Author Topic: K100LT bogging after long idle (stop light long)  (Read 4762 times)

Offline Putz1103

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K100LT bogging after long idle (stop light long)
« on: May 17, 2013, 10:09:27 AM »
I have a 1991 K100LT that recently underwent major surgery (my own fault).  I accidentally tried to jump start it with the terminals connected in reverse (there was a trickle charge adapter with aligator clips that I assumed would go red to red with jumper cables, I was wrong).  So my trickle charging adapter wires melted through because of too much current.  The motorcycle battery died and there was a weird backfire that blew off the throttle body equalizer caps.  So that started the surgery.

I have resolved all the problems apart one.  If the bike idles for too long if you try to go it will go about 1/8 mile and then start to bog, then be fine again after a few hundred feet (if it doesn't die).  It seems like it's either flooding or starving.  This used to be much more prevalent, but it now only happens in first and second gear.  There have been a few times when I let it idle for 5-10 minutes there comes a point where the idle noticeably decreases for a moment (30 seconds), then back up to normal (from an idle of 1300 to maybe 7-800 RPM and back).

Things I have done in the surgery:

New Spark Plugs
Cleaned Air Filter (K&N)
Cleaned injectors (and tested with a paper towel, nice cone shape spray)
Replaced the s shaped crank case hose
Ran for a mile without fuel filter, no change
Cleaned tank and fuel pump pre-filter
Checked all throttle body rubber for leaks
Checked air intake for obstruction
Oil and filter change



I haven't checked anything in the exhaust, but it feels like it's flowing fine out of the exhaust pipe.  There was also once when I got finished with a 30 mile ride that I opened the gas cap and it looked like smoke was coming out (not steam, actual smoke).  The fuel pump could have just gotten really hot because I was low on fuel or the pump could be going, I don't know.  I really don't want to spend several hundred on a fuel pump if that's not going to help either.

I will try to take a video later today to show exactly what's going on, but it's really intermittent so I don't know that that will work.

Offline Putz1103

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Re: K100LT bogging after long idle (stop light long)
« Reply #1 on: May 24, 2013, 02:49:53 PM »
I have now replaced the fuel pump and fuel filter and the problem has gotten slightly worse.  Could the injector computer being fried cause this kind of problem?

Offline johnny

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Re: K100LT bogging after long idle (stop light long)
« Reply #2 on: May 24, 2013, 03:10:38 PM »
greetings putz1103...

i musta missed your 1st post...

welcome to motobrick.com...

im not following you... it starts and the idle hunts around between 1300 and 800 rpm... then when you start rolling it will go 1/8th mile and you lose power... you turn it off and it will start immediately and repeat... is that right...

how long have you had this moto... how has it been running before this... before the jumper meltdown... did you do anything to it before the melt down...

just need some better info... the more the better...



j o
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Offline Putz1103

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Re: K100LT bogging after long idle (stop light long)
« Reply #3 on: May 28, 2013, 04:15:14 PM »
It idles beautifully on start.  In first and second gear it will intermittently bog.  After you have moved and you are idling once again it may or may not bog.  This bogging only lasts 10-15 seconds and then everything is right with the world again.

Since I have replaced the fuel pump the bogging has become a two stage bogging.  I'll be accelerating in first or second gear, then there will be a noticeable acceleration reduction bogging) then bogging even further.  Then 10 seconds later it will do the same two step de-bogging back to normal acceleration.

I don't think it's a vacuum leak because it is too controlled.  The bogging is very defined.  If it were a leak I would asume it would run rough all the time, not just in 10-15 second bursts.

Before the miswiring I hadn't done anything to the bike (apart from standard maintenance).  Since then I have done just about everything...

Offline mystic red

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Offline Putz1103

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Re: K100LT bogging after long idle (stop light long)
« Reply #5 on: July 10, 2013, 10:18:35 AM »
I just resolved the issue last night.  I took everything from the intake to the throttle bodies apart and cleaned/reseated everything.  Put it all back together and nothing was resolved.  I was on my last string because I have done everything that I could think of and replaced over $500 worth of parts in trying to fix this.  I remember reading three years ago that some people solve bad idle issues by removing the fuel pressure regulator hose coming out of the fourth throttle body and sealing off the throttle body.  I said "Screw it" and unplugged the hose and sealed the hole in the throttle body.  Then the bike drove like a dream.

So now my question becomes: Is there any problem with leaving that hose unplugged and buying a new rubber cap for the fourth throttle body hole?

Offline Scott_

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Re: K100LT bogging after long idle (stop light long)
« Reply #6 on: July 10, 2013, 07:48:00 PM »
Why not replace the fuel pressure regulator.
Sounds like you may have damaged it with that nasty backfire you said you had.
I would not permanently bypass it.
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