1972 johnson 25hp need timing plate and carb sync procedure

[werewolf]

I just traded for a 72 Johnson 25hp checked compression and has 110 lbs both cylinders, found no spark on lower plug, pulled flywheel and found the guy tried to make a flywheel key which was may to small and the points cam and flywheel were out of time, went and got one inspected the new points and reset them to 0.21 spec shows 0.20 so I allowed for some wear , I need to know the best way to sync the timing plate with carb opening between the two marks on the timing plate , fires great and starts right up but doesn't want to idle correctly , I also need the float adjustment carb number is #315

 

[F_R]

Knowing the requirement of getting betwene the two marks is difficult at the least, all I can suggest is get it as good as you can, favoring being closed at low idle.

Float level is parallel with the carb body when held upside down.

Not meaning to be a pessimist, but we had complaints of poor idle on those motors when brand new out of the box. Problem was OMC's effort to reduce fuel dumping into the water. Some crankcase drains were eliminated, and what was left was discharged into the upper cylinder, making the upper cylinder run richer than the lower. People who traded in their older 18-20hp motors were especially unhappy.

Make sure you run 50:1 fuel mix for best results.

 

[werewolf]

thanks ive tried to get the roller between the two marks with the throttle plate close to being closed , how critical is the throttle shaft clearance ive got it where it will start right up first time with choke or second crank , um going to pull carb again because I know they didn't have the float set high enough , I do have the oil rich right now because it sat for awhile and want to play it safe , I found a manual free download but I didn't notice any timing procedure so im going to look again this morning, I had one of these motors back in 75 and it ran like a scalded ape [no harm to animals done]

 

[racerone]

Did you install a factory replacement key or something else ?----At idle there usually is a space between roller and cam.-----Throttle plate MUST open at the correct time.----Have you check thermostat ?----I usually find them missing or stuck open.

 

[werewolf]

I put a new flywheel key in and took points out to inspect and they were set way too wide I set them to 0.21 it shows 0.20 , didn't figure 0.01 would matter using a infared thermometer on heads they show 150 on bottom head and 140 on top head after running for 30 minutes , it wants to idle better now , I went by what the manual said on float level 1/16 above bowl , but it may need to be flush with carb bottom , I have a tach clamp for my fluke meter im going to put on after I raise the flat 1/16
there is no gap on throttle roller at idle right now

 

[racerone]

Points are set at 0.020 " not as you stated 0.20-----Typo ?-----On most motors there is a gap at the roller at idle.----I would say there is something wrong.----But I can not see / hear / feel your motor.-------Good luck with it.------These are an excellent motor if in good condition and properly adjusted.

 

[oldboat1]

Make sure the cam roller is intact and not worn down. Point at which roller contacts cam is the point at which the throttle plate begins to open (throttling up begins). As described above, before then the engine idles without the roller contacting the cam -- or should, if the carb jets are clean and air mix is correctly set.

 

[werewolf]

ok racerone the points are set at 0.021 plate shows 0.020 , the old roller was nylon and worn down so I made a temporary one from a aluminum valve from an old transmission valve body which is about 0.015 larger than the old roller, once I can get it closer to the marks ill order a roller for it, as it sits right now it starts right up idle seems a little high, and it revs in gear in water barrel all the way up without bogging down , the carb float is currently set at 1/16th above the carb body and someone said it should be flush so im going to try setting the float at flush and see how it does

 

[oldboat1]

Better to buy a new roller (and clip at top [c-clip?]), set points at .020 after cleaning with acetone or similar. The carb float should be horizontal to/level with the upside-down carb body top. Distance from the carb body is not an issue.

 

[werewolf]

Ok I know the point recomended setting is 0.020 . 0.001 wont matter , I already plan on replacing the roller with the factory nylon type , I am going to raise the float to level with bottom of carburetor body ,its currently 1/16th above the bottom, the roller I made is temporary anyway just had to have something on it , I think the carb/timing is causing higher idle than it should be, so I checked my 14 Evinrude plate and the carb roller is new and doesn't touch the timing plate until it gets to the marks on plate it runs and idles perfect. and runs like a scalded cat [no harm to animals done]

 

[oldboat1]

Get an adjustable open air tester, and measure spark on both leads. Remove both plugs for testing. Try for half-inch spark and work backwards if none found. Note the measurement of the spark you find. This is a test of ignition output, and can also indicate whether points are clean and set correctly -- that and whether the engine idles smoothly. No sustained revs unless on the boat.

You should feel a slight resistance on the points gap gauge at .020. Plug gap is .030 on Champion JC4.

For what it's worth (actually, about $120 or so), I usually just replace points, plugs, coils, condensers and wires on a motor that is new to me, along with a fresh impeller.