Diagnosis and repair of 4 Stroke Outboard motor Carburetors. A look at the common issues. 

I've been cleaning carbs for more than 40 years. I've worked at an outboard shop & a couple of motorcycle shops. This is the best description of what to do, how good it needs to be done & why you need to do it, that I have ever come across. You did a great job. Two thumbs up. I watched this video because I needed to find the idle mix screw on a Merc carb & it was a dead ringer for the one carb that you showed. I saw the location of the screw on yours. I didn't see the plug on mine at first because it was behind the choke linkage. You taught an old dog a new detail. Thank You

The best lesson on small boat carburettors I have ever seen. I have 4 small engines that get little use and long periods of storage. Yesterday I partially stripped down a Yamaha 4 carb, hoping cleaning a few bits would help. It did start but ran very roughly. Today I've done it again understanding what I was actually doing... ( Yes it helps) Now it running beautifully.... Thanks for a great lesson.

What an absolute fantastic video on carburettor cleaning.Thank you for the great explanation.

The best video on RU-vid with regard to sorting out a carburettor. Perfect. Many Thanks.

Thanks for doing such an informative video. I’ve cleaned lots of carbs but I feel enlightened by all your good information.

I save all my old guitar strings for cleaning carbs they work wonderful. Thanks for your hard work and wisdom sir.

Ok, I must comment. This is hands down the best outboard carburetor instructional video on RU-vid. I rarely ever subscribe to the content creators but I certainly said I must subscribe to this channel! I've repaired my Yamaha four-stroke carburetors numerous times, but I've had to reclean them. This video gave me a much better understanding of the carburetors and how to go about troubleshooting. I really appreciate you taking the time and wish we had such a good mechanic down here in San Diego.

Excellent video of how a carb works and how to check for plugged circuits and dirt the best i have ever viewed

Wow! The best and most useful carb description I’ve ever seen. A gem of a video.

I have been tearing my hair out getting my 6 hp Tohatsu to run reliably and your video has given me the confidence to tackle a thorough carby check. Excellent video ,Thank you!

Best educational video I have seen on carbs

Great educational video on the 4 carburetor circuits and how to race trace in the casting. Love the use of aerosol lubricant to check passageways. Also great explanation of the needle and seat and confirmation of when the needle and seat is open and when its closed. Thanks so much for sharing!

I would say that this was really good! One of the best I have seen. Helped me today with my Hide(Yamaha) and will help me with my Tohatsu when I will fix that one. Thanks

Wow really great video. Unbelievably solved my problem. You saved a fisherman's boat from Turkey. :) You knowledgeable people, glad to have you. 😀🙏

Thank you for the extremely informative and detailed video

Thank you for this! Helped me fix my grandparents’ mercury

Perfect explanation. Thanks for making the video.

Excellent training, appreciate this.

There is absolutely nothing but great information in this video but just a point from my 9.9 use and quick but permenent fix. My best friend was a carburetor man for 45 years the absolute best. He couldn’t clean repair mine after tearing apart couple times. I bought a new on not that expensive.Didn’t work I new the motor had plenty hours but I new motor was perfectly good. Then he noticed in the picture same carb upper left hand ther is a round circle with a plug in it. Popped it out there was the air fuel mixture screw. Epa requirement cap for new factory setting not to be touched. Wear tear varnish whatever just a little turn giving motor more air and it ran like new. That motor keep running like new for three more years putting 400 hours a year on it. Bought a newer boat and gave that motor to a friend. It’s still going like new. Hard starting rough idling that’s your baby. I live at the beach and it’s worked everytime I showed that cap trick to others that come and go from resort.

wow thanks so much sir great video helped me troubleshoot my 8hp yamaha outboard on my sailboat BIG THANKS

Very informative and well explained, will apply your teaching to my next maintenance on my carbs, Thank you

Perfect explanation.Very useful.

Great video. Very informative. I had to clean my Yamaha 25 carb yesterday. It was just like the one you showed from your junk stash. I wish I had watched your video first as it would have made things much easier and I would have understood what was going on more. I did manage to get it apart and back together and it seems to run fine now.

Fantastic! Thanks for the great explanation.

I am sitting on a yatch in a remote part of Australia, population density 1 person per 100 square kilometers. 😀300 nautical miles, 2 weeks from the nearest Yamaha outboard service centre. My outboard will not idle properly and cuts out when turning the accelerator. This is a brilliant step by step explanation of what could be wrong with the carburetor and how to diagnose it. Thanks Canada Wild

Very informative video.Thanks!

this vidio is so good ive subscribed you thanks for info ..best description ive seen .

