Solved some problems today. J90TLCUR

[chubcobear]

Found #4 spark plug was shorting to left upper latch cover bolt (cut in rubber plug cover). That helped top end RPM 600-700. Idles better now also.
Pesky temperature alarm (going off at 140-170*)was faulty head temp switch on starboard side. Disconnected it and no false alarm. However, in order to find it, disconnected VRO system, added port temp gauge, etc., before that final test because I read that the head temp switches were the most dependable. Have re-connected VRO and all runs well. All this was possible from reading many, many threads on this forum. Thank you for all the help.
T. C. Bear

 

[jonesg]

Re: Solved some problems today. J90TLCUR

AHa , how did you zero in on the latch, put a meter on it or touch it ?

 

[chubcobear]

Re: Solved some problems today. J90TLCUR

In the process of trying to locate source of alarm sounding when temp was between 140-160 at start of every trip (had installed port/starboard head temp gauges), I removed cover when underway. Change in RPM was immediate. Located split in plug wire cap which was grounding to upper latch bolt on cover (#4 plug, bottom cylinder, port side). Replaced plug wire. Insulated cover bolt.
Also eventually found alarm to be caused by faulty starboard head temp switch.

 

[tashasdaddy]

Re: Solved some problems today. J90TLCUR

very common problem with older plug wires.