Idle issues

[doors67us]

Hey guys,I'm stumped on what's going on with my 71 Johnson 25 HP, I've rebuilt the carburetor with a OEM kit,new fuel pump, lines, ignition system rebuilt,new low speed needle,it won't idle down,will run with the magneto lined up with the 2 marks ,but when I lower it past there it dies,I've adjusted the slow speed needle, many times to no avail,even changed fuel pumps but no effect,not sure what it could be, usually don't have this much trouble getting one running

 

[davidmbv]

Did you do the carb link and sync?
Do you have the idle adjustment screw set accordingly?
When you said it dies when throttle down, I’m assuming it’s only running at high revs?
Checked spark? Running on both cylinders?
Low speed jet set to 1 1/2 turns at first then start adjusting once warmed up?
Points set properly?

 

[davidmbv]

YouTube : this old outboard -he has a few videos on setting link and sync on your motor somewhere .

 

[doors67us]

Did you do the carb link and sync?
Do you have the idle adjustment screw set accordingly?
When you said it dies when throttle down, I’m assuming it’s only running at high revs?
Checked spark? Running on both cylinders?
Low speed jet set to 1 1/2 turns at first then start adjusting once warmed up?
Points set properly?

Yes I did the Link and sync,it's sparking on both cylinders,Ive done all the above mentioned,it has to be,a fuel related issue,I think,I've done about 6 outboards,never had this issue before,

 

[Crosbyman]

idling requires a clean low speed circuit in the carb... idle carb needle is one thing but the top idle chamber drip holes must be clean as well as the carb side channel leading "bowl fuel" to the top chamber. make certain idle needle packings are in.
make certain the throttle plate closes enough to exercize vacum against the top drip hole otherwise you will end up with to little fuel pulled to sustain ignition and to much air


see old carb top idle needle and chamber see side channel to the top idle cct very small and MUST BE 100% CLEAN otherwise fuel won't climb up to the top drip chamber

your 71 25hp is just the son of Johnson FD_RX RD s a good book to service oldies even if the book stops at 1964 is the johnson manual 450 pages + on oldies like tn jw ad cd fd..qd & RX _RDs ...

nothing much new under the sun for oldies except CDI ignition and cosmetics. the book is full of general knowledge to help undetand how things work ....

1922-1964 Johnson 302231 Outboard Service Manual

Johnson Outboard Motor Service and Repair Manual # 302231 Tenth Edition covers all Models 1922-1964 .pdf download

watercraftmanuals.com

 

[davidmbv]

Also check the carb float and adjust per service manual .

 

[davidmbv]

The pics attached are from the 1971 25hp Johnson service manual.

 

[doors67us]

idling requires a clean low speed circuit in the carb... idle carb needle is one thing but he top idle chamber drip holes must be clean as well as the carb side channel leading "bowl fuel" to the top chamber. make certain idle needle packings are in.
make certain the throttle plate closes enough to exercize vacum against the top drip hole otherwise you will end up with to little fuel pulled to sustain ignition and to much air


see old carb top idle needle and chamber see side channel to the top idle cct very small and MUST BE 100% CLEAN otherwise fuel won't climb up to the top drip chamber

Well I popped the Welch plug out previously cleaned out the drip holes in front of the low speed needle perhaps I need to do that again maybe there's some dirt in there or something I've had that carb apart 3-4 x

 

[cyclops222]

Some carbs have a packing around the idle needle thread section or a O ring of some sealing material. If missing ? Drive you crazy. Is this a new problem on a engine that ran perfect ? Or do you buy and resell after a tune up ?

 

[kbait]

When at lowest sustainable idle, if your low speed circuit is clean, you should be able to adjust low speed needle too lean.. making it lean sneeze (less than 3/4 turn out), and too rich (more than 1.5 turns) and start slowing/blubbering. If LS needle adjustment does both of those, likely a different issue. Good luck!

 

[Crosbyman]

I've had that carb apart 3-4 x....

cleaning is subjective... for ex: that side channel feeding fuel to the top is critical and with the needle backed away .... pressured carb cleaner must flow up and across the idle hole where the needle normaly restricts the fuel entering the drip chamber.

leave out all the linkage on the LS needle adjustment tune the engine by manually rotating the needle . clean HS & visually inspect the HS jet . make certain all LS needle parts are installed and lead plug installed (see #2) . All carb gasket holes line up (side channel)

lastly consider crankcase seal leaks sucking air and reducing the fuel vacum pull on the LS cct. :-(

 

[davidmbv]

Also Part #35 is easy to forget /forego

 

[doors67us]

I've had that carb apart 3-4 x....

cleaning is subjective... for ex: that side channel feeding fuel to the top is critical and with the needle backed away .... pressured carb cleaner must flow up and across the idle hole where the needle normaly restricts the fuel entering the drip chamber.

leave out all the linkage on the LS needle adjustment tune the engine by manually rotating the needle . clean HS & visually inspect the HS jet . make certain all LS needle parts are installed and lead plug installed (see #2) . All carb gasket holes line up (side channel)

lastly consider crankcase seal leaks sucking air and reducing the fuel vacum pull on the LS cct. :-(

View attachment 398092

Upper crankcase seal has been replaced,thing is it ran well late last summer, only thing I did was, replace the LS needle and fuel pump

 

[Crosbyman]

assuming needle is ok what happens if you help the fuel pump with hand pumping. if no change then the fuel pump shoudld not be the suspect.

why did you change needle (missing???) broken tip ? still stuck in the idle passage ( remove welch plug... you should be able to see the needle tip sticking out 7 movement in the drip chamber side hole when the needle is close dall the way.

 

[doors67us]

assuming needle is ok what happens if you help the fuel pump with hand pumping. if no change then the fuel pump shoudld not be the suspect.

why did you change needle (missing???) broken tip ? still stuck in the idle passage ( remove welch plug... you should be able to see the needle tip sticking out 7 movement in the drip chamber side hole when the needle is close dall the way.

I replaced the needle, because I dropped it,bent the tip of it, replacement was an nos OMC needle

 

[cyclops222]

They sold you the WRONG type for your carburator !!!

 

[Crosbyman]

post picture side by side of each needle

 

[cyclops222]

A correct needle for any adjusting will have a LONG slowly tapering end. Long needles give you a wider stabile area of adjustment.

 

[doors67us]

They sold you the WRONG type for your carburator !!!

Why do you say that?

 

[doors67us]

post picture side by side of each needle

Ok I'll get some