1975 Johnson 85hp has me scratching my head.

MotoBoat

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Jan 31, 2011
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Symptoms:

Rough idle.
Fuel coming from front of lower carb only when engine is running.
Raw fuel trail begins at lower engine cowl, and runs down outside of Exhaust housing and onto lower unit.
Grey foamy substance exiting center of prop where exhaust exits.
With engine running on ear muffs, a oily, raw smelling gas residue appears on ground behind where exhaust exits prop.
#4 spark plug remains clean as new. #2 spark plug is showing signs of firing but not as dark as #1, and #3.
Looking at spark plugs all are wet with un-burned fuel at base of ceramic center.


What's has been tested:

Compression.....good.
Removed spark plug boots with engine running. No change in RPM with #4 spark plug boot removed/replaced.
New Champion Spark plugs installed set at 0.28 gap.
Coils #4 and #2 sensor wires and spark plug boots switched. #4 cylinder remained unchanged when plug boot removed.

Both Carbs removed. Blew through fuel inlet with carbs upside down to test for needle seat closing. Needle/seats are fine. Cleaned and rebuilt BOTH carb's anyway, using OMC kits that included new floats set when upside down even with carb bowl base, floats set when upright with 1" drop. Weighed old floats (5g). New floats (6g). Tipped newly rebuilt carbs upside down, blew through gas inlet, needle seated.

With air silencer removed, placed my hand in front of carb throats when engine running, could not feel air back flow.

I have had the fuel line connected to the motor, with primer bulb pumped until firm, over night. Checked 12 hours later and there is no fuel coming from front of carb or running down outside leg of motor where fuel appears with engine running.

My extensive reading tells me this is not a Reed problem. But that is where I am leaning. On this motor could this be a Fuel pump over pressure issue (With only carb barfing fuel) ?
 

racerone

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Dec 28, 2013
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Could be water getting into # 4 cylinder.------Could be crankcase compression issues.-------Could be the bottom crank seal.------Could be the metal crank sealing rings too.-----I do not know how to interpret " good spark "-----Does the spark jump a gap of 7/16" on each lead, yes or no ?----Post the compression numbers as I do not know what " good compression " means either.----I think this is an easy fix !
 

MotoBoat

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Does ALL Spark plug leads jump a 7/16" gap.........Yes.

Compression:

Cylinder #1.....124
#2.....126
#3.....118
#4.....116
 

F_R

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It is impossible for the fuel pump to supply too much pressure.
 

oldboat1

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You might check to be sure the choke plates are fully opening.
 

MotoBoat

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F_R - Thanks for clarification. Had a Outboard carb rebuild guy comment that fuel pressure sounded like it might be high.

ob1 - Choke plates are fully opening as visibly seen with cowl off, air silencer off, carb throats visible, motor running.

racerone - That was my thought, and was hoping to have you guru's confirm that bad reeds are NOT the problem based on
symptoms!

Another question. When I removed Carbs from motor to rebuild the old gaskets installed between carb body and intake manifold had a dark substance on them. That substance is likely Evinrude Johnson OMC Gasket Sealing Compound #508235. Before re-installing gaskets dry, I contacted two different Lund dealers to ask if Evinrude Johnson Sealing compound was reccommended be applied to gasket between intake manifold and carb body, both indicated that they did NOT use, they installed gaskets dry. What is your guy's opinion whether I use that on any and all Gaskets that attach to Aluminum surface of Engine block?
 

MotoBoat

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Removed lower Carberetor. Needle is out of a brand new BRC carb kit and has all metal needle, including tip of needle.

Needle seat is copper. Both needle and seat are pristine, no scratches or marks of any kind. While carb was out I verified that low speed and high speed jet were stock and not oversized by previous owner.

Float weight was 6g before install. Weight is same after inspection.

Float adjustment is within specs.

Needle does pass the blow through fuel inlet with carb upside down test. No air passes when blowing as hard as possible. Air does pass with carb turned upright (as positioned when installed).

Fuel still dumping down outside of Outboard exhaust housing.
 

jimmbo

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May 24, 2004
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There are gaskets between the inlet seat and the carb body?
You have the correct Float? The new ones weigh 20 % more than the old ones
You didn't manage to install the Float upside down?
 

MotoBoat

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There are gaskets between the inlet seat and the carb body?..............Answer: Yes. White nylon type washer.

You didn't manage to install the Float upside down?...........Answer: Float is not upside down. I don't think needle would "seat" and therefore pass the "blow in fuel inlet tube" test.

You have the correct Float? The new ones weigh 20 % more than the old ones .............

Answer: Float included in OEM BRP kit was identical in size, shape, and color to old floats. I had anticipated and hoped old floats to be Cork and therefore fuel soaked. Instead, old floats were identical in shape, size, depth, thickness, color and appeared like identical material's. I have owned this boat/motor combo since 1990 and had no idea if carbs were ever removed during 1st and 2nd ownership. Wouldn't the difference between 5g (old float) and 6g (new float) be an increase of 20%? 20% of 5g would be 1g?
 

MotoBoat

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I am officially checking Reeds off the list of potential failed part or parts.

Since I have replaced gaskets dry. Again, can someone enlighten me with to use or not to use Evinrude Johnson OMC Gasket Sealing Compound #508235 on gaskets such as carb body to intake of block? Use of Gasket Sealer is not clear in the Clymer Shop Manual.
 

fireman57

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I have never have used sealer there. Make sure you have the little "clover" gasket on the main pickup tube.
 

MotoBoat

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By clover gasket are you referencing a dog cone shaped (kind of) plastic appearing piece that is press fit on end of brass tube that extends down into carb bowl? I have two pick up tubes in each carb and neither carb had these. I don't think this model came with them. I will verify in my Model,year, and horse power specific Johnson Service Manual.
 

fireman57

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this is not press fit. It looks like a clover cutout on a brown round rubber gasket that fits over the pickup tube. not pressed on but easily forgotten.
 

MotoBoat

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I never did have clover gaskets on pick up tubes when carb's originally removed and disassembled. What was apparent was that after rebuilding carbs and reinstalling on motor, starting did not improve, and #4 cylinder was still not firing with engine running. Still had as much or more unburnt fuel passing through exhaust hub of propeller.
 

MotoBoat

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Update: Out of frustration I left fuel hose connected from fuel tank to motor. Pumped bub until very tight. left over night, looked out out side of exhaust housing for flowing fuel. None was present. I leave for a funeral, was warm out 80's. Returned from that funeral 3 hours later. Close to a gallon of fuel was missing from fuel tank. Outside of motor exhaust housing was wet with fuel, and instead of one side, was now flowing from both sides, and dirt was below motor skeg was soaked with gas.
 

MotoBoat

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Next day, I do another search on Iboats for anyone having my issue, and searching youtube vid's also. I came across a clue on both websites that reveal a fuel pump diaphragm failure CAN cause fuel to pass through pulse hose oriface of fuel pump.

Finding this out at night, I ponder if this could cause excessive fuel/flooding issues.

Next day I pull pulse hose off of fuel pump and pump primer bulb, fitting is passing fuel as if a fuel inlet line. I plug open end of pulse hose and pulse side of fuel pump. Prime carbs and start motor. Must squeeze primer bulb every 30 seconds for so to keep motor running since fuel pump has basically been disabled.

#4 cylinder was now hitting again. Foamy grey substance was no longer showing at exhaust of propeller, and raw fuel smell during running stopped.

Problem solved. fuel pump ordered.
 
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