The Whole Fuel Priming System Explained - In a 2-Stroke Carburetor. (by Craig Kirkman)
Вставка
- Опубліковано 5 лют 2025
- A Fascinating Explanation showing how the WHOLE Primer System Works Inside the Carburetor. For Quick and Reliable Starts, Preventing Engine Flooding, Fuel Efficiency, Reduced Maintenance and Repairs, Equipment Longevity and Safety.
So let's begin: A Two-Stroke Carburetor Primer Bulb System is a feature commonly found in small engines, such as those in line trimmers, chainsaws, or leaf blowers. It serves the purpose of simplifying the starting process and ensuring a smooth flow of fuel to the carburetor. Let's break down how this system works to help you understand it better:
Primer Bulb: The primer bulb is a small, flexible rubber bulb located on the side of the carburetor. It's easily accessible for the operator to press.
Fuel Circuit: The primer bulb is connected to the fuel circuit of the carburetor. This circuit is responsible for delivering fuel from the fuel tank to the carburetor.
Fuel Suction: When you press the primer bulb, it creates a partial vacuum within the fuel circuit. This action results in the suction of fuel from the fuel tank into the fuel circuit.
Fuel Enrichment: The fuel drawn into the fuel circuit by the primer bulb is typically mixed with air. This enriched fuel mixture is essential for cold starting or restarting a warm engine.
Filling the Carburetor: As you press the primer bulb repeatedly, it fills the carburetor with the enriched fuel mixture. This is particularly useful when starting a cold engine because it ensures that the carburetor has the right mixture for ignition.
Cold Starting: The primer bulb system is most beneficial during cold starts when the engine needs a richer fuel mixture to ignite. The enriched mixture makes it easier for the engine to fire up and run smoothly in cold weather conditions.
Reducing Flooding: The primer bulb system also helps prevent over-flooding of the engine. By manually controlling the amount of fuel delivered to the carburetor, you can avoid an excessively rich mixture that could lead to engine flooding.
In summary, the Two-Stroke Carburetor Primer Bulb System simplifies the starting process by allowing the operator to manually enrich the fuel mixture for cold starts. It provides a quick and effective way to ensure that the carburetor has the right fuel-to-air ratio for ignition, making it especially useful in situations where smooth engine startup is crucial.
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!
Thank you so much for watching.
Craig Kirkman (Owner and Creator of the 'The Repair Specialist' Channel and its copywrited content)
Please check out my amazon shop. I have recommended some useful items from Amazon below. I guarantee you that these items are the sorts of things I use on a daily basis so I know they are good. I have to be careful in recommending products because I have my name and credibility at stake. So I will only recommend good products. www.amazon.co....
#PrimerBulbSystem
#EngineStarting
#FuelEnrichment
#CarburetorTechnology
#SmallEngine
#ColdStarting
#FuelDelivery
#MechanicalComponents
#SmallEngineMaintenance
#OperatingPrinciple
#FuelMixture
#EnginePerformance
#StartingProcess
#MechanicalEngineering
#OutdoorPowerEquipment
#UnderstandingEngines
#FuelSystem
#EquipmentMaintenance
#PrimerBulbOperation
#EngineIgnition
The creation of information in this description was helped by ChatGPT
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 😊👍
I've watched dozens upon dozens of "How-To" videos for the various projects that I take on. I watch anything from motorcycle repair, auto repair to carpentry. My friend, this is by far one of the very best tutorials I have ever seen anywhere. It's simplicity along with your visuals are fantastic. I had to pause the video to make this comment so I will get back to it now. Thank You !
If I had a teacher like you when I was a lot younger, I would have been a rocket scientist. I have never seen any one explain anything as through and clear as you do. You sir, were born to be a teacher and should continue to do so. Thank you very much for your contribution to the sharing of knowledge.
At 13:58 in the time line of this video, can you please illustrate exactly where that check valve is and how it functions in the Stihl Zama carburetors for the HT75 pole saw.
