CHAINSAW CARBURETOR DIAPHRAGM: 'Fuel Pump Diaphragm' Causing BOG, Won't Start!

Mastery of the Chainsaw Carburetor: Unveiling the Mysteries of the Pump, Bogging Down
Very few people know this, but there is a very special Pump inside your Chainsaw Carburetor, and any malfunction of the pump and can cause a whole host of problems (bog, incorrect running and starting issues, to name just some). Powered by the fuel pump diaphragm, this pump is the heart of the 2 stroke chainsaw carburetor. The diaphragm, in turn, is powered by the 2 Stroke Engine.
Removing the fuel pump cap on the 2 stroke carburetor will expose the Fuel Pump Diaphragm. So lets now see how all of this works. Fuel is sucked through into the fuel inlet pipe where it's drawn down internally towards the carburettor body. When it gets there, the first thing it meets is the one way valve flap that it part of the Fuel Pump Diaphragm. The fuel passes this one-way valve and continues to be drawn down a second hole that is the entrance to the fuel pump chamber/reservoir, all situated underneath the Fuel Pump Diaphragm. So the pump, above, moves up and down due to alternating positive and negative pressures from the impulse line generated by the up and down movement of the piston during engine running.
Each time the negative suction pressure from the upward travel of the piston draws the fuel pump diaphragm up (via the pulse line, attached to a special connector on the fuel pump cap above the fuel pump), it sucks fuel in, underneath it, from the fuel tank. When the piston travels downwards, this sends the positive pushing pressure, via the impulse line, to the top of the diaphragm, which then pushes it downwards. This pushes the fuel out from underneath it. Upon doing so, the fuel can only go one way because of the valve flap system built into the fuel pump diaphragm. The flap that the fuel came through when the diaphragm rose up
This principle works for most types of Chainsaw saws, and the following also helps with Chainsaw maintenance. So, whether you are using a Stihl Chainsaw, Husquvarna Chainsaw, basically, all types of Petrol Chainsaw are valid for this principle, as well as many types of or a 2 Stroke Engine. The Electric Chainsaw, of course, escapes this whole principle!
If, by the way, you are having problems with your Chainsaw Not Starting, then please do take look at my other video, where I help you get back you and running again if your Chainsaw Won't Start, or your Chainsaw Won't Stay Running. • Chainsaw WILL NOT STAR...
If you need a easy to follow video on Chainsaw Carb Tuning. So here I take you step by step should the Chainsaw Carburetor Adjustment be required: / watch
v=74p9FLmIkkw&t=47s
Here is a detailed instructional presentation type video of mine explaining the meat and bones principle of why a Chainsaw Bogs Down: • Chainsaw Carburetor Pr...
I hope you find this video useful, and I really hope you enjoy it.
Many thanks indeed
Craig Kirkman (Owner and Creator of The Repair Specialist Channel and its Copyrighted diagrammatic content)
#ChainsawFuelPump
#ChainsawCarburetor
#FuelPumpDiaphragm
#EnginePerformance
#ChainsawMaintenance
#ChainsawProblems
#ChainsawEngine
#TwoStrokeCarb
#FuelSystem
#FuelPumpPrinciple
#EngineDiagnosis
#ChainsawTips
#ChainsawRepair
#EngineComponents
#FuelFlow
#2StrokeEngine
#ChainsawKnowledge
#CarburetorFunction
#ChainsawMechanic
#PetrolChainsaw

[@TheRepairSpecialist]

Hi guys I just wanted to Introduce to you my other Channel "Kirkman's Academy" - which i'm just getting started. It's a go-to channel for simple explanations for hard to grasp subjects such as physics, maths and chemistry etc. Here is the link: www.youtube.com/@kirkmansacademy/videos . Thank you so much for looking, and if these topics interest you then I hope to see you the there. Many thanks indeed. Craig 😊👍

[@Hydrogenblonde]

This is the best explanation of the two stroke fuel pump system I've seen on KZbin.

[@markopalikko6986]

I agree.

[@miltonkphotography1380]

Always the best detailed descriptions

[@NesianDope]

I understood it! People actually pay for this kind of explanation in a classroom. This was for free in exchange for views, we all benefit from this system. Thank you for the videos!!!

