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1975 Evinrude 70hp no WOT

U

usm98

Member
I put the boat in the lake last weekend. Checked out the motor on muffs started and ran fine, maybe just a little skip at 1000RPMs on the muffs.

In the water on my 20ft pontoon could only get 2800 rpms no more at higher throttle only more smoke.

Checked spark looks good. Compression #1 145, #2 120, and #3 140. After puttering around the lake for an hour pulled new plugs #s 1 and 2 were turning black and #3 was completely clean. What do I need to check or where do I go from here?:confused:
 
Got spark on #3?
If not, try to switch coils.
Got spark OK, perhaps time for a carb clean and re-build.
As a side comment, your Cyl #2 may be developing a problem.
 
You have 25 psi difference in compression between the highest and lowest cylinder reading..... not good! Suggest you remove the cylinder head in order to inspect the piston, cylinder walls, sealing surfaces of the head and block, etc.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
 
Thanks Joe I was afraid that was the next step to take, was hoping for an easy out. Anything special I should be looking for?
 
Just let us know what lurks under that cylinder head...... steel particles embedded in the head's dome area, deep scores in the length of the cylinder sleeve, top piston area melting away, corrosion and/or pitting at the combustion sealing area that might be causing a problem...... and lastly and hopefully a failed head gasket that's the cause of the compression loss, and finding that all else is okay.
 
Post a pick of engine with dismantled cylinder head as well as the cyl head combustion chambers.
If no marks on the head and cyl walls, you may be as 'lucky' as only rings are sticking.
Take a thin feeler gauge, turn the engine so port is open, insert the gauge between piston and cylinder and carefully turn the engine with piston at top.
Move the gauge around the piston. It should be an even resistance all way around, if not you have a sticking ring problem or loss of tension in the rings.
In that case, dismantle engine, hone cyls and put in new rings.
 
I have pictures it appears sometime in a past life this motor had a come apart there are grooves that I can feel with my fingernail and the head has old damage. Head Gasket looked good. is it possible this is usable and the issue is somewhere else? Trying to upload pictures...
 

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Uuhuh Clean piston is the result of several applications of Seafoam. Wanted to make sure I had de-carboned sufficiently sometimes I subscibe to the theory...if a little is good then a lot is ... may have gone overboard so to speak.:D
 
Okay meant to bring some gauges from work this weekend and in my rush to get away I forgot to bring them home. Can the 3 cylinder be resleeved? Bored out to oversized and how much is the limit? Overall question what is the best thing to do? I am pretty fair mechanically but never rebuilt boat engine. I was originally on the search for why I had a 25 psi differential I believe I found it. Can or will this motor run as is if I find the reason for the no WOT or is this the reason for no WOT. One of the things I noticed last week was that in neutral I still could not get over 3000 rpms????
 
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