Lawnmower Fuel Cap Venting Test

Lawnmower Fuel Cap Venting Test
In this video I show you an easy way to check if your fuel cap is venting properly. A fuel cap that does not vent properly may cause your engine to not run properly.
This procedure will apply to most outdoor power equipment.
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Easy to follow and thorough step by step tutorials do it yourself (DIY) to help you with your broken lawn and garden equipment including snowblowers.
I do my best to teach you how to easily diagnose problems the fastest, quickest and most efficient way with real repairs beyond just replacing a spark plug. These tips are for both the homeowner and shop owner.
Whether it be a handheld, two stroke, two cycle engine like a chainsaw, weed eater, weed wacker, string trimmer, grass trimmer, line trimmer, hedge trimmer, strimmer, brush cutter, leaf blower, or four stroke, four cycle units like a lawnmower, wood splitter, lawn tractor, snowblower, pressure washer, generator or a ride on mower that needs parts installed or replaced, I’m your go-to guy.
My favorite brands of spark plugs are NGK and Champion and are the ones I recommend.
I’ve been a small engine mechanic for many decades and also run my own repair shop so my videos are loaded with tips and tricks that I have learned and want to share with you. You will also find many tool and product reviews from top brands on my channel as well.
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Due to factors beyond the control of DONYBOY73 “The Small Engine Doctor”, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. DONYBOY73 “The Small Engine Doctor” assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. DONYBOY73 “The Small Engine Doctor” recommends safe practices when working with power tools, hand tools, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of DONYBOY73 “The Small Engine Doctor”, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not DONYBOY73 “The Small Engine Doctor".
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[@donyboy73]

Doing this EASY TEST will help you determine if your fuel cap is defective!

[@Draega007]

Is a whistling sound coming from the cap normal? Even when my mower is in the garage it whistles every 15 seconds or so

[@DonnaMSchmid]

Yet again, terrific information that's presented clearly! Thanks, Don -- you're the best small engine channel on KZbin!

[@ConductorDon]

such an easy fix. now I don't have to take my carb apart. I just love the way you present the information in such an instructional and professional manner.

[@demetriusjohnson3677]

Thanks my Guy... That's exactly what my TB200 lawnmower us doing. Run for about 5 minutes and sputter and then die out. I let it sit for a minute crank right up run for about 5-10 minutes of cutting shuts off like it's out of gas.

[@lmdetect]

There's a simpler way sir. If you suspect that your gas cap is not venting properly, just loosen it when the engine starts to sputter. If the engine smooths out, your cap is bad. When you loosen the cap, it allows air in, breaking the vacuum and allowing the gas to flow. A lot less trouble than your method. No disrespect intended. Love you vids.

[@MertUluc]

This is by no means simpler or more definitive. When you are troubleshooting, you want to isolate the suspected component and reduce the number of parts involved to get a definitive reading. Running the engine will introduce all the other possible causes.

[@darrenswoodworks8695]

Had that problem on a John Deere riding mower, loosened the cap while it was spitting and sputtering and it ran fine. Was a quick discovery to a plugged fuel cap vent.

[@hkk3656]

Same here. Lawn mower would run for a very short while and die. Loosened the cap a little creating a vent. It ran like new!

[@mcmaster22]

Great video Dony, I love how you make things simple and easy to understand. Have a Great weekend.

[@Arkslippy]

Thanks for this, my mountfield has been running for a few seconds and cutting out after it hasnt been used for a while, had two lots of it and brought it for services where it they couldn't find the issue. Tried this and boom working perfect. 😉🤘

[@wakeywakey4289]

hard to determine...most people stop the mower when it starts to sputter and check the gas level which lets air back in and then restart and it runs fine til next time..lol

[@michaelchilders6056]

You taught me something new and valuable today. Thank you for doing these videos.

[@aleblanc3547]

Simple, quick test. Thanks Dony.

[@Pterocarpous]

Well I'll be!. Great idea. Never occurred to me to check gas cap (new to small engine repair). After my mower has been running off a full tank for about 15 mins or so, It looses power significantly. Have been down the carburetor repair kit etc route. Issue persists. Won't that be something if it turns out to be the gas cap. Thank you for another excellent instructional video. Very much appreciate your generosity, sharing your expertise.