Great content very informative just what I was looking for.

Great video explained very well and clear

Best video I've found. And like you said, so simple. Thanks. Hopefully i get it running now. Especially since it was running before i decided to take it apart. But it wasn't running happily over half throttle.

An excellent presentation. I learned a lot. I just bought a boat that wasn't prepared properly for winter and having issues getting it to start. It will run with a light spray of starting fluid, but not beyond that. It's looking like I will have a carb teardown in my near future.

The corrosion is the part that tells me. You are 100% correct. I would advise the owner not because of the varnish Gunk build up cuz that could be cleaned it's more of a metallurgy seating issue. If you can get one and afford it that definitely qualifies is investing in the new body at least not to mention gasket kit that's why, don't leave fuel in your engine. Outboards like to be run honestly all the damn time at least twice a week the buildup one stress on impellers when you break in a motor have a system where I protect the water jackets with a thin layer of lubricant it is for impellers as well run fresh water through them once in a while also a very good tip. But this guy is good he knows his stuff

Exact video I needed!

Awesome video!

good informative video thanks

Thank you Mr Canada man!

Very informative video. I have a yamaha 8hp and the idle 'hunts' like it's not getting enough fuel. This will help me a lot in doing a tear down and clean. Thanks!

Very very good!👍

Thanks awesome video

Very good video! Have a good day!

So easy, thank you : )

Thank you very much!

now i have an idea how a carburetor work, just become your royal subscriber ：）

Again, thank to share your expertice. Yoy are a geniuos. And mechanical Enginieers, please, as you see, the carburator has 100% chance of failure !! You must know other ways to restrict flow other than tiny holes that can be blocked any time, any where.

Awesome

And now we know why they invented fuel injection. Great video. Wish I watched it a month sooner.

Thanks for sharing your wisdom. I learned alot and managed to pull apart a triple carby, clean and replace it thanks to you. I have the mercury carby shown in the accelerator circuit. My question is, if fuel is leaking from the bellows on the accelerator pump, would this cause bogging? The jet it feeds into is still working and squirting fuel yet the engine bogs at mid throttle.

Great explanation. Thank you. How important are those little inline green filters that are sitting in carburator inlets for gas? I have water separator and little net filter in engine. Just did carb service on my f90tlrc.

You are correct. I would say more than 90% of the time probably 95.99 unless it's totally obvious it's always a fuel issue if you have spark you have compression it's easy to test for that do you feel resistance when you pull when you pull the boot off the plug small flathead screwdriver inside the boot gently fuel for a shock of electricity. I know that's old fashioned but it works let you know that the kill switch is not the culprit the Magneto is not the culprit could be the actual plug though but I digress I recommend depending on if the motor had not been running a long time especially the fuels left in the system it will turn to Varnish clogging the Jets. Sometimes you can get away with a can of carb cleaner but that's not the right way to do it. Drain the carburetor Pump Fuel through the system trim the motor all the way up after putting in screw back in carburetor Bowl need it trimmed full up Prime system with fuel start motor I know it's in the air I know the angle don't worry your impellers will get water soon enough chances are if it's that they're cracked anyways it won't overheat in a couple minutes but it will allow motor to run. Just thought I'd pass that on to you oh yes if you do have a separator make sure the motor is getting fuel clean out the Racor if you have. But the love of God just don't start turning screws and then call someone like me to come fix it although that's easy too turn back to factory specs all the way tight count rotations you will get your air fuel mixture correct but their Motors it could be a lot of things the trim up tip was the best key I could give you but this is meant mainly on bigger motors with push start

Thank you very much for this great explanation of how carburettors works. I have a Yamaha 2002 F60TLRA from new with 1800 engine hours, it is a trailer boat used in freshwater for walleye and lake trout trolling. The engine is hard to start when cold or first time that day, it normally stalls a least 10 times before it runs fine . I suspect it is caused by a vacuum leak in the prime start system, (as you describe in the video) i also idles a little bit rough around 700 to 900 rpm. i plan to rebuild the carburettors with 4 new carb kits. When the engine was new i had a lot more power (same boat not much added weight) i know that it is quite common that engines lose some power with time, but i am wondering if it is possible to gain some power back? Spark plugs are dry and more on white colour (all 4 plugs similar colour), indicating lean mixture. I am wondering if new larger main jets would yield more power in the mid range 3500 to 4500 rpm?. . Thank you very much in advance. Any thoughts or suggestions will be greatly appreciated.

