1995 40HP Johnson J40ELEO Running Slow

[Rick.]

Hello all. I'm having problems with the above engine. It has been a great engine. Yesterday I went out and it would not plane the boat and only reached about 8 mph. Normal full throttle gets me 25 mph.
I don't have a tach gauge but the rpm is way down from normal at full throttle. Prop looks good. Compression is 120 psi on both cylinders (cold). Both plug wires have good snappy spark jumpin 1/4 inch gap. Plugs are new. It is using VRO2 and using oil from the tank. I'm not getting any alarms but did check the temp. alarm this morning and it alarms when grounded. Carb throttle plates are wide open at full throttle and closed at idle. Fresh gas which I mixed with oil until I get the motor running right. Fuel filter is clean and not restricted. Hose/ primer bulb appear to be good an pumps fuel freely.
Im wondering what else I should be checking? I haven't cleaned the carbs. Haven't tried a different fuel tank and hose. I'm an hour and a half from the lake so want to check as many things as practical before going for a test run.
I assume if it goes into "safe mode" I would also be getting an over heat alarm but I'm not certain.
Thanks for any help you might offer to get me going again. Rick.

 

[jakedaawg]

Do a cylinder drop test. Use plastic pliers and pull a spark plug boot off one at a time. Note changes.

 

[Rick.]

Thanks Jakedaawg. I think you are onto something.
Ok. Tested at home with water flusher. At idle pulled the top wire and rpm dropped, motor continued to run. Pulled the bottom wire and rpm dropped and motor stalled in under 5 seconds. Tried this three times with the same result. Something else that happens is a lean sneeze on the top carb. I would assume it was sneezing on my last trip but I didn't really notice between the grandkids, wind and motor not getting to speed. It did stall several times at the ramp now that I think about it. Rick.

 

[Rick.]

I'm very unsure what to do or check next but I just connected my timing light and reading for rpm jumped up and down a fair bit on both plug wires. Ranged between 950 and 1020 on both so it seems I'm getting consistent spark on top cylinder but not enough to keep the motor running when I do the drop test. Any ideas what to try next would be more than appreciated. I'm in over my head now. No points to clean/adjust. Lol. Thanks, Rick.

 

[racerone]

Check the reed valves.

 

[Rick.]

Will do. Is that strictly for the lean sneeze? I'm unsure what to look at for the failed drop down test. Thanks, Rick.

 

[racerone]

Carburetors do show an adjustable low speed mixture screw.----Have you done anything with them ?

 

[Rick.]

I haven't tried adjusting the carb but was thinking I should to see if I'm too lean at idle. Do you think I should give it a try before looking toward the reeds?

 

[Rick.]

I opened the top carb idle needle between a 1/4 to 1/2 turn and the sneeze is gone and idles much nicer now. Tried the drop down test and motor stops when lower wire is remove and continues to run ( at lower rpm) when upper wire is removed. Not sure where to go from here. Many thanks, Rick.

 

[racerone]

Head gaskets are cheap.------I would remove cylinder head to inspect cylinder walls for scoring.