[@philfalz01]

thanks again for taking the time to make the videos

[@patthesoundguy]

that is a great test. what I also do is when the motor runs badly, and I suspect the fuel cap is bad with the engine acting up I unscrew the gas cap and see if the motor smoothes out. then I do that drain test to be sure.

[@anneshaw9681]

Airflow through fuel cap. Worked it out. Goes through thread. The thread is not complete. There is a gap where the air goes through. Helps to know if the cap is venting properly. Funny when you Google this I get no answer. Thanks Don

[@frbhobbyprojects-itswhatid2707]

Thank you, your videos are very straight forward and helpful.

[@frbyd9884]

I love you, man! This is great. Thanks so much!

[@thejohnsons7901]

Will check my snow blower today, thanks again!

[@martyheffernan1672]

Great video mate I enjoy watching them. From all the way over here in Australia. I have a small engine and lawn mower repair workshop in my shed. Have you got a shop tour video?

[@louieferrer7416]

thank you for the tips and demonstration. Great video

[@Tommyr]

Another great Video Don! Thanks a lot!

[@enfd85]

Your videos are very informative. Thank you

[@noahriedel801]

Ok, I will definitely try that. Thanks Dony.

[@jamesmullins3219]

thanks for another good video........good photography and good edits

[@donyboy73]

thanks

[@sandy7m]

Hi Donny Learned a lot from your videos Saw this one and thought "that does not cover problems with Honda tanks". I now have a set of steps that will cover your trouble shooting method and some. To begin with, a tank problem usually shows up as an engine that gets started up but dies or idles badly soon after. It may also present as an engine that will start and idle fine but will not rev up well. These problems are either fuel or air related. Removing the air filter and going through the running checks will confirm if it is a fuel problem. For a suspected fuel tank feed problem, have the tank at least a quarter full. When disconnecting the hose to drain into the container, disconnect it at the carb end. Watch the flow. If there is a decent flow to start with, and the fuel cap vent is blocked, the flow should tail off and nearly stop within a minute or two. Remove the fuel cap and if the flow increases dramatically then the cap is the problem. If the flow hardly increases then there is an issue with the fuel line and any plastic type fuel filter in the tank. To remedy this - Clasp the nozzle of an aerosol can of brake cleaner in to the end of the hose MAKE SURE THE FUEL CAP IS REMOVED AT THIS POINT. Operate the aerosol can to blow through the line to the fuel tank. Do this gently to start with to avoid damage and spillage. It should only take a few short squirts to clear blockages (don't get too aggressive as you might blow the tank filter off). Remove the aerosol can from the hose and observe the flow into the container. It should have improved. As a last check, put the fuel cap back on to make sure that does not impair the flow rate again. Hope this helps

[@mattz2900]

sandy7m where is this video of yours? I would like to see it for my HRR216

[@rosaliosanchez6248]

Loved your tutorial! Easy to follow, well explained, and clear voice which helps my hard-of-hearing issue. Now my question; I ordered a new fuel cap for my BOLENS BL160 string trimmer because the original leaked. It also leaked with the new one, so I added the gasket of the original on top of the new gasket and NO MORE LEAKING! But now I have a new problem; my engine will not run at full speed--it goes up and down. How do I correct this problem?

[@dreamingcode]

Great easy to follow directions👍

[@59chevt]

Great info as usual thanks.

[@RosaStringWorks]

Good tip.

[@dfields9511]

I have seen that happen on a briggs quantum before once . How would this work for the pulsa primer style Carbs on briggs ?

[@mercoid]

Thanks Don. Very helpful

[@brianb5779]

You got me thinking after learning this from you and im always trying to come up w other ways of doing things. I wonder w the tank empty if a vacuum pump was hooked up to the line and you pumped away if you would get a vacuum if its bad (not venting). Whats your thoughts on that? Im just thinking if it would work then might be a little cleaner and less messy and/or another way of checking it. Justa thought!!

[@jimboy7102]

As always a great video.

[@FabioAS]

Hi there, I have a 6hp Briggs mower and a rounded piece of plastic in the cap is broken. I had to replace with a rubber one I've made, now it's giving me some problems, parts for this mower here can be very expensive and hard to find, what do you suggest in this case to vent it. Should I make a tiny hole on top or try and loosen up the cap when starting the engine? Thank you Couple of days ago noticed some gas on the deck, came from filter housing after sitting thru the night. Thanks for the video

[@semco72057]

I have not had that problem with my lawn equipment, but do have a problem with my utility tractor cranking for some reason, and I know the battery have plenty of power. The engine just don't crank and I am trying to diagnose the possible problem for this.

