1998 Johnson 250 Ocean Runner Timing Problem

Pufahl

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Joined
Aug 9, 2011
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3
I have a 1998 Johnson 250 Ocean Runner and suspect the timing is off. The motor has a label on the top of the air box that goes over the 6 carbs and says 18 BTC. Suspect the timing should be set to 18 degrees before top dead center? If so, I attempted to adjust it but could not get it any further than 10 BTC. It was at 6 After Top Dead Center and suspect thats why it was sneezing and poping and then stalling. I just bought this boat and it clearly needed a tune up which I have done. The last step was to verify the timing. Can anyone provide some help?
 

Pufahl

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Joined
Aug 9, 2011
Messages
3
Re: 1998 Johnson 250 Ocean Runner Timing Problem

The carberators have a plastic cover that is held on by two thumb screws and it has a sticker that reads 18 BTC on it and assume that is the correct timing. I have a manual for this engine but it is at home and I'm in Florida for the holdiay. I have borrowed a friends timing light and will try again today to set the timing based on the help provided so far. Mekkamaz your link is of much help but not sure I fully understand everything needed to be done to get the timimg correct but will give it a try today. BTW....my engine does have the Start Advance. I have noticed the idle is a little high until the motor warms and then the idle drops down. If anyone is familar with my engine and can provide any addtional help it would be greatly appreciated.
 

daselbee

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Joined
Jan 20, 2009
Messages
2,765
Re: 1998 Johnson 250 Ocean Runner Timing Problem

You are green regarding this motor...it is obvious.

But, mekaz is right, the timing shown on the air silencer is 18* BTDC at WOT (wide open throttle) (5000 rpm).
Now there are various ways to achieve this adjustment. One way is to hang off the back of the boat on smooth waters, and set it at speed. I do this often. Another way is to disconnect the timer base linkage, start the motor with throttles at idle, and manually rotate the timerbase to the full stop position. Engine will race, but not bad, and you can set the timing that way.

Another way is to follow Joe Reeves timing method, which is done at starter cranking speed (engine never starts), and you have to disable Quick Start, and you have to set the timing back 4* from spec, as Joe says it will pick up when the engine is actually running.

I personally prefer the second method mentioned above. The idle timing should be around 4-6* ATDC in gear idling. That will give you about 750 rpm. And of course no more that 18* BTDC at 5000 rpm. Two different distinct timing settings.

Now, the details of this are in the OMC Factory manual. These settings are critical to the proper running of the engine, and accidentally setting the WOT timing too far advanced will kill your motor over time.

So, get a book (not seloc, not clymer), read up on timing and how to adjust, quit guessing at what you are doing, before you do some real damage.

If you are close to me in FL, I would be glad to set it up for you. PM me if interested.
 
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