| Author |
Message |
    
mike mangham
New member
Username: snapperwhipper
Post Number: 1
Registered: 11-2009
| | Posted on Sunday, November 01, 2009 - 05:29 pm: | 
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I am having a hard time getting my 1986 johnson 90 hp to idle correctly.I have rebuilt the carbs but didn't replace floats(not in kit) replaced fuel pump,all fuel hoses and clamps cleaned the filters and replaced water separator all new gaskets and also tested all electrical power packs ignition coils spark plug wires replaced 1 power pack just for the heck of it and it still won't idle right,it just stalls out. Oh yes I have adjusted it with my shop manual as best as I can but it won't idle below 1200rpms.Now the darn thing run great at any speed but idle,WOT about 5700 rpms no problem cruise 4000 rpms great.Should I be looking for a fuel problem or an electrical problem???? |
Martin Johnson
Member
Username: martino1
Post Number: 38
Registered: 05-2009
| | Posted on Sunday, November 01, 2009 - 06:01 pm: |
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I'll beat him to it. What are the compression numbers on your engine? |
Dcramer
Advanced Member
Username: dcramer
Post Number: 186
Registered: 05-2008
| | Posted on Sunday, November 01, 2009 - 09:01 pm: |
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Joe's on vacation.
First the basics. Compression as Martin suggests. Make sure the link & sync is correct including the carb pickup timing. Make sure the little roller aligns with the big mark on the lever as they begin to touch. Make sure the throttle plates are all closed at idle. Make sure the thermostats are present, and the engine is running at the proper temperature. Note that this engine is designed to run hotter at idle than at power.
Find out if it's too rich or too lean. Push in the key to activate the primer at idle. If it smooths out, it's running lean. Check recirculation valves. Make absolutely sure carb idle circuits are clean. Check the gaskets around the carb bases and front half for leaks. Also make sure the gel seal between the crankcase halves isn't blown out. Check the bypass covers on the side near the power packs to make sure the gasket's aren't leaking.
If the engine dies out or no change when you prime, pull a hose off the primer to make sure it isn't leaking. Check the pulse hose from the VRO pump to make sure fuel isn't being sucked in from there.
You should be able to idle that motor down to 650 with ease. Mine ran even slower when trimmed down and it was stable down below 500. |
Billy Winter
Advanced Member
Username: bw94
Post Number: 102
Registered: 04-2009
| | Posted on Sunday, November 01, 2009 - 11:00 pm: |
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sounds like your low speed jets might still be dirty. |
mike mangham
New member
Username: snapperwhipper
Post Number: 2
Registered: 11-2009
| | Posted on Monday, November 02, 2009 - 10:46 am: |
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First thanks for all your input.OK compression is 95-100 in all cylinders not bad for 23 years and maybe original,I've have it for 8 years and it gets lots of use.I used a cheapo rebuild kit that had no floats so I've ordered a OMC kit and all gaskets from my dealer and will install.I need to recheck the link and sync(I do have shop manual).Both throttle plates are closed at idle.This engine has never had thermostats(removed by previous owner)but has always idled OK till recently.I will check those bypass gaskets.this engine doesn't have a VRO I premix fuel.I'm not clear on recirculation/check valves and how to check |
jwbmarine
Senior Member
Username: jwbmarine
Post Number: 5078
Registered: 11-2005
| | Posted on Monday, November 02, 2009 - 07:08 pm: |
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i recommend,a FACTORY service manual to help u service ur eng correctly.they r commonly avail nowdays. |
Tim Lyden
Member
Username: tal55lyd
Post Number: 17
Registered: 11-2007
| | Posted on Monday, November 02, 2009 - 07:51 pm: |
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The engine on most motors should idle with
nothing touching the carbs throttle arm should run by carbs only, best beat carbs still dirty or water in them, remove jet in bottom of bowl take drain plug out remove jet |
Dcramer
Advanced Member
Username: dcramer
Post Number: 188
Registered: 05-2008
| | Posted on Monday, November 02, 2009 - 10:52 pm: |
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Put the 'stats in! |
Phil Kicksee
Member
Username: red_goat
Post Number: 68
Registered: 05-2009
| | Posted on Thursday, November 05, 2009 - 10:28 pm: |
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In a nutshell you set your idle by adjusting your timing.
If the adjusting screw lets the timing go too late the thing wont idle.
You should set it so the timer moves just before the carbs start to move when you push on the throttle.
Its not like a four stroke where you set the idle by adjusting the carb. |
