How to diagnose carburetor vacuum leaks on your motorcycle
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- เผยแพร่เมื่อ 1 ก.พ. 2011
- This is a simple video demonstrating the best method to detect vacuum leaks around your carb boots. Vacuum leaks are a fairly common problem in older bikes, and luckily they can usually be remedied quickly and easily, the first step however is diagnosis.
If your bike is running rough, won't rev up or has an irregular idle, before you take off the carbs and open them up, check for vacuum leaks. A vacuum leak occurs when too much air is introduced into the combustion chamber via a failure in one or more of the carburetor boots or other rubber mating surface. When too much air is sucked in, then the bike cannot combust the gasoline efficiently; there must be an optimal ratio. Therefore it is up to you to detect these leaks, and either plug them up or replace the carb boots.
In this particular bike, the engine was running VERY lean. Not only did we have vacuum leaks, but the baffles were taken out of the engine, and the previous owner had removed the air filter and neglected to install a new one. This is not only dangerous by allowing foreign material to enter the engine, but it also makes the engine run much hotter, as lean explosions create more heat than regular ones (think about blowing on a fire in your fire place: more air, hotter fire). This can be detrimental to a variety of parts in the engine, and it is a good thing we didn't ride this bike around too much before finding the problem.
If anyone has any questions as to why this is important or how to find/repair these leaks, leave a comment and I will respond.
Thank you - ยานยนต์และพาหนะ
Fuck spending thousands in mechanic school when you can watch videos like these posted by fellow youtubers spreading knowledge for free
Beer Drinker lololol
I've watched several of your videos to diagnose multiple issues on my cb750. You've not only corrected the issues, but have made my bike run literally like it's new. Keep up the good work and thank you!
Glad to help
I know this is like 12 years later but I have the same exact motorcycle with the same exact problem. You are a true godsend man and you don’t know how much I appreciate you making this
Glad to help bro, and I hope you get it sorted out
Thank you so much! Finally fixed my bike after watching your video and seeing my bike had the exact same problem! I am forever in your debt my man.
U fam Bru inni
Thanks for the awesome video! My father in law has an LTD 440 with the same symptoms that I told him I'd take a look at for him this winter. This will be extremely helpful. Thumbs up and subscribed!
Great video - another one of yours on how to free a stuck engine allowed me to resurrect my seized Suzuki Dr200se.
I'm struggling with a surging issue on my '88 KLR650 - I've gone through lots of possibilities and ruled out the petcock, air/fuel screw, needle, enricher. I now suspect I've got some air coming in to one or more places, starting with checking the boots. Going to pick up some starter fluid tonight. Thanks for the clarity and straightforward approach in your vids.
Sir, Dude, Dudorino if you're into the whole brevity thing. You are awesome! Thanks for all you videos. What you do by making these videos is everything that is right with the world.
Ace! After a recent top-end rebuild, my bike has had the craziest, most inconsistent idle and idle screw doesn't seem to make a difference. Probably didn't put a hose and/or clamp back on correctly. Cheers for posting this. Genius idea, sir. Many thanks.
you, sir, are a genius.
Hey Max. Keep up the great videos helping out us less mechanically inclined people :)
I have a 2002 Honda Shadow Ace 750 that sat for two years in my garage. I had someone clean the carbs, I cleaned the fuel tank put new oil, plugs, battery,fuel filter and fresh gas and the bike starts up and idles fine but stalls if I touch the throttle. I used your techique with carb cleaner and seems I have an intake leak because the idle will increase and smooth out for a few minutes every time I do this.
Great vid. Had a problem with my bike, thought i would use youtube to see if I can find a solution to my problem. Your vid was the first vid I watched and I got my problem solved. Thank you
This has helped me identify the issue with my bike that I’ve had since late January 😢 thank you 🙏
Glad to help bro
Thank you! I’ve typed in so many things to try and figure out why my 82 kz650 was revving out of control!
Great video an good advice. Ive never considered using propane. Ive worked on small engines for years an I always enjoy a decent how to.
Great video i did it yesterday as i had my homemade manometer hooked up. Two of the airboots on my 94 ZX6R was leaking. Im replacing all four of them for a crazy price of $65..
Good simple demonstration, exactly what I was looking for.
