# Yamaha 50HP 2 Stroke Bogging



## Full Up (Aug 9, 2021)

Hey all this is my first post here - as I am at a crossroad right now with getting my motor running. Looking for some insight and expertise here before taking it to a mechanic.

So some background…bought a skiff with a 2006 Yamaha 50 HP 2Stroke and ran it a week or so after buying it. Ran fine, got up to 5700 RPM at wot. Later that day it would start to die randomly while at idle. That eventually progressed only being able to run the boat around 1500 rpm the whole way back to the ramp. I ended up doing the following: cleaned gas tank, replaced all fittings, replaced gas line from tank to motor, replaced bulb, replaced onboard fuel filter, replaced motor fuel filter, replaced gas pump, cleaned jets and carbs. Took the boat back out and it ran a lot smoother, but then it wouldn’t go past 2300 rpms. This time it wasn’t bogging down or anything, it remained at a steady 2300 at wot - couldn’t even get on plane. Went back to the drawing board… replaced the impeller and thermostat incase it was a temperature thing because it quit peeing one night when I had it on muffs in the driveway. Took the carbs out again, cleaned, and replaced the floats and gaskets. Replaced all 3 spark plugs. Put in new gas with a small amount of sea foam and took the boat out this morning. Now it bogs down and almost dies at 1800 rpm. Idle seems fine.

I am kind of stuck at this point… the only thing I can think of is replacing the spark plug wiring, checking the oil filter, replacing the choke module. Does anyone have any suggestions or other steps I can take to pin down what my problem is now? I find it odd that I could previously run at wot and replaced all these parts and it’s still not fully operating. Your input is appreciated!!


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## Smackdaddy53 (Dec 31, 2012)

Do a full carb rebuild with Yamaha parts. Clean all parts by soaking in ChemDip per the directions on the can. Assemble with stock carb settings and sync carbs and run straight gasoline with no snake oil other than oil injection if it still has the system. Make sure fuel pump is rebuilt, fuel system from tank is clean and in good operating condition and if you are skeptical, run on a remote tank with fresh gas and make sure the spark plugs are clean if not new. Also make sure you have no false alarms that are limiting RPM but not sounding the alarm.


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## Full Up (Aug 9, 2021)

Smackdaddy53 said:


> Do a full carb rebuild with Yamaha parts. Clean all parts by soaking in ChemDip per the directions on the can. Assemble with stock carb settings and sync carbs and run straight gasoline with no snake oil other than oil injection if it still has the system. Make sure fuel pump is rebuilt, fuel system from tank is clean and in good operating condition and if you are skeptical, run on a remote tank with fresh gas and make sure the spark plugs are clean if not new. Also make sure you have no false alarms that are limiting RPM but not sounding the alarm.


I basically rebuilt the carbs. I cleaned out the jets by soaking for several hours and blowing compressed air through them. All the floats were replaced with new. All the gaskets were replaced with new. I have been running straight gas since it does have the oil injection system. Fuel pump is brand new. Tank has been recently cleaned, all new lines. What determines if a tank is in good operating condition? It has a vent that is in the fuel line that I fill up the tank with. I will use a portable tank directly to the motor next time. I have new spark plugs. I am not sure what you mean by false alarms... there are no sounding alarms and there are no alarm indicators on the tachometer.


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## fishnpreacher (Jul 28, 2018)

Are there any fuel lines on the motor that haven't been replaced?
I'm assuming the linkage opens the carbs and advances the timing correctly, or is timing controlled electronically? I'm no marine mechanic, just throwing out ideas....


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## backcast (Apr 9, 2013)

I had same problem. Mine corrected with what you have done. If you have a pressure/vacuum gun such as the mityvac to test the float closing on carb. I used it to pressure fuel inlet side with carb upside down to test the float needle seat holding with something like 4 lbs pressure. I also used it to test fuel pump. I have the Seloc Yamaha manual for 2 strokes which gives good instruction on how to test various parts.
Joe


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## Smackdaddy53 (Dec 31, 2012)

Basically rebuilding carbs and doing an actual 100% rebuild are not the same thing. Did you replace all the parts that come in the Yamaha rebuild kits?
The jet orifices get varnish build up inside them that restricts the fuel flow by just enough to cause issues no matter what parts you replace. I use a piece of twisted copper wire to clean the varnish out then blow through with carb cleaner spray. Don’t use welding torch tip cleaners as they are too hard and will remove material from inside the brass jet and open it up too much which throws off the air/fuel mix. Copper won’t.


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## Full Up (Aug 9, 2021)

fishnpreacher said:


> Are there any fuel lines on the motor that haven't been replaced?
> I'm assuming the linkage opens the carbs and advances the timing correctly, or is timing controlled electronically? I'm no marine mechanic, just throwing out ideas....


