57thompson
Cadet
- Joined
- Aug 16, 2006
- Messages
- 6
Hi from North Georgia. Hope this doesn't get too long.
Older inline 6 on the back of a restored all-wood Thompson. I run it 1-3 times per week all year long. Starts first crank, runs without a complaint or whimper for two years. Perfect.
This started last week: running fine, about half throttle, then suddenly, power drops 20%. Boom. 5 seconds later, back to normal. Vroom. 30 seconds later, drops 20%. Boom. 10 seconds later, back up. Vroom. This is major..like the motor is being kicked in the nads. RPM's drop, and feels like putting on the brakes. I start to go over everything in my mind, while this up/down pattern settles into about a 30-second rhythm. Boom/vroom/boom/vroom. I get myself back to the marina quickly.
I changed out the plugs (not new since last year) even though they didn't look extremely fouled. Then I thought about trash in the carbs. I popped the top one out and saw some crap in there, but nothing major. I loaded all carbs up with Seafoam (using test tank) and let it sit overnight.
Next day, that RPM up/down thing hit a couple of times, not in rhythm, and maybe once every five minutes. Far, far less frequently. I shrugged it off as I-Can-Live-With-It, and fished all day.
Yesterday, I'm back out, and that UP/DOWN pattern was back in full effect. 10 seconds at proper RPM, 10 seconds of 20-30% reduced RPM. Almost in perfect rhythm...like a clock.
This is making me crazy. Please tell me this sounds familiar to someone.
Appreciate all input.
David
Older inline 6 on the back of a restored all-wood Thompson. I run it 1-3 times per week all year long. Starts first crank, runs without a complaint or whimper for two years. Perfect.
This started last week: running fine, about half throttle, then suddenly, power drops 20%. Boom. 5 seconds later, back to normal. Vroom. 30 seconds later, drops 20%. Boom. 10 seconds later, back up. Vroom. This is major..like the motor is being kicked in the nads. RPM's drop, and feels like putting on the brakes. I start to go over everything in my mind, while this up/down pattern settles into about a 30-second rhythm. Boom/vroom/boom/vroom. I get myself back to the marina quickly.
I changed out the plugs (not new since last year) even though they didn't look extremely fouled. Then I thought about trash in the carbs. I popped the top one out and saw some crap in there, but nothing major. I loaded all carbs up with Seafoam (using test tank) and let it sit overnight.
Next day, that RPM up/down thing hit a couple of times, not in rhythm, and maybe once every five minutes. Far, far less frequently. I shrugged it off as I-Can-Live-With-It, and fished all day.
Yesterday, I'm back out, and that UP/DOWN pattern was back in full effect. 10 seconds at proper RPM, 10 seconds of 20-30% reduced RPM. Almost in perfect rhythm...like a clock.
This is making me crazy. Please tell me this sounds familiar to someone.
Appreciate all input.
David
