drops rpm`s at hi speed 140hp johnson??

[billybaja]

Hi everybody ,Bill here again have a strange problem I have a 1984 140 johnson I have only been out a few times new to boating anyway had it out today starts right up idles great and moves along nicely.. My problem is that at wot we are doing about 5200 rpm`s I have a 13x17 prop new wires new plugs & wires had the carb`s open they are spoltless rebuilt fuel pump all new fuel lines and water seperator compression 118-120 all cyl`s , I would be running along for 5 min or so temp perfct and then all of a sudden it slows down on it own almost shut`s off and then picks up back to speed or rpm`s. Stick or throttle is not vibrating down checked it did it a few times ran the engine for about 3 or 4 hrs and ran great with that exception ?? I had the gas tank removed from the boat at the start of the season and flushed it out .. I think the rectifier/regulator (unfortunetly under the flywheel, the expensive one) is bad was curious if this would cause this type of problem?? any advice , thoughts would be appreciated ., Thanks Bill

 

[tashasdaddy]

Re: drops rpm`s at hi speed 140hp johnson??

the rectifier's basic job is to convert AC current to DC current for charging the battery. have changed fuel line to new alcohol resistant lines, carbs to fuel tank. is the primer bulb collasping (going flat), vent clear on fuel tank. carbs and timing properly linc n Sinc'd?

Do you have the OEM Johnson Service Manual, not a Clymer or Seloc?

 

[billybaja]

Re: drops rpm`s at hi speed 140hp johnson??

unfortunetly I have the Seloc, had I have know I would have gotten the factory one I believe I purchased the alcohol fuel lines bought from iboats along with the fuel pump rebuild kit and carb kit ,I did not notice the bulb going flat it is odd it will run for quite some time before doing the rpm drop I have to read up on the timeing issue .. I don`t think it is that simply because it would be all the time ,this will run for an hour or so and then it happens ?? Is it possiable it could be poor quality fuel?? yesterday it would not shut off right away when I turned the key to the off position,almost dieseling, checked in the search and most of the same problems with not shutting off were related to bad gas.. thanks Bill

 

[jonesg]

Re: drops rpm`s at hi speed 140hp johnson??

junk in the fuel tank clogging the pickup or the vent hose is blocked.
or the anti-siphon valve at the top of the fuel pickup pipe is no good.
Something before the bulb is clogged to make it go flat like that.

I had a seloc, waste of money, I got a factory manual and tossed the after mkt book.
www.outboardbooks.com

Dieseling can be caused by glowing carbon in the cylinder making the engine run on like a glow plug ignition, do a decarb with seafoam, compression will probably go up too.

You're almost there.

 

[emdsapmgr]

Re: drops rpm`s at hi speed 140hp johnson??

The fuel pump may be weak. When it starts to slow down, have someone constantly prime the bulb on the fuel hose. This will force extra fuel directly into the carb bowls. If the engine picks up and runs ok, consider replacing the fuel pump. That engine should run just over 5500 rpm's. Probably 5600 to 5700. At 5200 rpm, you are actually lugging the engine. Consider changing to a lower pitch prop once you get your running problems sorted out.

 

[billybaja]

Re: drops rpm`s at hi speed 140hp johnson??

Thanks something is not right , I dont remember the bulb being flat it is new goes from a water seperator and from their to a clean recently flushed removeable alum tank with all new lines right to the carbs, and vent..(ARROW ON BULB IS towars carb. CORRECT)I actually tried to purchase another rebuild fuel pump kit but they were out of stock today at iboats..I am only getting up to 5200rpm`s by triming the engine up after it starts to plane off.. not a big hole shot either but steady I really think it should be quicker.. I tried 3 different props so far a 13x15 seemed slow did not record rpm`s , a 13x 17 pretty good that had 5200 rpm at wot only by triming motor and a 13x19 but I did not try timing out the motor with that prop and did not record the rpm`s.. I guess I should look at the timeing .. This motor is supposed to have 2 hrs run time on it don`t know for sure just told by the p/o who seemed pretty trustworthy and said he had rebuilt it two years ago ran it for ihr in test tank and than on water and then winterized it and stored it.., it is very clesn and does have some assembly oil on it.. maybe timeing?? Thanks Bill

 

[emdsapmgr]

Re: drops rpm`s at hi speed 140hp johnson??

Try bypassing the fuel/water separator and see what happens. These engines were not designed to have one in the fuel system. Some of them can significantly restrict fuel flow. The hose bulb should not go flat (indicating a fuel restriction) but should not stay hard either.

 

[billybaja]

Re: drops rpm`s at hi speed 140hp johnson??

ok I will give that a try if the weather gets a little better after work tom (Rain),maybe sneak it for an hour or so after work.. i wish I could remember if it went flat really do not think it did..(really need to take better notes when doing test run`s).. I did put on a brand new rebuilt fuel pump that I had just rebuilt and installed on my other motor and then found a bad cyl so I just put it on this motor only started it a few times., thinking maybe I made a mistake but really a pretty simple rebuild .. What about timeing?? Thanks Bill

 

[emdsapmgr]

Re: drops rpm`s at hi speed 140hp johnson??

The ignition timing should be set when the engine is running at 5000 rpm, under load. There should be a label on the front of the airbox which will state the factory max timing. Could be something like 28 degrees. You should check both the #1 and #2 cyls, and set the timing for the cylinder which has the highest reading-resetting that cyl to the factory recommended degree setting. If you want to do your own maint., you may want to acquire a factory service manual. You can get on from Ken Cook Co., in Milwaukee.

 

[vrundquist]

Re: drops rpm`s at hi speed 140hp johnson??

I just set the timing on my 225 Johnson. At WOT it was at 16 degrees and dropped out occasionally. After setting it to 18 degrees like the air bos says it runs like a top.

It took my self and someone to drive the boat to set the timing. I connected the timing light, had my helper run the boat up to WOT ant 40 MPH. I looked at the timing for about 15 sec and noted the reading.

We then shut down and I adjusted the WOT throttle screw two turns (one for each degree) and checked the timing again. Now it is at 18 degrees.

One note... The way I did it can be dangerous on a crowded waterway that is choppy. I did mine at 6 AM on a remote cove with no other boat traffic. Leaning over the outboarf while at speed is not my kind of fun!

Good luck.

 

[billybaja]

Re: drops rpm`s at hi speed 140hp johnson??

I have a funny feeling that is my problem ,I really do not believe they (the po) did that with this motor.. It is going to be difficult to do that simply because of the traffic here,and water conditions.. Might have to run it up to a lake by my brothers house it is about 75 miles away but would be nice to spend the day their.. I guess I am going to have to get that factor manual for it ,I have the seloc manual but it is not that good really like to read up and understand the whole timeing procedure..I know I can probally do it just not sure of it.. Thanks for the advice Bill