02 150 johnson WOT losing 500 rpm

[tcooper@spinxs.com]

Have a strange problem with a 02 carb type johnson 150. It seems to gain 500 to 600 rpm's at wot intermittantly. (once or twice over a week's use)It's as if a switch is thrown. Tried pumping the ball, no change. Changed plugs, all looked the same. Tried decarbon, no change. Tried hitting the prime, no change. I'm an automotive tech and it feels like the timing is getting to total advance only intermittantly. When new the engine ran at about 5200, since this problem developed it makes 4600 or 4700. Any advice for checking total advance, or tips to narrow down the problem would be appreicated.

 

[Walker]

Re: 02 150 johnson WOT losing 500 rpm

First make sure your timer plate is advancing all the way to the stop bolt. Then try cleaning all the coil ground straps and the engine block where they bolt on.

 

[rodbolt]

Re: 02 150 johnson WOT losing 500 rpm

hahaha that is why automotive techs need to stay away from outboards.<br /> yall get no experience at fuel or ign problems at WOT. any how I wrenched on them dang autos for years.<br /> check and clean all the ign grounds. also check the primary ign coil caps. they can arc through. but it sounds more like a fuel problem. sometimes you can remove the airbox and remove the drains and flush them out with carb cleaner.Ign timing on that motor is mecanical. if it goes once it will go all the time.<br />that is what makes working with high performance machine so much fun. where else can you run an engine at its rated horse power for hours at a time and not get pulled over <br />good luck keep posting and when your working on your outboard forget everything ya know about cars.

 

[jy118lfd]

Re: 02 150 johnson WOT losing 500 rpm

Rodbolt you are right on I worked on cars for ten years and now I must relearn everything I ever knew cause everything is sooooo!!! different when it comes to two stroke outboards Sometimes I want to swallow a bullet

 

[tcooper@spinxs.com]

Re: 02 150 johnson WOT losing 500 rpm

Thanks for the reply's. Sure is easier to connect a scanner and go for a ride! It sounds like you guys suspect a cylinder dropping out, could the engine run so smooth on 5 that the miss would be unnoticeable? The plugs all had the same wear and color. If a cylinder is dropping out at the high rpm's only could I find the cylinder with a temp gun on the base of the plug while running? Thanks for the help.

 

[Walker]

Re: 02 150 johnson WOT losing 500 rpm

An inductive timing light would tell you if you are loosing spark at high RPM

 

[james roach]

Re: 02 150 johnson WOT losing 500 rpm

Your tach is telling you that you are losing spark at high RPM's. Check your coils as Rodbolt said. That is most likely your problem.

 

[Dhadley]

Re: 02 150 johnson WOT losing 500 rpm

500 to 600 rpms is just about exactly what you lose when you lose spark on one cylinder at that rpm. If you use your timing light you may be able to see which one it is. It may be just a coil. <br /><br />If you take the top cover off you can check the timing too. keep in mind the sometimes a timing light has a funny effect on the optic sensor (eye). Look real close at the encoder wheel to make sure it isnt cracked.<br /><br />What spark plugs are you using? Make sure its a Q type Champion. <br /><br />If it were mine, I'd be looking for more than 5200. Those dont like to be lugged.

 

[tcooper@spinxs.com]

Re: 02 150 johnson WOT losing 500 rpm

Based on replies, I'm guessing a missfire can occur with no noticeable roughness. Not a problem to check full throttle spark with test lite. The last poster said 5200 max was too low. I have a jet conversion pump as my lower unit with a four blade stainless impeller. Does anyone know if impellers are rated in the same way as props? I looked through the service manual and was not able to find the obtimum full throttle rpm. What would be a good range to shoot for?

 

[seahorse5]

Re: 02 150 johnson WOT losing 500 rpm

Be sure to use the Champion QL78YC plugs (.030") as other types and brands may give off RFI which will affect the optical ignition sysem on that motor.

 

[tcooper@spinxs.com]

Re: 02 150 johnson WOT losing 500 rpm

Turns out the lower left carb throttle plate was not opening, the adjustment had loosened up and the plate was staying closed. The problem was hard to find due to the inability to see the plate without a mirror. Link and sync and all is well.