1994 250hp motor

[neverenoughx2]

I am baffled. I have twin 1994 250hp yamaha outboards. I keep losing rmps at 3900rpms. It will fluctuated down to 3700-3600 then back up. It happens quick to where you can't miss it. When I run at 4200 rpms it doesn't happen. I tested all the coils and found one bad one and went for a ride and still happened just not as bad. So I swapped out the coils between the port and starboard motor. The problem remained the same on the same motor (the port). I changed all the fuel pumps same problem, rebuild all the carbs, same problem. swapped out the fuel filters same problem. I guess the cdi unit is next on the list. Any one have any ideas? Oh compression is 105 on every cylinder. will the pulser coil do this? Is there a way to test it?

thanks Tom

[bajakeith]

GRrr !

Ya need to test your fuel system first !!

[rodbolt17]

for the electrical its called buying/owning a stevens CD-77 or at least a digital meter with a DVA adapter and at least the Yamaha tune up spec guide.
the diagnostic test lamp will also be of value.

[99yam40]

as Rodbolt said having the proper test equipment to test the inputs and out puts to make sure they meet specs is the best way to see what is happening with electrical and testing at the problem RPM while the problem is there is a must

[neverenoughx2]

I have the test lamp. Is that the winky blink your talking about. I have the Manuel and test meter. Where should I go next is my question. Looking to brain storm. I changed everything fuel relayed. What else is there?

[rodbolt17]

next step is to simply understand how and why the system works.
its actually very simple.

[SeaDawg3]

Peak Voltage/DVA