[@TheRepairSpecialist]

You're very welcome, and I'm delighted to hear that you found the explanation of the 2-stroke carburetor in my video helpful! It's wonderful to know that the content I create can provide valuable insights and explanations that are on par with what you might receive in a classroom setting. You're absolutely right; the beauty of platforms like this is the ability to share knowledge and information freely in exchange for views and engagement. It's a mutually beneficial system that allows people from all walks of life to access educational content without barriers. Thank you for your support and for tuning in to my videos. Your feedback and viewership are greatly appreciated, and I'm here to continue sharing knowledge and insights on various topics. If you have more questions or if there are specific subjects you'd like to see covered in future videos, please feel free to let me know. Happy learning! Thank you Craig

[@peterbaumgartner4006]

This is the first time I understood how the pump works. Thanks you very much for clear explanation and the lot of work that went into the video!

[@TheRepairSpecialist]

Thank you for the nice comment. I really appreciate it. Craig 👍👍👍

[@beebester4106]

44 years old and finally a simple articulate explanation of a carburetor. So we'll explained that I feel I will actually; remember it.

[@GuysPlayingWithTools]

Nice video. Not many people think about how the gas goes uphill to the carb with no external pump

[@joeorapellojr6417]

Best explanation of 2 cycle fuel pump. Thank you for this video. Excellent!! I’m 63 years old and finally understand it.

[@TheRepairSpecialist]

Thank you for your kind and motivating feedback. Craig 👍👍👍

[@joeorapellojr6417]

@@TheRepairSpecialist Craig the illustration software you use is so helpful. I will share your posts. 👍

[@kenward48]

Absolutely the best explanation of how the carburetor works I have ever seen. I finally know now what all the holes and flaps are inside and their functions.

[@TheRepairSpecialist]

Thank you for your kind and motivating feedback. I really appreciate it. Craig 👍👍👍

[@IRDeezlSmoke]

Absolutely awesome teaching and explanation. I have a whole new understanding now of the service needs of my older saw. This video also somewhat explains why some prefer to pull the start rope a few turn overs before turning the switch on. The piston pulse will freshen the fuel load in the carb chambers and make starting easier. Thank you so much for taking the time and efforts to make such an awesome educational video. I definitely hit the like button and may subscribe after browsing your channel for a bit.

[@TheRepairSpecialist]

Thank you. Craig 👍👍👍

[@twizz5727]

Epic, I can't believe its not been seen more! Hopefully that will change for you No cutesy BS Just knowledge in a clear understandable way. Thank You Sir✌🏽

[@TheRepairSpecialist]

Thank you for your kind feedback. Craig 👍👍👍

[@691lucian]

When I saw the illustration on the thumbnail I knew this would be the best video on 2 cycle carbs

[@TheRepairSpecialist]

Thank you for your awesome comment. Craig 👍👍

[@100vg]

I just found you through your *Setting 2 Stroke Carburetor | This Happens Inside - How to Tune,* which I fortunately found, and this one was suggested next. I have to say that I love your work! So descriptive with such brilliant illustrations. Thank you, Mr. Craig, and Good Day across the pond.

[@cm5838]

Long time mechanic, short time 2 stroke mechanic so always looking for more knowledge. I’ve encountered other common problems with lower end equipment, crank seals going out very early in life, and rubberized parts including carburetor parts that simply do not appear to be fuel rated materials. I have a pile of chainsaws that I keep threatening to bring back to life.

[@bertgrau3934]

I have worked on a few chain saws, it's usually just as cheap to order a new carburetor, rather than trying to fix an old carburetor. Just a suggestion. Also, change the fuel lines, and fuel filter. Be sure the gas tank is clean. To check a primer bulb, put 2 lines on it and dip the ends into a small amount of gas and see which way the fuel is going. On the 2 stroke carburetor, apply a small amount of vacuum to each fuel line inlet/exit if it will not allow air through that's for the return line (back to the fuel tank) . Good luck. It can be fun to work on chain saws, weed eaters, and lawn mowers.

[@gronowens]

You have made a fantastic set of videos !!! I use these carbs on RC Planes and they are exactly the same Walbro type carbs. I now know exactly how they work and have now invested in a pressure tester! Again, many thanks.

[@TheRepairSpecialist]

Thank you very much for your kind feedback and letting me know. Craig 👍👍👍

[@DavidJones-smiley]

Thank you sir I learn more and more each video I watch!

[@TheRepairSpecialist]

You are very welcome. Thank you. 👍👍👍

[@thadrepairsitall1278]

I'm glad to hear I've been doing things fairly well for years. I definitely learned a few things since I'm a fuel injection guy.

[@TheRepairSpecialist]

Nice one. Thank you for your feedback. Craig 👍

[@jamesnicholson3313]

Thankyou for such a good demo of how the carburetor works and really really appreciate the effort you have gone to using diagrams to explain their wordings. Jim from AUSTRALIA.