No fuel lines that I have not replaced. Linkage and timing is correct (mechanical). I am not a marine expert either, just a Youtube connoisseur  



backcast said:


> I had same problem. Mine corrected with what you have done. If you have a pressure/vacuum gun such as the mityvac to test the float closing on carb. I used it to pressure fuel inlet side with carb upside down to test the float needle seat holding with something like 4 lbs pressure. I also used it to test fuel pump. I have the Seloc Yamaha manual for 2 strokes which gives good instruction on how to test various parts.
> Joe


I do not have a vacuum gun. I am also thinking the floats are not properly seated. When i tried to blow through the gas intake on the carbs it felt as if it were restricted... I am planning on checking that out first.



Smackdaddy53 said:


> Basically rebuilding carbs and doing an actual 100% rebuild are not the same thing. Did you replace all the parts that come in the Yamaha rebuild kits?
> The jet orifices get varnish build up inside them that restricts the fuel flow by just enough to cause issues no matter what parts you replace. I use a piece of twisted copper wire to clean the varnish out then blow through with carb cleaner spray. Don’t use welding torch tip cleaners as they are too hard and will remove material from inside the brass jet and open it up too much which throws off the air/fuel mix. Copper won’t.


I am not going to lie... I replaced with an OEM equal part and only replaced the components I spoke of earlier. Everything looked fine in the carbs so I did not want to buy more than what was necessary. I used copper and sprayed carb cleaner through the jets when I cleaned them.


I had a brief conversation with my buddies mechanic today and I am thinking that I did not seat my floats correctly. This is in line with some of the suggestions here as well. Just for everyone's knowledge.... you can crimp your line or pump your bulb when running the boat and find out if you are running lean or heavy. I am going to go ahead and see what's going on with these floats. Anyone have any suggestions as to what to look for with them? I plan on yanking them out tomorrow.

Thanks for all your input so far its appreciated!


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## devrep (Feb 22, 2009)

floats on 2 strokes don't usually cause a bog. they can cause fuel to run out of the carbs if the float needles aren't seating or the floats are letting too much fuel into the float bowls or they can cause you to run out of fuel at wide open throttle if they aren't letting enough fuel into the float bowls. if it's far enough off to cause a bog you would be losing a lot of fuel into the water.


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## devrep (Feb 22, 2009)

as smackdaddy said, there is no I kinda/sorta rebuilt the carbs. you do it right and you do it complete or you're wasting your time. a set of acetylene torch tip cleaning drills works great on carb jets just don't go too big a size or too vigorous with them and ream out the jets.


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## Mako 181 (May 1, 2020)

Plastic piece on my linkage broke once. Run like a top but slow to get up and would only run 2800. It was the timing advance linkage. 
Small black plastic piece that threads onto rod with ball and socket.

Good Luck !


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## Smackdaddy53 (Dec 31, 2012)

devrep said:


> floats on 2 strokes don't usually cause a bog. they can cause fuel to run out of the carbs if the float needles aren't seating or the floats are letting too much fuel into the float bowls or they can cause you to run out of fuel at wide open throttle if they aren't letting enough fuel into the float bowls. if it's far enough off to cause a bog you would be losing a lot of fuel into the water.


On that note, floats can crack and fill with gas then you will see bogging


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## devrep (Feb 22, 2009)

Smackdaddy53 said:


> On that note, floats can crack and fill with gas then you will see bogging


great point. that will also cause the bowl to leak fuel if they do as they will go to the bottom and cause over filling from the float needle dropping.


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## lemaymiami (Feb 9, 2007)

If this were my motor it would be headed to a pro Yamaha tech... and I'd be expecting that the trouble was not your carbs (or fuel system at all....).... Me, I'd be expecting some kind of an electrical problem (charging or sparking...) with the motor itself that was causing it to bog down that way... 

Please post up what the trouble was when you finally sort it all out...


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## Full Up (Aug 9, 2021)

Smackdaddy53 said:


> On that note, floats can crack and fill with gas then you will see bogging


To your point... If the floats are not set to the proper height that would limit the amount of fuel allowed in the bowls. This would result in running lean and bogging down at higher RPMs. Am I missing something here?

And for those commenting on the carb rebuild... I took them apart, cleaned all the jets with copper wire and carb cleaner, soaked everything for several hours, and ran compressed air through the jets. I then replaced the floats and the gaskets. Not sure what else you can do other than replacing the jets - which are clean as a whistle at this point.


