1998 Johnson 25hp, will only run at idle, help!

[Ppopps]

2 stroke motor, pull start, has always run perfect even all last week, then all of a sudden I start it the other day and it will only run at idle. Can rev it in neutral, but put it in gear and give it throttle and in surges and will die unless I back it off, then it idles ok again.

Thought water in fuel, checked bottom of tank though (none), pulled carb off and emptied float bowl (it’s clean with no water), blew out the carb passages, reassembled, and ran it on a different tank with new premium and has exact same problem. I took the fuel pump apart and also checked the screen there, no issues. If I squeeze the primer bulb while it’s struggling it makes no difference, so I doubt it’s fuel pump?

Should I be wondering about power pack and or coils or even stator next? Do the symptoms suggest ignition? Would it idle fine if any of those were a problem? I pulled the plugs and both have good color and gap. How would you troubleshoot this further? Thanks in advance.

 

[Bosunsmate]

check spark on both cylinders,
then compression

 

[Ppopps]

In terms of spark, I have a timing light and one of those little inline lights at my ready, do you suspect it's only losing spark at high RPM or under load? Does that make sense/possible? Would it idle if one cylinder had no spark?

how do I check compression on a pull start motor, just screw in the dial, pull off the high tension wires, and pull the start cord?

 

[Bosunsmate]

it may be failing at higher rpms, you need to test it jumps a 7/16 gap.
you can use the timing light while out on boat to see if a cylinder goes dead at load
yes thatl check compression,

 

[Ppopps]

OK. And not to jump too far ahead but how would I tell if the problem (assuming I have a spark issue) is the coil packs or the power pack? I highly doubt a compression issue as the motor looks mint, has never overheated, and ran like a champ just last week. This is an all of a sudden problem.

 

[Bosunsmate]

OK. And not to jump too far ahead but how would I tell if the problem (assuming I have a spark issue) is the coil packs or the power pack? I highly doubt a compression issue as the motor looks mint, has never overheated, and ran like a champ just last week. This is an all of a sudden problem.

http://issuu.com/cdielectronics/docs/troubleshootingguide

 

[Ppopps]

OK, update, still runs the same. I've replaced the plugs and gapped them. I've been through the carb twice and am running new premium from separate tank. Compression is 120 on both cylinders. Motor looks like new. I'm down to spark now. I have looked at that CDI link and can't find a section that exactly applies to my motor, but I have tried to measure the key impedances.

Looking towards the flywheel (so the stator end of the wire plug?) I get 930 Ohms from brown to brown yellow and 42 ohms from black white to white black and solid black is high impedance to ground. Look towards the power pack I get 520 ohms from both brown to gnd and brown yellow to ground and 635 ohms from black to ground.

Both the coils measure 270 ohms across their respective two terminals. Any of that off? Again, motor runs perfect first pull and idle and midrange, but it in gear and try for WOT and it surges and dies.