[@stuungar3390]

Brilliant thanks, you've made an essential function of a diaphragm carb, easy to understand.

[@TheRepairSpecialist]

Thank you for your awesome feedback. I really appreciate it. Craig 👍👍👍

[@gwizz9175]

Very helpful instructions thanks 👍

[@kiteglinton]

Yet again another superb video with clear explanation, it's really helpful so thanks for taking the time to share your expertise Craig

[@michaelglynn2638]

Very well explained, great graphics too. Thanks, I learned something there. 👍

[@TheRepairSpecialist]

Thank very much. I really appreciate your feedback. Craig 👍

[@thediddly]

Thank you, you added all one needs in this video to understand the topic

[@TheRepairSpecialist]

Thank you very much for your motivating comment. I really do appreciate it. Craig 👍👍

[@Indeewoods]

Excellent video!!!! It sure makes diagnosing and tuning engines easier when it’s understood how they work.

[@TheRepairSpecialist]

Thank you so much. I really appreciate it. Craig

[@17penobscot]

Thanks again, I learn so much from your videos 👍

[@JOEZEP54]

As usual great explanation of this system. Stay well, Joe Z

[@TheRepairSpecialist]

Thank you Joe z, I really appreciate your motivating comments. Craig 👍👍👍

[@JOEZEP54]

@@TheRepairSpecialist You're welcome ..👌

[@tomasrosas3512]

Good video.I’m learning a lot about carbs. Thanks

[@yoyomamamma2260]

Excellent job explaining !

[@TheRepairSpecialist]

Thank you. I really appreciate your comment and feedback. Craig 👍👍

[@timkirkpatrick9155]

excellent graphics and animations! Have a Wonderful Holiday Season!

[@DEtchells]

Huh, good to know about! I tend to use my chainsaw very intermittently. So far so good (I only use non-ethanol fuel), but now I know to look out for this in the future!

[@longdriver2]

Very good explanation of this system Thanks.

[@andrewsmith7287]

Great video Craig love your videos

[@KensSmallEngineRepair]

Another great Vid Craig! Thanks for sharing!

[@TheRepairSpecialist]

Thank you for your kind feedback as usual I really appreciate it. Craig 👍👍👍

[@markproulx1472]

A superbly done video. Thank you.

[@garyc.8488]

Thanks for the presentation, nicely illustrated and greetings from South Carolina USA and a new subscriber too. Gary

[@rickhamm3962]

Great videos and explanations.

[@RaleysSmallEngines]

You must be a computer Genius also, aways Awesome visuals. Great job my friend.

[@TheRepairSpecialist]

Thank you very much! I really appreciate your kind feedback as always. Craig 👍👍👍👍

[@garrysekelli6776]

İ've recently purchased 2 small electric chainsaws. After realizing how complex a gas chainsaw is and how many points of failure they have i think that i would just go the easy route and simply use electric chainsaws. Also slightly less noisy.

[@garrysekelli6776]

The smallest of these 2 electric chainsaws is basically just a cordless drill but with a chainsaw instead of a drill as the business end. İ don't use them often. But they are usefull. The second is a cord type which attaches to the mains and reuires chain oil.

[@ratoneJR]

I have been using a Remington limb and trim 14" electric for over 20 years. I don't use it much, but I will buy another one if it burns out. Love it.

[@biffmalibu3733]

@@ratoneJR It's surprising what it can do. I bought one about 2 years ago in a thrift store for 30 dollars with 2 extra chains. My Stihl chainsaw barely gets used now.

[@user-ce9do4gf4t]

Much less noisy but it depends on what you must cut and where you are....

[@globeeartheulogy9126]

Amazing video buddy! ❤ Thank’ya

[@mrtennessee6862]

Great job

[@barrylionel]

Very good explanation - thanks.

[@TheRepairSpecialist]

You are welcome! Thank you for your kind feedback. Craig

[@IAMNOSLEEP]

Thanks for sharing. Cheers.

[@jaxcavatorclarke9622]

Nice one mate. Cheers

[@AodhMacRaynall-dr1sf]

great vodeo and good visuals.

[@larryperry2094]

Good video. Wonderful explanation.

[@jsimm4587]

Great video wish you’d went the rest of the way

[@josephpuchel6497]

Hey excellent video tutorial.

[@OhioFootHills]

Uploaded 2 weeks before I needed it. "Ironoc" - Alanis Morissette

[@TheRepairSpecialist]

Don’t you think!

[@harrygmarshall5157]

Best of the Best 👍🏻👌🏻👏🏻

[@Carlo.]