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## Smackdaddy53 (Dec 31, 2012)

Full Up said:


> To your point... If the floats are not set to the proper height that would limit the amount of fuel allowed in the bowls. This would result in running lean and bogging down at higher RPMs. Am I missing something here?
> 
> And for those commenting on the carb rebuild... I took them apart, cleaned all the jets with copper wire and carb cleaner, soaked everything for several hours, and ran compressed air through the jets. I then replaced the floats and the gaskets. Not sure what else you can do other than replacing the jets - which are clean as a whistle at this point.


You never mentioned replacing the float valve needles. They get eroded where they contact the seat. Once you remove them and put them in differently than they have “worn in” they never seat right again. I have been doing outboard engine work a long time, rebuild diesel engines from scratch, make my own custom parts and fuel systems and work in the oil and gas industry where I rebuild complex regulators and controllers too. These are very simple but one component that is not right will make your outboard run like crap. 
I used aftermarket Yamaha rebuild kits one time and will never use them again. I threw all of it away and started over with Yamaha parts and the outboard has run like a sewing machine for the last two years. My fishing time is too precious to be dicking around with junk kits to save $50-60 and lose time on the water and do a carb rebuild twice.


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## Full Up (Aug 9, 2021)

Smackdaddy53 said:


> You never mentioned replacing the float valve needles. They get eroded where they contact the seat. Once you remove them and put them in differently than they have “worn in” they never seat right again. I have been doing outboard engine work a long time, rebuild diesel engines from scratch, make my own custom parts and fuel systems and work in the oil and gas industry where I rebuild complex regulators and controllers too. These are very simple but one component that is not right will make your outboard run like crap.
> I used aftermarket Yamaha rebuild kits one time and will never use them again. I threw all of it away and started over with Yamaha parts and the outboard has run like a sewing machine for the last two years. My fishing time is too precious to be dicking around with junk kits to save $50-60 and lose time on the water and do a carb rebuild twice.


It says it’s Yamaha brand. I got it off Amazon in order to save time, can’t beat that shipping. Here’s what I ordered.
OEM Yamaha 40-50 2-stroke Outboard Carburetor Repair Kit 6H4-W0093-03-00 Amazon.com: OEM Yamaha 40-50 2-stroke Outboard Carburetor Repair Kit 6H4-W0093-03-00 : Sports & Outdoors
I’ll check the seats again when I check the floats. Any suggestions on the needles and setting them? I am counting down the weekends to get on the water in the keys right now.


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## devrep (Feb 22, 2009)

if you put in new float needles and new float needle seats there is no adjustment as they are all new. some needles have machined tips and some have rubber tips. they are made to seal with whatever seats they come with. I can't remember on the yamaha carbs but typically you have to set the float level per spec on most carbs, it is commonly done by bending a soft brass tab and measuring the distance the float sits in relation to the carb where the bowl gasket goes. read the instructions for the kit or a service manual to confirm for your specific carbs.


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## Smackdaddy53 (Dec 31, 2012)

devrep said:


> if you put in new float needles and new float needle seats there is no adjustment as they are all new. some needles have machined tips and some have rubber tips. they are made to seal with whatever seats they come with. I can't remember on the yamaha carbs but typically you have to set the float level per spec on most carbs, it is commonly done by bending a soft brass tab and measuring the distance the float sits in relation to the carb where the bowl gasket goes. read the instructions for the kit or a service manual to confirm for your specific carbs.


This

And those carb kits look like knock off Yamahas, especially at that price.


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## Full Up (Aug 9, 2021)

devrep said:


> if you put in new float needles and new float needle seats there is no adjustment as they are all new. some needles have machined tips and some have rubber tips. they are made to seal with whatever seats they come with. I can't remember on the yamaha carbs but typically you have to set the float level per spec on most carbs, it is commonly done by bending a soft brass tab and measuring the distance the float sits in relation to the carb where the bowl gasket goes. read the instructions for the kit or a service manual to confirm for your specific carbs.


10-4 thats what I figured. I believe the float height for Yamah 50hp is 15mm +/- 1mm. I will let you all know how it goes. Thanks again.


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## Surffshr (Dec 28, 2017)

Knock off parts are irritating as hell.


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## Smackdaddy53 (Dec 31, 2012)

Surffshr said:


> Knock off parts are irritating as hell.


Yes they are. China goes as far as printing counterfeit packaging these days. I can get a Powerstroke oil filter off eBay for $15 less than a certified dealer but they are fake. The filter media breaks down and will cause a massive engine failure...all to save $15.