There are teachers and there are teachers like this geezer. Even a plank like me can understand so beautifully explained in a layman’s terms. Hats off to you sir 🫡
This is the best instructional video on how something works I have ever seen. My first thought was if my teachers were this good not only would school been easier but I would have enjoyed learning more. Thank you
This video alongside your metering and fuel pump video allows someone to completely understand a diaphragm carb. You sir are a genius.
I have worked on my small engines for many years ( self taught ), and I do know most of what you stated here, but i must say it is still a great video. Your explanations are on point. The best I've seen!
I've just spent 3 days trying to learn how a carburetor works. BEST explanation anywhere. Got my sub,.
Wow, your message just made my day! 🌟 I'm thrilled to hear that my explanation helped you finally understand how a carburetor works. It can be quite a complex topic, but I'm delighted that I could simplify it for you. Your subscription means a lot to me, and I'm grateful for your support. If you ever have more questions or need further explanations on any topic, don't hesitate to reach out. Keep that curiosity alive, and happy learning! Craig
An excellent instructor. I watch every video uploaded. If you want to understand how small engines operate then this is the place.
Best dang video on zama carbs and priming problems on youtube. I hope you're making money on this video. You deserve it.
Human ingenuity in a complex, intricate, delicate but robust piece of precise engineering. And once again explained brilliantly with diagrams to match. Thank you again.
I have worked on small engines for 30 years, Honestly, this is the first time I understood how these small carbs worked....GREAT JOB
As all of your other videos the full and thorough explanation leaves the viewer in no doubt about what is happening. Thank you so much for making these to help people like me to understand the workings of the carburettor. I am certain that my repair work has benefitted from watching all of these because I am able to think about the process before making a diagnosis and clean and check the carb in the order of fuel flow and can be relatively certain that it will work when refitted. I would suggest that there are many occasions where a new carb has been fitted that simply didn't need to be. Thanks again. Super stuff.
Brilliant, thank you for your kind comment
I completely agree with tompfbear I can't thank you enough
woah. That was an incredible explanation. Thanks
My primer bulb won't come back up once I push it down to create suction. Any advice?
Mine was doing the same thing, primer bulb not coming back up, and would run good for a few minutes then just die. I just took the gas tank off and found the fuel lines inside the tank were broken. There are a few excellent videos on how to fix those lines here on u-tube.
That was a hell of a good breakdown of a two stroke carb. Very good! Extremely helpful.
I have been trying to figure out why my weedeater will not run properly. It has a new primer bulb so I know that isn't the issue. I've taken the carb off and sprayed it out with carb cleaner. No luck. Even tried a carb from another just like it. I am befuddled as to what the problem is but the video has been a great instructional video in understanding these carburetor functions. I can't thank you enough for this education.
I really appreciate your hand-drawn diagrams. Best explanation on the planet.
Fantastic video. Best explanation I have seen on UA-cam hands down. One thing I would offer is that the carburetor you have only has two check valves on the diaphragm, not three. In fact, I think most of not all 2 cycle carbs have only two. One at the inlet (upstream of diaphragm) and one at the outlet (downstream of diaphragm) if you’ll notice, the two that you have drawn downstream of the diaphragm are redundant.
Again, thank you so much for the explanation.
Well this one blows me away! I felt your simple diagram video I watched just before this one was a little too ... little, but here you're not holding back! Diagram and real carbi together is just so right and so helpful. I read a comment saying you should be a teacher...I would be quite amazed if you weren't already one. Thanks a lot for sharing
There’s plenty of excellent and very helpful channels on youtube to help us diagnose and fix our small engine problems but there’s NO ONE that does it with such in depth detail of the total inner workings of small engines that help us truly understand how they work and help us actually come up with our own diagnosis. You rule!! Thanks for all the effort you put into your videos and the time to take to explain them.
It took me a minute to see how the gas went into the combustion chamber but now I got it, and can see how some time a motor runs and then stops. You made it so clear. Once again thanks!
Brilliant explanation. Opened my mind to the inner workings of all those flaps and holes, suction etc.