Super spiegazione!! 😎💯

[@TheRepairSpecialist]

Awesome. Thank you 👍👍👍

[@curtchanning5074]

Have you ever experienced the pump side of the carb has a very small amount of leakage around the single screw cover when you test the fuel inlet with 7psi of pressure

[@davidhawkins2799]

Very helpfull

[@jonp.6131]

What do the welch plugs do? Excellent video!

[@pennyhelga3628]

What i found that was important was the little bucket screen . Now they are a fine mesh you can't see through and clog easy . Easy fix though . Get you some weed screens and cut them to fit .

[@TheRepairSpecialist]

Awesome 👍

[@steveriggenbach90]

Great videos, I knew but now I can see it in my head. What are the common micro. filter sizes? I want to have extras. Thank you.

[@jasonhuhare]

Hi, would you make a video about how to adjust the carburetor with a tachometer? Thanks.

[@johnmccabe4596]

The screen in the carb also brakes up any air bubbles in the fuel from vibrations.

[@incidentalauditor]

Can you do a video to help diagnose blowback... lately I have several saws giving blowback and my guess is its carb jet screws bad but idk

[@raymondthompson4222]

Great job. Stihl weed eater not sure which # to adjust the H speed 10000rpm or 8400rpm fs55

[@TheRepairSpecialist]

All Episodes -for 2-Stroke Carburetors Here. Thanks. Craig: kzbin.info/aero/PLrlXp3PlwgRI5OLvm3P91LJr1CYnO5TRD

[@vascopires2045]

why do carb kits comes wih an all metal needle when the stock needle has a viton tip

[@user-kw8qf5if8o]

Dilinizi anlamiyorum keşke anlasaydım kendi dilimede çeviri yarapamiyorum ama görsel efekteler ile anlamaya çalışıyorum teşekürler

[@justharryjohnson7250]

In your opinion, which is the best diaphragm to use in the repair kit the slightly white/clear one or the black one ?

[@TheRepairSpecialist]

You’ve just given me another idea for a video. I will make one explaining the different types and their uses. It won’t be yet though because I have several to get through first. In the mean time, I personally use the dark black one. although this one is not the best resistant the ethanol it does still last well and pumps better. Again, in my opinion!

[@ianmchardy8219]

Has anyone have an answer to this carburetor problem, My stihl 46,starts runs fine, even after sitting 6 months, will run all day, but if you blip the throttle just once it cuts out and refuses to start, You have to go through the hole starting up precedure before it will start,

[@stuungar3390]

To a non expert, it sounds like fuel starvation. Blocked filter allows enough through for tick over. Prob a good idea to watch Craig's videos and fully service, before tuning.

[@kevinsturgess1475]

👍

[@TheRepairSpecialist]

👍👍

[@joseluisortiz6917]

When I bought spare diaphragm it comes with a similar piece transparente material. Is it only for packaging purpose? Or should it be placed on top ?

[@trwilkinson4623]

My understanding is that there are 3 types of material used for pump diaphragm. Original, black, newer, blue, newest pale tan. The order of resistance to ethanol content in fuel, black, blue, tan. In some machines, may find tan too " stiff " to work correctly. Hope helps you.

[@mattaitchey4917]

​@@trwilkinson4623hi from Australia.. thanks for this! just to confirm tan is the most, or least ethanol resistant? Thanks :)

[@trwilkinson4623]

@@mattaitchey4917, sorry for the confusion, TAN is most Ethanol resistant.

[@mattaitchey4917]

Thanks very much for clearing that up I will seek a kit with tan diaphragm

[@aresmares8059]

I changed the new diaphragm diaphragm of the carburettor, now how do I accelerate, just touching the button (accelerator) turns it off, why?

[@TheRepairSpecialist]

HI thank you for reaching out with your question about accelerating your chainsaw after changing the diaphragm in the carburetor. It sounds like you're experiencing a stalling issue when trying to accelerate, which can be frustrating after performing maintenance on the carburetor. Here are a few potential reasons why this might be happening and some steps to address the issue: Carburetor Adjustment: After installing a new diaphragm, the carburetor may require readjustment of the idle and high-speed screws. Improperly adjusted carburetor settings can cause the engine to stall when accelerating. Try adjusting these screws according to the manufacturer's specifications to achieve a balanced air-fuel mixture. Diaphragm Installation: Double-check the diaphragm installation to ensure it was correctly positioned and sealed within the carburetor. Any misalignment or improper installation can affect fuel delivery and engine performance. Fuel System Issues: Check for any issues in the fuel system such as clogged fuel lines, dirty fuel filter, or inadequate fuel flow. Insufficient fuel supply can cause the engine to stall when attempting to accelerate. Air Leaks: Examine the carburetor and intake system for air leaks. Unwanted air intake can disrupt the air-fuel ratio and cause the engine to stall. Ensure all connections are tight and sealed properly. To troubleshoot and resolve the acceleration problem, I recommend the following steps: Re-adjust the carburetor settings for idle and high-speed operation. Confirm the correct installation of the new diaphragm and check for any signs of damage or misalignment. Inspect and clean the fuel system components to ensure proper fuel flow and quality. Check for air leaks around the carburetor and intake manifold and address any issues found. If these steps do not resolve the problem, it may be beneficial to seek assistance from a qualified technician who can diagnose and address the specific issue with your chainsaw's carburetor. I hope these suggestions help you get your chainsaw running smoothly again. If you have further questions or need additional assistance, please feel free to ask. Thank you for being part of our community and seeking solutions to improve your equipment! Best regards, Craig

