Carb or no Carb?

[Jon Thunda]

Just purchased a 14' aluminum boat with a 35 hp Johnson (74-86?). Ran some cuffs to it and started it in the yard for some minor adjustments and cleaning. Ran fine on the hose. when in the water the motor will hiccup... cough... whatever you wish to call it. It literally feels like you have struck something under water. Was only doing it at high speeds but seems to be degrading and doing at all but trolling speeds. I wish to be clear that is very quick when it occurs not lasting more that a half a second if even that long... hence the feeling of striking an object. I considered prop blow out but that seems unlikely at lower speeds. (the man I purchased it from has an adjustable pitch prop on it for more speed)

Have been told the carb is probably dirty, but I find that reactions don;t match up to the diagnosis.

Any help would be appreciated.

Thunda

 

[HighTrim]

Re: Carb or no Carb?

Welcome to iboats

That cough is usually due to a slightly lean running carburetor.

Remove the carburetor face plate. With the engine running and with that coughing condition existing, stick two fingers into the carb throat. You will be acting as a manual choke of sorts.

If you find an offending carb, the rpms should increase slightly and the cough should cease to be. This would reveal an idle air bleed jet that has a slightly too large inside diameter.

If you can't find anything wrong with the fuel system, consider a possible leaky lower crankshaft seal, admitting air to the lower cylinder and resulting in a lean sneeze.

Also post your model number so we can give you a year for ordering parts.

 

[Jon Thunda]

Re: Carb or no Carb?

Sorry... it is J35ELCTS. Why would this occur only when the boat is in the water and not on the hose?

 

[ezeke]

Re: Carb or no Carb?

That is back pressure from the water. How deep in the water is your midsection when you are idleing?

The feeling of hitting something might be a spun prop.

Have you done a compression check? Have you checked the flywheel torque?

 

[HighTrim]

Re: Carb or no Carb?

and BTW it is an 83

 

[itstippy]

Re: Carb or no Carb?

"It literally feels like you have struck something under water. Was only doing it at high speeds but seems to be degrading and doing at all but trolling speeds. I wish to be clear that is very quick when it occurs not lasting more that a half a second if even that long... hence the feeling of striking an object."

This is a classic description of a worn clutch dog slipping. The ears on the dog get worn down and rounded, and it slips and then grabs again. The most common cause is "easing" the motor into gear instead of doing the proper "snap" the motor into gear. The fix is to replace the clutch dog.

 

[Jon Thunda]

Re: Carb or no Carb?

"It literally feels like you have struck something under water. Was only doing it at high speeds but seems to be degrading and doing at all but trolling speeds. I wish to be clear that is very quick when it occurs not lasting more that a half a second if even that long... hence the feeling of striking an object."

This is a classic description of a worn clutch dog slipping. The ears on the dog get worn down and rounded, and it slips and then grabs again. The most common cause is "easing" the motor into gear instead of doing the proper "snap" the motor into gear. The fix is to replace the clutch dog.

itstippy:

After some more research and some dismanteling, I agree with your diagnosis... not that I know anything about motors. I asked around and during some work I found the lower unit had not a drop of gear oil in it. I tried a refill and hoped for the best but to no avail... damage is already done. I shall persue the dog clutch and see what comes of it. Thanx for you time and input.

 

[F_R]

Re: Carb or no Carb?

No oil?? Probably much worse than a dog. Prepare for the worst.