Two Stroke Chainsaw Carburetor 'Impulse/Pulse Line (How it Works!)

* VISUALLY EXPLAINED
An issue often overlooked when a 2 stroke engine fails, such as when a Chainsaw Won't Start, is the Pulse Line. Exclusive to the two stroke engine, the Pulse Line is responsible for carrying air pressures from the engine into the carburetor and operate the fuel pump diaphragm.
If the pulse line is damaged (leaking) then the vital pressure cannot be carried to the fuel pump diaphragm resulting in the pump not working. The obvious effects of which is that no fuel can the carburetor's main jet to supply the engine. This results in engine failure.
The impulse line in a chainsaw engine plays a crucial role in the proper functioning of the carburetor. Its primary function is to create pressure pulses that help operate the fuel pump diaphragm within the carburetor. Here's how it works:
Pressure Pulses: The impulse line is connected to the engine's crankcase. As the engine runs, it generates pressure pulses in the crankcase due to the movement of the piston. These pressure pulses are then transmitted through the impulse line.
Activating the Fuel Pump Diaphragm: The pressure pulses from the impulse line create alternating vacuum and pressure conditions within the carburetor. This movement is harnessed to activate the fuel pump diaphragm, which, in turn, pumps fuel from the carburetor's fuel bowl into the intake air stream in precise quantities.
Problems that can occur if the impulse line is damaged or malfunctioning:
Loss of Fuel Delivery: If the impulse line is cracked, broken, or disconnected, it will fail to generate the necessary pressure pulses. As a result, the fuel pump diaphragm won't function correctly, leading to insufficient or erratic fuel delivery to the engine. This can result in poor engine performance, stalling, or difficulty in starting.
Lean Running: When the impulse line is damaged, it may create a constant vacuum or pressure, disrupting the fuel-air mixture's balance. This can cause the engine to run too lean, leading to overheating and potential damage to internal engine components.
Hesitation and Acceleration Issues: A damaged impulse line can result in hesitation and poor throttle response. The engine may not respond promptly when you accelerate, affecting overall performance and cutting efficiency.
Engine Damage: Prolonged operation with a faulty impulse line can lead to severe engine damage, including piston scoring and overheating, due to the incorrect fuel-air mixture.
In summary, the impulse line is a critical component in a chainsaw engine, as it ensures the precise delivery of fuel to the carburetor. Damage to this line can lead to a variety of problems, ultimately affecting the chainsaw's performance and potentially causing engine damage if left unaddressed. Regular inspection and maintenance of the impulse line are essential to keep the chainsaw running smoothly.
There is a lot more to this topic than what I have explained but I have covered the basics here.
In my experience, some of the symptoms of pulse line damaged/leakage can be:
-the engine will not start,
-engine will start but not run correctly (loss of power, over revving, under revving, uneven running, carburettor will not adjust correctly, and many more)
-engine will BOG down
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!
Many thanks indeed
Craig Kirkman (Owner and Creator of the 'The Repair Specialist' Channel) 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....
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#FuelSystemMaintenance
#ChainsawSafety
#SmallEngineKnowledge
#ChainsawMaintenanceGuide
#ImpulseLineFunction
#EnginePerformance
#DIYChainsawMaintenance

[@TheRepairSpecialist]

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

[@eriklong6390]

I gotta say, I have never seen a better explanation of this. Absolutely great video. Well done. You have made it simple so that a person with little to no knowledge of this type of thing can understand what is actually happening in their equipment. Well done!

[@sineadnugent3381]

The best explanation I've ever heard, thank you

[@TheRepairSpecialist]

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

[@pavloskourris277]

Thanks, now I understand all those pipes connected to my carburetor, hopefully you have another video for the rest. A lovely harmonious and timely function of the fuel pump, piston and carburetor, LONG LIVE THE COMBUSTION ENGINE!