Thank you very much! A major confusion I faced was knowing which line is the supply side and which is the return. Now, not only do I understand that with no doubt whatsoever, I also understand the reed-valve membrane and all other functionality of this mysterious chunk of parts. Again, thank you for your very kind generosity in putting this video together.
An amazing teacher and gentleman. A Scholarly approach to conceptualizing small engines. Well done, as always
Thank you so much for your nice feedback. It's comments like yours that motivate me to continue making these videos. Craig 😀👍
Absolutely love all of your videos. This is probably the most comprehensive break down and explanation of a 2 cycle carb I’ve ever seen. Cheers mate and thank you again for your content
You're a Grand Master; i am an automobile engineer,for 40 years,and i did not know this; Thank you very much for sharing.
Excellent explanation. I ended up here because the bulb on my chainsaw split and I was researching how to replace it, this video is an education with really clear commentary and diagrams. Now I can replace the bulb but more than that I know how it works.
Wonderful tutorial, sir. Thank you for taking the time and effort to teach the rest of us.
I have always wanted to learn more about small engine repair, and yours is by far the best instruction on the matter I have ever seen.
I know this is the old video but I swear to God this is the best video explain everything I ever seen thank you so much for make it so simple and easy to learn how that works🙏🙏🙏
Brilliant explanation, had no idea how these little carbs worked or how they managed to work at all angles, I do now. Thank you.
This is one of the best videos I've seen of any kind!!! That's what I call teaching people something! Thanks for teaching us. This was really excellent.
Outstanding video! It clearly explains not only how a primer bulb works (contrary to the popular misconception that the primer bulb pumps fuel into the carburetor, it draws air out of the carburetor, replacing it with fuel.) It also explains that the carburetor contains its own inline fuel pump, metering diaphragm and metering valve to control fuel flow into the carburetor. I wish I had the benefit of this knowledge 50 years ago when I first began tinkering with small gasoline engines. Bravo!!
The most complete video that I've ever seen. My hat comes off for such a great job. If one doesn't get this, maybe they are too young to do this type of work.
This was an amazing tutorial. I just had issues with my weed trimmer and I had the lines connected backwards. Then I went to see how to connect them and the video I found had them backwards!!! No help at all. lol.Then I went to learn how the primer bulb worked and found your video. Wow did I get my moneys worth here. 5 stars my man. You're an incredible teacher. I know exactly which one connection is is which and why. PS: Subscribed.
As a process engineer I must salute you for this video. Extremely well explained.
Only "mistake" is that you should use underpressure instead of vacuum.
Ok, thanks 👍👍
great 'devil in the details' video.. I really like your step by step schematic overview of explaining what is going on before I start on a repair.
I have several 2 stroke engines including grass mowers, weed wackers, air blower, chain saw and branch trimmer all with primer bulbs.
In the past when one of my devices stopped working (invariably a 'fuel' issue) the solution was to take the device to my local small engine/mower repair shop to be repaired. Typically it's going to cost anywhere from about $75 plus parts to get my machine back in action (and, if this happens in early spring, I may have to wait 2 or 3 weeks for the shop to get to it.
these how to vids of yours not only save me money (lots) and reduces my frustrations but also provide me a great deal of personal satisfaction of being able to effect repairs myself.
thanks for taking the time to share your knowledge and skills with us..
BTW.. I have found during the 'off' seasons when I am not using them if I keep them filled with fuel and then every few weeks (3 or 4) I fire them up and let then run for a about 5 mins.. I have found that this preserves the plastic fuel lines and they dont become brittle and crack as a result of sitting dry and idle over the winter.
Another excellent video. I have looked for a long time to find such a detailed description of how 2 cycle carburetors work. Thank you.
I just Spent 8 hours cussing, sweating and scratching my ass trying to figure this out on my own. I then watched 5 other videos and cussed some more and THEN,,,, I found YOUR video..You sir are a genius! You have explained this in such a way that is so easy to grasp and I now know exactly how to fix my problem. Thank you so very much for sharing your knowledge.....
