1972 Johnson 25 Rough Idle

[Xcakes0X]

Hey everybody, I got a 25 Johnson that spits and sputters at idle and sometimes likes to die at idle. Sometimes it seems like a "lean sneeze" but when I adjust the idle mixture and richen it until the motor dies the coughing never disappears. The motor only does this when it gets warmed up and runs almost perfectly fine when I start it cold. It also starts very easily cold usually 2-3 pulls but at most 5. Ive replaced points and have done the link and sync. I replaced the old pump with a new Chinese fuel pump and at times there are bubbles in the fuel line but its coughing even when I see 0 bubbles in the line. I suspect I could be dropping a cylinder at idle or I have a crankcase leak somewhere. If anybody has any knowledge it would be appreciated.

 

[Crosbyman]

heat often affects coils...or condensers . have you done any tests or replaced them... ?? the rest is wires, dirty points cracked plug wires .

Johnson

plug boots to engine should give a SOLID 4-8kohms approx.

bubbles are odd it should suck just gas from the tank...check connections for air leaks

Johnson

 

[Xcakes0X]

heat often affects coils...or condensers . have you done any tests or replaced them... ?? the rest is wires, dirty points cracked plug wires .

Johnson

plug boots to engine should give a SOLID 4-8kohms approx.

bubbles are odd it should suck just gas from the tank...check connections for air leaks

Johnson

Thanks I’ll look at the resistance tomorrow but sorry I forgot to mention I replaced the condensers with the points. The previous owner put new coils on it but failed to put new plug wires on so I’ll check those out. It’s got spark in both cylinders but don’t know how strong it is or if it’s dropping out at idle. I’ll mention as well that the motor runs perfectly fine over about 1500 rpm so it’s just at idle this happens.

 

[Crosbyman]

different story.... check the low speed circuit of the carb incl the drip holes under the dime size cap on top .

carb has a small side channel leading to the top drip chamber ....clean it blow it ... check the LS needle for tip breaks

your carb has no bottom needle just a fix jet behind the bolt head..

sparks should jump 3/8 inch

 

[racerone]

It is a 50 year old motor.-----Perhaps 5 owners.-----Post the results of a compression test.

 

[Xcakes0X]

It is a 50 year old motor.-----Perhaps 5 owners.-----Post the results of a compression test.

Compression is 130-135psi in both cylinders

 

[Xcakes0X]

different story.... check the low speed circuit of the carb incl the drip holes under the dime size cap on top .

carb has a small side channel leading to the top drip chamber ....clean it blow it ... check the LS needle for tip breaks

your carb has no bottom needle just a fix jet behind the bolt head..

sparks should jump 3/8 inch

I tried to clean the slow speed previously with a wire and carb cleaner but never took the Welsh plug out might order carb kit and look under that plug.

 

[racerone]

Do an ignition " stress test "-----Does spark jump a gap of 5/16" on a test device , yes or no ??-----And is the thermostat in place and working?----They often stick open.

 

[Xcakes0X]

Do an ignition " stress test "-----Does spark jump a gap of 5/16" on a test device , yes or no ??-----And is the thermostat in place and working?----They often stick open.

I don’t have an adjustable gap spark tester yet so what I did is I hooked my lamp style spark tester up and it seems like every time the motor idle roughs up I loose spark on top cylinder. So issue is unconstant spark in top cylinder. I’m going to get a new plug to check that but could this be that the old spark plug wire is going out or the connection to the boot is corroded?

 

[racerone]

But good spark can jump a gap of 5/16" so why would a bit of corrosion stop it ??-----Good tools and simple testing makes outboard repair easy.

 

[Xcakes0X]

But good spark can jump a gap of 5/16" so why would a bit of corrosion stop it ??-----Good tools and simple testing makes outboard repair easy.

Well just I’ve heard that corrosion on the plug boots can cause issues.the coils are new,condensers are new, points are new and set to 20 thousandths, but plug wires seem factory that’s why I think there the issue.

 

[Xcakes0X]

Update : got it running good turns out there was oil or grease on the points cause somebody extremely overgreased the magneto base so I suspect that some made its way to the points or I got grease on my feeler gauge and thats how it got there. I doubt it was caused by a leaking upper crank seal because there was 0 two stroke mix on the magneto. Thank you guys for helping