TuxedoPk
08-28-2004, 10:57 PM
Had my prop balanced and refinished- ran great at about 4900 rpm for about 45 minutes yesterday then dropped down to running only about 4400 rpm.
Took the boat out today- problem was gone for about 20 minutes running at 4900 rpm (WOT) then I noticed it started dropping 4800, 4700...down to around 3800. Idled for a while then raced it again at 4900... sure enough startdd dropping rpms again. Then BOOM. I'm not sure if what I heard was a misfire, metal clanging on metal or what- but it didn't sound pretty. Also noticed smoke coming out the rear exhaust.
This has happened to me a few other times (smoke/BOOM).. never when the mechanic is around though.. This was the first time I noticed the dropping rpms though... but it might have been been doing it w/o me noticing.
All the 2" guages read normal...
What's changed since the problem began?
I had the wiring harness replaced and more significantly I was told that my Crane Ignition was defective so a new one was installed. Also the spark plugs were replaced.
The battery is strong (Purchased at Cumberland). According to the manual that came with the Crane ignition it states that misfire at high rpm is usually due to coil failure, including internal arcing or arcing at the high voltage terminal as well as arcing across spark plug boots or the distributor cap. They also suggest routing all magnetic trigger connections away from any other wiring especially CD unit coil cable and any high voltage sparg plug wires. They rectify correcting misfiring problems by replacing spark plugs and checking that the plugs are the proper type, heat range, and gap size.
** Does the dropping rpms and noise sound like an intermittent misfire? What else might cause this to happen?
I was really happy with the new prop until this crap started up.
Took the boat out today- problem was gone for about 20 minutes running at 4900 rpm (WOT) then I noticed it started dropping 4800, 4700...down to around 3800. Idled for a while then raced it again at 4900... sure enough startdd dropping rpms again. Then BOOM. I'm not sure if what I heard was a misfire, metal clanging on metal or what- but it didn't sound pretty. Also noticed smoke coming out the rear exhaust.
This has happened to me a few other times (smoke/BOOM).. never when the mechanic is around though.. This was the first time I noticed the dropping rpms though... but it might have been been doing it w/o me noticing.
All the 2" guages read normal...
What's changed since the problem began?
I had the wiring harness replaced and more significantly I was told that my Crane Ignition was defective so a new one was installed. Also the spark plugs were replaced.
The battery is strong (Purchased at Cumberland). According to the manual that came with the Crane ignition it states that misfire at high rpm is usually due to coil failure, including internal arcing or arcing at the high voltage terminal as well as arcing across spark plug boots or the distributor cap. They also suggest routing all magnetic trigger connections away from any other wiring especially CD unit coil cable and any high voltage sparg plug wires. They rectify correcting misfiring problems by replacing spark plugs and checking that the plugs are the proper type, heat range, and gap size.
** Does the dropping rpms and noise sound like an intermittent misfire? What else might cause this to happen?
I was really happy with the new prop until this crap started up.