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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Puccini on March 03, 2016, 11:47:47 AM
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From reading other posts here I see that there a re a multitude of questions about engines sputtering and cutting out.
Luckily my 85 K100RT is 99% reliable but it does have an annoying habit.
It always starts and idles fine. On the road , at cruise speed its great. The problem comes when I accelerate off idle at a light.\
Every now and again it acts like it's shutting down for a second of two then goes right back to running fine. Once or twice I've gotten a sputter at slow speed but not often.
There is no indication that it's electrical as the lights stay on and the tack doesn't dive , etc. (but the tach does fall to zero sometimes and tapping the speedo housing brings it back up)
I've checked the fuel pump connection at the tank and it's fine. Cleaned all the connections under the tank I could find with Dioxit contact cleaner.
Fuel filter and fuel hoses have been repalced, injectors were professionally cleaned. New battery and ground cable. Air filter is fine.
Sidestand cutout switch was eliminated and wires soldered together and insulated.
New plugs and NGK Plug wire installed. I've checked the coils and all the wiring seems clean and tight.
I've tried disconnecting the throttle position switch and it makes no difference either way.
One thing I like to cruise pretty fast on the open highway. Usually 75-80mph for long stretches.
Sometime. but not always, this shuddering happens after a red light stop at the end of a long high speed run.
As I said most of the time the bike is ok, but it's unnerving to have the engine lose power for a few seconds when starting off from a stop.
One other point is that it idles fine at the stop and doesn't die until it has accelerated from the stop for a second or two.
I'd appreciate any hints people can give.
Gerry
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From your description, it sounds heat related. Maybe take a look at everything that has to do with heat dissipation and monitoring.
Is your coolant full and fresh?
Is there coolant in your overflow tank - and it is more full than normal when it sputters?
Does the fan come on when it's supposed to?
Are your electrical connections to fan and a sensor(s) clean and strong?
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When was the last time you checked the valves?
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you disconnected the TPS...but have you adjusted it?
issue really sounds like a mixture problem to me...idle mix is already too lean, you open the throttle, that makes it even leaner...and it stumbles.
Idle mixture?
Throttle body balance?
air leak check?
fuel pressure?
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You've helpfully explained what you've done, Puccini, and it appears you are approaching this in an orderly way. In addition to the checks Tim and Marshall have suggested, if your air filter is clean, while you're checking for air leaks be sure the vane of the mass air flow sensor is operating smoothly in its full range.
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When was the last time you checked the valves?
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Never checked the valves. bike has about 30K on it.
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From your description, it sounds heat related. Maybe take a look at everything that has to do with heat dissipation and monitoring.
Is your coolant full and fresh?
Is there coolant in your overflow tank - and it is more full than normal when it sputters?
Does the fan come on when it's supposed to?
Are your electrical connections to fan and a sensor(s) clean and strong?
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Coolant is full and pretty fresh.
Fan is loose and has come on occationally in the summer
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you disconnected the TPS...but have you adjusted it?
issue really sounds like a mixture problem to me...idle mix is already too lean, you open the throttle, that makes it even leaner...and it stumbles.
Idle mixture?
Throttle body balance?
air leak check?
fuel pressure?
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I balanced the throttle body balance last season and it was OK.
Remember that the stumbling does not happen all the time. Only occationally.
Other than that the bike runs really great.
When it does happen it's very alarming as it happens on initial acceleration when I have cars behind me.
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When was the last time you checked the valves?
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Never checked the valves. bike has about 30K on it.
But the bike has excellent idle and performance usually
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When was the last time you checked the valves?
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Never checked the valves. bike has about 30K on it.
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Check the valves. Not cause of this issue, but guarantee they are out of spec.
Look for an intake air leak.