, but so far so good. The idle seems to run up maybe 100 rpm every once in a while, but no crazy surging like before and it settles right down when you chop the throttle. I'm not sure if it was the screws, the clogged air jets, or the needle clip being too high.. but it picked up a significant amount of midrange punch as well. It wants to pull the front off the ground by itself in second gear now.. didn't do that before.

    So to recap...

    It appears it was the new fuel pump all along. I harvested the points out of the new pump and soldered them into the old pump housing (the old points were TRASHED) and things are going great.

    I think I also figured out why the new pump was stroking more times than the old one. The points were so worn down each stroke went substantially further than in the new pump.. so it would have taken more strokes with less throw each to equal the amount of fuel. 3-5 times as much? who knows.

    So yeah.. if you do something as simple as change the fuel pump and it immediately starts acting funny.. dont suspect a bunch of other crap.. suspect the pump. Even if it's brand new.
    #19