Johnson 15hp bogging down

[tdp63]

I have my first o/b. 1976 Johnson 15hp. Starts ok, idles ok then when throttle up it bogs down and will stall if you let it. However, if I slightly throttle up only little to raise the revs for about 10 secs it will then take off ok. It does not seem to reach highest rpms compared with another motor (same but 1974)I have. After about 2 minutes of running flat out the revs will slightly drop but it still goes along ok. I have been using it as it is a manageable problem but I have now noticed that with this use it is becoming harder to start when stopping and starting from tree to tree fishing. Any help appreciated.

 

[mikeyzx2]

Re: Johnson 15hp bogging down

welcome to iboats! <br /><br />first things first, let's give you a checklist:<br /><br />1)compression check, numbers should be around 100 or higher, and close together. <br /><br />2)spark check, should be bright and snappy and jump at least 7/16" gap<br /><br />3)if you're unsure of maintanence, you'll need to overhaul carburetor with kit, and it needs to be cleaned and the passages blown out with compressed air to dislodge any crud. Check into the waterpump impeller, if it's old it's probably brittle and the vanes with break off. Motor will start overheating. Change out gear lube, new spark plugs, and inspect the wiring.<br /><br />There's a few other things to be added, and I don't want to throw too much in and get you twisted up. <br /><br />Just give us updates or ask for help anytime.<br /><br />Mike

 

[MCM]

Re: Johnson 15hp bogging down

Looks like a good starting point to me. also since this motor would seem to be new to you, you may want to read this thread.... it covers many of the points Mikey referred to.<br /><br /> http://forums.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000033 <br /><br />This link will also provide alot of helpful and valuable info pertaining to your motor.<br /><br /> http://www.wisnersinc.com/Fishing Info/Johnson 9.9_15.htm

 

[tdp63]

Re: Johnson 15hp bogging down

Thanks Mike - here we go. Comp test 95 & 100, spark all good as required, carb has been o/hauled etc., water pump/impeller new and operating very effectively, gear lube has ben changed, new plugs installed, wiring appears OK.<br />How's that for starters. I will be waiting with baited breath for more. A friend of a friend said he had similar problem and resolved by changing fuel line connector at motor. I have another full line to try as soon as I get a chance

 

[mikeyzx2]

Re: Johnson 15hp bogging down

How about the fuel pump? check the fuel hoses too from gas tank to motor

 

[MCM]

Re: Johnson 15hp bogging down

When you get the chance see if pumping the primer bulb helps the next time it acts up. If it helps it could narrow it down to fuel delivery problem such as a bad fuel line or pump.<br /><br />Just as a side note: experience taught me to carry an extra fuel line in the boat. (God bless oars)

 

[tdp63]

Re: Johnson 15hp bogging down

I have referred back to the above links regularly. Especially with the 2nd by WISNER printed out and kept in my shed next to me. Great articles. <br />Fuel pump is good. Took one off a perfectly working motor and replaced mine. No change to problem. I have to do some gardening now to keep in good books then I am off to the boat ramp with borrowed fuel line and tank which are working fine. Thanks guys. Back soon.

 

[tdp63]

Re: Johnson 15hp bogging down

And I will be getting a manual as soon as I can afford it. Need to battle on with suggestions/advice for the time being.

 

[OBJ]

Re: Johnson 15hp bogging down

Well I'll throw in $.02 worth. Couple things.....is the cam follower roller been set correctly? The roller sets to the rear port side of the carb and rides against the cam under the flywheel. <br /><br />On the cam is a hash mark. This mark should be in the center of the roller just as the throttle plates begin to open. You can adjust the cam in or out by losening the screw that hold it to the magneto plate.<br /><br />Low speed needle adjustment.....start with the needle GENTLY seated then back out 1 1/2 turns. Run the engine at full throttle for a few minutes and then idle down for needle adjust ments. Turn the needle inward in 1/8th turns and tune for best low end idle. If you get there, back the needle out a little to prevent a to lean mix. This adjustment should be done on the water underway.<br /><br />When the carb was rebuilt, was the float set correctly? With the carb inverted, the float should set level in reference to the bowl gasket surface....just a smidgen high in front is good.<br /><br />The reason for the above, it sounds as if the engine is getting a little to much fuel. If any of the above are out of adjustment, the engine could run fat.<br /><br />Do keep us informed tdp......Good Luck!