[@mikeatv]

my homelite weed wacker had that same proplem...... those hose clamp pliers look good ... what brand are they. ?... thank

[@brianb5779]

FREAKEEE,,,was just wondering yesterday if there was a video out there on how to test...having problem w pressure washer just shutting down but will start if i choke, pull, then unchoke and pull again..Thanks for the info...

[@Soulcommander]

as always great tip. thanks!

[@BearE9090]

Thanks for the tip about the fuel cap metal dish.

[@MrGarcon98]

how would you do a weed eater ? a kawasaki industriall its about over 13 years old but its running ok , i have to loosen the cap now and then not to get surging ! and its a new cap at that ? thanks for you vids they are interesting

[@Jflowboston1]

thanks for all the info bro, you are the beast

[@donyboy73]

thanks

[@fartsmccracken1445]

Beast?

[@dougdrefus3554]

How do you test a two cycle weedwacker gas cap. If I put my finger on the gas cap vent and pump the primer bulb a couple of times it seems to start easier.

[@num1booger]

AS ALWAYS GREAT VIDEO AND INFO.bLESSINGS TO YOU AND YOUR FAMILY,THE BIG GUY IN BEAUMONT CALLY USA

[@shikpolam8968]

Nice and easy way, smart thinking.

[@zx8401ztv]

A good practical test :-D

[@GmGarlo]

is there a similar way to check the fuel cap on a outboard motor fuel tank?

[@SteveRobReviews]

Good idea. 👍👍

[@geojor]

thank you for this ...

[@THEMOWERMEDIC1]

Good Tip!!!

[@cochoa12]

Excellent video

[@mackendw]

I bought a Kelch non-vented gas cap with gauge for my john deere 210. I added 2 small holes in the clear plastic on the cover to vent it. Before doing the venting I would only make it around 2 laps or so on my lawn before the tractor would start chugging, coughing and about to stall. I diagnosed the venting issue. Question: is drilling the holes in the outer clear portion of the cap sufficient to allow enough air in to allow the fuel pump to work properly? The mower has a pulse cam-lobe driven fuel pump. Now my symptom is the engine starts warming and getting hotter as I continue to mow and eventually blows a head gasket. Before doing this it starts laboring and struggling to continue running. Might the carb be possibly starved for fuel? How to diagnose this?

[@300zxdriver]

Ok why do caps go bad? What happens? and can you fix them? Have old John Deere snowblower cap has course threads hard to fine.

[@Hunterslife315]

Is that why also my mower bogs down then when the gas is almost gone it runs like there's no problem at all?? I put new oil and oil treatment in thought that was the problem but I'll put a full tank in and it spits and putters till the end of the gas is gone.

[@mattz2900]

My Honda HRR216 is missing the sponge- fuel cap breather, which goes in between a gasket and fuel cap. You’re saying with this little sponge absent, it could have a noticeable effect on my lawnmower’s performance?

[@willf5768]

Hey Don just where do these gas caps vent and can you simply repair them or create another vent option?

[@declyn8]

THANK YOU!!!!!

[@jesseh3806]

Thanks buddy!

[@georgeho6772]

I have a new Turbo lawn mower. the fuel tank cap has gas leak. What should I do? Thank you for your response in advance.

[@seagangstab2637]

Thanks brotha!!

[@southsurreybc]

Excellent video! I was hoping for a demo of a faulty fuel cap where the fuel would stop flowing. Then the moment you open up the cap, it would flow once again. But we get the idea, and thanks for the tip!

[@kwebster62]

That would have been better.

[@markb8954]

Exactly, me too.

[@lattina62]

This things incredible

[@scottfirman]

I find this more of an issue on weed wackers more than anything. I have had them leak but more than anything its the ethanol will melt the little green valve in the cap so it cannot breathe. I keep spare caps handy for that reason alone. Craftsman seems to be the ones most affected but it happens to others as well.

[@maddenmobilegod7737]

Will this method work on other equipment?

[@BrucesShop]

Good one. It is like holding your finger on the top end of a full straw.

