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1988 Johnson wonbt idle properly

rich639

New member
" I bought a used 1988 Johnson

" I bought a used 1988 Johnson V4 90 that has never idled correctly. The throttle plates need to be slightly cracked open for the engine to idle. If I turn the ignition advance idle screw in almost all of the way, the engine will idle okay, but this can't be the way the engine is designed. It runs great 1500 rpm through 5000 rpm. 1000 rpm in driveway with muffs is about 700 rpm in water. As I gradually retard the timing with the idle screw, the engine stalls around 600 rpm, which is when the butterfly valves fully close.
I bought the factory manual and parts book, cleaned and rebuilt the carbs, VRO, checked compression to be 110, 115, 108, 105 for cylinders 1-4 (manual says differential within 15 psi is okay), get a strong blue spark jumping a 7/16" gap, plugs are all tan, although plug #3 (108 compression) is slightly darker than the others. 6 gal tanks' pickups have clean screens, new gas, all fuel lines have recommended clamps and appear tight, drain lines checked ok. I set the thottle sync. pickup, then WOT with engine cranking speed with plugs removed at 24 BTDC (should be 28 BTDC running), set the cam follower pickup at TDC at cranking speed with plugs out because it idles better than when set at 4 BTDC (specified running follower pickup)at cranking speed. I tried putting grease on the throttle bushings to see if air was leaking there but no improvement in idle. Reed valves look okay through carb venturis, and don't get fuel spitback through carb. Last year I pulled the powerhead and cleaned the carbon buildup out of the exhaust manifold area between the powerhead and the center section of the engine. The idle bleed jets are .034" and were cleaned, but I am wondering if I should run a #65 drill bit (.035") through them? The screw slots are slightly mangled from a prior rebuild.
Why would I need the throttle plates cracked to run; what is the best sequence to set the timing;
and what should I expect to get for timing with the engine running at 700 rpm in fwd in the water with the throttles fully closed? Thank you VERY much in advance for your assistance.
-Rich (rich639) "
 
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