 

[tdp63]

Re: Johnson 15hp bogging down

Well, using different tank and fuel line didn't change anything. However the motor seemed to idle beter with the cover off. That maybe a separate and non-related issue. I thought the carb had been overhauled but found out tonight it was just a pull down and blow out. No it is getting a soak. My man doing the carby was interested your comment OBJ re having the float a sidgen high in front as it wasn't. Will be at it again tomorrow evening when it cools down a bit. By the way, do I just keep updating at this original post or if there is some time delay between posts do I start a new one?

 

[OBJ]

Re: Johnson 15hp bogging down

Just keep updating the original post tdp. Easier to keep track of that way.<br /><br />And yes, do soak it out. Follow up with carb cleaner in a can and blow out all passages followed up with compressed air. <br /><br />When I say a smidgen, I mean just that....just a smidgen.....so that you have to look to see it..... <br /><br />After she is fired up, take a look around the block and see if there are any exhaust leaks that may be getting under the hood while it's running. Breathing it's own exhaust will slow it down also.

 

[tdp63]

Re: Johnson 15hp bogging down

What are the symptons of a damaged/leaking crank shaft seal? Is that a possible cause of problem?

 

[joaklay]

Re: Johnson 15hp bogging down

Read this thread too, basically the same outboard:<br /> http://forums.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=28;t=038460

 

[tdp63]

Re: Johnson 15hp bogging down

Well i think i have all the above covered but still got the same prob. OBJ, I have an 'outboard motor mechanic' mate here, but he is only 26 years old and has not worked in the industry all that long- hasn't seen it all yet - it has him a bit stumped too. I reckon it all may come back to the roller pin and cam plate set up. Tell me more about that. I don't reckon it's right. What exactly do you mean by 'throttle plates'? I am watching the pin through the carb that indicates that the butterfly is moving. At the slightest movement the roller pin is almost centre. This is hard to explain in text. Exactly what does 'begin to open' mean? and are we talking about the same thing. May be some confusion re terminology. What do you mean re 'throttle plates'? I am close to throwing this down the tip!

 

[OBJ]

Re: Johnson 15hp bogging down

Besides making a mess under the flywheel, a bad crankshaft seal can cause the engine to cough and hack....this being due to the extra air being pulled into the engine from the seal. If the seal is bad, again, you can tell by the mess under the flywheel.....namely fuel/oil mix spilling down around the block.

 

[tdp63]

Re: Johnson 15hp bogging down

I must have been typing my last thread as you were typing yours. Sorry. Checked and seal appears OK.

 

[OBJ]

Re: Johnson 15hp bogging down

Well, I used the plural of plate, (plates) and shouldn't have. We are talking about the "butterfly" as you call it. (Sorry for the "American" terminology..... )<br /><br />But yes, just as the butterfly begins to move, the hash mark on the cam should be center with the cam roller. If your mate has a service manual for any 9.9/15hp John/Rude, the procedure will be in there.

 

[mikeyzx2]

Re: Johnson 15hp bogging down

Just to reference the butterfly opening, you can tell by watching for the throttle shaft roll pin to start moving.

 

[tdp63]

Re: Johnson 15hp bogging down

Ok, good. Now in reference to 'start moving', are we talking the slightest amount that you can only just see when looking really close up or enough movement that is obvious. We have a difference of opinion here. I feel there should be an obvious amount of movement and if that is the case the setting is out. My mate reckons he can see slight movement earlier than me which makes setting ok. This seems the only thing left that could be causing my problem.

 

[OBJ]

Re: Johnson 15hp bogging down

I use what the service manual calls a throttle plate shaft amplifier.....which amounts to a piece of white wire (white for visibility) crimped to an aligator clip. I attach the alligator clip to the end of the throttle plate shaft (on the starboard side of the carby) and watch the end of the wire. When the end of the wire just moves, the hash mark should align with the center of the cam roller. Not a lot of movement...but it still moves. Hope this helps.