rough idle at start

[the oats]

We have an 89, 175 hp Johnson. Most times when we cold start we have a period of 3-30 minutes of rough idle that we can't reduce the neutral throttle to put it in gear, it will stall. After awhile we hear a click in the motor and then the idle smooths out and we can put it in gear and go. Once we are out fishing after running we can shut it off and it will start again with no problems. Any thoughts?

 

[jonesg]

Re: rough idle at start

offhand no idea ,

I would go through the whole engine, tune it up , rebuild carbs, link sinc and all that stuff. Have you done any maintainance to it?

 

[the oats]

Re: rough idle at start

My husband's out of town but i'll answer. We have tuned it up and replaced the fuel lines. The only thing is we don't have a water separator fuel filter on it. Someone said that might be the problem but I don't think so because once it's running it's fine. I'm surprised no one else has any ideas. Every mechanic we've talked to seems stumped and there is no repair shops where our boat is located. Thanks anyway.

 

[tashasdaddy]

Re: rough idle at start

ethanol and carb cleaning. sounds like low speed pickups. http://forums.iboats.com/showthread.php?t=299680

 

[emdsapmgr]

Re: rough idle at start

When OMC went to the single pack in 89, they added the Quick Start feature into the logic of the pack. When the engine first starts (cold) the pack advances the timing for better cold idling. This advance reaturns to normal timing when the engine senses a powerhead temp of 96 degrees. After the engine is warmed up, the quick start advance repeats for 5 seconds only each time the engine is restarted. The quick start advance is nullified when the engine rpm increases above 1100 rpm. Quickstart is activated through the white/black lead between the pack and the starboard head temp switch. This is normally a desirable feature when it functions properly. If you have a problem with it on your engine, you may want to check the service manual and run the system checks indicated to see if the quick start feature components in your ignition system are performing to the specs.

 

[jonesg]

Re: rough idle at start

I have faststart on mine but still have to bump the choke injector every now and then to keep it idling when cold, after about 30 seconds its fine.
30 minutes is beyond the limits.

Anyway, you need to do some troubleshooting when its idling rough, use a timing light to check all the cylinders are getting spark for sure.

Use a gap tester and check the spark jumps 7/16th inch on each cylinder, all plugs out and grounded.

Champion plugs only.

Draw a jam jar of fuel and let it sit, see if it seperates into fuel/water.

But it sounds like ignition, odd problem.

 

[the oats]

Re: rough idle at start

Thanks, I'll have my husband read these when he gets home. One question, do you guys recommend the water separator fuel filter or not. Are the put on in addition to your other filter or in place of it?

 

[countvlad]

Re: rough idle at start

Thanks, I'll have my husband read these when he gets home. One question, do you guys recommend the water separator fuel filter or not. Are the put on in addition to your other filter or in place of it?

YEs you definetly need the fuel water separator.... if you have that you dont need the inline filter.. one filter is fine.. replace it every year...

also definetly a decarb with seafoam and go from there... Seafoam does wonders to dirty things ... good luck