[@workingshlub8861]

you can squeeze the tank and put your ear to the cap..you should hear the air escaping.

[@mrsemifixit]

How does it actually vent? On top it looks completely sealed?

[@bradendebraga651]

Great video!

[@donyboy73]

thanks

[@elcidlord]

Mine is a Craftsman r1000 and acts like running out of fuel. Briggs & Stratton engine. Replaced plug, fuel filter, clean gas and tank is spotless, new ignition coil ( $70.00 wasted) and it still acts like running out of gas after 30 minutes or so. Have blown out fuel cap several times. If I let her set 20minues she runs fine then stars all over again like running out of gas and dies. Have to try your test.

[@workingshlub8861]

my snowblower started fine but would die as soon as i hit snow..thought it was dirty carb so i cleaned it..same problem..it was the cap not venting. that is one of those things easily overlooked.

[@jpp9876]

I'm working on a honda horizontal shaft, for a roto tiller. It has a fuel pump. I am guessing it is not venting. Was told it will run 3 to 5 mns and shut off. With the cap off it has run now for 15 mns. I see it moves excess gas from the pump back into the gas tank from an upper fuel line.

[@TheBoomerbaby]

How do we clear a clogged fuel cap? My Craftsman mower has a fuel cap similar to the one with a metal cone, but it's a flat plastic disc suspended inside the cap. How do I clear the clog?

[@samuelduran5903]

I have a Crapsman Lt1000 riding mower. After running it 10 minutes it shut off. Ill restart it and it will fire up for 2 seconds then die. I can do this till the battery dies. Ive tried 2 different carbs from Scamazon but the same result as mentioned above. I ordered a new gas cap, hoping this will fix the problem.

[@DougHinVA]

simple and saving 1 repair visit is VERY cheap if you need only a new cap or NO new cap.

[@tink0801]

love your vids

[@donyboy73]

thanks James

[@pizzadave9812]

I have a 2014 rear engine snapper mower with a non-vented cap from the factory after about 15-20 minutes of running it the engine wants to stall and it does if I need a vented gas cap why did they put a non-vented one from the factory? Please help. ...

[@agevermoreinfinity20]

I have an old Stihl trimmer w/ a cracked tank, that uses a vented gas cap. I brilliantly?? decided to use a donor tank and cap from an Echo trimmer. Trimmer would not run at all. No gas to the carb. Pinched line? Clogged filter? No, it needed the old vented gas cap in order to work. Was very frustrated while trying to figure it out. Hope this saves you some time 'tho.

[@Mike_The_Hog_A_Nator]

I have a newer 52" ExMark Radius & it will die out after a few minutes of running. It will continue to run perfectly fine if I keep the fuel cap loose & my fuel filter stays full of fuel. Any suggestions???

[@rubencano7022]

Don why would the fuel in the gas tank gets empty when it sits in storage for 2 to 3 days no leaks detected and or wet areas on deck or floor what could be the problem

[@99carnot]

Helpful!!

[@donyboy73]

thanks Steve

[@brianmott728]

How do I troubleshoot an engine that is having trouble picking up the fuel even though the carburetor is clean?

[@ckennedy309]

Looks to me like the Metal cone in cap just prevents you from tightening down past a certain spot on the lid that probably has small groves for air to come in. so you have a tight lid without it closing totally ....just guessing...so if you dont have a cone just screw the threads up on the lid or something

[@continental_drift]

Kicking myself that I idn't see the video 6 months ago. It took me a lot of trial and error to figure this out, the trouble is you have to suspect what the problem might be before you can test for it. Now I know.

[@neilbillings1609]

Another great video, it’s a pleasure watching your explanations very clear concise and to the point. Which brings me to my reason for contacting you. I have an older PB403 Echo backpack blower. It needed a tune up, I had been using a very oil rich mix and the discharge was not good, so I decided to rebuild the carburetor, I ordered a rebuild kit, and an inexpensive Chinese copy from amazon. The amazon kit included spark plug, air filter, replacement bulbs, etc and was not very expensive. I have, since following your lead rebuilt the carb, and replaced all the fuel lines and the gas filter, and for some reason I can’t turn this thing over. The pumping of the gas bulb does not inject fuel into the carburetor (no matter how much I pump) I have since replaced the re-built original carburetor with the replacement, too no avail? When I spray starter fluid the engine of course kicks over, I was hoping it would start the gas flowing, needless to say it didn’t. I have decent spark, I tried a pressure test on the with the bulb and fuel line module and it held in a flask of water, no air leaked. I tried starting with a loose gas tank cap, I have the high, low setting at the right settings. What am I missing? Everything is tight, gaskets are in place, 50:1 fuel mix, (FRESH). I failed to mention the obvious, of course I soaked the old carb in carb cleaner and throughly dried it using my compressor. I must have pulled the cord one hundred times with the choke on and off, I have good compression, my arm will attest to that. Any thoughts on what I Might be missing? Thanks in advance!

