1971 25hp Johnson running rich

[davidmbv]

Hello all, I have been working on my old 1971 25hp Johnson. I have replaced various parts with OMC replacement parts but my issue is the outboard still runs way too rich. I get a lot of sludge in the barrel and some loss of power. My mechanic thinks it may be a hole in the water jacket or stoppage. We have rebuilt the carb, new kit. Adjusted the low speed jet and it seems to idle in gear but still getting some fouling on the bottom cylinder. I’m hesitant to remove the water jacket because the bolts show signs of corrosion. Does anyone ha e any input on water jackets causing the motor to run rich if plugged or damaged? I have done the following:
Checked spark -good spark
Checked compression-good compression
Replaced points and set gap and timing
Set the link and sync correctly
Replaced coils/condensers
All new ignition wires
New top seal
New plugs-currently using JC8 also tried JC6 and JC4 but same issue
Adjusted low speed jet
Replaced high speed jet
Cleaned and rebuilt carb
Set float bowl etc
Cleaned all passages in carb and new plugs
New T stat
New gas
New fuel tank and lines
New water pump and gear oil
Any thoughts?
After running in barrel a large amount of sludge is present in the barrel ...
It was running great then began losing spark on one cylinder. I discovered one coil wire was not tucked away properly and rubbed against the flywheel causing a short. Replaced the coil and it’s been running rough ever sense . I’m thinking maybe unburnt gas/oil plugged up some water passages?
Thanks
Dave

 

[racerone]

???----A hole in the water jacket ?-----Did you check fuel pump diaphragm.-----If ruptured it would allow fuel to go directly into one cylinder.-----If ruptured , a new diaphragm is the easy / cheap fix.------And that motor running in perfect condition will sludge up a barrel of water.

 

[davidmbv]

I recently replaced the fuel pump with the OMC pump . Good to know about the sludge in a barrel. I’ll try taking it out and running the heck out of it and see what happens.

 

[Crosbyman]

generally 2 cycle engines have crankcase purge valves to dump excess accumulated/unburnt fuel oil mix pooling in the crankcase. on older models it just goes out the back door via an internal drain channel. Along with it goes portion of the new incoming fuel/oil mix in the cyl. during the down stroke . It will exit with the exhaust fumes in the bucket

all this will pool in the bucket and look like a chocolate brew after a few minutes !!

Topic: Gas / fuel leak help on a 1954 25hp Johnson RD-15 – Page 2 – Antique Outboard Motor Club,Inc

www.aomci.org

Topic: 1954 CD-11 Convert from 2 line to 1 line fuel – Antique Outboard Motor Club,Inc

www.aomci.org

 

[racerone]

I guess I missed the new fuel pump listed in post #1.----Perhaps inspect the exhaust cover divider plate as your mechanic suggested then.----Does spark jump a gap of 1/4" plus on a test device ??----What are your actual compression numbers ?-----Working on a 1975 model 20 HP this week.-----Same motor as yours.-----Full teardown and inspection.

 

[oldboat1]

JC8 plug is too hot -- should be tuned to run well with JC4s, with JC6 as alternative. Sounds like idle air mix is too rich -- may need leaner setting after thorough cleaning of idle passage on top of carb, under expansion cap. Make sure the orifice is clear (no broken tip of another needle, and bushing at tip not jammed -- perhaps with one from an earlier needle.)

 

[Crosbyman]

ain't saying it is.... but I would check the crankcase drain circuit to ensure the small flapper valve is not stuck and the hose is not blocked or crudded up preventing the lower crankcase cavity from draining excess fuel oil and causing an overly rich lower cyl.

behind the valve are 2 small holes which drain both crankcase cavities and they should be flushed with carb cleaner then air pressure blasted to clear any accumulated crud.

see text on my previous document about crankcase drainage and servicing

 

[Crosbyman]

see pict. of an older model but same concept .. in your 1971 version the juices are routed to a small hose in front it may also dump the fuel-oil in the lake while on older engines it is routed (dumped) in the lake via an internal passage just below the flapper valve ... same principle different routes.

