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

* 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

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#ChainsawCarburetor
#ChainsawFuelDelivery
#SmallEngineMaintenance
#ChainsawPerformance
#EnginePressurePulses
#ImpulseLineRepair
#FuelDeliverySystem
#ChainsawDiagnosis
#ChainsawTroubleshooting
#EngineRepairTips
#MaintainYourChainsaw
#ChainsawEngineProblems
#FuelSystemMaintenance
#ChainsawSafety
#SmallEngineKnowledge
#ChainsawMaintenanceGuide
#ImpulseLineFunction
#EnginePerformance
#DIYChainsawMaintenance

[TheRepairSpecialist]

All Episodes -for 2-Stroke Carburetors Here. Thanks. Craig:

[erikredbeard]

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!

[sineadnugent]

The best explanation I've ever heard, thank you

[pavloskourris]

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!

[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.

[tonyday]

I've just learned something new and valuable, I'm guessing that this is the problem with my ancient Jonsered 535, thank you.

[magicone]

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,

[colinhargis]

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.

[danygraph]

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

[willits]

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

[bruceedwards]

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

[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.

[TK]

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

[arthurfricchione]

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

[vanellusx]

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?

[charleswest]

Excellent description and explanation! thanks!!

[Null-hc]

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

[Andrezero]

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

[meesau]

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?

[promechanics]

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...????