Can you make the main jet a little larger (maybe make the percolation tube air holes a little larger as well) and get more performance (hp)? Maybe you have to bore the air chamber out some too??? No that probably wouldn’t work, the throttle plate would need to be larger after doing that, right? Is there a pretty simple “trick” to get a little more high end performance on a 15 yammy? Thank you for the information just past 22:05, I definitely learned something there, really the whole vlog 👍🏻👍🏻👍🏻 Had to rewind a bunch of times. You do a really good job of getting small parts in the middle of the screen and not moving around much, it helps when I zoom in to see it. Also learned it’s pretty important to have an external fuel filter/water separator to keep the dog’s hair and water out of the fuel system. 30:20 thanks for showing how to view the idle transfer holes ❤❤🎉🎉🎉

Great video! I do have a question about my Yamaha 40 Hp 4 stroke, I have a diaphragm assembly and there is a spring on there that wasn’t engaged I think I put it on right but now I need to adjust it so it works in accordance to the throttle

Thank you for a great video. My engine starts well, idles fine, and runs wide open fine. The problem is when I run at midrange it will run for a bit then stall out. Or if I run wide open and then start idling down it stalls nearing idle. Any ideas? Thanks for all the help.

Hi. Thank you so much for the create video explanation how the carb works. I am actually very interested in the mecury carb plunger (video 19.12 min) could a wrong adjustment of it also make the engine run rich? Ive adjusted the airflow and got the engine run in idle very nice but sparks are dry black. Carb is cleaned and Checked the needle like you showed upside down blowed and it seals of nicely no leaking. I cant get my head around why the sparks are black every time after I tripple checked it and adjusted it. Greetings from Holland. Davis.

Thank you great informative video. My question is at what RPM does the idle function stop and you go on the main circut. I have a 20 HP Honda that idles fine and runs great at mid range and WOT but trolling at 1000 to 1200 RPM the engine stalls but restarts instantly. Sometimes this happens every minute and is frustrating. I have an inline fuel filter and that was clean. It gets a great squirt of gas from squeezing the inline fuel pump. The plugs look great. Any direction would help thank you

Very good video. Question I have a 2011 90 Hp Mercury 4 stroke. My will take off from idle and get on plane and run for about 200 yards then bogs down. Do you think that the float is sticking and not allowing fuel to enter the bowl or something else?

Hi great job, I have a F9.9 MSHC High Thrust 2004 with the electric choke solenoid on top and I wondering if this carb can work or even fit or may not work as the CDI units needs the feed back from the electric choke for timing? any help is appreciated

This was a great video. I am hoping you can solve an issue I have. I am leaking gas out of the accelerator plunge/boot. After my 2001 Mercury 25 hp 4 stroke runs and shut off, the gas will start to leak/drip out of bottom of boot. I bought a rebuild kit and replaced all pieces and gaskets and made sure the float and seed is good to go per your video. I have not stated the engine yet, but I installed the carb and moved the plunger/accelerator up and down and I am still getting gas leakage after 4 WOT pumps (by hand). I don't want to run the engine unless the air vacuum keeps the gas and air from leaking. while running. I appreciate your time. Any help would be appreciated.

Hi, I have the same carbs on my F75 yamaha. I pulled the carbs off and cleaned them up, reassembled and reinstalled but still popping and backfiring at idle and worse with increased rpm. The only thing I didn't remove on the card was the idle jet on the side because the needle has a brass cap on the outside...should I remove this cap and remove needle screw or not. Great video, sure would b great to chat to you. Thanks

Thank you very much for such detailed explanation of how all these works. I have 2004 F90TLRC, new to me. Low hours and clean carbs. It idles at between 9000-1000 when warm. Spark plugs are dry and more on white color(all 4 plugs similar color), indicating lean mixture. I am trying to avoid possible overheating and want to run engine in optimal way. Dont have starting problem or power at high RPM/speed. Engine runs and responds fine. I put about 20 hours on it with no problem. Questions: 1.Do these engines tend to run a little lean(emission regulations) and I do not have to worry about plugs being not tan in color? 2.Do I want to play with butterfly screw on bracket to bring RPM down to 800ish? May be play with idle muxture screws? But there are 4 of those and I do not want to mess existing setting. Thank you very much in advance. Any thoughts or suggestions will be greatly appreciated.