I wish you lived in the Cleveland, OH area. I just learned some awesome techniques to diagnosing issues. Thank you for the vid!!!!
great video man, nice and clear. The way you describe your method of approach and what you are thinking is excellent - thanks for posting
Thank you for your many older bike videos. I own a 1978 Suzuki GS 750, which is in really good shape. 27 years of loyalty. Vacuum leak video helped me so much. I pulled the carbs could but not remove the manifold boots due to the bikes age, heat, PB, impact wrench, etc. Sprayed the boots with silicone, problem gone
Thank you, I didn't even think about having it idle high choked. I have brand new intake boots, was still leaking around carbs and boot
Thank you I had the same problem I never thought of putting a boot over the intake connection, I sprayed starting fluid right on that spot and the engine rpms raised. but have been unsuccessful at stopping the leak but I believe you gave me the solution thanks for the video.
Man your explanations are extremely clear
really great video ! thank you my Suzuki 550L been doing the same ! !
thanks again !
This is the best info to know. Thanks for the trick with the starting fluid
Sweet man glad you got it figured out. And thanks for the invite, but Im driving all day tomorrow picking up 2 new project bikes, maybe another time
thanks saw those but while tempted as they are the same age and millage of my failed ones I reluctantly opted for new. Can only face taking these carbs off one more time this year!
Welcome to Canada! Home of good social services and high prices. LOL Price includes shipping, rings and clamps. Thanks tons for all your videos I am new at this and they were a big help.
@edempsey3 Typically if you modify your bike with pod filters, you will want to increase your stock main jets by 2.5. So if you are running 100 mains, throw in a set of 102.5 and see if that gets you closer to where you need to be. Good luck on your project, and thanks for watching!
I have a '79 GS 550L that I'm fixing up. Got it running better than when I bought it but at about 60% throttle it flattens out and dies back down. I'm going to check for a vacuum leak today but I'm thinking I need bigger jets to go with the new pod filters I put on. My carbs are Mikuni Kogyos and I was wondering how do I figure out what size jets to buy. I'm addicted to your videos and really appreciate the help. You're doing an amazing job and a great service!
Just a note that may help a few that have a need for a Quick fix for old cracked rubber intake boots.....3M polyurethane windshield sealant. It is black and Seals all cracks and leaks it seems to vulcanize to the rubber better than silicone .
And for The guys that pull the baffle need to pull the main needle on the throttle slides and move the clip 2 or even 3 clicks to the bottom of the needle to fatten up the mixture in transition from idle all the way to full throttle. It will be an immediate differnce in the way it responds from idle. Has worked for me for over 40 years.
@vasylivy To help illustrate my point, take out the air filter in your bike and see how it runs. Even with the benefit of all carbs running equally lean (as opposed to just one leaking carb-airbox boot) the increased airflow will still create a lean mixture. This is why re-jetting is so important after adding pod filters... if increased airflow before carbs had no effect on lean mixture, then all you would have to do is dial down your idle screw after adding pods
I watched it twice because it was so helpful
1978 GS750 I rebuilt the carbs, head and valves machined, installed new rings, electronic ignition, chain and sprockets and new carb boot o-rings. It ran well except at full throttle. The fuel petcock also would not work except on prime. I did vacuum test but the idle did not change. I found some very tiny cracks in the carb boots after smearing them with RTV the issues disappeared. I think the vacuum issue only manifested at full throttle. Just food for thought. Thanks for your video
Good call. Just bought a chopper and it falls on its face when i choke it down off high idle. I hadnt thought of vacuum leak..
Man you reply to a lot of your viewership, nice! I'll subscribe!
I try to answer every question
Okay, i'm going to try what you did in the video in the morning, thanks.
Really helpful video bro, thanks for posting!
thanks for all these videos! on my 83 CB650 I'm trying to find out how to reconfigure my carbs after cleaning them. are pilot screws typically screwed in all the way? the fuel/air screw (with the tiny washer and o-ring) is 3 turns out?
very well spoken and the info was great....gonna try this right now ..ty
Thanks. Since motorcycle shops here in Northern California charge $90/hr I can't afford to take it in & I need to try to get this machine running as smooth as possible b/c I just have a permit to ride for now. But when it come time to take my safety & skills test I don't want the bikes performance to be a reason why I flunked the test for my endorsement.
