no top end power

[sailingwest]

Hi all ,and greetings from scotland ,I am looking for advice took my boat up tp loch lomand today for its first run of the year ,its a 50hp mercury mid seventies and a cold compression shows 130 across all 4 cyls .The engine runs smoothly on tick over and revs freely when not in gear .problem is under load speeding up it will only go to 2000 rpm and no more .I did notice that when priming the fuel that fuel was leaking from around the float bowl on the upper carb ,could this be causing the problem ? thanks in advance for any help .........Jim B

 

[Plainsman]

Re: no top end power

Welcome to iboats!! Could be the float is sticking. Have you ever rebuilt the carbs? If you do rebuild them it might not be a bad idea to rebuild the fuel pump as well.

 

[sailingwest]

Re: no top end power

hi plainsman,I have not had this engine long so have not touched it yet apart from gear oil and new plugs the fuel leak is from where the bowl seat into the carb body could air be sucked in here? or if air were being drawn in would it cause the power shortage

 

[Plainsman]

Re: no top end power

It sure could. And you may want to get the impeller changed if the motor is new to you.

 

[sailingwest]

Re: no top end power

Thanks for your help plainsman ,forgot to mention changed impellor when i changed gear oil ,pumps water like a fire fighter ,will strip and clean carbs and let you know how i get on.....Jim B

 

[sailingwest]

Re: no top end power

hi all ,stripped down leaking carb last night and found problem was float needle valve not sealing ,petrol overflowing through carb mouth ,my question is apart from obvious problem of overflowing are there any other problems that it would cause ......Thanks ...Jim B

 

[sailingwest]

Re: no top end power

Hi All, stripped carb last night and found leak was not from bowl seal but from float needle not seating have ordered carb kit ,my question is apart from the leaking petrol could this non sealing valve cause my lack of power ? Thanks for your help .....Jim B

 

[Chris1956]

Re: no top end power

JIm, if the carb is flooding, it could cause the spark plug for that cylinder to foul, causing lack of power.

 

[Chris1956]

Re: no top end power

Jim, You might like to make sure you have spark to all four cylinders. Use an inductive timing light on each wire. Also watch for the plug wires arcing to ground, which is common on those old motors.

 

[sailingwest]

Re: no top end power

hi chris ,thanks for the input ,i have good spark on all four cylinders .i think you may have something re carb flooding and causing top two cylinders to foul spark plugs i see where you are coming from ,i suppose it would be like choke on a hot engine ?.......Jim B

 

[sailingwest]

Re: no top end power

no luck took her out today for a run after float service no change gets to 2000mpm and then no more ,pulled sperk plugs after it had run and noticed num 1 spark plug was as it should be but number 2 plug was fouled ,both these cyl share the same carb ,would this point to a faulty ign coil ? good spark on tickover on all 4 cyl,thanks again ..Jim B

 

[redjmp]

Re: no top end power

I have the same motor and the same symptoms. Leaky top carb was rebuilt.
after running for 10 minutes, I pulled all the plugs. 3 were hot and showed deposits from firing and 1 was cold and clean with gas.
That coil metered less than 1 ohm across the primary and 1000 ohms across the secondary just like the others. On further inspection after removing the rubber casing, I noticed some cracks. Swapped it out with a blue coil from my '86 115 and it ran like a champ.

 

[sailingwest]

Re: no top end power

thanks for the input red think its time for coils

 

[sailingwest]

Re: no top end power

replaced all 4 coils running like new ,ordered coils from US dealer and even allowing for shipping to Scotland cost roughly half what i would have had to pay here ,Thank for assistance all ....Jim B