Thank you so much for your nice feedback. It's comments like yours that motivate me to continue making these videos. Craig 😀👍
@kate st martin I believe you meant to direct this question to the person who authors this channel. I am only a viewer of this channel. You probably ought to redirect your questions to "therepairspecialust"..
Thank you!! That explained alot to me and how all them ports and vavles work. I appreciate you taking the time to explain in very good detail!
Best explanation of this type of carb operation I've ever seen. Excellent graphics and descriptions in an orderly way through all phases of operation. Impressive. Thank you.
Wow. That's some really awesome feedback. It's very good of you. Craig 👍
I think you are a very educator and teacher.
Thank you for your efforts. You have helped me in mechanical repairs.
Keep up the good work.
Brian
Very well thought out and executed. Particularly, I like your combined use of visual aids and narration paired with your ability to relay information in an unusually digestible way. Thanks for taking the time to do this. Much appreciated from IN USA
Fantastic explanation from this gentleman, I really liked the diagram approach coupled with the actual physical parts on the carb. Well done..
Well thank you so much for your kind and motivating feedback. I really appreciate it. Craig 👍👍👍👍
EXCELLENT video! Wow, I understand now why my trimmer carb isn't drawing fuel into the bulb and where, and why, to look. GREAT job, thanks so much. I couldn't have done better if I had tried.
Most have said what I would say - one of the best you tube videos I have seen. Going to fix a couple of carbs that have haunted me now that the mystery of operation is now resolved. As for the 139 that disliked the video, I feel for you...
You are absolutely brilliant, thank you for helping me understand what's going on when I push that little bubble! Now it makes sense why I've just thoroughly cleaned the carburettor and it's still not starting and I'm having issues with the primer . I think I need a new carburettor. I didn't realise how easy it is for a problem to arise in this complex little vacuum system.
This is absolutely brilliant video. Thanks. I was able to diagnose the problem with my weekwracker. It was the one way check valve inside the primer bulb that was broken so the motor dies every time I pull the trigger. Tried every method online trying to solve the problem but none worked for me. Finally I saw your video and boom problem solved after I replaced the broken valve. It seems rare but that was exactly the cause of my problem
Outstanding, I got alitle repair shop in my garage, The fuel flow has been a mystery for some time. Got it, thanks so much.
Bloody brilliant.
These little carbs are very complex, thank for lifting the veil.
Remember that this type of carb (diaphragm) will allow the engine ,and carb, to be run upside down or at any angle. Not at all like the old style motorcycle carb, or mower engine. So any part of the fuel circuit that does not seal off a port (or a split primer plastic bulb)correctly means that it will NOT draw fuel correctly. A new diaphragm kit and absolute cleanliness when doing the repair and making sure that all ports are thoroughly cleaned out with some sort of pressurised aerosol spray usually results in a good working carb again.
Nice video presentation, thank you.
Hi, thank you for taking time to give me your feedback. I really do appreciate it. Craig
such a great explanation. it is really incredible the design of something like that. simple but almost complex. my gas bulb had a hole in it and i could not get my weed eater to start. i sort of figured that that little bulb was important. and i find out it is. no gas coming into the bulb so now i have to find a replacement. thanks for you video. was very good.
He sounds like an engineer to me. Great job here and it sounds like others u put out there too. Thank you
Thank you so much for this and the other carburetor videos you have. No longer will I fix a carb by simply saying "OK, I think this piece came out this way, so I think it goes back that way..." and will actually know more about what I'm looking at! If you have the time, I'd love to see more about the valve mentioned at 13:50 and how it only opens when the engine is running. This indicates to me that overuse of the primer bulb shouldn't lead to flooding, but my experience indicates this isn't always the case. I'd love to know more about what is supposed to prevent over-priming when the primer bulb is used. Thanks again!
Excellent job. Reminds me of my training classes when I worked for the airlines as a mechanic before I retired.
