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Old 02-17-2013, 03:45 PM   #1
bloc OP
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Fuel pump change -> hunting idle?

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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Old 02-17-2013, 05:48 PM   #2
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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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Old 02-17-2013, 08:29 PM   #3
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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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Old 02-18-2013, 12:11 AM   #4
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Quote:
Originally Posted by bloc View Post
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.
Do you want to get rid of the old pump?
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Old 02-18-2013, 12:20 AM   #5
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Do you have crash bars installed?

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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Old 02-19-2013, 07:28 PM   #6
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Do you want to get rid of the old pump?

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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Old 02-19-2013, 11:22 PM   #7
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There is a chamber with two one way valves.

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.
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Old 02-20-2013, 07:32 AM   #8
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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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Old 02-20-2013, 07:43 AM   #9
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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.
Exactly.
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Old 02-20-2013, 08:22 AM   #10
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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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Old 02-20-2013, 09:36 AM   #11
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Exactly the kind of experience I was looking for. Thanks for the help.
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Old 03-06-2013, 07:52 AM   #12
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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.

bloc screwed with this post 03-06-2013 at 08:06 AM
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Old 03-06-2013, 08:12 AM   #13
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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.

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.

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Old 03-06-2013, 08:55 AM   #14
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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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Old 03-06-2013, 10:23 AM   #15
bloc OP
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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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