1984 Johnson 50hp with compression problem?

[DMPS4]

Engine starts and runs but once its in the water, it only goes abut 10 mph. Boat and motor sat for a couple of years, had carbs checked, guy said they were fine but after reading some of the things posted on here, I'm beginning to wonder. We've replaced the plugs and drained oil. Any help would be greatly appreciated. <br /><br />

 

[Fish Head]

Re: 1984 Johnson 50hp with compression problem?

I would have it checked by a different guy. Was he a marine mechanic. Sounds like a fuel,carb, or throttle problem to me.

 

[G DANE]

Re: 1984 Johnson 50hp with compression problem?

What do you mean by carbs checked ? Were they removed, soaked over night in carb cleaner, cleaned, reassembled and put back on again ? Only then you will know if they are ok. After that do the entire sync´n-linck procedure in manual, which can cause some of the problem too. If this wasnt done, get another mechanic, or even better do it yourselves with the help og a manual if you are familiar with a little mechanic work. You will miss some experience, but you will have all the motivation, and be very satisfied when it runs. <br />These big twins are very fine motors, what was the reason for naming your topic "compression problems" ? Were there any problems before it sat ?

 

[DMPS4]

Re: 1984 Johnson 50hp with compression problem?

A mechanic checked the carbs, not sure how he checked them said they were fine...said he did a compession check and said motor needs a new piston. We have one spark plug, (lower) that is wet while the other(upper) is dry. In response to your question as to whether the carbs were removed, no they weren't. We are new to boating and really appreciate any help you cn provide.

 

[DJ]

Re: 1984 Johnson 50hp with compression problem?

DMPS,<br /><br />There is no effective way to "check" carbs without removing them.<br /><br />However, you need to find out what your compression is first. If you do indeed have a dead cylinder, all the carb. work in the world won't fix it.<br /><br />The two cylinders should have compression readings within 10% of each other.

 

[ob]

Re: 1984 Johnson 50hp with compression problem?

DMPS, Djohns has it. You need to get the specific readings of the compression test.The mechanic should have provided that for you.If indeed the compression is excessively low on one cylinder the carbs are a moot point.If on the other hand one cylinders compression is slightly low ,it could be due to something as simple as running with a slightly fouled plug and a decarbonizing of the engine may remedy it.Obtain a new compression reading and tell us what you find.

 

[DMPS4]

Re: 1984 Johnson 50hp with compression problem?

Thanks for the help...I let you know what happens!!