Topic: Compression – Page 6 – Antique Outboard Motor Club,Inc

This topic has 61 replies, 17 voices, and was last updated 3 years, 7 months ago by fleetwin.

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September 9, 2021 at 9:22 pm #246433
Boonie
Participant
Canada Member
Hey guys. Here’s an update on this Evinrude. New ignition components installed. Points set with a meter and new plugs installed. I am using starting fluid for testing. Spray fluid in spark plug holes and it fires. Spray spray fluid in carb throat and NO fire. Pressure tank is making pressure. So in a nut shell, no change with the new ignition. So it looks like we’re back to either carb or intake. Needless to say frustration is setting in. Going to pull the intake next and have a look. Stay tuned!
September 10, 2021 at 6:50 am #246437
stanley
Participant
US Member
Or seals
September 10, 2021 at 7:15 am #246438
Boonie
Participant
Canada Member
Yup, or seals.
September 10, 2021 at 11:18 am #246445
Mumbles
Participant
There are no crankshaft seals on the 7.5 horse motors. The oil in the required 16:1 fuel mix does the job. There might be a problem with the rubber check valves which pressurize the tank or the reed valves (petals) themselves as it seems the crankcase can’t develop enough pressure to charge the cylinders. Worst case scenario the bottom bearing is fried.
- This reply was modified 3 years, 8 months ago by Mumbles.
September 10, 2021 at 4:03 pm #246460
stanley
Participant
US Member
Yes,Mumbles you are correct,no seals.For some reason I thought this thread had moved from a 5.5 and 7.5 to a 25hp.Tired old brain.
September 10, 2021 at 5:07 pm #246462
Boonie
Participant
Canada Member
Well I have to put this one aside for now. Going to pick up a 1957 Zpetsrborough dart tomorrow with a 18 hp Johnson.
September 10, 2021 at 5:13 pm #246464
Boonie
Participant
Canada Member
That should read Peterborough Dart.This the motor that comes with it.
September 11, 2021 at 4:53 am #246476
Scott Springer
Participant
Does replacing the head gasket about always improve compression? Or is just by chance
September 11, 2021 at 9:22 am #246483
Buccaneer
Participant
US Member
Scott Springer wrote:

Does replacing the head gasket about always improve compression? Or is just by chance

I would think an improvement in compression “only” if you cure some leakage,
or use a thinner gasket, and that would be marginal.

Prepare to be boarded!
September 25, 2021 at 8:49 pm #247244
james hobson
Participant
What’s the difference between a 9.9 and a 15 hp evinrude I was told they are both the same the only difference is the 15 has a different carb , I have a 9.9 but was wanting to buy a 15 hp can I just change carbs and make the 9.9 a 15. Thanks for and help
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