1975 Johnson 135 High Idle

[xraydude]

Rebuilt powerhead just installed, one new piston (with cylinder bore) all new rings/bearings/gaskets. 150 psi all four cylinders. Rebuilt carbs (floats/seats/valve). Correct #30 idle orifices. Throttle / Shift controls disconnected at engine. Timing/throttle linkage adjusted per manual and synched. Throttle butterflies completely closed. Cranks right up cold with just a short choke and sounds okay (no obvious mechanical crunching noises from my rebuild). Idles at 1800 rpm in barrel. Timing at 5 degrees. If I adjust idle timing stop all the way down to TDC, it will idle about 1200. No more adjustment left. Why can't I get this thing to idle down at proper timing?

 

[xraydude]

Re: 1975 Johnson 135 High Idle

Pulled flywheel, key okay, timer base moving smoothly. Pulled carbs and double checked my rebuild. Idle orifices snug and clean. Floats parallel to body, valves seat properly. Put all back together and tried again. Same results. Sprayed carb cleaner around all gaskets and throttle shafts on carbs while idling and no noticeable change in RPMs. Water pump / thermostat working, get spray when up to temp and no overheating cylinders (hand test). Still idling at about 1800 at 5 degrees and 1200 at TDC in barrel, a little higher on muffs.

 

[JTKelleyiii]

Re: 1975 Johnson 135 High Idle

Are you trying to set the idle on muffs or in the water. Makes a big difference.

 

[JTKelleyiii]

Re: 1975 Johnson 135 High Idle

Sorry, just read u were running in a barrel.

 

[xraydude]

Re: 1975 Johnson 135 High Idle

Yeah, tried on muffs and barrel. I took the carbs off again today, cleaned the mating surfaces on the carbs and the intake and re-installed with new gaskets. Same behavior. It may just be still not enough backpressure in the barrel, but prior to the rebuild, I never had a problem getting it to idle down. I am very much at a loss, so going to take it down to the river one afternoon this week and and see how it behaves in the water. BTW, JT, I'm in Louisiana too, just outside Hammond. Thanks for the response.

 

[emdsapmgr]

Re: 1975 Johnson 135 High Idle

You may find the idle rpm's will go down once you get the engine on a boat and it's floating normally in the lake. You are looking for 650-700 rpms when floating at normal level, set when the engine is in forward gear.