So it will increase in idle only if you have a intake leak? I sprayed all around intake seals and carb seals and in one spot the idle actually dropped back down like it was supposed to be?
So I just got a 80 ltd 550. The bike sat for a while. I can get it to start but it dies. The choke has to be on my carb boots look fresh. The last owner went to pod filters. I just took the carb off to try to clean. Should I find the original air box and got from there. When clean what should I look for
The tube hanging down is probably an overflow tube, in which case yes it should vent to the air. If you have very poor condition airbox boots they may leak air which could lean out your mixture. However a bike that performs well on the flat but bogs on hills is a classic sign of float levels being off, because the gas level in the float bowls will flow to the side of the bowls on an incline and either enrichen/lean out the mixture. Check the floats
Thanks for that, I will try that tomorrow and hopefully i will have some luck with it!
i have a 1989 Kawasaki ninja ex250 f . i just did a carb re build. i think somethings wrong with the vacuum hose(last owners had it cut and screwed shut) just wondering how i can test to see if petcock is the problem? it sucks a lot of gas through the vacuum hose.. enough to where it leaks out the exhaust while running! could the petcock be the problem? it wont idle. and should i do the same as the last owners and just block it off? thanks
love your videos ive got a 250 crx and it'll only fire when im blocking ther air intake on the carb. any idea what it could be ?
wont start with the it wont draw in fuel with the airbox attached.
Max, great vids all around. I have a '98 YZF and am having some idle issues that point toward a vacuum leak, but I have been through the carbs a couple of times and inspected the boots for apparent leaks and have found nothing. Is there a way to ensure that everything is completely tight on the re-install? The carbs sit directly on top of the motor and it feels like everything is seating properly. I'm stumped, any friendly advice?
Hi I have a 2001 fazer 1000 and when I start on full choke the bike runs for 30 seconds on 3500 revs and then dies out... I have to restart it three times any ideas or advice please
whats the good thing to sealed around the diaphragm? when i got my carburator it has like a rugby glue. i clean the carb one time and took off some of the glue like. then the bike idles good,start right up but when i rev up fast throtlle the bike seems to stall its like doesnt want to run or it has like a limit. need your feedback please.
@mrmaxstorey thanks alot for the videos it's very helpful. i have a question for u. how can you tell if a bike is running rich or lean. for me my bike feels like when i go 65 mph plus it feels like it's loses a little bit of power? what do you think.
thanks for teaching me a new method. Do the boots heat up and get softer and more air sealed?
Es un paso de la cincronizacion del motor ; buen video, para usar el vacuometro para ajustar el chichel piloto ,...
Thanks for posting. I have KZ 440 that is having that exact same problem. Once it's warmed up it runs ok. But starting it I have that same problem to a tee. I thought it was a issue with the jets. What did you use to seal it up?
Is the petcock vacuum line disconnected? That might explain both the petcock malfunction and the stumbling at high rpms due to a lean condition
I'm having the same problem with my mx175. I'm going to replace the manifold gasket but the boots are too expensive so I'm going to fill the cracks. What do you use for that and doI just do a complete seal around the whole boot where it connects to the carb?
Good simple video Nice work
Would the same issues apply with a 2=stroke 250cc engine. I have an old one that hadn't been started in 25 years until a few days ago,.. Took only a few kicks to fire up, but it died after running about 10 minutes. Since then it only starts if you pull it and the engine only runs at high revs with the choke on.
The carb is an amal monobloc
Just found your video and I think I might have a similar problem, so maybe you can confirm. Kawasaki Vulcan 800A with 2 cylinders, sometimes (1-2 times a month) after you start it with choke and the engine gets a little hot, it dies and fuel starts leaking from the carb. You can only start it after that by acceleration at 3-4000 rpm. If you run it afterwards, fuel won't leak, only when you stop and try to keep it in idle state (it will die if not accelerated). Thank you for your time and video, I'll check the vacuum system. Have to mention that the carb it's serviced and clean.
