1999 JOHNSON 90 HP Backfires at idle

[aquaholicjavi]

Hi guys,
I have a 99 Johnson 90 HP which for the past 4 months has been backfiring in idle from time to time, normally it turns off after a backfire and the it turn back on just fine. The engine run excellent and this hasn't been a problem that I've been worrying about for the past 4 months but I would like to get it fixed. I cleaned the carbs last year, and just recently replaced fuel filters, spark plugs, and cables.
Any suggestions?

Thank you.

 

[psteurer]

Re: 1999 JOHNSON 90 HP Backfires at idle

Sounds like a slight adjustment to the carburetors may be needed. Since it only happens occasionally maybe just turn your needle valves out a small amount since you might be running a bit lean at idle. Check out this link on adjusting carburetors: http://forums.iboats.com/showthread.php?t=167352

Also, you may want to do a decarb if you have not done so recently.

 

[ezeke]

Re: 1999 JOHNSON 90 HP Backfires at idle

Sounds like a slight adjustment to the carburetors may be needed. Since it only happens occasionally maybe just turn your needle valves out a small amount since you might be running a bit lean at idle. Check out this link on adjusting carburetors: http://forums.iboats.com/showthread.php?t=167352

Also, you may want to do a decarb if you have not done so recently.

The initial low speed settings for these motors are specified in the linkage and synchronization sections of your model-specific factory manuals and elsewhere.

After checking that the throttle plates are fully closed at idle and perfectly synchronized through their entire range of motion, the initial low speed setting is 5-3/4 turns out from gently seated.

 

[aquaholicjavi]

Re: 1999 JOHNSON 90 HP Backfires at idle

The initial low speed settings for these motors are specified in the linkage and synchronization sections of your model-specific factory manuals and elsewhere.

After checking that the throttle plates are fully closed at idle and perfectly synchronized through their entire range of motion, the initial low speed setting is 5-3/4 turns out from gently seated.

Would this be 5-3/4 in all 4 carburetors for this engine? If I still experience a little bit of backfiring after adjusting them to those specs should I make them richer or leaner. How many quarters of a turn should I move at a time for final adjustment?

Thank you.

 

[ezeke]

Re: 1999 JOHNSON 90 HP Backfires at idle

If it is too lean, turn it out in 1/8 turn increments until it improves, waiting 30 seconds or more for the engine to catch up with the adjustment. The motor will cough if too lean, and it will speed up if if you add fuel by tapping the primer solenoid if too lean.

This kind of adjustment should be done under load with the engine warmed up.

You also have to be sure that the problem is not caused by an air leak or water in the fuel.