20hpmercury
Cadet
- Joined
- Feb 6, 2011
- Messages
- 12
Need some opinions please on a problem I have with a 1984 75hp 4cylinder 2 stroke:
Runs great cold, idles great in my tank (or pond in my case, LOL's!), runs great in my tank for extended periods, but rpm's never get above 3 or 4000 since the boat is on the trailer. Motor ran great for 3 years after I rebuild it, but not the powerhead (already had good compression)
Take it out on the lake and it runs great for 20 mins and then rpm's drop off from 5500 at WOT to 4000 at WOT and it idles ok but sounds a little rough. Take it home, some 30 min later, ohm check on stator, trigger, coils, all check out ok BUT I see tiny aluminum deposits on #1 plug, ugh!!! check the compression and #1 is off 15 psi from the rest.
More info as I have had a number of these episodes and have not found the problem yet:
*Rebuilt carbs and changed fuel filter &cleaned tank
*Rebuilt the control box as I thought the neutral switch might be shorting out
*Cleaned all of the connections
*Problem seems to be only on #1 plug, other plugs look great
*Problem is heat related, runs great cold on the lake until heats up
*water pump pees great the whole time
So,
I think it is the switchbox going bad when it gets warm, I do not have DVA meter (yet), would need to check hot on the water I guess
Or
#1 coil deteriorates and fails when warm and at high rpms
Stator and trigger would not affect only #1, would it????
Thoughts, guesses, feedback???
Much Thanks!
Runs great cold, idles great in my tank (or pond in my case, LOL's!), runs great in my tank for extended periods, but rpm's never get above 3 or 4000 since the boat is on the trailer. Motor ran great for 3 years after I rebuild it, but not the powerhead (already had good compression)
Take it out on the lake and it runs great for 20 mins and then rpm's drop off from 5500 at WOT to 4000 at WOT and it idles ok but sounds a little rough. Take it home, some 30 min later, ohm check on stator, trigger, coils, all check out ok BUT I see tiny aluminum deposits on #1 plug, ugh!!! check the compression and #1 is off 15 psi from the rest.
More info as I have had a number of these episodes and have not found the problem yet:
*Rebuilt carbs and changed fuel filter &cleaned tank
*Rebuilt the control box as I thought the neutral switch might be shorting out
*Cleaned all of the connections
*Problem seems to be only on #1 plug, other plugs look great
*Problem is heat related, runs great cold on the lake until heats up
*water pump pees great the whole time
So,
I think it is the switchbox going bad when it gets warm, I do not have DVA meter (yet), would need to check hot on the water I guess
Or
#1 coil deteriorates and fails when warm and at high rpms
Stator and trigger would not affect only #1, would it????
Thoughts, guesses, feedback???
Much Thanks!