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## Full Up (Aug 9, 2021)

I messed around with the floats and it still feels restricted. Taking it to a mechanic on Saturday, will let everyone know what I did wrong


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## bonitoman (May 20, 2021)

Surffshr said:


> Knock off parts are irritating as hell.


squeeze your fuel ball when running to see if rpms go up even though you put a new fuel pump on


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## Full Up (Aug 9, 2021)

I got it back today and she ran like a charm. They went through and cleaned the carbs and the water line for the cooling system. Ends up I was missing a ground for one of the cylinders… I’m an idiot. The line for the water pump was also partially clogged, causing an overheating issue.
At WOT I’m seeing 5000 RPMS not loaded down and just myself. Getting about 35 mph when properly trimmed. Anyone have any suggestions for a prop that they use with their 50 yammy on a skiff? I’m wanting to get 55 or 56 out of this motor when it’s just me and 39/40 MPH.


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## backcast (Apr 9, 2013)

What boat are you running? I have Caimen with tunnel and 50 yamaha 2 stroke. I have been trying different props. I have a 4 blade PT with no cup and it cavitation badly. I saw 5500 rpm with that prop. I may try to cup it some. It is a 10 pitch. I tried a Solas 11 pitch with cupping and cut rpms down to about 4K. I have Jack Foreman prop and it has worked the best but still cavitates . It is 11 pitch 3 blade. I need to go back to Foreman and see what to do next.


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## Full Up (Aug 9, 2021)

backcast said:


> What boat are you running? I have Caimen with tunnel and 50 yamaha 2 stroke. I have been trying different props. I have a 4 blade PT with no cup and it cavitation badly. I saw 5500 rpm with that prop. I may try to cup it some. It is a 10 pitch. I tried a Solas 11 pitch with cupping and cut rpms down to about 4K. I have Jack Foreman prop and it has worked the best but still cavitates . It is 11 pitch 3 blade. I need to go back to Foreman and see what to do next.


It’s basically a Mitzi 17. I have a spare prop that I’m going to try out. Not sure what pitch I have on mine right now but it seems like I can pump it up some. Thinking I’ll probably get something 1/4” smaller. Is a higher pitch preferred for hole shot or does that just deal with going from 3 blades to 4 blades?


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## backcast (Apr 9, 2013)

I am not that up on propellers choices. Usually higher pitch is for speed and lower pitch is hole shot with some loss of top speed. Some believe the 3 blade will do as well or better than 4 blade. I had a 4 blade on a Mitzi 15 and it was a really good prop. Do not know pitch of that 4 blade. It never slipped or cavitated. I am having trouble getting prop for Caimen with tunnel and 50hp Yamaha 2 stroke.


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## lemaymiami (Feb 9, 2007)

An electric problem…. Hmmm


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## Smackdaddy53 (Dec 31, 2012)

backcast said:


> I am not that up on propellers choices. Usually higher pitch is for speed and lower pitch is hole shot with some loss of top speed. Some believe the 3 blade will do as well or better than 4 blade. I had a 4 blade on a Mitzi 15 and it was a really good prop. Do not know pitch of that 4 blade. It never slipped or cavitated. I am having trouble getting prop for Caimen with tunnel and 50hp Yamaha 2 stroke.


That is not really how props work. There are many more factors involved as to how a prop makes a hull and outboard move than just pitch and three vs four blades.

Your outboard has a red line which is the maximum RPM it can effectively run without risking damage to the power head. Running a prop that can’t reach that RPM is dogging your outboard and killing not only your fuel economy but also overloading your engine which is like driving a truck with a standard transmission starting out in third gear. Your outboard has one forward gear so you need a prop that can make the best out of the power band which is the RPM range the engine is designed to run. Prop diameter, pitch, cup, cup placement, number of blades, rake, blade shape, barrel size, barrel flare, porting etc are all factors that can be combined to make a prop do different things. 
There is also a myth about hole shot props are four blade and speed props are three blade. That is an incorrect generalization started decades ago by internet armchair prop gurus that has stuck around far too long. I’m no prop guru but I can hold my own.
I think instead of thinking you need to tell Jack Foreman what to do to make that prop work you should give him numbers and how those numbers change in different scenarios. If you have a three blade custom Foreman and it’s blowing out he’s going to ask you at what point does it start losing grip and what is your WOT RPM when you have the trim tabs, trim, jackplate and weight distribution optimized. 
When I open my full time boat shop I’ll be incorporating guided fishing trips and also offering customers time on the water with me showing them how to run their boats and find the sweet spot then if it needs any tweaking I’ll make suggestions and make those changes either at the boat ramp or back at my shop. Lots of people think they are able to run a boat but could use some help.


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## lemaymiami (Feb 9, 2007)

Speaking of props... the first thing I try to do on any skiff is to look exactly where the motor is sitting on the transom before anything else (exact height of that plate in relation to hull bottom), then make a careful examination of the actual hull bottom using a known straight edge to see exactly what the configuration of the hull itself is... After that it's all the stuff Smack has mentioned... 

One of the reasons I don't like jackplates is that it adds one too many variables for me... but that's just me...


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