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2003 50 HP Yamaha 2 stroke bog at throttle, all help appreciated

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2003 50 HP Yamaha 2 stroke bog at throttle, all help appreciated

Old 05-15-2018, 11:56 AM
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Default 2003 50 HP Yamaha 2 stroke bog at throttle, all help appreciated

Hi Guys,

New to the forum but I am having a very frustrating issue that I cannot resolve on my 2003 Yamaha 50 hp TLRB 2 stroke outboard. The engine is on my 17 ft. Carolina Skiff flatbottom boat. We bought the engine backll in 2009 and ran it hard for commercial fishing purposes and it was tremendously reliable, never had one issue. The boat began having issues after one winter of sitting. The problem from the start has been the same, the engine starts up and idles awesome in the yard in neutral, revs up just fine, and seems like it is good to go. Once on the water under load, the engine still starts up and idles fine but immediately when throttled up begins to bog down and almost die unless you bring the throttle back down.

To me this seemed blatantly like a carburetor issue / fuel issue and the engine was not getting the fuel it needed. I've now become an expert on dismantling the carbs and cleaning everything. This spring I'm determined to get the engine back up and running well but it is proving difficult, this is what I've done so far:

1. Replaced all three spark plugs
2. Replaced inline fuel filter inside engine cowling
3. Replaced all fuel lines from tank to engine
4. Installed and replaced new water separator
5. Replaced engine fuel pump
6. Replaced cold start priming mechanism on second carb and rebuilt priming system
7. Bought carb rebuild it, fully disassembled carbs, chem dipped all metal parts over night
8. Rebuilt carbs with new kit
9. Scrubbed and cleaned all jets and parts related to carbs
10. put carbs back together and reinstalled

I blew out both jets and the carbs really looked fully cleaned when I put everything back together and I was feeling certain that the boat would finally run good. I dropped it in today with the priming system set to "oN" and the engine started first turn and sounded good. Went to throttle up, same issue, immense bog into almost die, into throttle down. I also, noticed that when the throttle is in gear, if I put my hand in front of any of the carbs to restrict the air flow , the engine perks up and sounds much better and runs stronger. As soon as I take my hand away, same problem. So, to me it seems that the mix is lean, but I have NO idea how that would be since the carbs aare fully rebuilt. Does anyone have any ideas? Maybe the reed valves? Head gasket? Electrical issue? Powercore? Do the carbs need to be retuned??? Anything would be much appreciated, cheers!
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Old 05-15-2018, 12:01 PM
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When you cleaned the carbs did you run a small thin piece of copper wire or monofilament THROUGH the low speed jets, and also the little passageways of the idle circuits? If not it's easy to miss and is the crux of many of these issues.
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Old 05-15-2018, 12:13 PM
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I sprayed carb cleaner through all jets and made sure they were clear, "the idle circuits" i'm not sure what you are referring to there. We chem diped the carb bodies over night as well so they were pretty clean when they went back in . Although I had to admit I did not use monofilment or copper wire to make sure.
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Old 05-15-2018, 12:15 PM
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Originally Posted by zcarpman View Post
I dropped it in today with the priming system set to "oN" and the engine started first turn and sounded good.
Is it set to the "normal" position? I have a 1999 C50TLRX and the 3 positions on mine are Normal, emergency, closed.

Originally Posted by zcarpman View Post
I put my hand in front of any of the carbs to restrict the air flow , the engine perks up and sounds much better and runs stronger
Does this mean you don't have the air box installed?
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Old 05-15-2018, 12:18 PM
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Originally Posted by zcarpman View Post
I sprayed carb cleaner through all jets and made sure they were clear, "the idle circuits" i'm not sure what you are referring to there. We chem diped the carb bodies over night as well so they were pretty clean when they went back in . Although I had to admit I did not use monofilment or copper wire to make sure.

