Running on only 3 cylinders

sammons · Jun 22, 2008

Need some help Have Evinrude 140 78 model and its only idling on 3 cylinders last time I had it out on water ran great no problems but when I reached the dock it was idling very low rpm and staling out got home and found out I had only 3 cylinders. Checked spark and it is very strong about a half inch gap but not sure if its getting fuel, plug is a little wet and oily but not sure if its getting enough fuel to spark. Just wondering what would be the best way to check if I am getting enough fuel to this cylinder and if not what the problem could be. \

Thanks for any help.

HighTrim · Jun 22, 2008

Re: Running on only 3 cylinders

Exactly which cylinders are you dropping? And how do you know that they are dropping? They are all sparking as they should you say?

guy74 · Jun 22, 2008

Re: Running on only 3 cylinders

A 1978 140 is a V4, right? Which cylinder isn't hitting? Is it the one that the fuel pump is on. I had a fuel pump on a 90hp evinrude that went bad and flooded #4 cylinder at idle, but it ran fine at higher rpm. Could this be your problem, since you say the plug is wet?

sammons · Jun 22, 2008

Re: Running on only 3 cylinders

Its the bottom starboard cylinder and yes its a V4 and its a 78 model.
I remove one wire at a time as its running and they all drop rpm or stall motor except for the cylinder in question it has no effect when I pull the plug.

HighTrim · Jun 22, 2008

Re: Running on only 3 cylinders

Yet you are getting a strong blue spark that will jump a 7/16 gap on an inline tester?

R.Johnson · Jun 22, 2008

Re: Running on only 3 cylinders

If you have a strong spark, and a wet plug, start with a new plug, then a compression test.

sammons · Jun 23, 2008

Re: Running on only 3 cylinders

I think its bad news checked compression have 120/115/110 but only 35 psi on the cylinder in question, I'm guessing this means a rebuild.

HighTrim · Jun 23, 2008

Re: Running on only 3 cylinders

That is not good no. Have a look first before you decide what you want to do. If you post some pics of what you find, there are some experienced guys on here that will lead you on the right path.

Good luck.

sammons · Jun 23, 2008

Re: Running on only 3 cylinders

Should I just pull the cylinder head and look at the condition of the rings and piston first.

SKEETR · Jun 23, 2008

Re: Running on only 3 cylinders

Yes pull the head first, may just be a blown head gasket. You will probably see pits and dings all over the piston and head you lost a ring and need to rebuild. If not and the cylinder walls are not scored too bad you could remove your intake bypass cover and check the rings out further. If by some slim chance all looks pretty good try spraying some sea foam in the cylinder bolt it back together and run it out then recheck your comps.

sammons · Jun 23, 2008

Re: Running on only 3 cylinders

Not Looking To Good for me!

sammons · Jun 23, 2008

Re: Running on only 3 cylinders

Another pic

sammons · Jun 23, 2008

Re: Running on only 3 cylinders

something rubbed on the outer portion of this the scrape is not good.

sammons · Jun 23, 2008

Re: Running on only 3 cylinders

another shot of the inside

SKEETR · Jun 23, 2008

Re: Running on only 3 cylinders

Looks like it passed that chunk of ring just fine. Unfortunately that piston is a gonner. How many hrs. on the motor since last rebuild? It is a 78 right?

sammons · Jun 23, 2008

Re: Running on only 3 cylinders

I dont think its ever been rebuilt I bought it about a year ago and it sat for about 8 years until i bought it. Ran great until now.

iwombat · Jun 24, 2008

Re: Running on only 3 cylinders

That cylinder looks awfully dry - either that or its been steam cleaned by a leaky head gasket. You need to find out why it ate a ring before you rebuild.

SKEETR · Jun 24, 2008

Re: Running on only 3 cylinders

looks like you have the exhaust off what do the rings look like from the side? From your picture it looks like the piston edge is warped. If you plan to do the rebuild yourself get a factory manual and avoid alot of the guess work in reassembly. You will need to take the block into a macine shop to re-hone the cylinder. Insist that your machinist chamfer all the intake/exhaust ports. As far as parts go it depends on what you want to spend and how much you intend to keep using the boat. A complete rebuild by yourself with all new stuff could run up to $1700. If you just address the one piston and your bearings look good enough $3-400.

sammons · Jun 28, 2008

Re: Running on only 3 cylinders

I have a question does anybody know what the torque rating should be for the rod bolts my manual says 42 ft lbs but that seems way to high already snapped one off at the head trying to torque that high. I went by what the manual recommended to torque them both halfway then ? but when I tried 42 that?s when one of them snapped.
Also if anybody knows were I can get a good used rod for a v4 cross flow let me know cause I cant find anybody that makes them anymore and I cant get the broken bolt out of the rod. Thanks

Running on only 3 cylinders

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