Its time to clean those carbs again, and this time put in an inline fuel filter between the petcock and the carbs. You may have a little grit in your tank which keeps getting into the carbs, causing one float to stick open or one of the float needles not to seat properly. Any time your carbs overflow its not a vacuum leak problem, its a carb problem. I have a couple videos up on how to clean the affected part, and how to set float heights. Good luck
@@mrmaxstorey So inline fuel filter. Also forgot to mention that after it leaks and I run it for 20-30 km at high rpm 3500-4500 then it comes back to normal, no more leaking. Those Kawasaki model carbs have some rubber on the carbs needle which makes them close pretty good.
Yeah most carburetors have that rubber tip, but if you have a tiny piece of sediment it could be as small as a grain of sand, it will cause the carb to overflow. The vibration of the motor from you running it at speed will temporarily dislodge it, but it finds its way back over time and overflows again. Clean the carbs, set the float height, and put in a filter. Done
Hi.I just got a Gs650L.1982.Same problem.So I looked for the problem.So as I went through my checks I found if I played with the throttle cable in went back to normal.So if I turn my bars to the ringtone it revs high.Hope this might help someone else.
hi max i have a 1981 xj 550 seca yamaha and it revs up sometimes after you give it a rev it would hold the rev for 2-3 secs then slowly rev back down again i have checked for vac leaks and there is no change in the revs after spraying easy start on the inlet boots and the carbs has had a strip and cleaned any help would be great thanks...philip
it's sounds like the spit pop I described before and my tank is off the mounts so it literally jumps a half inch when this happens. Had me a little jumpy after a time or two
@lauriejennifer It still sounds air/fuel related to me. What kind of bike are we working on here anyways? Does it crank up well and pull hard and even? Float set appropriately? Petcock delivers fuel well? Air filter mounted properly?
hi max I have a 1982 yamaha maxim xj750 it did start but barly ran and i took off the carbs cleaned out jets and boals barly would start at first than did all that but now hard to start and does that rev up thing 4500 than after while dont wanna start back up till later? could my clamps on boots be loose? air suckd in? what elese should i do? vac plungers are good and the thing that goes up down is good thanks leonard
very nice info :)
what are the alternatives you can spray?
Thank You for the informative video.. I recently got a 1978 hondamatic cb750a and have the same problems..the bike ran great about 1 year ago then it sat in someone's back yard..right noe the bike idles normally, but in order to start it i had plug up what i think was a vaccum hose and have the choke up..going to try your technique asap! Are all vacuum leaks predominately outside, or would i have to take the carbs off? i wouldn't really want to try that on my own kind of new at this whole thing.
The low ignition is the point, it means that it can help you detect even a small leak since it is so highly combustible, and even a very small amount will raise the RPMs. And no it no longer damages the upper end like older starting fluid did, because most fluid made today is made with cylinder and upper end lubricant. Carb cleaner is not as combustible so it is not as good at detecting leaks, although it still is somewhat effective
Love the channel- great resource! I have a KZ1000 and recently replaced the carb boots, but I got them used and the bike still revs by about 3-400 rpms when I spray the boots with starter fluid. Is this normal? I've also found that spraying my relatively new air filters has about the same effect. Thanks a ton!
Stock intake, or is the air filter aftermarket too? Everything is all hooked up like the boots and airbox, etc?
Could you please tell me what that small pipe going from the carby to the engine that had the leak is called. my crf 100 2008 model has a pretty visible crack on it and im trying to figure out what the part is called so i can order a replacement. you kept pointing at it during the video but never said its name.
Awesome, thanks for watching
Hey I have a KZ650 that runs great on choke but dies when I give it gas. Ive had the carbs off and cleaned them three times now and I cant figure out the problem. Do you think this could cause it? I also might think the pilot jet or the other third jet might be plugged. It ran great after I cleaned the carbs the first time but I ran it on bad gas and then after I turned it off and tried to run it a second time later it sucked. Then i started to clean the carbs the 2nd and 3rd time.
@mrmaxstorey
Its funny you mentioned checking the charging system b/c I just bought my 1st multimeter yesterday to see if there was any issues. With key off the battery was putting out about 12.8V, key on about 12.3V, running @ idle about 13V & reved @ 3500 it hovered about 14V. But this test was all done within 3 minutes. I will try again after a d mile ride & see what reading I get then. The light do dim when I use ether brake or turn signals. Thanks for the reply..... Joe
great vid, helped me out a lot! thanks
Yes you need an air filter. Also if gas is coming out the exhaust, that means that cylinder is not firing. You might be running on only one cylinder. Is that exhaust pipe getting hot?