Thank you for awesome video, I have 2001 Yamaha T50TLRZ I’ve have clean the carbs, where do I start setting the air/ fuel mixer at some forms Start at 2-1/4 on carbs 1,2 and3, 4 carb at 2 1/2 turns out? Do you know where it should be. Thank you

If I was in 🇨🇦 I know exactly who I would take my outboard to for repair. 150 👍🏻 I also know where to get parts too. Liked and a repeat subscriber, my other RU-vid account got lost (maybe that’s why guys lose subscribers sometimes, RU-vid figures out the accounts aren’t being used anymore?) when I couldn’t remember the password to the email account it was linked to 😔

Will an incorrect float height create a lean running condition? I recently replaced 4 floats on a Yamaha F100. I was getting a lean sneeze around 2800-3200 rpm. Inspected the plugs and saw #1, #2 and #4 running lean. I’m thinking the float height will need to be looked at again. Idling great, and high speed boat runs great. I was thinking of enriching the idle mixture screw to compensate, but I think I’ll tear it down again and make sure floats are set correctly, as they should be.

Thanks for that good video and the explanations. One question: to follow the pipes, you put what in? Which spray is this? If I understood correctly, also WD40 works but do I than have to clean the carb again because of the oil? Or does the oil not harm the working of the carb? Thx a lot for your help.

Hi, I am disassembling the carb assy. on my 2001 Yamaha 50 HP 4 stroke. Can you tell me what the trick is to releasing the link rod bridging the 4 carbs and also the link rod from the accelerator pump at the carb end? Both parts seem to be snapped into place, no cotter pins involved. Is it a matter of pulling at the joint to release? I don't want to damage anything> Thanks again for all your great videos and explanations. Jim Murphy

Thank you for the information, I have 40hp 4 stroke and I have had the engine not speeding up no matter how much gas I put on so I thought it's the carburetor and got it off cleaned it and replaced it back but it's still the same , I'm thinking to buy new jets Any site recommendations ? Maybe you think I have a different problem? Thank you in advance

Hi there my Yamaha 2007 T 9.9 it was running only with the chalk little bit out. I can drive it that way, but as soon as I put the chalk in it stops I came up to your video which is one of the best I watch lately thank you for your good work I took my carburetter apart the way you showed when I came to the idle jet, somebody’s been there before me and broke that slot for the screwdriver. I couldn’t take it out so I decided I’m going to use a small easy out to pull it out. I was doing good but soon got hart to turn it but all of a sudden got tight and I didn’t succeed. Is it anyway that this carburetter can be used by drilling and doing something else so I don’t have to buy a new one. Please advise what is my options? Thank you.

Great video , do you any online resources for ajusting a suzuki 9.9 four stroke carb thanks.

With the ambient temperature being around 70-90 deg Fahrenheit, do you think I could use sae 30 break in oil for my new Honda 9.9outboard? Then when the break in is done would switch the oil over to 10w-30 which the manufacturer recommends.

Hi I have a 8 hp 4 stroke 2006 . Do you know the factory seting for that small jet . I took it out without checking . I will try one full turn . Nice to know. Thanks.

is there a screen under the needle seat ? having trouble blowing air through to the bowl even without the needle in . having a hard cold start but runs well after i get it going . 03 8 horse 4 stroke yamaha with nikki carb

Following and rechecking based on comments to another user - my carbs have been fully cleaned, and I simply have a bog when you hit it and also a miss at about 1/3rd throttle. This is a 30hp merc 4 stroke 1999. I went to add/adjust the idle mixture a little richer - but there are no adjustment needles - there is a boss in the casting which looks like it may have been in the past but no longer. Idle is perfect. You can nurse it up to higher power and it is perfect up there. Coming back down I can create a miss consistently, but only in a tight range then it goes away. I don’t have a tach easily available. It would seem to me that I need to go a size larger in the low speed jet. - any alternative suggestions?

Good video! Why is the pilot circuit part of the main jet ? On my motorcycle, they are separated.

Other than the float needle what would cause fuel to come out of the overflow?

Can I remove the welch plug covering my idle mix screw? It doesn't need to be replaced after either? Great video, I learned a few helpful things, been tearing carbs apart for 30yrs as an amateur, lol.

I’ve got gas coming out of the breather line for the accelerator pump on a 08 merc 20hp 4stroke, is that common when the plunger doesn’t seal anymore?