THAT Sir, was invaluable information, indeed definitive, on the Primer Bulb and Main Jet function of these tiny 2-Stroke Carburettors!! 👏👏👏👏
I'll be getting my first 2-Stroke Engine, in a 1:5th Scale Gas Buggy. As a Retired Auto Technician, specializing in full size, motor Car Carburetors, I was a little lost.... Something that happens when you've learned *too* much about something similar, yet different in form and function.
This has been a tremendous help. Thanks!
A fabulous, insightful and (in my case) helpful explanation of this system. Thank you.
Awesome explanation! Thank you from someone who's been beaten so often over 40+ years by one of these little suckers...
I get smarter ever video I watch of this dude! I love it
Thank you for your kind feedback. Craig 👍👍👍👍
Absolute genius way to explain a 2 stroke carb. Very complex operation made simple.
Brilliant video and well explained,took my stihl blower out today after sitting for pretty much all of winter, purge bulb had no fuel in it, tryed priming numerous times. No fuel arrived into bulb and bulb very slow to come back to shape. Stripped out carb, cleaned up with some carb cleaner, checked bulb while not connected to the carb to see if it would draw fuel, it did! Ensemble everything back together but still won't draw fuel???
You Sir, are an excellent teacher. Thank you so much for the effort that you put into this video.
Excellent use of props! You are a great teacher. Thanks
I am a novice with small engines. I always was afraid I would flood the engine if I pumped it too much. This is invaluable information. Thank you.
In a word, brilliant !
Thank you explaining, so clearly, how it works.
is there actually someone who wouldn't understand ? with way you explicitly break down the explanations with excellent visual aid? And always taking us into the interesting journey of the inner workings of these lilly bitty engines and their components? thanks a bunch to your 25 years plus experience. you really are good at this, and to appreciate, I didn't just LIKE, your subscribers just increased by one.
Olajide Oyekunle, wow, thank you for your motivating feedback. It's comments like yours that motivate me to continue making these videos
After searching the web, you have made the best explanation I can find. Thank you.
The very best explanation of these carbs I have found. Excellent!!!!!!!!!
I love the excruciating detail. Leads to better understanding and recall. Like your other videos, simply excellent! Thank you!
Have watched several of your videos, all brilliant!!! Made by a person that knows their craft inside out.
Finally! Thank you so much for the great video. I've learned the intricacy of how these little carbs work in so much detail and now understand what I have to do to fix mine.
It's highly unlikely, but if I ever meet you, I will buy you a pint. Thanks for your time and effort in making a concise and clear video of the workings of the now not so mysterious carburetor.
All of a sudden I loss vacuum on my Poulan weed trimmer. This video will guide me on how to dismantle the primer bulb and see if the vacuum line is plugged up. Thanks for an excellent video how the fuel works on the carburetor.
THANK YOU thank you.
Your tutorials are the finest!
I pride myself on being able too figure anything out, however I have frustrated myself on these carbs/2 stroke engines since the intro of primer bulbs and the discontinuation of slide/ Venturi carbs! I have thrown endlessly, good money costing weed eaters rototillers and chainsaws in the garbage out of frustrating surrender.
No more,, thank you.
You may have created my next income,,,, @ 63 years of age! Thank you thank you
Thank you thank you! Please read my post. You have most likely no idea how many people you have saved
This is perfect. I now know how each hole works, and I know why certain parts of the carburetor need a rebuild kit. The screen is mostly at fault. But how the diaphram works is wonderful to know. I just rebuilt a carburetor with a kit, and I can see why it was needed.
Thank you for this awesome video. I just got my first two stroke motor and wasn't sure what would happen if I pressed the primer bulb to many times, now I know I don't have to worry like I do with my lawn mower.
Saml01, thank you for your positive comment. I really appreciate it
Saml01
All Episodes -for 2-Stroke Carburetors Here. Thanks. Craig:
ua-cam.com/play/PLrlXp3PlwgRI5OLvm3P91LJr1CYnO5TRD.html
I had no idea that these little fuel plungers were so precisely engineered. Thanks for the in depth explanation.
a very clear expert class . From a master tech. and I've been in the trade 35 years.
