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Old 14-08-2016, 12:30   #1
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OB starts, runs, but stalls at idle.

I ran out of gas... the Yamaha 4stroke 8 died stopped of course. Rowed to the gas dock and topped up. Some trouble starting at first... but then she motor would not idle and seemed to like the choke out at the lower RPMs... stalls at idle.

I am thinking the carburetor is messed up... or perhaps the small fuel filter in front of the carburetor is clogged... and so the engine is sort fuel starved... and the fix would be replace the filter. I did not examine it, but this occurred to me driving home.

I would sure like to NOT have to take the OB to the mechanic to clean the carburetor.

It was working perfectly before this incident.

Please comment.... with you experience.
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Old 14-08-2016, 13:08   #2
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Re: OB starts, runs, but stalls at idle.

Replace the filter? You multi-millonairs make me sick! Just take it out and wash it in some fuel
See if that works

If not, you may have picked up some bottom tank gunk... But more likely water... So that would come out when u clean the filter, wouldn't it?

Even more fun is a high speed rip around the bay and see if it blasts it out
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Old 14-08-2016, 13:11   #3
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Re: OB starts, runs, but stalls at idle.

Quote:
Originally Posted by Sandero View Post

Please comment.... with you experience.

Ooops, sorry, i didnt read this.
My experience: Poor, high speed drunk.

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Old 14-08-2016, 13:15   #4
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Re: OB starts, runs, but stalls at idle.

Start with fuel filter.
4 stroke carbs are horrible. float valve might be stuck, tap lightly carb with screw driver handle. If no go take off fuel line and blow some carb and choke cleaner in it. try again.
Might have to remove carb, disassemble, clean all jets with carb/choke cleaner and reassemble. Not a hard task, first time will take a few hours, later in life will be able to do it in about 30 min.
We have a tohastu 9.8, had to do that very 20 hours. Since then have installed a sierra fuel/water filter on transom between tank and engine, this has helped a lot, now only have to do it every 40-50 hours.
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Old 14-08-2016, 13:23   #5
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Re: OB starts, runs, but stalls at idle.

Thanks guys... I would def start with trying to clean the filter... and spray some starter fluid into the carburetor..

I did about 15 minutes at full throttle thru the harbor to no avail... so that didn't clear whatever is blocking... I am wondering what could get past the filter to foul the carburetor... salt water? As it was perfect one moment and screwed up the next it was clearly something from the bottom of the tank.

Let's hope cleaning the filter works... Stay tuned.
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Old 14-08-2016, 15:01   #6
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Re: OB starts, runs, but stalls at idle.

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Originally Posted by Sandero View Post
Thanks guys... I would def start with trying to clean the filter... and spray some starter fluid into the carburetor..

I did about 15 minutes at full throttle thru the harbor to no avail... so that didn't clear whatever is blocking... I am wondering what could get past the filter to foul the carburetor... salt water? As it was perfect one moment and screwed up the next it was clearly something from the bottom of the tank.

Let's hope cleaning the filter works... Stay tuned.
All it takes is the smallest speck of contamination in just the right place to make a small engine carb misbehave. If cleaning/replacing the filter doesn't work then its likely in the carb. The only effective way to clean a carb is to tear it down and clean it. Squirting majic junk into it is unlikely to work.
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Old 14-08-2016, 15:19   #7
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Re: OB starts, runs, but stalls at idle.

You want to learn how to do this job yourself, because it is common, fairly easy to correct, and you to do not have the time or money to have a professional do it each time.

You can clear the fuel system from tank to carb by disconnecting the fuel line at the carb. Replace the filter, put in fresh fuel, and make sure it flows freely at that point. You probably can clear the carb by removing the basin and dumping it out - note if there is a "bubble" of water or trash in the bottom. Possibly, just possibly, the clog is in the siphon tube from the bowl to the carb throat or is due to a stuck float valve. If the float valve stuck, the carb bowl will be empty. Note how the card refills with the float valve, and if necessary blow out the siphon tube. That's about all there is in a small four cycle - they usually use gravity feed (included tanks, not separate?), but if not, you also need to see that the pump is working, but that is a bit more complicated.
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Old 15-08-2016, 10:08   #8
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Re: OB starts, runs, but stalls at idle.