I recently cleaned my Merc. 15hp 4 stroke carburetor. I’ve no leaks or purging. Seems to run as should. However, the primer bulb on the motor itself, not the fuel line primer doesn’t get firm. Any idea what the cause could be?

My f25 Yamaha 4S without a spray of starting fluid. Which circuit needs cleaning pls?

I do locking for a carburator for mercury 9.8 outboard

How do I get the plug out that covers the air fuel mixture screw?

I have a automatic choke dose it make it harder to clean and disassemble john

I have learned quite a bit by watching your work. I have a 1999 Evinrude 6RL4EEM 99, 6 hp, 4 stroke. The carb has an accelerator pump on the bottom, which water flows through. Have you ever seen a carb like that? There are no parts available for the accelerator pump, but the carb kit is available. The engine bogs upon acceleration but otherwise starts and runs good. I haven't rebuilt the carb, but took the carb off the motor and took the float bowl off and it's very clean inside. Is there any sense in rebuilding the carb since I can't fix the accelerator pump? Also, the motor uses a very rare fuel pump. No rebuild kit available and a replacement fuel pump is $166.00. It's a good little motor used on a sailboat. When docking, sometimes you need a little rev and that's when the motor bogs and sometimes dies. Not sure what to do. Thanks

Good day, If you can help. I have second carburetors that you show, Mercury, Tohatsu. ITs overflow on idle. I clean all 20x times, needle is sealing, but still on idle it overflow after 10 seconds of working. Thank you upfront.

Great video

Nissan 20hp Four Stroke Boggs at half throttle. Any tips on where best to start? Not sure if it’s idle a few adjustment or something else.

Hi Greetings from Australia Got a 2016 suzuki 8hp 4 stroke outboard How many carb adjustments for this motor pls ? How many turns out for base speed for full throttle top speed performance pls ? Thanks Glen Australia

Hey there man quick question I took out he carbs cleaned them and now there a couple linkage on the motor I can’t seem to figure out how to put back together

Turns out my accelerator was sticking open. Don’t know if that was the problem?? But it started. Now I have to figure out why it’s sticking or run it at idle only for now. The little spring at the carb maybe, or the plate has salt water buildup been the throttle plate and acceleration plate? If I can’t fix it, I can manually operate it, but that can become dangerous and subject the engine to more moisture since the cover has to be off and you’d have to turn around to slow the engine down, just want it right. She runs like a champ though, seems to be hitting the limiter now, it never did that before?? I’m at anchor so it’s my only way to shore, been oos for 4 days.

Hi there, I just bought a 2021 used Yamaha 2.5 very little hours. Started it for first time today in a closed loop circuit (my bucket). Was very eager to run it and the only water I could get was from a hot water hose as the cold water supply was closed for the winter. I went through different rpms and ran it max rpms in neutral for probably 2-3 mins, water in bucket was very hot. Engine shut off and made a quick cranking sound. Couldn't get it to start again. Checked compression by putting my finger by the spark plug hole and didn't feel any compression. Put an inline spark plug tester and the tester blinks when I pull the coil. Could the hot water have damaged the outboard? Any next steps to diagnose what needs fixing? Thanks!

i have a 2003 honda 15hp 4stroke. there is a screw on the side of the carb, facing out. i believe its the fuel/air mixture. its silver in color. do you know what the turn(s) to start out should be? i cleaned my carb and its in great shape. starts right up idle just fine. my problem is when i give it gas it hesitates then when i let off the gas i can hear it back fire though the intake. i dont know if this is the problem. i bought the outboard not running, and some parts already off. so i dont know if the previous owner turned it. any help will much appreciated

what is the best way to remove varnish from the carb? carb cleaner doesn't do it. terry clark

I'm trying to remove the old accelerator bellows boot to install a new one

I have 20 hp yamaha four stroke and on full throttle engine rpm flying high and lows. what's wrong?

I have a 25 4 stroke tohatsu with 3 carbs.I assume i will have to clean all 3.it will not idle.

I've cleaned my carbs out good and changed fuel lines. My issue is when I gas it and let off it dies. If I go slow she'll power up. It's when I come down from throttle it cuts.

I have the 9.9 prokicker and the boot on the enrichment port is leaking. I cant find a single vid on rebuilding this component. Anyone?

is the idle jet and pilot jet the same part?

Got a hole inside of my carburetor Yamaha 25 I got fuel coming out of it

Have you heard of float wharping ?

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