1988 johnson 90 misfire

sertommy

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Ok I Have A 88 90hp Johnson V4 Two Stroke-first Time Out Ran Like Hell So This Is What I Have Done So Far-removed Vro It Had A Problem Still Not Running Good (on Muffs) Drained Fuel Tank And Added Fresh Shell 87 W/amsoil Synthetic Premix Still Runs Bad Changed All Four Coils New Ngk Br7hs Plugs (gapped Properly) And Factory Johnson Wires On Muffs Has Good Throttle Response But At 1500 Or Lower Has Bad Misfire And Occasionally Is Stahling Will Cough Real Bad Before Stahl......anyone Have Any Ideas Where To Go Next....by The Way 119-120 Psi On All Four Cyl
 

sertommy

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Re: 1988 johnson 90 misfire

Also Not Sure If This Matter But Standing Behind Boat Left Two Cylinders Much Cooler Than Right Two On Muffs----just Trying To Give All The Details
 

tashasdaddy

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Re: 1988 johnson 90 misfire

possible broken flywheel key, throwing out of time.
 

jtexas

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Re: 1988 johnson 90 misfire

Spark test & cylinder drop test...what condition are the plugs in after idling? Inspect the coil wires & connections for corrosion, missing/burned/chafed insulation.

You mean first time out this spring, or you just bought it? If you don't know when the impeller was last changed or if it's more than a couple years, I'd go ahead & do that.
 

tashasdaddy

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Re: 1988 johnson 90 misfire

are you sure the plug wires are on the correct plugs.
 

sertommy

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Re: 1988 johnson 90 misfire

To Answer Some Questions Plugs Seem Like They Are Ok When Pulled None Look Real Lean Or Rich Or Oil/fuel Soaked I Dont Know What Timing Is At Or How To Check/adjust It Coils/plugs/wires Are All Brand New I Just Bought The Boat And Took It To The Water One Time.......what Controls The Timing On This Thing Theres No Distributor Is There How Do I Check It
 

sertommy

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Re: 1988 johnson 90 misfire

Oh And Also I Have The Wires Going To The Cyliners That The Coil Is Mounted To I Assume That Is Correct
 

CharlieB

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Apr 10, 2007
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Re: 1988 johnson 90 misfire

Coughs, stumbles and dies

Thats a 'lean' miss
1500 and slower is getting down to the primary, idle circuits of the carbs.
Time for cleaning, disassemble, carb cleaner and compressed air thru ALL passages.
Get your hands on a service manual, when all else fails, read the directions, get the float setting right, sync and link
 

jtexas

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Re: 1988 johnson 90 misfire

Your motor has a capacitor discharge ignition system; spark is controlled by the powerpack(s) (black box on the other end of the coil wires). Do it yourself maintenance will be next to impossible without a manual. Schematic diagrams are available on the BRP website here: http://epc.brp.com/login.aspx?Retur...rands=ej&lang=E&AspxAutoDetectCookieSupport=1

Need to narrow the problem down....first step cylinder drop test: Using an insulated tool or a spark plug boot tool (couple bucks at autozone), pull, and then reconnect, one spark plug wire at a time while the engine's running. RPM's should decrease noticeably with the plug wire off, otherwise that cylinder's not firing. Report your results.

couple more things:
Revving up much over 1500 on muffs is not recommended - risk of thermal runaway.
How she runs on the muffs, without backpressure on the exhaust or a load on the prop, is no indication of how she'll do on the water.
 

Solittle

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Re: 1988 johnson 90 misfire

Do a search on plugs - - Those OMC V4s like Champions.
 
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