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

not too many people know this but there's a small pump inside your chainsaw carburetor and at the very heart of this pump is a very special diaphragm so now I'm going to cover the function of this fuel pump and what goes wrong with your chainsaw should it fail so this video is as much for the knowledge lovers as it is for those looking for a diagnostic welcome to the repair specialist Channel I'm Craig the owner and Creator and having been in the trade for around 30 years I now make videos relating to the diagnosis and repair of small engines and machinery and how things work and why and in layman's terms using clear visual explanations to help you gain a deeper understanding and a firmer knowledge base why because knowledge is power so let's get to it mom right so I'm first going to take off the cap here and that'll expose the fuel pump diaphragm so here is the diaphragm with the gasket okay now let's take a look at how all of this works fuel is sucked through the fuel Inlet pipe where it's drawn down internally towards the carburetor body and as it's drawn closer the first thing it meets is this one-way valve flap which allows us a one-way Passage through into the carburetor taken in through the fuel veins and up through the other fuel hole there underneath this one-way valve flap it then flows over into this hole and it's been drawn this way by a suction pressure as it's pulled deeper down into the carburetor body before being pulled through further through this hole on this vertical face before it floods out into this Reservoir this is the fuel pump chamber the diaphragm sits above this chamber and it's this area of the diaphragm that's moving up and down working as the pump each time the fuel pump diaphragm Rose it created a suction pressure and pulled in fuel underneath it and as the diaphragm lowered it created a pushing pressure forcing the fuel this way and any fuel wanting to go back the way it came is immediately stopped by that one-way valve flap it's just come through so under normal circumstances when the fuel pump diaphragm lowers and raises thousands of times a minute a correct functioning valve flap should ensure that it maintains that flow this way through the chamber any stiffness or rigidness in this area of the diaphragm or any distortions even slightly you could see that it wouldn't put a good seal there to prevent the fuel from going back the way it came which of course should not happen and any less common problems such as punctures or tears in this diaphragm would of course also reduce the pump's efficiency so what can cause damage to these diaphragms well I do know some people in the trade that believe it's ethanol in the fuel that can distort these diaphragms what I've found can damage these diaphragms is just general aging if the machine has been standing and not been used for a while and it's got fuel in there with it I find that it tends to make the diaphragms wrinkly and distorted so in some ways not using the machine for a long period of time have found may cause this and also just general use of the machine if the machine's been used a lot for many years then these diaphragms are just going to slowly wear away and not be at their best but let's go back to normal working conditions so as we now know the rising of the diaphragm draws fuel out of the valve flap underneath it and that brings the fuel towards another fuel hole on the opposite side of the fuel pump chamber this area here and then it's the following downward motion of the diaphragm that pushes this fuel through this fuel hole and down this fuelway the diaphragm actually gets its movement energy from alternating crankcase pressures from a small air hole in the lid just above it connected to the engine's crankcase via the impulse line it's the upward and downward motion of the Piston that creates these pressures not to be mistaken from the engine's manifold which brings in air and fuel from the carburettor the area of the pulse line is usually situated beneath this and well below the piston so we're not looking down the inlet tube here instead we're actually looking down the impulse line at the source of the pulse pressures I've only Illustrated it this way so we can see that it is indeed the Piston that's creating those pressures therefore as the Piston Rises it creates a suction pressure beneath it pulling inwards towards it and as it lowers again it creates a positive pushing pressure away from it and so it's this positive pushing pressure that travels through the impulse line and pushes the fuel pump diaphragm down and then when the Piston Rises and creates that suction pressure that pulls the diaphragm back up and that continues as the engine runs so however many times the Piston travels up and down it's the same amount for the diaphragm so if this impulse line is damaged it's worn through or punctured in some way or it's not connected properly then we can see that the fuel pump is not going to work properly if at all and again there's going to be issues getting the fuel through the carburetor the way it should do so a healthy pulse line and a fully functioning fuel pump is a must and so the fully functioning pump sends the fuel this way through the exit hole and under the second valve flap where the pump's pressure forces it through this brings the fuel out into another compartment between the carburetor's body and the lid the pressure of the fuel builds up inside this compartment before flowing down in through another fuel hole into the carburetor body this hole next to the valve flap it's just come from it then goes through another fuelway then it spills out of this hole into the screen filter this flat metal filter is the last filtration that the fuel goes through before being used in the engine any dirt or crud that got past the fuel filter will hopefully now get separated on this filter when servicing the chainsaw this filter is often overlooked the need for this filter to be clean is equally as important as the fuel filter in the fuel tank I have commonly seen dirt and crud buildup on these filters and some to the point where it's restricting fuel through the carburetor and depending on how bad the situation is we could have symptoms ranging from running problems where it's difficult to get the engine running correctly and regardless of any adjustments to the fuel mixture screws the engine just wouldn't run right to also it being hard to start and having lean fueling and a bog down issue I personally make a habit of cleaning or changing these filters on every service I do on every chainsaw because I know then that the job's done thoroughly and there's less chance of any problems later down the line you can actually buy these in packs of multiples but they always do come in a carburetor service kit so it's always well worth tending to them and so now after the fuels pass through this filter it goes down to the metering area and it's now passed through the fuel pump system so I hope this has explained the importance of this pump how to keep it going at its best and certain running issues should it go wrong of course all the running problems I've mentioned aren't all down to the failure of this pump the same can be caused by other issues within the carburetor as well so this is the route the fuel takes through the carburetors fuel pump system and if you like that video then you might like this one and if you haven't done so already please subscribe and I'll be back soon thank you for watching [Music]

Channel: TheRepairSpecialist

Views: 89,394

Keywords: craig kirkman, the repair specialist, chainsaw wont start, how to tune a chainsaw, two stroke carburetor, 2 stroke carburetor, two stroke engine, 2 stroke engine, #ChainsawCarburetorMasterclass, #CarburetorTroubleshooting, #ChainsawMaintenanceTips, #CarburetorPumpRevealed, #StartupProblemsSolved, #BoggingIssuesExplained, #CarburetorTuningMadeEasy, #ChainsawRepairGuide, #FuelSystemDiagnosis, #OptimizingChainsawPerformance

Id: s4vG8UrXcLE

Length: 9min 36sec (576 seconds)

Published: Fri Dec 16 2022