The idle jets need more than just spraying out. You need to run a thin piece of wire through them. The insides of them are TINY and even if you can see daylight through them I guarantee that unless you ran something through them they are still dirty. It's the smallest spot for buildup to clog things up. The idle circuits are in the "square" part of the carb that you took off. Lots of tiny little holes in there, and the low speed adjustment needles are also in there, which can clog. Very tiny passageways once again. If you don't run something through them AND blow them out with compressed air you aren't getting all the junk out.
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Old 05-15-2018, 12:21 PM
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Sounds like it possbly has an air leak. Causing it to run lean.
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Old 05-15-2018, 12:24 PM
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If it was soaked overnight in chemdip, and then blown with compressed air (at least 50+PSI), it shouldn't need wire run thru it IMO. It obviously wouldnt hurt though.
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Old 05-15-2018, 02:25 PM
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The reason I'm telling you this is that I did the exact same thing and thought the exact same thing, and I was wrong. The only way to remove the varnish in there was by physical means. A piece of appropriately sized monofilment leader did the trick for me. My symptoms were the exact same as yours, an extreme bog on throttle up, but would idle allll day long. Also, there was varnish in/around the actually idle mixture adjustment screw. You're technically supposed to remove the welch caps and unscrew the mixture screws, but that's a pain in the ass.
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Old 05-16-2018, 07:17 AM
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@jim311 Thanks for that anecdote. I'm going to really go through the carbs and clean everything one more time, making sure all orifices are cleaned out. Thanks
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Old 05-16-2018, 07:18 AM
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interested as well
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Old 05-16-2018, 08:04 AM
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One thing that helps after soaking the carbs is to use an aerosol spray carb cleaner with the straw on the spray nozzle to make sure you are getting flow through every passage in the carb body and bowl before you put em back together.
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Old 05-16-2018, 09:18 AM
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X2 for the soft copper wire through the jets. Make sure the highspeed jet is clear (the one in the center), it sits low in the bowl and can ingest debris. Be sure the oring is still in place behind the carb and that the magplate linkage is working. There are plastic connectors that sometimes break.
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Old 07-02-2018, 09:17 AM
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Bumping this back with an update, I know it is an older thread. We have made some strides with the engine but it is still not perfect and we are stuck again! We just replaced the fuel pump and all internal fuel lines. The carbs are now CLEAN, ran copper wire through everything. Replaced the jets, cleaned thoroughly. We took the boat out on a lake and finally got to run it. Starts up first turn, idles well but sometimes grabs and will die, but once warmed up it will idle and run good. The engine finally has some punch. I gets on plane and will run nicely up to 16 knots about 3/4 throttle. From there if you bump up to full throttle, the engine starts to almost "skip" and studder but doesn't bog. If you bring it back down to 3/4 throttle it runs nice again. It will run all day at 3/4 throttle. Sometimes after running it will be a bit sloppy on start up ie. turn the key, fires up and grabs / bogs and dies. Next turn give it a little throttle from the start in neutral and its all good.

I'm really not sure what's going wrong at this point but we feel like its really close to be being back perfect. I'm thinking maybe a spark issue at full throttle?? Maybe a timing issue? Going to take the plugs out and try and replace them and then maybe seafoam / decarbon to see if that helps at all.

If anyone has any ideas that'd be awesome!
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Old 07-02-2018, 09:41 AM
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My 50 Yamaha just started acting up this weekend. Hard to start without manual primer and wants to bog and die from idle to plane. Will clean carbs this weekend.

Great little motors but sure wish I had a manual choke instead of the prime start.
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Old 07-02-2018, 09:57 AM
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They are awesome motors, when they run.... haha

We had prime start issues but they have been resolved. You can buy the new prime start plunger for like $160 on boats.net , installed that and rebuilt the whole system and it works well now. This new studdering issue is very strange.
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Old 07-02-2018, 10:01 AM
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Originally Posted by zcarpman View Post
Bumping this back with an update, I know it is an older thread. We have made some strides with the engine but it is still not perfect and we are stuck again! We just replaced the fuel pump and all internal fuel lines. The carbs are now CLEAN, ran copper wire through everything. Replaced the jets, cleaned thoroughly. We took the boat out on a lake and finally got to run it. Starts up first turn, idles well but sometimes grabs and will die, but once warmed up it will idle and run good. The engine finally has some punch. I gets on plane and will run nicely up to 16 knots about 3/4 throttle. From there if you bump up to full throttle, the engine starts to almost "skip" and studder but doesn't bog. If you bring it back down to 3/4 throttle it runs nice again. It will run all day at 3/4 throttle. Sometimes after running it will be a bit sloppy on start up ie. turn the key, fires up and grabs / bogs and dies. Next turn give it a little throttle from the start in neutral and its all good.

I'm really not sure what's going wrong at this point but we feel like its really close to be being back perfect. I'm thinking maybe a spark issue at full throttle?? Maybe a timing issue? Going to take the plugs out and try and replace them and then maybe seafoam / decarbon to see if that helps at all.

If anyone has any ideas that'd be awesome!
I'd do a basic link and sync, then change the plugs. If your problem still persists I'd start checking ignition components with a factory service manual at my side.
Based on what you have said about the new problem it sounds like a coil out of spec and is breaking down when it heats up...but that's just a guess on my part
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Old 07-02-2018, 10:57 AM
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Awesome, thanks for this twitch! I've seen a lot of "link and sync" mentioned. Is this a fairly straightforward process? Is this something we can do in our backyard? Some info on that would be awesome.
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Old 07-02-2018, 11:02 AM
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Originally Posted by jim311 View Post
the idle jets need more than just spraying out. You need to run a thin piece of wire through them. The insides of them are tiny and even if you can see daylight through them i guarantee that unless you ran something through them they are still dirty. It's the smallest spot for buildup to clog things up. The idle circuits are in the "square" part of the carb that you took off. Lots of tiny little holes in there, and the low speed adjustment needles are also in there, which can clog. Very tiny passageways once again. If you don't run something through them and blow them out with compressed air you aren't getting all the junk out.
this!!
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Old 07-02-2018, 11:03 AM
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Also, those motors run tons better plus about 8 degrees advanced timing.
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Old 07-02-2018, 11:18 AM
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I don't know where to start as far as adjusting timing / syncing , any info / documentation on this would be super helpful!
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