'98 Johnson 70 hp Flame Out On Acceleration

[ken paul]

Hello,<br />Looking for a little help to pass on to the local Johnson service people. This is the Model J70TLECB bought by a previous owner in Fayetteville, NC. Since my purchase last year here in Utah (with a reported run time of less then 10 hours)from a military person, I have had it in the Shop three times. After the last visit which I requested a dyno load test, they concluded loose clamps associated with the VRO in improving acceleration rev-up. The engine now performs worse then ever and the only way I got it going this weekend is rev'ing in neutral then dropping in gear before the RPM tails off (ugly). The carbs have been looked at (and cleaned) without observed problem. Tank venting - no problem. Supposedly re-jetting is not necessary with altitude differences. Where I ran this last weekend, the altitude was about 5200 feet and otherwise the elevation mostly used is about 4200. Guessing where this engine came from is about sea-level. The service people have already discounted plugs, tank-vent, and carbs (where they have spent most their time). Always runs good after about 2500 RPM.<br /> kpaul70643@cs.com

 

[JB]

Re: '98 Johnson 70 hp Flame Out On Acceleration

Howdy Ken. What are the compression readings? Has the link 'n' synch (between carbs and ignition timing) been confirmed? When she is stumbling and coughing before clearing out and revving up, does she smoke? Have the reeds been checked? What plugs are you using? Who decided altitude doesn't justify a corrective jet change?<br /><br />I think it is a bad idea to discount any suspect until the cause has been proven. That includes a carb low speed circuit and/or float setting.<br /><br />Let us know the above.<br /><br />Red sky at night. . .<br />JB

 

[clanton]

Re: '98 Johnson 70 hp Flame Out On Acceleration

Check compression, if plastic 6 gal tank check pickup tube. OMC altitude chart suggests jet change at 3000 feet. The chart I have stops at 1987 or i would give you jet size. OMC service manual for your engine has jet chart.

 

[clanton]

Re: '98 Johnson 70 hp Flame Out On Acceleration

Check compression, if plastic 6 gal tank check pickup tube. OMC altitude chart suggests jet change at 3000 feet. The chart I have stops at 1987 or i would give you jet size. OMC service manual for your engine has jet chart.

 

[my new fishmaster]

Re: '98 Johnson 70 hp Flame Out On Acceleration

I was having the same problems at Jordanel last week. I changed my jet for the higher altitude and she runs better now. I belive you are having fuel starvation problems at the lower rpm levels. Check you fuel pump and replace the diaphram with a kit.

 

[petryshyn]

Re: '98 Johnson 70 hp Flame Out On Acceleration

J.B. has some very important questions which leads you to determine if its a mechanical failure, lean/rich issue or an ignition problem. What effect does the idle mixture screws have on idle? Does it run better with the screws turned in close to bottoming, or backed way out? (helps determine a lean/rich condition)Does the primer bulb hold hand pressure when squeezed? A leaking intake gasket, carb base gasket, hose fallen off, bad main seals, timing out of synch, uneven compression, weak ignition, leaking fuel pump diaphram, poor fuel quality all can give the same symtoms.(poor idle, OK high speed) Thats why more trouble-shooting is needed and the best place to start is by answering all of our questions and see where it takes us. GOOD LUCK