Author Topic: Intermittent Misfire ( ST1100 ) *  (Read 5014 times)

Offline KoTAOW

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Intermittent Misfire ( ST1100 ) *
« on: April 04, 2009, 11:58:36 AM »
Original article can be viewed here:

Submitted by Mike Martin.


ST1100 Intermittent Misfire

Paul Kolbo submitted the following information. You might benefit from his experience.


A friend had purchased a 99 ST off Ebay at April last year which seemed, at $2000 off list price and low mileage, too good to be true. I had some trepidation about this deal but he contacted the owner who explained he was going through a divorce and wasn't going to be getting the money anyway (or something to that effect.)

From the moment my friend flew down to Chicago and picked the bike up it was clear something wasn't right with it. On his return ride to Mpls he stalled in Eau Claire. At the time I thought it was carb icing and instructed him to stuff a rag in the air duct. For the next 18 months we fought with this issue as it would come and go at random. The symptoms were loss of power and hesitations. Everything we did would seem to fix the problem (bypassed the vacuum valve, replaced coils, replaced plug wires, cleaned the carb bowls, ultrasonic cleaned the jets, replaced the carb boots, gas and air filters, pairectomy). Probably the most frustrating aspect is the problem would disappear for thousands of miles at a time. It would always disappear the minute he pulled it into my garage.

Two weeks ago it started cutting out again only this time the problem finally remained as he pulled into my garage and we were able to finally apply some fundamental troubleshooting (rather than blind swapping). We were able to determine that one of the coils was not supplying the spark (but I had already replaced the damned coil!) Out of desperation and lack of anything else to try I fiddled with the coil primary leads (going to the coils) and voila, I was able to make the problem come and go by farting around with the harness. Now it made sense, the problem would heal itself as we messed around with the coils and carbs because we would inevitably move that harness around while being in the area.

I fabricated my own harness and he drove the bike for four days with no problems, A close inspection of the harness revealed a break near the connector to the coil) but inside the insulation. Depending on the position of the harness would either make or break the connection. There was no stress on the harness so it's hard to imagine how that could have broken like that (besides being that way from the factory.) I don't think I had ever heard of a primary harness failure on an ST. (Mike M. you might want to put this one on your website.)

Done! Thanks for the write-up, Paul.

2008 M. E. Martin, all rights reserved
« Last Edit: April 10, 2016, 06:00:58 PM by KoTAOW »