1978 55hp evinrude running on 1 cylinder ?

[Mybadomen]

Hi guys . I bought a 16 foot aluminum Grumman bow rider with a 1978 evinrude 55hp engine . Engine starts right up and will run all day but has no power at all . It wont go over 3000 rpm in gear at wot and in neutral it will only hit 4000rpm . It almost seems like it's only running on 1 cylinder . I just rebuilt both carbs ( it's a 2 cylinder 55hp) I was told by the person I got the boat from that he did a compression test and that both cylinders had good compression. I believe I'm getting spark in both coils but is it possible under load or high rpm a coil is dying out ? I read allot of people with the same issue that say same problem after replacing coils so I'm nervous about replacing them seeing I have to order them and wait over a week to get them . Any ideas guys ?

 

[racerone]

Check flywheel key.

 

[Zack19919853]

Maybe main jet is somewhat clogged on a carburetor.. try squeezing some gas into the carb when WOT and if is acts better then it’s the carbs possibly or if it bogs down then you know it’s getting correct amount of fuel. Just a though and wouldn’t hurt to try... Try a spark gap tester 3/8 or more blue spark with a snap sounds is what you want on both I had nothing on one had to replace cost around 30 dollars on eBay.

 

[Mybadomen]

I haven't checked the flywheel key but I have just rebuilt the carbs with no change. I'm starting to think it's a headgasket but I am not sure . Anyone ever experience a blown headgasket on a 2 cylinder? I have sprayed WD into each carb while wot each cylinder did cut down a bit .

 

[Zack19919853]

Maybe a clogged main jet possibly? To me it’s seems like a fuel related problem. You can check compression. Blown head gasket usually is in result of an over heat and will fill a cylinder full of water and a hard start.

 

[racerone]

Good compression would be 140/145 PSI on that motor.

 

[Mybadomen]

I will try checking the compressor again but was told both cylinders compression was good. I bought the boat from a family member who has had this issue and that's why he sold it and one of the first things they did was a compression test . But the boat is on a dock right now so I'll try my best to see what else I can post when I get back to it . It will idle but not as good as it should . And really seems it's only one cylinder running . The other thing I noticed which could be normal I'm not sure is when in neutral and I rev it up it will skip at like 4000 rpm. But it dont skip in gear . In gear the boat justbwont plane off . The boat new came with a 40 hp and went well with it . With the 55 it won't go over the 3000 rpm .trying my best to explain the issue

 

[racerone]

Some accurate trouble shooting needs to be done.----Somehow folks are reluctant to report facts on their motors.----So what are the compression numbers today ?-----Does spark jump a gap of 7/16" on both leads , yes or no ?

 

[Mybadomen]

Some accurate trouble shooting needs to be done.----Somehow folks are reluctant to report facts on their motors.----So what are the compression numbers today ?-----Does spark jump a gap of 7/16" on both leads , yes or no ?

Yes I'm trying my best to get some accurate tests done but yet again I went to the boat at 90 degrees out and a huge lightening storm hit . Figures.i did get as far as pulling the plugs and looking at them . They both look good. And I tested for spark and both do fire but bottom one definitely seems weaker so possibly just a coil . It's just horrible getting parts without ordering and waiting. When I can get there next hopefully with a compression and spark tester I'll inform you guys more .

 

[Mybadomen]

Hi guys . Well I got some boat time today and took the boat out . Ran sea foam through it . Pulled the coils and checked them , cleaned the screen in the fuel pump and then I noticed that the motor does reach 5000 rpm if I run the throttle from the carbs in neautral . I am almost 100 percent sure that it's the prop is way to big . The prop looks pretty new to the engine and is 12 x 17 . Which to me for a 16 foot aluminum boat didn't seem like much prop . But the boat does have full interior and is a bow rider so many its allot heavier then I thought . So I'm going to grab another prop but i am confused by the math of it . According to what I read dropping a pitch = 200 rpm increase . And dropping an inch in diameter = 500 rpm increase . But then I talked to a boat shop and they said if I'm at 3000 rpm now and and swap to a 12 x 13 prop I should be over 5000 rpm at wot ? That sounds great but the math dont add up or am I missing something ? Thanks in advance for any input on the matter ..

 

[Mybadomen]

Just wanted to update that the problem was solved . The prop was way to big for the boat . I swapped from a 12 x 17 prop to a 13 x 11 prop and can reach 5200 rpm with 2 people and gear on boat or roughly 4500 rpm now with 4 people and gear . I also believe that the foam under the floor is waterlogged so after this season the floor will come out to remove the foam and then re prop the boat next season. Thanks guys for the help and hope this thread helps someone else with this problem before going through everything I did . On a good note now I have all rebuilt carbs and everything else I went through.