[@TheRepairSpecialist]

Awesome. I really appreciate your feedback. Thank you. Craig

[@pavloskourris277]

@@TheRepairSpecialist Graig I have recently bought a Honda Generator 300 1965. The carburetor has so many fuel lines/lines going and leaving it and I have not found anybody explaining their function. Two come from fuel tank. One goes to feed the carburetor the other goes to the carburetor floater. This confuses me to what it does or has somebody just connected it wrongly

[@colinhargis8736]

Really helpful thanks - and a split or leak in the little impulse tube causes all the symptoms of an inlet air leak - difficult starting, unable to get proper idling etc. Not all engines have the reed valve, but the impulse works much the same.

[@TheRepairSpecialist]

👍

[@ScottLRoyal]

Awesome Video Craig. I appreciate the time it took to put that together. You just helped me better understand that impulse line I may need to replace. Thanks dude.

[@TheRepairSpecialist]

Thank you for taking the time to message me with that nice feedback. Craig

[@user-zc6dn9ms2l]

Usually it's in the port on a two stroke so it does not affect reed valve . Likely midpoint hight wise crossing both port . Most chainsaw stop at first port . But it's 3 mm more to get both port . It should help at high rpm

[@magicone9327]

On old 028WB, the tank vent originally was two fine treaded inserts specifically located. These would allow for tank pressure to equalize. The newer vents seem to only allow air to pull into the tank to eliminate a vacuum. Are the older original carbs incompatible with the newer vent function as the tank pressure can get quite high and put a lot of fuel pressure and possibly more volume into the carb per each sequence of the needle opening,

[@MNMoto]

This helped explain the functions of the lines on am old snowmobile I am resurrecting. All lines were disinigrated so I am having to do some reverse engineering. Thank you so much for the full explanation.

[@josiahpeterson962]

Haha same here

[@vanellusx2785]

thank you! never quite understood how this worked until seeing your video. I guess this is why a chainsaw still gets fuel regardless of the way it's being held?

[@scotturiah3498]

Instablaster...

[@Brian..........]

That was thorough!

[@TheRepairSpecialist]

Thank you so much 👍

[@TK42138]

Nicely explained. I'm rebuilding a Stihl ts350 disc cutter. I couldn't see how the carb fuel pump worked until watching this video.

[@will7its]

Learned how those little flappers functioned. Well done, Thank You

[@bruceedwards2069]

IT KIND OF HARD TO A GOOD ANSWER FOR THIS impulse line ON A CARBURETOR UNTIL FOUND YOURS THANK YOR SIR GOOD ILLUSTRATION

[@danygraph2910]

Thank you for taking the time to explain this with the graphics. Good job!!

[@arthurfricchione8119]

Great video. Will be watching all of your videos. Nice presentation. 👍

[@kellonpitts2650]

Thank you. Straight to the point

[@TheRepairSpecialist]

Thank you so much. This was actually a shortened version of the original video I made about how a 2 stroke carburetor and engine work together. Just in case you want to see that then its here in the link : kzbin.info/www/bejne/joHKknljf6eqmdE . Thanks again. Craig

[@promechanics2395]

When piston moves downward at that time needle valve is closed as their is no suction in ventury to move diaghram of metering area up to open the needle valve but at the same time upper impulse line diaphragm is pressurizing fuel above needle valve does valve gets opened by that pressure when piston moves down or valve remains closed only pressure builds up there...????

[@benoloksa3535]

Thank you!

[@charleswest3008]

Excellent description and explanation! thanks!!

[@kevinhoffman8214]

try CAR-BUR- RAATOR 😆 great video and explantion

[@Andrezero8]

How likely is it that the compression fails to create a vaccum to the pump? My fuelpump is dead and I orderd a new one. Havet checked if there is any vaccum in the line when i crank it

[@michaelgutter2004]

Thanks for the video, I have a zero turn that is not getting any suction from the pulse line. Do you have an idea? The fuel lines are open, everything is good, the fuel pump is good, but I’m not getting any vacuum from the pulse line

[@MunawarZaman-cx7pk]

Good thanks

[@comet7894]

Hi, on my two stroke string trimmer, there is no separate rubber pulse line going from the engine to the Zama carburetor. Is the impulse transmitted through a passage cut in the barrel of the carb? Thank you.