[@anthonymazzone2875]

I'm working on a Stihl 029. It was missing parts when I got it. I've got all but one thing sorted. On the clutch side (right side) is a lever and spring. Part numbers 1121 162 5010 for the lever, and 0000 997 0628 for the spring. I now have them both, but I can't work out how they attach. When I connect the spring to the lever, and then to the stud above it, it become misaligned and won't work correctly. I'm thinking that I'm doing it wrong, or still missing something. Can someone help advise? I can't find any videos on this.

[@petersack5074]

Hi, check out '' TARYL FIXES ALL'............here on KZbin. Expert, in all areas, for over 45 years. ! plus, funny too, with his 2 boys. ! Also, Dony Boy and Steves' Small Engine Saloon (....good, beer man)

[@codyhatch4607]

Suction is a misnomer, you should be calling it a vacuum.

[@TheRepairSpecialist]

No. Not really. I refer to ‘suction’ because I have had so many negative comments regarding the use of Vacuum in the past. I used to regularly use the word ‘vacuum’ and the consensus for that was that the word ‘vacuum’ can be confused with the physics term, which is: space, entirely devoid of matter. So, because if this, I refer to it as suction pressure, which explains it more than well enough anyway. It’s seems that even the people who comment on this incredibly light Issues indeed can’t even agree amongst themselves on the correct term!

[@codyhatch4607]

@@TheRepairSpecialist I guess they never took physics is school.

[@petersack5074]

Hi. i repair weed-eaters. Zama carbs, are another example, of a diaghram pump. Connected by hose, to the 2 cycle engine crankcase; this draws/retracts, the membrane, which pulls fuel from the tank. BE CAREFULL, DON'T knock out the one-way ball valve, in the hole. !! Good luck, all. we need it, ' cause its' a PLASTIC generation, we find ourselves in.

[@spaceted3977]

I always replace the carburettor !!!! The cost of a new carburettor is not very much, and it can take hours to check everything !!!!! It's easier to throw it away and fit a New One !!!!! Even better, I have bought Powerful Electric Machines which are much better than Petrol Ones !!!! This ethanol fuel is horrible stuff for 2 Stroke Engines !!!! I have 3 Powerful Electric Brush Cutters and 3 Electric Chainsaws !!!! If you use Petrol Equipment it's best to use up all the fuel and Store it with no Petrol in it at all !!!!!

[@petersack5074]

....i agree, ethanol should be BANNED FOR 2 CYCLES, and ''' We, the People '' ...ought to use water, and the method, to DROP OUT the water, in gas we buy; if we cannot find NON ethanol gas. ..crazy world, eh ? Lower benzene in the gas would also help 2-cycle diaghram carbs, work better for L O N G E R ....

[@cavscout62]

The really sad part is all this carb crap is 100% unnecessary and designed to stay in your pocket in the final analysis.

[@CuriousKL]

This is incorrect. I have rebuilt many 2 cycle carbs. I seldom see this particular diaphragm with an issue. Now on the otherside is the metering diaphragm. Now this one is usually the cause if it is found to be very stiff and hard. I have even seen them with a hole or a tear which caused a fuel leak. To this day I have seen maybe 1 pumping diaphragm that was needing replaced.

[@TheRepairSpecialist]

What you are saying is incorrect. I have serviced hundreds of these types of little carbs in the past and they do wear and become damaged by age. To this day I have replaced many because they did indeed need to be replaced.

[@MrUtubeobia]

When I received a rebuild kit, it came with what looks like a spacer a few times thicker than the diaphragm), to go over or under the fuel pump diaphragm. But, it does not say if it goes over or under the diaphragm.

[@carolkampstra3474]

@@MrUtubeobia Over it