1985 90hp Johnson V4 runs well on hose - not in water

I have a Johnson 90 hp that will runs very well while hooked up to water hose. When put in body of water it will not even try to start. Take it straight back to the water hose and it will again start right up and run smoothly. Is it a water pump problem. Only thing I can come up with.<br /><br />Thanks for any help or ideas.

Re: 1985 90hp Johnson V4 runs well on hose - not in water

Welcome!!<br /><br />It has to do with backpressure. If the motor has been sitting or its history is unknown, cleaning the carbs would be a good place to start. Even if the water pump want working at all the motor should still start. Most likely a carb issue, kinda common. But just to be sure, check spark. If its only running on 2 then it will run on the hose but not in the water.<br /><br />While the motors running on the hose, very carefully -- and with insulated pliers -- pull the plug wires off one at a time. If you pull one or two and nothing changes, then that one is probably not getting spark. If you can hear spark but the motor runs the same, its probably not getting fuel.

Re: 1985 90hp Johnson V4 runs well on hose - not in water

Thanks for the info. Just do not understand why it runs so well under the hose and not in water.<br /><br />I will try your suggestions. Had been taken to shop for service, guess they did not look at carbs since I did not speciffically ask them to.

Re: 1985 90hp Johnson V4 runs well on hose - not in water

rich...Like Dhadley said, it runs on the hose because there is no backpressure on the exhaust coming out of the prop, once you put it in the water there is backpressure on the exhaust and it puts a small load on the engine making it slightly harder to run. If you have weak spark or a clogged carb or carbs and then engine can't handle this small load, it stalls or won't even start, which is what is happening to your motor. What kind of service was done at the shop, did you mention to them that it doesn't start in the water?

Re: 1985 90hp Johnson V4 runs well on hose - not in water

I did not mention that it did not run in the water. It was started on a hose and cranked right up when I was looking at buyinh it. I just took the chance that it would be a good motor and probably still is. The shop just changed the plugs and whatever they do when they give it a "seasonal" tuneup? Not real sure what they did?

Re: 1985 90hp Johnson V4 runs well on hose - not in water

If you just had a shop give it a seasonal let them mess with it - I assume they guaranteed their work.

Re: 1985 90hp Johnson V4 runs well on hose - not in water

I will do that. Question - if it has weak spark, what excactly does that require to fix? Does a carb job fix that problem?<br /><br />Thanks again for the help

Re: 1985 90hp Johnson V4 runs well on hose - not in water

Took my Johnson 90 hp that would run on hose but not in water back to a new shop and explained the backpressure problem that you suggested I might have. They tell me it is fixed and it had to do with the idle on it, that it was not idling enough to prevent the back pressure. They tested the compression and checked the carbs etc. and tell me it will work in a body of water this time! Out of curiosity, what should the compression be on this model. Looking forard to picking it up and testing it in the water - I am o for 4 so far on getting it to run. Hopefully this will be it. Thanks for your help in getting me going in the right direction.