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engine miss 1976 9.8 hp

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kbeers

New member
just replaced impeller in my 1976 9.8 mercury outboard engine ran fine. One pull engine started idled good after running it for about a hour started getting a high end miss but runs fine at lower speeds kind of stumped any body got any ideas that could be my problem? Could I have a slight blockage somewhere?I have a good steady stream of water coming out didn't think it was the culprit.Got any ideas?Any help will be greatly appreciated.
 
Re: engine miss

You have to track down whether the miss is being caused by the ignition or the fuel system.

A stator, trigger or coil that is starting to fail could cause a miss.

Likewise, an air leak (at a fuel line or a gasket), a fuel pump diaphram on the way out or a clog developing in one of the carb jets could also cause a miss.

I suspect that it is coincidental that you discovered the miss after changing the impeller and do not think they are related.

Since it's occuring at high rpms it's a little more difficult to check the ignition with a timing light if it's "occassional" - it would be better tested in a tank with a test wheel.

This may be one of the cases where, if you plan to troubleshoot yourself, you may have to wait a bit until the problem gets worse before it can be narrowed down to something specifically to look at.

It's very very tough (almost impossible) to find a periodic ignition problem until one of the components actually fail (or get really bad)....
 
Re: engine miss

I found the wires for the kill switch very dry rotted and falling apart I'm gonna replace the switch if I can still buy it . I checked the fuel line found no cracks.It starts with one pull thats what has me stumped.Is it possible that I still have a slight obstruction in the cooling ports and is it possible to back flush the system ? It only misses after it has been run for a while.The engine does't seem to be running hot but the water exiting the engine is warm.When I run the engine in a tank of water It doesn't seem to miss.
 
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Re: engine miss

If you have the model with the square cowl with the pintle style hold down at the rear check your spark plug boots and make sure they are not ripped open somewhere, also make sure that your coil wires are secure and seated well in each coil.

The pintle would rub against the spark plugs boots rip them open and start to arc against the cowl hold-down.
 
Re: engine miss

I ordered the service manual off this site I found my kill switch wires were dry rotted next to the block .I fixed them and put a new switch on.I took my kids out fishing for crappies to test the motor out but got rained on didn't get to open up the motor much but what I ran it it seemed to run ok. I'll check the plug wires they look like they been on there since 1976.....lol thanks for the help!
 
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