 

[davidmbv]

It’s been few months since I checked the compression but I recall it was within specs and somewhere around 110 on each

I guess I missed the new fuel pump listed in post #1.----Perhaps inspect the exhaust cover divider plate as your mechanic suggested then.----Does spark jump a gap of 1/4" plus on a test device ??----What are your actual compression numbers ?-----Working on a 1975 model 20 HP this week.-----Same motor as yours.-----Full teardown and inspection.

Thanks for the input. We will plan to inspect the exhaust cover divider plate. I checked the compression few months ago and I recall it was around 110 on one and 112 or so on the other. Cant recall the exact numbers but I read it was within spec. I finally took it back into a local shop last week because I couldn’t get it to run without a miss. The mechanic rechecked the compression and said it’s good. Also tested spark and said it’s good. He re-rebuilt the carb and said he found a piece of the slow speed needle bushing way inside that I missed. He pulled it out. I’ll plan to reorder another one. Also, checked the link and sync again that I had set and the mechanic said it looks good and idles ok but the low speed adjustment is very sensitive and it’s running rich .

 

[davidmbv]

JC8 plug is too hot -- should be tuned to run well with JC4s, with JC6 as alternative. Sounds like idle air mix is too rich -- may need leaner setting after thorough cleaning of idle passage on top of carb, under expansion cap. Make sure the orifice is clear (no broken tip of another needle, and bushing at tip not jammed -- perhaps with one from an earlier needle.)

I’ll try to tune it with the JC6 but figured the hotter plugs may not foul as quick. I also read somewhere that well used motors may run better with JC8s . I’ll throw the JC6s in and try to tune it with them

 

[davidmbv]

ain't saying it is.... but I would check the crankcase drain circuit to ensure the small flapper valve is not stuck and the hose is not blocked or crudded up preventing the lower crankcase cavity from draining excess fuel oil and causing an overly rich lower cyl.

behind the valve are 2 small holes which drain both crankcase cavities and they should be flushed with carb cleaner then air pressure blasted to clear any accumulated crud.

see text on my previous document about crankcase drainage and servicing

Thanks! I’ll check the parts you recommended. I know the only hosed I haven’t replaced are the crankcase hose you recommended I check . I’ll check those areas and see if that helps.

 

[merkdawg0084]

Search Leeroy’sramblings. There is a lot of information on Evinrudes there. Not sure how the head is on the 25hp, but I know on the 71-75 15hp. There was a recall back in the day, because the way the head was designed it was letting fuel mist not burn off. Fouling the plugs. In the article it talks about orientation of the plug to help keep it from fouling.. Hope this is of some help.

 

[davidmbv]

Search Leeroy’sramblings. There is a lot of information on Evinrudes there. Not sure how the head is on the 25hp, but I know on the 71-75 15hp. There was a recall back in the day, because the way the head was designed it was letting fuel mist not burn off. Fouling the plugs. In the article it talks about orientation of the plug to help keep it from fouling.. Hope this is of some help.

Thanks I’ll search through his posts. I’ve read a lot of good info on his posts related to other topics.
Thanks for the info.

 

[davidmbv]

Well we cleaned the exhaust cover divider plate /new seal and cleaned/rebuilt the carb again. Lots of old carbon in the exhaust cover water passages that was cleaned out.
Cleaned out the crankcase drain circuit and made sure everything was not plugged up. When we pulled the crankcase bypass hose unburnt fuel came out when it was running. I’m thinking it running too rich...

Still had intermittent spark on the bottom cylinder so we replaced one coil with a new spare I had and replaced the points and condensers again. Got good spark now on both cylinders but it still seems to run rich but is idling good and runs good at high rpms. It’s strange that the low speed jet idle adjustment only takes a half turn to get good idle setting. The only thing I can think of that is causing it to run rich is that I had replaced the high speed jet/orifice (72) that I damaged when rebuilding the carb, with a new OMC replacement (72D). The parts catalog show two different part numbers for the 1971 25hp Johnson but they appear to be the same jet. One just is stamped 72 and one 72D.
Does anyone have any other ideas why it’s running rich and fouling plug at lower trolling speeds and the low speed jet only takes 1/2 turn to run correctly? When I was attempting to remove the old orifice to clean the carb, I broke it but was able to remove it and insert the replacement. I have since invested in a jet removal screwdriver. Maybe I messed up the threads a bit but will not know until I remove it agin.
Thanks