Merc 150hp will only do 10-15mph

[Corey64]

I recently bought a 1981 silverline with a merc 150 hp outboard on it the motor is around the same year. The problem is when i took it out it would only do like 10-15 mph and the rpms were very low as well I think around 2000. Then one time when we were out on the like trying to get it to go it just took off and reached 45 mph in seconds then shortly after it bogged down again and we were back to the 10-15 mph. <br />The motor has a miss to it and is not running on one or 2 of the cylinders but I cannot find the prowblem. I have already cleaned the carbs,put a git in the fuel diaphram,and replaced plugs. Does anyone have any idea what could be causing this? Thanks

 

[05GlastronSX]

Re: Merc 150hp will only do 10-15mph

if you think its not a fuel problem, its most likely spark...check to make sure you have spark on all six cylinders and go from there.

 

[Plainsman]

Re: Merc 150hp will only do 10-15mph

Welcome to iboats!!<br /><br />Have you done a Compression test on all cylinders?

 

[studlymandingo]

Re: Merc 150hp will only do 10-15mph

Compression check, and spark check. You can purchase a spark gap tester at the local auto parts store for less than $10.00. While you are there, pick up some Deep Creep in a spray can, and a can of Sea Foam; do a decarb on the engine. Use the red "SEARCH" button at the top of this page. <br /><br />Also, while running, have you tried to pump the primer bulb? Though you serviced the fuel pump, there could still be a problem with the fuel lines or the primer bulb.

 

[tashasdaddy]

Re: Merc 150hp will only do 10-15mph

do you have any history on the motor, how long it has sat without running? give us the serial # so we know witch engine you have..

 

[Corey64]

Re: Merc 150hp will only do 10-15mph

Hi there is spark on all 6 put it seem that when i pull the plug wires off the bottom cyclinder there is no change indicating something is wrong. I have poured some seafoam in already but no change (how long untill it takes affect?) I have not done a compression check yet but will if I need to. As for pumping the primer bulb i have done that to there is no change. I am not to sure how long the motor sat but at least 8 months but could have been a full year. I will also try to get you guys a serial number. Thanks for all the help (also i should add that after i cleaned to carbs and fuel diaphram the motor smokes alot more now, what is causing this?)

 

[tashasdaddy]

Re: Merc 150hp will only do 10-15mph

get some seafoam deep creep spray. the black smoke is carbon burning off the inside. search debarb in the faq section. due a compression check. it takes three things proper spark, fuel mixture, and compression. lets start eliminating. no change in #6 points to compression maybe.

 

[dajohnson53]

Re: Merc 150hp will only do 10-15mph

Corey, just start out with the compression check and spark test on all cylinders - like others have said. Both are very easy and straight forward. That's your starting point just to know what issues you might have to solve. Do this before you go through any other seafoam or other stuff (not that de-carb isn't good, it's just that compression and spark are more basic and more likely to be the issue(s) for you) Get an adjustable gap spark tester and buy or rent a compressoin tester. Both tests are well described in these forrums - There is a thread going on right now here in this forum about spark testing.<br /><br />Post your compression numbers and spark test result and go from there - good luck.

 

[Corey64]

Re: Merc 150hp will only do 10-15mph

Hey thanks for all the help, i took it out to the lake today hoping that it would just magically just start working... and it did! runs awsome its starts great and has perfect rpms and speed i have no idea what fixed it but i dont really care as long as it runs good. The only minor problem is it is ver hard to steer to the left at high speeds and its a little slow of the start but im sure i can fugure that out. Thanks for all the ideas though

 

[tashasdaddy]

Re: Merc 150hp will only do 10-15mph

still due the compression check and spark check. it's no fun getting towed in. or killing your by dragging a dead cylinder.

 

[ricksrster]

Re: Merc 150hp will only do 10-15mph

To balance the steering you can adjust the trim tab behind the prop.