[@gordbaker896]

Have you checked/replaced the coil/plug? Float sticking? Fuel valve turned on?

[@markebill1]

@@gordbaker896 reverse fuel lines

[@redskool8498]

thanks again awsome stuff ... †

[@donyboy73]

thanks for watching

[@arnoldogarza4387]

What do i do if the gas is leaking from the top of the fuel cap

[@853rudedogs2]

What is metal dish for?

[@jacobc.8655]

How exactly does the metal dish work? I noticed that there is no vent hole in the Tecumseh cap.

[@FabioAS]

Good question

[@chuck1prillaman]

Looking at mine, it apears that the rubber diaphragm has 2 tiny notches at the lip where the cap seals against the tank opening. I think these serve to allow air in when theres any negative pressure. Mine failed and I suspect the foam liner is so compressed that it can't maintain enough space between the rubber diaphragm lip and the cap. I just drilled a tiny hole in the side of the threaded opening. Damn the EPA: I have grass to cut here.

[@zyplex1]

Good info, could you drill a small hole on the cap to vent?

[@donyboy73]

you could but fuel would most likely leak through it

Would vapor a little.

[@ontheone9559]

I have a Honda ice auger, would a non venting cap be the cause of it bogging down under a load?

[@donyboy73]

sounds more like a carb issue

[@cartee72]

Is there another test to try? Can a cap be unclogged ?

Just drill a little hole in a cap.

[@noahriedel801]

Hey Dony. My mower drips fuel out of the carburetor after sitting in the sun. Is this a Fuel pressure issues due to a faulty gas cap?...or a faulty needle and seat. Only happens when in the sun, never happens in the shade. Plz respond. thanks

[@donyboy73]

try with cap loose, if it doesn't happen then you know it's the cap

[@cnmtech8086]

Can you supply a link to purchase new updated gas cap? Thanks for your videos. Always learn something new.

[@donyboy73]

just added link

[@peterhunter5695]

Where's the link

[@joeyojoeyo3613]

I am working on mine. It can run 5 to 10 minutes and then nearly shut down then resumes running with intermittent shutdowns as before. Mostly 5 minutes or less intervals.

[@43128lucky4]

I use a clear tygon line. if it's not running right I'll just take a peek

[@andrewveldman]

Hello donyboy. I'm looking for a walbro carb for my pioneer chainsaw p 26 . Wa-22a. Any advice where I can find one. Asked on walbro web site ,tried eBay.thanks andy

[@donyboy73]

try chainsawr.com

[@sheriakers6418]

Hey Donny boy do you have an old bar for a stihl ms 250 around 16-20" I think I might make a sawmill thanks!

[@SheikShak]

Thank u…

[@kenhilson786]

I have a briggs 775ex. Tank drains but if i loosen cap it drains faster. Is that part of design?

[@donyboy73]

yes, it's normal

[@seamusblack5876]

How do you fix a defective fuel cap?

[@kelpaso1]

I think your videos are great and have helped me a lot. But, as in this one, and some others, you don't explain HOW it works. How does the cap vent? I don't see any holes in it.

[@cluelessbeekeeping1322]

+Kei Pas It works via *_Magic_*

[@johnpileggi5257]

The part number for the black cap is 37844. I'm told it is identical to the red cap except for color.

[@maddenmobilegod7737]

Hey Donyboy, where can I get a container like the one you used in the video?

[@donyboy73]

I got those from a factory as rejects, they are no longer available

[@maddenmobilegod7737]

donyboy73 What would you recommend me getting that will be similar to the one shown in the video?

[@massageguy1421]

I have cut the bottoms off gallon size oil and antifreeze containers and they work fairly well. Not as rigid as what Don has, but will suffice in a pinch.