1989 8 HP Johnson won't run WOT

[Don Powell Sr]

My son has been working on our 8 hp because it will start and run beautifully at idle, and at about 1/3rd throttle, but stops abruptly when wot is applied.Squeezing the bulb, chocking, does not keep it running. If returned quickly to 1/4 throttle, it will run. The motor sat for 2 years, and he thought the carb was fouled. He has checked, or done the following. New tank, fuel line, connectors, rebuilt carb, replaced fuel pump, cleaned filter. I looked at it and found good looking spark on both, installed new plugs. I did not have a compression gauge, but both cylinders seemed to have good compression. I looked at the linkage and advance looked ok. I will try to obtain a wheel puller to look at the coils and points. This motor has been used very little, but now we need it. Any ideas of what to look for.

 

[Kev]

Re: 1989 8 HP Johnson won't run WOT

Don,<br /><br />Most problems can be traced to fuel, spark, or compression.<br /><br />Your motor starts and runs smooth at low speed so it must have fuel, spark and compression at least at low speed.<br /><br />When you try for WOT and it starts to die, you say choking and/or squeezing the fuel bulb does not help so you probably don't have a fuel delivery problem. You could also try spraying some premix into the carb as you increase the throttle and see if that prevents the motor from dying.<br /><br />Have you spark tested each wire at WOT as the engine is dying to see if you are losing spark at WOT? (obviously you'd have to do this on the water) If you are losing spark at higher speeds, the powerpack or coils are suspect.<br /><br />I'd be inclined to rebuild that carb and clean it some more. Did you soak it in carb cleaner at least overnight, and blow out all the passages with compressed air? Did you remove/replace the little plug to blow out the idle jets? Most problems of motors idling OK but not running to WOT can be traced back to dirty carbs.<br /><br />Are you sure your link 'n' synch is correct? If your timing is off that could matter.<br /><br />Any chance you are using old bad gas in the motor?<br /><br />Lastly, do you have a service manual? That will help a lot.<br /><br />Check these things out and let us know what you find. With everyone's help, you'll get your motor running great in no time.<br /><br />Good Luck,<br />Kev

 

[Don Powell Sr]

Re: 1989 8 HP Johnson won't run WOT

Kev, thank you for your reply. The gas is fine, it ran in another motor just fine. I should have tried spraying gas mixture in the carb throat, but I didn't have a means to do it on the water. I do need to find and purchase a repair manual. I had been convinced that it was a fuel starvation problem but now I realize that I cannot leave any stone unturned. Are some manuals better than others? It is difficult to work on this problem with only having the lower unit in a tank. I will get a manual, check the coils, wiring, and set the points. Then have all necessary tools, spray and such, to check it on the water under load. Thanks again.

 

[Don Powell Sr]

Re: 1989 8 HP Johnson won't run WOT

Motor still won't run well at WOT. We cheched the ignition all looked good. Removed the carb, disassimbled, cleaned checked all holes, and ran copper wires into all holes, all were open. Adjusted carb float. It ran well in the tank. Ran on the lake yesterday, it does not quit now but the only way to get full throttle is to choke it. We can get full, or at least near full, throttle by, pulling choke open halfway or I can get wot by using my fingers across carb throat to manually choke it.We removed choke assembly and it seemed to work fine, it would squirt gas when pulled and the outlet seemed to be well regulated by plunger position. So, the engine carb is running very lean, and I cannot understand why. I examined and cannot see how the manifold can be getting air,carb gasket is new, as well as all the parts in the carb. Carb appears bad, but cannot see how. Any other ideas? Would appreciate greatly!

 

[tashasdaddy]

Re: 1989 8 HP Johnson won't run WOT

manual at kencook.com pricey, but worth it. or get the manual # and look in ebay. the original mfg. manual is clearer. check that gas tank is venting properly, loosen cap while running.

 

[Don Powell Sr]

Re: 1989 8 HP Johnson won't run WOT

Thanks for the reply. This new tank and fuel line works fine on another motor.The new fuel pump is working fine. Fuel delivery to the carb is not the problem. Any other ideas would be much appreciated. Thank you for your input.

 

[Kev]

Re: 1989 8 HP Johnson won't run WOT

Don,<br /><br />Have you confirmed that your link'n'synch is set correctly? If the throttle plate in the carb is opening too fast/too much it could cause the motor to run lean as you described.<br /><br />When the twist grip is set to the START position, the throttle plate should just barely start to open. When the twist grip is at full throttle, the throttle plate should be open all the way. To adjust your link'n'synch on your motor you run the allen cap screw on the cam follower in or out, though I don't know the exact calibration method for your motor. A manual would help a lot here.<br /><br />I looked at some parts diagrams of your carb. It looks like you've got a fixed high speed orifice, and a Slow Speed Needle. If you ask around, someone can you tell you how to confirm that the Slow Speed Needle is set properly. It might affect your fuel mix.<br /><br />I also saw that the primer on your motor (I think what we call the choke) has two hoses attached to it--one to the carb and one to the manifold (?). Check these hoses for air leaks too.<br /><br />Also check the carb bowl gasket for air leaks.<br /><br />Sounds like you are either getting too much air at WOT or not enough fuel, or a combination of both. That's about all my ideas.<br /><br />Here's a link to find parts diagrams for OMC motors.<br /><br /> http://epc.brp.com/default.aspx?brands=ej&lang=e <br /><br />Also do some searches on this forum for "Slow Speed Needle Adjust", "Carb Adjust 8HP", "Link Synch", and other variations. Joe Reeves is the expert on carb adjusting and lots of other stuff. You'll turn up lots of good stuff from him.<br /><br />Hope it helps!<br />Kev

 

[Don Powell Sr]

Re: 1989 8 HP Johnson won't run WOT

Hi Kev,
This is my third attempt at logging on. For some reason, it would not recognize my password. Well, the link and sync are ok. I discovered tiny cracks in the body of the carb. I have no idea how they got there, except having the motor in the shed during the winter and having water present in the carb? I think this is the problem. Now I have to find out how much I have to spend for a new carb. Thank you for all your help.
Best Wishes, Don

 

[tashasdaddy]

Re: 1989 8 HP Johnson won't run WOT

he found the problem!!!!