@513mccreary Could be any number of reasons, check out my other videos on bike diagnostics too much to go into here
hey, I got that same bike u got. I was wondering. when I start the bike choke fully open she idles OK, and if i start closing the choke the idle begins to rise proportionally until it is fully choked then she runs rough and shuts off. Is that how the choke is supposed to work?
Thanks man got a link to that video? The GS line might just be my favorite line of bikes
My 2 stroke scooter is doing this but going full throttle as soon as it starts. This is the closest thing I have found on the internet to helping Xd I guess my reed valves, carb etc needs gasket maker in between it all cos I can't figure it out. I donno if my carb is bypassing too much air or something as it is a weird one with some sort of pump/diaphragm on it, any help would be awesome thanks. Its a Suzuki 50cc Carna. I can't find any info about the carb
Hi, I have this engine on a go kart project, & I can not get the clutch to disengage. what is the correct way to adjust it. Thank you.
I have a pit pike ssr 125 and their is a air leak because what he said is exactly what is Happening on my ssr. But I've tightened down all the places really right and their still is a air Leake. Someone please help how do I fix this
this really helped! my kawasaki ar 50 with an 80 engine upgrade has the same problem but smokes a bit to
(my-space-bar-doesn't-work)...I-had-this-problem-at-one-point,-but-like-you-said-to-do-i-replaced-the-carb-boot.-now-it-runs-without-the-choke,-but-it-kind-of-stutters-while-it-runs-(with-and-without-choke).-does-this-indicate-grime-in-the-engine-or-perhaps-another-small-vacuum-leek?
hi max i did these checks today and found a crack in the air box and i welded it and i rechecked my air filter which was ok, the bike has improved altho it still does a little rev after i give it a rev ... i have bench sync the carbs with a needle.. would it run better if i got them syncernised properly? also it would run idlol for a good while then just die, it would start back up again with no delay thanks for your help philip
@mrmaxstorey my bike revs up crazy like when i use the choke to crank it and it's kinda hard to calm it down. i tried this test but the idle didn't change. any other ideas? it's an 84 kz700 by the way. would it just happen to be normal? thanks
No, I installed a new petcock kit as well. As soon as I siliconed the boots and the air box boots the running lean and the petcock issues disappeared. I suspect that the vacuum leak was only an issue when the carbs were sucking at full capacity. Anyway I am now confident enough that boots were an issue to spend the $150 on new ones.
my bike when it eventually starts idles fine, doesn't rev hardly then if i catch it revs well at high revs, the idles high, does this sound like it could be an air leak?
Nice video! Very helpful! :)
Awesome video, thanks buddy
What will you use to seal the cracks? Great video BTW. Thx.
i have the same problem my bike is so hard to start and when i start it if it runs below 3000 rpm i cant throttle it up. im new to bikes sir
Same thing been happening to me the same place as well I’m working on a quad and every once in a while you hear like a puff sound coming from the leak along with a puff of smoke
i replaced valve shims on my bmw f650st,i also cleaned carburator.unfortunatelly now the bike wont start and when i release starting button i hear a sucking sound from carburator.what can be the problem?thx
Sounds like good work so far. Also check your float heights
very very helpful, thank you very much!
could you please elaborate on your problem?
You can get rubber pipe couplings in the plumbing section at Home Depot for $5. From the looks of it, you could cut one coupling in half and use it for both carbs. You can catch them on sale and buy a few different sizes. They come in handy.
is it resistant to gasoline?
Can I spray gasoline instead of starter fluid or propane fuel as I don't have any of that to check for vacuum leaks? Or is there any other fluid that I can use that would be available at a general home.
I have a 82 suzuki gs300l just cleaned the carbs. Bike will only start and run on full choke and idles very high. I can't find any leaks my boots look new. Any ideas
Yeah a sync might help. Have you checked float heights? Are you getting good fuel flow out the petcock, no clogged fuel filter?
Hello, you seem to know what you are doing, so maybe you can help me too, i've just bought this new bike(second hand) honda xr125, but it keeps cutting off and i have to keep it reving for it to stay on, every time i let the throttle go it cuts of, what do you reacon it is?