1986 Johnson 25 hp J25RDC

[zedhead665]

Hello all,

New here and kind of new to outboard motors but not carbs or combustion engines. I own a 1986 25hp J25RDC engine and have had it for about a year. The engine is in great shape and appears to have been well kept and maintained over the years. The engine would start first pull almost every time and didn't require the use of the primer plunger seen here 1986 J25RDC Johnson Outboard MANUAL PRIMER SYSTEM Diagram and Parts About 4 trips out ago it became very hard to start and required me to pump fuel in manually via the primer (about 5 to 10 pumps) until it would idle fine on its own. It would run great all day and fire back up first pull. But if it sat over night or longer I would have the hard start issue. So I figured I had a little trash somewhere in the slow speed needle valve or a passage way and I would clean it out and be back to running like a top. Well that isn't the case at least I don't believe.

My carb (1986 J25RDC Johnson Outboard CARBURETOR Diagram and Parts seen here minus the bowl on mine is different) and every passage way appears to be clear and as clean as the day it was made. I've check all fuel lines and they are clear. I've taken the fuel pump (1986 J25RDC Johnson Outboard FUEL PUMP Diagram and Parts mine looks like this but uses o rings instead of a gasket #2 I believe its a newer version the old owner put on) apart and it seems to be fine. I also got the engine running and watched it pump fuel after disconnecting the fuel line from the carb. So I believe it is working as it should. If I cover the carb throat almost 90% or maybe a bit less she runs like a top at idle. So either I have a air leak or I'm starving it of fuel. Float level is set to the proper height, parallel with the carb body.
What are your thoughts on this?

I've sprayed carb cleaner over all lines and area's I believe could be sucking air and didn't seem to change anything. I don't know what else to look for at this point. I'm not saying I haven't overlooked something so I am willing to start over and try anything again. Thanks for any and all help you guys give me. By the way the tag on the carb reads 396167 MX 16 AL that helps.

 

[jasper60103]

Welcome aboard, zedhead665.
Did you adjust the slow speed needle after cleaning the carb?
The initial setting is two turns out, then dial in from there.

edit: Another thing I would try is after the motor has warmed up, try clamping the primer lines (going to carb and manifold) when its idling rough. It could be drawing air.

jasper

 

[zedhead665]

Yes I did set the slow speed after cleaning. I will try clamping the lines and give a report. Also I replaced the needle valve retainer (http://www.boats.net/parts/search/BRP/JOHNSON/1986/J25RDC/CARBURETOR/parts.html #17) because the old one was trashed. Does this need to be pressed in with some force or should it just drop in. The reason I ask is it seems like it may go back a little further if pressed in. Maybe not just asking.

 

[jasper60103]

Yes I did set the slow speed after cleaning. I will try clamping the lines and give a report. Also I replaced the needle valve retainer (http://www.**********/parts/search/B...TOR/parts.html #17) because the old one was trashed. Does this need to be pressed in with some force or should it just drop in. The reason I ask is it seems like it may go back a little further if pressed in. Maybe not just asking.

I can't recall how much effort it takes to seat it, but I would make sure you got a good seal for sure. Also, I know mine is very tight around the needle making it difficult to turn.

 

[zedhead665]

Ok pulled the hoses cut them back a bit checked them over and reinstalled with zip ties, same problem. I can keep the motor running by priming it every 5 secs but its like it isn't drawing enough fuel at idle from the bowl. Once I get it running and choke it I no longer have to keep feeding it fuel via the primer it will pull from the bowl. But I must keep choking it or it will die out. So its either keep feeding it fuel manually or choke it and let it draw fuel from the bowl. Which means the air fuel mixture is way off, and yes the slow speed is adjusted close enough to get me started. If I slap it into gear and give it some gas it seems to do fine. I cant do that to much before the trash can is to low for the water pump pick up.

I have looked over this carb ten ways from Sunday and its clear. The high speed jet is clear, the emulsion tube is clear, the passage where it draws vacuum for the emulsion tube is clear, the three orifices behind the butterfly are clear including the chamber they draw fuel from. The slow speed adjustment is clear. The fuel passage way from the fuel line in to the float needle valve is clear. The emulsion tube is tight and so is the outer tube. The hose that recirculates the unused gas and oil from the bottom of the crank case to the top seems to be in perfect condition. I know all these area's are clear by using light and a wire to check and carb cleaner to check. All show light and no obstructions.

This carb was not dirty when I took it apart and shows no reason for it to be the problem. But, either I'm sucking air or I'm starving for fuel, or its something else I cant find. Reed valves look perfect also. I got to say I'm at a total loss. I understand exactly how this carb operates but yet here I am. Also I installed a rebuilt kit after the problem started just to cover the basics. So new gaskets and seals all over.

*EDIT* I got 98 PSI on both cylinders cold.

 

[jasper60103]

I'm out of ideas and hate to keep guessing. Hopefully others will chime in. Keep us posted.

 

[zedhead665]

I was looking up under the flywheel today and found some oil gas seepage. Called my somewhat local shop and they said that isn't causing the problem. It needs to be repaired but its not causing my air/fuel issue. Isn't that a great place to draw air into the crank case and cause the air/fuel mix problem I'm having?