[@jaytodd5809]

Should be a passage around the carb intake that takes advantage of crankcase pressures and usually the passage is ported directly through the carb gasket and into the diaphragm area..

[@asphaltcowboy7868]

I'm thinking of building a weed wacker powered bicycle...wondering if I was to use a bigger fuel tank and it was placed just shy of two feet away, would it still work? Would the piston still be able to create enough vacuum inside the engine to draw from that kind of distance???

[@TheRepairSpecialist]

I can't see why not. Just make sure the tank is elevated above the engine and the atmospheric pressure should help bring down the fuel nicely. Thank. Craig

[@uadcro]

Is it possible that the engine could have good compression but for some reason not sending any pulse on the line causing the spark plug to be dry even though the carburetor is full by manual pumping and the carburetor being new?

[@meesau2112]

Great explanation but I have a craftsman blower and don't have a tube from crankcase to carb instead is built in to intake near carby. My question is how does the carb get it's pulse line pressure to the carb. The hole in the intake lines up with a hole on base of carb but isnt a passage on the carb I can see that would connect to metering side or fuel pump side of carb just a hole with a solid bottom. Am curious if you have a explanation for that?

[@amitdesai2421]

Thank you for a video....!

[@TheRepairSpecialist]

Thank you so much for the nice feedback. I really appreciate it. Craig

[@noorzaidi220]

Excellent to the specialist ! # You talk on logic and the truth ! Tq i wonder what is your origin,n how old r u ? im in early 60 yrs of age , i owned my old TZM BIKE MODEL 1996 im a pentioner use to ride when i feel i want too, i stay in kuala lumpur my favourite destination is the kingdom of thailand about 450km from here ! Tq again kindly drop by to kuala lumpur incase u travelling to singapore,australia , new zealand oso kingdom of brunei darus salam , * hope 2 c u soon !

[@budgillett9535]

Absolutely awesome!!!

[@petersparkie]

This is brilliant information. Thankyou

[@asphaltcowboy7868]

So if I was to place the fuel tank, say two to three feet away.. the carbs pulse line should work to draw the fuel in..like a pulse pump???

[@TheRepairSpecialist]

It shouldn't effect the pules line. The line doesn't bring in the fuel directly through it. There is only crankcase pressure (both positive and negative ) through this. This pressure operates the fuel pump diaphragm, and if you have the tank elevated anyway, then atmospheric pressure with the action of the pump driven by the pulse line should be fine. I say, SHOULD! Thanks. Craig

[@TimmyC079]

Are flexible fuel lines ok for the pulse line or will it dampen the pulses?

[@jankowalski4651]

but when the fuel tank is much higher then carb.(like on motorcycle) do we really need those lines? my engine seems to work fine ... btw great channel

[@acamotokultivator]

If we don't, should this line be opened or closed ? How higher fuel tank should be ?

[@mrbanana7167]

I'm here for that exact thing lol Want to put a soviet chainsaw (109cc) carb on a motorized bike because I'm tired of not being able to adjust my air/fuel mix with the stock carb because I can't get precise jets where I live nor drillbits for it

[@YML1357]

If there's a primer bulb, will it still run momentarily if the pulse line is disconnected? Thanks

[@TheRepairSpecialist]

I would say that it wouldn't work well even ii it did run. I haven't tried this to be honest. Sorry but I have no idea. Thanks. Craig

[@xx3868]

