Johnson 100 does not pick up speed

[wild n crazy]

Hi , I currently have a 100 HP Johnson with a 17-1/2 aluminium flat bottom boat, when I bought it the seller took me out on a lake, and it seemed to pick up speed with no problem, but when I brought it out myself, it seemed not picking up speed fast enough, until someone on the boat goes to the front end and seat. What is my issues? and what's did I do wrong, I have my trim all the way down, it dont looks like it trim when the boat is moving, so can any one advise? Thans in advance

 

[emdsapmgr]

Re: Johnson 100 does not pick up speed

Any idea what year this engine is? What is the pitch on the propeller that you are using?

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

Sorry, I have no clue what yr but I do have a model # which is 100 TLR79S and it's 13-3/8 X 17 , I also just have new hub packed onto the prop

 

[boobie]

Re: Johnson 100 does not pick up speed

Is it running on all four cyl's ?? Pull one plug wire at a time when running and see if you have a dead cyl.

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

MR Boobie, what do I need to look for when I pulled the the plug wire?

 

[emdsapmgr]

Re: Johnson 100 does not pick up speed

Each time you pull one of the plug wires off it's spark plug, the engine rpm's will drop noticeably. Start the engine. If you pull one plugwire off and the rpm's don't drop, that plug is probably not firing.

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

I checked it out this afternoon, it's droping RPM on all 4 sparksplug

 

[emdsapmgr]

Re: Johnson 100 does not pick up speed

Have you done a compression test on each cyl? Good to know the compression is solid before investing any more time/$ into the engine.

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

Thanks to all the help, I finally have the time to work on this motor, I rebuilt both of the carbs, the top one seemed to be alright, the bottom one the float fill pin does not have the little spring to pull down the pin if the gas is not filled. so I installed the spring , blow out all holes, engine sounded ok, but havent got a chance to take it to the water yet. I'll be back with the result later, and sorry about the late thank you

 

[emdsapmgr]

Re: Johnson 100 does not pick up speed

That engine will seem to run fine on the garden hose with 2 or 3 cyls firing. Once you launch the boat and the prop exhaust is 20" underwater, you need all 4 cyls firing. Weak ignition components tend to fail once the engine heats up to normal operating temps, so recheck your spark after you've run it for a while. When you had the carbs down, did you remove the jets and visually inspect them for any debris. Did you blow out the carb passages with a specific carb cleaner-like a Gumout product?

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

I have bough a spark tester kit, and evry one of them have a little shiney spark on the glass tube, it even zaped too, LOL. I also blew down the carbs holes, even the little tiny holes with air only, and I can feel the air exited sharply, but I didnt use any cleaner at all, which now that you have instructed so, I wish I did it, but I'll repost when I take it out in the water, thank you for your latest advise...It's good that there alway some one up here sharing like you did.

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

Ok, I am back, Took my boat out today, cant run it over 7.5 mph...I have to pump the ball , when I do, it picked up a little bit, but the ball have a suction on it. when it back to full it sucked out my fuel and the engine went wack slow until I pumped the ball all the way down again..., I hoped that because I didnt use any cleaner does this, or my fuel pump is going south?

 

[Daviet]

Re: Johnson 100 does not pick up speed

Normally pumping the primer bulb will bypass a defective fuel pump. But if you have a defective fuel pump and pumping the primer bulb did not make the engine run properly, you still have a problem elsewhere. When you cleaned the carbs did you remove the high speed orifices and make sure they are not restricted of plugged?

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

Now that's something I wasnt aware of, what is the high speed orifice and where can I find this item.. please explained, Thanks

 

[emdsapmgr]

Re: Johnson 100 does not pick up speed

If you are trying to overhaul the carbs and need to know where the jets are, you should check out the factory parts lists online for your engine: epc.brp.com. You may also find an original factory service manual may be of help as you continue other maintenance items on your engine. Check out outboardbooks.com.

 

[Daviet]

Re: Johnson 100 does not pick up speed

1979 100hp
Look below at #32 in the float bowel, that is the high speed orifice. There are two of them in each carb, one on each side.
You can check/remove them by removing the drain screw in the float bowel, they screw in and out. If you don't have the special tool, you can use a strand of soft copper wire to see if they are plugged. Best to remove them, but sometimes that is not possiable.

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

Thnx emdsapmgr and Daviet, I'll retake them apart tommorrow and this time will clean and use the carb cleaner on them

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

Ok, stupid problem occured.. I took the carbs back out, cleaned all the holes that I can visual with Gumout carb cleaner. bought new fuel pump repair kit, bought and replaced new fuel hoses, the problem I see here is the fuel pump have 3 ports, 1 inlet 1 outlet, stupid me doesnt know or remembered where the 3rd one landed, didnt see extra hose for it, checked my compression , they are all 120 or 119. cleaned all spark plugs, adjusted the cable. put prop in 55 gal drum, accelerated almost pushes my boat forward thanks to the stoper I've put at the tires everytime I park my boat. LOL... can someone please tell me where the 3rd port goes on my engine please?

 

[wild n crazy]

Re: Johnson 100 does not pick up speed

OK here's the good new....took the boat to the shop to get adjustment of motor, cost 250$ engine is fixed up, runs good now, thnx to all with nice heart and time answering question.

 

[sunwest]

Re: Johnson 100 does not pick up speed

OK here's the good new....took the boat to the shop to get adjustment of motor, cost 250$ engine is fixed up, runs good now, thnx to all with nice heart and time answering question.

can you please tell us what they fixed to fix your problem? Just to help others.