1975 9.9 johnson bottom cylinder problems.

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May 2, 2010
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Hi everyone.I have a 1975 9.9 Johnson.I can't figure out why it is only running on one cylinder.It only runs on the top cylinder.So this is what I have done.Carb kit,points and condensers gapped .20,,new plugs gapped .30,compression is 68 both cylinders.I took the coils off and switched them and then pulled the plug wires again one at a time and the bottom cylinder still isn't firing.Both coils spark.I put the plugs against the block and they both sparked.Has anyone ever seen or had this happen to them.I can't figure it out.Thanks.
 

OptsyEagle

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Re: 1975 9.9 johnson bottom cylinder problems.

You should probably do a proper spark test using an external spark tester to ensure your spark is strong enough. The spark should be able to jump a 3/8" gap, as a minimum. Seeing a spark on a spark plug is not sufficient to confirm that your ignition system is working.

Next I would switch the spark plugs or replace them both to confirm that the bottom one is not fouled. If you switch them, use NGK B7HS spark plugs instead of the recommended champions. The foul less and tend to work a lot better in that series of motor.

The next thing to look for is evidence of water in the cylinder. When it is running on one cylinder, is the bad cylinder all wet and oily or is it clean and shiny. Clean and shiny would indicate water getting in there. Wet and oily would be normal for a cylinder that is not working. My next move would be to run the motor and spray WD-40 all around the seems of the motor to see if the crankcase is leaking anywhere. I would also look into the carb throat and air silencer to see if any fuel was being spit out signaling a reed valve that might be stuck open.

After that I would start thinking it is the bottom crankcase seal and unfortunately to check and replace that the powerhead would need to be removed, so it would be a last resort.

Those are my thoughts. Maybe others can think of something.
 
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May 2, 2010
Messages
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Re: 1975 9.9 johnson bottom cylinder problems.

Thank you optsy eagle.I put new plugs in it and they are NGK B7HS.The bad cylinder is wet and oily.I will try spraying the WD-40 tomorrow and check the carb as well.
 

raczekp1

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Re: 1975 9.9 johnson bottom cylinder problems.

90 psi is low but 68 is too low
 

the machinist

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May 7, 2002
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Re: 1975 9.9 johnson bottom cylinder problems.

I agree that 68# sounds low, BUT not all compression testers come up with the same numbers. Then it can make a difference just how fast you pulled the cord and how many times when doing the testing. And I have seen many of these motors run at 70#.

I may have missunderstood, but are the points new or just regappped? If used, you may need to clean the contacts with Acetone or something, as just contaminated by a fingerprint can effect them.

I agree with Optsy, do the spark gap with a spark tester, (cheap at automotive stores) however on these magnetio ignition systems I am happy it it jumps 1/4".

Also on that magnetio system, check the wire connections of the blue wires coming from under the flywheel. One of those wires are tied to the kill button & a motor I was working on recently found the wires were frayed at that connection to where there were only 2 strands making the connection, enough to show spark, but not enough to fire the engine.
 
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May 2, 2010
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Re: 1975 9.9 johnson bottom cylinder problems.

Hi The Machinist.O.k. so I pulled the head this morning and the head gasket was leaking bad at the bottom.The top and middle head bolts were really easy to get out and the bottom were really tight.Someone put a new head gasket on before I bought it and didn't torque the head bolts down.The head gasket has sierra on it that's how I know it had been replaced.I sanded the block with fine sand paper and a block to stay square.The head was warped a bit and I used fine sand paper and a sheet of glass to sand it flat.I will be heading off to get the head gasket at the Johnson dealer and I will let you know how it runs after I put it back together.I believe the head bolts need to be torqued down to 120 is that right.
 

AlTn

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Mar 9, 2010
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Re: 1975 9.9 johnson bottom cylinder problems.

18-20 Foot-pounds...216-240 INCH-pounds for a 1978 9.9/15 hp...click on leeroys link at the bottom of his post and make certain it's the same for a 1975
 

OptsyEagle

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Re: 1975 9.9 johnson bottom cylinder problems.

Yes. 18-20 Ft-lbs. Divide it by 3 and torque them all 6 ft-lbs, then 12 ft-lbs, then 19 ft-lbs, all in a spiral fashion like this, from 1st to 6th bolt:

3 4

2 1

6 5

After you use it for an hour or so, re-torque them again. Never hurts to put a little anti-sieze on the bolts in case you need to remove them again.
 
Joined
May 2, 2010
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Re: 1975 9.9 johnson bottom cylinder problems.

Thank-you everyone for the reply's.The head gasket will be in tomorrow and I will torque them the way Optsy Eagle suggested.I have some anti seize that I will apply. Happy boating everyone.
 
Joined
May 2, 2010
Messages
28
Re: 1975 9.9 johnson bottom cylinder problems.

Hello everyone.Well it ended up being the head gasket.I put the new one on and torqued it down then took it for a ride.Idled smooth and ran 100% better than before.Thank-you everyone for you help.
 
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