Logo

1995 Johnson 225 GAINS power suddenly when warm

Mr Gobble

New member
So, interesting question... I've read a lot of forums about parts failing when heating up, but haven't seen anything about parts starting to work properly when hot.
I have a 1995 Johnson 225 (J225TXEOB) which is very down on HP when it's cold. When running for about 20 minutes or so there is a sudden and very noticeable increase in power with no corresponding throttle change.
This weekend I was cruising at 30mph, and suddenly I was doing 38mph. All with no input from me!
The idle does feel like it's missing, however there is spark on all 6.
This is a bit undesirable as water skiing first thing in the morning is what I have the boat for, but being so down on HP makes it a bit harder getting out of the water.
I'm pretty mechanically inclined, so I can pretty much tackle anything, but I'd like some advice before I go throwing expensive parts at it!

Thanks in advance
Brodie
 
Thanks for your responses racerone and faztbullet. I will do a compression test and timing light test as soon as I can get the boat out again - daylight saving starts this weekend (New Zealand), so I'll have some more light in the evenings
 
Compression test numbers as below. Unsure on what these are supposed to be, but the variation is a bit much for my liking. What do you reckon?

First number is cold, second is after 30 mins of running at 3500rpm average

2 - 130 120
4 - 105 100
6 - 95 95

1 - 115 110
3 - 120 115
5 - 110 105
 
Right, a year on and NZ is back in a covid lockdown. So I'm back working to diagnose this motor.
I have borrowed a timing light, which shows no spark on cylinder #2. Spark is intermittent (maybe firing once out of 15 or 20) when in quickstart mode, but when the motor leaves quickstart, there is no spark on #2 at all. Consistent spark on all other 5.
I did originally have a no-spark on 2,4,6, but a disconnect, and reconnect of the kill leads (at the pack, blk/yel + blk,org) brought 4 and 6 back. Not sure if that's significant or not, but thought I'd mention it.
I have not replaced port head gasket yet - but I do have the gasket in the garage.
Any ideas as to the next step from here?
 
Last edited:
Righto. Pack ohm tests (ignition coil input) to the timer base connectors from 110 to 150ohms.
I did also notice that there seemed to be a reverse pulse on the #2 lead - ie clipped the timing light on backwards, which lined up with TDC #4. Unsure of significance of this yet, don't know whether that suggests pack or timer base. Maybe someone else has seen this before?
I am working on building a DVA to test further - don't have any 400V capacitors in my stash, so will have to wait till Wednesday to get one.
 
I've got the port head off, and to me the pistons look a bit loose in the bore. I've never had the head off a 2-stroke before (only 4 strokes) so I have no idea if this is normal or not. I can see past the top to the top ring, and the gap looks pretty small, so that part looks OK, just not sure on the piston. I know there's supposed to be some clearance, and the ring is what does the sealing anyway, but does anyone have any experience with what's normal on these motors?
All 3 pistons are similar.
Part number on 4 indicates it is original.
See video
Cheers
 
Back
Top