Incredible description of how the carburetor operates. Very well done. P
This video taught me what I needed to know to diagnose and correct the starting issues on my 26cc gas trimmer, thank you :)
That was fantastic!! I wasn't sure if mine was working correctly and now I understand exactly what I should find. Thanks very much and keep up the good work!!
This was excellent! I have cleaned over 20 carburetors. Being successful with most, but now i can go about it with a complete understanding. Thank you. I had many of them pull fuel through with the primer bulb, but had air bubbles in the primer bulb after. Now I know either the bulb valve is not closing properly or it's not able to pull fuel through the carb system properly causing the bulb valve to pull air back through. A clean system(pathways and valves clear and functioning) will have no air (or little air) in the bulb after priming. Thanks.
Leftyloveschicken, fantastic news, I'm really pleased it has helped. Thank you for your positive feedback.
Great explanation . Lot of air bubbles in primer bulb now know check valve is not seating
Thank you! I’ve been trying to figure out why the priming bulb on my lawnmower engine needs 12-20 pushes before the engine starts. The engine runs well and the bulb doesn’t leak fuel. Now, I can begin to see how to troubleshoot that.
A brilliant exposition of the working of a 2 stroke carb. Many thanks.
All other vid's, show cleaning. No explanation of what's going on. You show where the gas is going or not going, and what the carb parts are doing. I appreciate that. Thank you for caring about people like myself wanting to know what exactly the carb is doing.
Very good description. Only thing I would like to add, and I’m sure this depends on ones location, but it is actually a purge bulb. It purges the fuel system. A primer would push fuel into the venturi.
Clear, concise, illustrated. Thanks for the time you put into this for our benefit.
Great explanation , few people that kind of ability to communicate such technical stuff. Well done
What that was absolutely fantastic. Very good explanation.
Very thorough explanation. I never really understood how the priming system worked. Good job.
Ron Everist xq
I have not found another teacher as didactic as your thanks.🎓📖
That is fantastic feedback. Thanks
100% fantastic. Thorough and insightful. Well explained. It's so easy to fix things when you understand the system.
Thank you for your help. My mower is curretly stopping and starting, which i know could be a number of things, but at least i now know why i have to prime the carb with the buld. Thanks for sharing.
This is an excellent description of how the priming system works. It is clear and easy to understand. One thing that does not seem to be mentioned is what is on the other side of the metering diaphragm. In the video the cover plate is shown briefly and it appears to have a hole in it. That would suggest the dry side of the metering diaphragm is exposed to atmosphere. Is that right? Thanks for posting this educational video.
Imagine a completely clear, see through carb demonstrating all of this, be very cool
Absolutely
Lovely illustrations. You really have gone to a lot of work. Thank you, great job.
Thank you so much for your nice feedback. It's comments like yours that motivate me to continue making these videos. Craig 😀👍
Absolutely brilliant explanation, gone is my notion to bypass it and now i will purchase a new primer bulb. Mine corroded and imploded.
Thank you once again for the effort. Brilliant.
Cheers to your Mom and the LOYL.
Thanx for these videos!
The excellent explainer helps me too much, now I really clear. Thank you a lot!
Thanks for sharing this. A fantastically clear explanation of how this works.
Hi again Craig,Would you ever make videos on brushcutters /strimmers/lawnmowers,showing there problem in real time showing what the machine is doing and what needs to be done to fix it,or even if some one else worked on it and you explained what he or she is doing,That would be brilliant,I have a brush cutter that slows down on acceleration it loses speed I know its more likely due to the due to the setting on the carb is wrong because you have explained that in one of your other video`s,but I do like to visually see the machines in question being worked on` I find it stays in my head much better.I appreciate all that you have shown us on the diagrams as this takes a lot of your time up so thank you for that.
Great job Sir! Cant thank you enough, absolutely the best explanation of operation I’ve ever seen!