I would bet my bottom dollar you have used good old pump gas in it at some point and its a water absorbent fuel. The kind sold at marinas is non alchohol. Water, and it only takes a small amount, accumulates in the bottom of the tank and gets drawn into the float bowl when you run out. Remove float bowl, or check for drain, some have them, change or back blow that fuel filter to make sure you get it all out or you may find yourself draining the float bowl again, and reinstall all parts checking for fuel leaks. Start engine and go on merry way until you get gas station type gas again and then repeat procedure. Water molecules are big and don't like to atomize well, gas does, idle jet wont allow passage but the big hole in the main jet will allow the gasoline to pass through therefore it will run full throttle, even with the choke on it will run up better when you have water in the gas, water heavy, gas light. boats humid and water environment, alcohol fuel, bad juju
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Old 15-08-2016, 10:10   #9
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Re: OB starts, runs, but stalls at idle.

Have a 4stroke 8 hp Yamaha myself. You perfectly described the low speed jet clog. 2 bolts to remove the carburetor. Use small screwdrivers to remove the Jets, laying all parts on a towel so that they don't roll. Now carb cleaner spray all jet holes in the carb and jet needles. About 1 hour first-time. I would also replace the filter on the motor gas line while you have the carb off which makes it easy to reach.

I have had blue flakes from non-ethanol evaporation clog the jet a3 filter. The blue flakes look like dandruff.
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Old 15-08-2016, 10:39   #10
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Re: OB starts, runs, but stalls at idle.

Quote:
Originally Posted by Billnpr View Post
Have a 4stroke 8 hp Yamaha myself. You perfectly described the low speed jet clog. 2 bolts to remove the carburetor. Use small screwdrivers to remove the Jets, laying all parts on a towel so that they don't roll. Now carb cleaner spray all jet holes in the carb and jet needles. About 1 hour first-time. I would also replace the filter on the motor gas line while you have the carb off which makes it easy to reach.

I have had blue flakes from non-ethanol evaporation clog the jet a3 filter. The blue flakes look like dandruff.
Good advice.. One thing I would add is to actually "poke" the jets. I use a single bristle from a wire or brass brush. It clears the sticky clogs that carb cleaner does not dissolve.

I'm a little shocked about the Tohatsu comment. We have a 9.8 and have 100s of hours on it down here in the tropics. 3/4 of that was running ethanol fuel and we only had to clean the carb once when I got fouled fuel.
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Old 15-08-2016, 15:32   #11
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Re: OB starts, runs, but stalls at idle.

pull the plugs out warm them up to remove moisture /or replace plugs/if contaminated with salt don't try to clean them just replace
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Old 15-08-2016, 16:37   #12
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Re: OB starts, runs, but stalls at idle.

Guys... thanks for all the great advice...

I will try the conservative approach...

clean and or replace the fuel filter...
Plugs are new.... I don't think they are wet...
If that doesn't work.... open the carb maybe...

or

bring it to the mechanic on Monday and pick it up on Friday repaired

I just don't want to spend much time fiddling with the OB... which could be a disaster! and I would be stranded with NO way to get to the boat. I am not rowing a mile!
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Old 15-08-2016, 17:24   #13
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Re: OB starts, runs, but stalls at idle.

Before you take it to a mechanic go to Boats.net & look up your motor. Click on carburetor & you will get an exploded view of your carburetor. It makes it easier to see how to break it down. I'm no mechanic & I know these things can be scary the first time but it's a good idea to know how to do this yourself & it's really not too hard. The advice on the plugged jet is correct from my experience. If it was the filter it would get enough fuel to idle but not enough to accelerate. The jets on these carburetors are really small & clog easily. With Hondas the dealer I spoke to won't even work on the small carburetors because they're hard to clean & it actually costs less to just put a new one on. I tried cleaning the carb but it didn't work so I tried replacing the jet but that didn't work either so I bought a new updated carb & problem solved. Now I know how to pull it off & tear it down or replace it.
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Old 15-08-2016, 17:48   #14
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Re: OB starts, runs, but stalls at idle.

If this is your first time cleaning a carb, you need to return any mixture screws to their original setting. This is easily done by screwing the adjustment screw in while counting how many turns it takes to lightly seat the screw. Then you may remove the screw for cleaning. When reinstalling adjustment screw the screw it all the way in then back out the number of turns you counted earlier.
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Old 15-08-2016, 18:05   #15
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Re: OB starts, runs, but stalls at idle.

A quick tip that sometimes works is; Get it running around the bay as you have done, then pull the choke out and keep it flat out for a bit. This can often pull a "Little bit" of rubbish through the jet, if it's possible. Certainly worth a try before you clean out the carby idle circuit.
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