How can you test the pulse line for amount? does a warn engine give too little pulse? i have fuel tank above carb and no primer bulb but if i run the engine out of fuel before i turn it off, how can fuel get into pump if it need fuel around those flaps to make it pump or not? Hi, i got a REALLY tricky fuel problem or pulse hole maybe It Bogs down when open throttle and only sort of idles so i suspected carb or fuel starvation So as i done before, i open carb and all parts looked ok but i cleaned and replaced all the diaphragms ect and it run for 10 mins idle and full power and then starved off. I also put a brand new carb on just to eliminate the carb and same problem. I then suspected the pulse hole leakage or engine leaking at oil seal or gaskets causing air to get in maybe when warmed up and leaning the mixture. Put vac of 9 psi and it held steady after blocking off inlet and exhaust so the engine isnt leaking. i tried compression next and got 120 psi ? is that enough to make pulse hole work ? i attached a vac gauge to the little pulse hole and pulled rope and got about 2 psi vac and pressure on the gauge so dont know if thats enough? I notice when i try to start , there is no fuel being drawn through the fuel line to the carb so how can it even idle? Also i bypassed the filter to make sure fuel was available from the tank above the carb. This weed machine dosent have a prime bulb so does the 2 little pump flaps have to have fuel in the carb to start pumping? It worked in past as it is so i guess it will pump until fuel gets to carb but i dont see any going down the line so PULSE line issue not making the pump pump anymore? I used new gaskets and made sure the little gasket hole lined up ect to reach the carb and complete the air pulse circuit. I am at a loss on this machine.

[@greggbiebelhausen8414]

Very useful info, thank you!

[@TheRepairSpecialist]

so Glad it was helpful, Thank you for your kindness :D -Craig

[@bobklimple1740]

What causes the metering diaphragm to function

[@bobklimple1740]

THANK YOU!!!!

[@TheRepairSpecialist]

Hi. Thank you for your question. To best answer this I have included a link to another video of mine, which is only a few minutes long but it explains how the metering diaphragm works alongside the other components of the two stroke cycle carburetor. The actual info about the metering diaphragm it at position-2.11 onwards, but for the sake of a few minutes you would most certainly benefit by watching the whole video to gain a full picture and understanding. I hope this helps Thanks. Craig : kzbin.info/www/bejne/eX7FnXydf8uSnaM

[@user-sagar855]

Sir Please help me? I am from India My machine shuts down after a while. What can I do now?

[@TheRepairSpecialist]

Hi. Yes usually, and most commonly, this is due to the ignition coil pack. They sometimes stop producing electricity to the spark plug when hot and then when cooled down they work again. Very confusing. The only way to know for definite is to fit a new coil pack or one that you know for definite is in good working order. Then, run your machine to see if symptoms are still present. It is Not always the coil pack so it is a financial risk you may have to take, but it is common. This is the best place to start in my opinion. I will make a video on this after I have completed a few other requested videos. Many thanks Craig

[@treesplease4053]

Masterful, Thanks very much.

[@laneburgess1643]

I love this video.

[@susanhunte1400]

Interesting

[@jankotze1959]

Hi, does the fuel feed pipe from the tank goes to the Metering side or the side where the bigger black diaphragm sit, I check a lot of videos and non specifically mention that

[@theinterpretationstation]

Great videos!

[@TheRepairSpecialist]

FULL 12 REASONS VIDEO HERE: kzbin.info/www/bejne/iaTLiX5ues2gbZY

[@leonelceballos3709]

Could I use fuel hose as pulsation hose

[@jsb63]

As long as it’s air tight in good shape don’t see why not.

[@xx3868]

My little 2 stoke barrel has no flap on the carb inlet or pulse hole. Is this correct? just 1 large and small hole into cylinder from the side and the exhaust on the other side

[@2strokefather863]

If it’s gravity fed dose it need Thai

[@paulaguirre1276]

i have been tearing my hair out trying to figure out why my echo HC150 hedge trimmer isn't starting. i have changed the carburetor and fuel lines, replaced the magneto and spark plug (gaped @ .028"), completely dissembled the entire engine clean, lubed and reassembled (good compression)... replaced the clutch, greased oiled and inspected all gearing and blades, replaced the grounding switch and wiring, added 2.5 ounces of two cycle oil to a gallon of fresh gasoline (87 octane) and filled the tank, primed entire system, and ensured that the impulse hole isn't plugged. i even tried to adjust the hidden high and low screws to no avail. does anyone..... i mean anyone have any idea what can be the culprit in this very frustrating issue. it would be very appreciated.

[@knappleeloo]

Is it working?

[@Carlostype]

Did you find out then??

[@susanhunte1400]

Awesom e videos

[@gh8943]

Seems to be easy.. but IT Isn,t