How to diagnose carburetor vacuum leaks on your motorcycle

[jquickj]

Great videos man! you're helping me out a bunch. I'm curious, what would the redneck repair method be to cheaply patch your boots?

Thanks!

[mrmaxstorey]

@jquickj Spread some rtv over the cracks, and then run the engine. The vacuum should suck it into the cracks, sealing them. It doesnt last forever tho, the rtv breaks down after a while

[OldFordsRun]

I have a 90" Honda vfr 750f. I cannot get the carbs to come out, even though ive loosened the screws for the carb boots, and everything else it still wont come right out. How do i remove these carbs?

[mrmaxstorey]

@OldFordsRun Squirt some pb blaster or wd40 around the carb boots, then heat them up with a hair dryer. The rubber should get more pliable as the lubricant expands, freeing them

[Tulippimp1]

it dies when i back it off choke. i think i should try your method cus that was simple and right to the point

[Tulippimp1]

I have a yzf 600r 2007. It will only start on full choke. I have 4 carbs on my bike. doesnt starter fluid ruin rubber? let me know. it just started

[mrmaxstorey]

@Tulippimp1 No it shouldn't ruin the rubber

[55jpk]

cool brov!!! very nice piece of info, happy dayz sees ya 321gone.

[neutronjet]

hey there, informative vid. my bike also has this surging, but it happens after riding for quite sometime(15km). the rpm which supposed to be at 2, surges to 3+. what is the cause of this?

[mrmaxstorey]

@neutronjet It could be the same problem, the boots may expand when they warm up and leak. Try the test with the bike warm and see what happens.

[TheAnigai]

to me that bike was sooooooooooooooo beautiful.

2 types of bikes i just have a thing for are

honda 90's and quackers (kawasakis)

[mrmaxstorey]

@TheAnigai I hear ya man, I have a thing for the small displacement bikes too. You shoulda seen this bike once I got it repainted and looking sharp, it was pretty cool

[TheDriftjockey]

very nice info :)

what are the alternatives you can spray?

[mrmaxstorey]

@TheDriftjockey I only use starter fluid or propane. Some guys use wd40 but I dont think it gives as good results because it is not as combustible. Other guys shoot water and wait for the bike to run worse, kind of the same idea but a different take on it. I don't do this because bikes with vac leaks run pretty poorly as is, so it can be harder to tell the difference.

[TheLamborghinimuira]

very well spoken and the info was great....gonna try this right now ..ty

[mrmaxstorey]

@TheLamborghinimuira Good luck

[heroes91092]

you are a smart man!

[spelunkerd]

Nice demo, Max.

[mrmaxstorey]

@spelunkerd Thanks dude

[MrFingersniffer]

nice example

this trick works for any carbed vehicle

[mrmaxstorey]

@MrFingersniffer Yep pretty much any vehicle actually with a suspected vacuum leak

[iloveturtles1011]

or maybe your bike is just cold blooded like my suzuki gs500f

[mrmaxstorey]

@iloveturtles1011 Lol a bike this cold blooded as in the video indicates a serous problem. Besides, I rarely accept the notion that a bike is "cold blooded from the factory", thats often what guys say to explain why their bike runs funny and they don't know why

[harrdyharrharr]

@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

[mrmaxstorey]

@harrdyharrharr No, bikes should always calm right down. Your air filter may have leaks or is not mounted proper, you may have exhaust leaks or baffles taken out, you may have pod filters that have not had the carbs re-jetted, vacuum line disconnected, carbs out of sync or valves worn down (do a compression test), idle screws out of adjustment. Send me a PM if you need more info I'll walk you thru it. Nice bike BTW

[vvvRASvvv]

I have a Royal enfield 350 which has got a mikuni carb leaking gas from the bottom hole . ( googled it it was a drain hole im not sure what hole is that )

I took my bike to the mechs at that time it was alright but when my bike returned it leaked gas when it is kept idle at garage. help me how to fix it cz i know in my country India real and gud mechanics are hard to find and most mechanics use dirty tricks to make the customer come again and again especially for Royal enfield rider.

[mrmaxstorey]

@vvvRASvvv Well if it is the drain hole, then there should be a plug in there which has been removed. However if that is the overflow hole, then you are having flooding problems. Go to my channel and look at the video called "carbs leaking? heres how to fix it" and it should explain what probably needs to be done.

[TheGreatDane1234]

Hey i have a kawasaki KZ750 LTD 1983 and it has upgraded filters so there is no air box and it bogs alot and doesnt idle very well please help

[mrmaxstorey]

@TheGreatDane1234 Check out my video on how to adjust carburetor jets

[GaryParkerJr]

I have a problem like this with my scooter it is driving me insane. PLEASE HELP!! first it can be tricky to start sometimes. most of the time i have to start with full choke and then it will rev high in and out and eventually die. sometimes it will let me give it gas and but then after it just revs even higher than i move the throttle!! what is wrong with it? I cant get it idle steady enough to find where there is a leak becuase it goes crazy!

[GaryParkerJr]

@GaryParkerJr I watched your video like 10 times and i downloaded it and showed it to my friend and he thinks its a carb. problem. but why is it so crazy going in and out of throttle by itself? and I cant drive it becuase it eventually dies.

[mrmaxstorey]

@GaryParkerJr Send me a message with more info on the scooter, brand, age, condition, etc and I will try to help out

[vasylivy]

why would it matter if there is a leak on the air box side?

[mrmaxstorey]

@vasylivy Besides the fact that your engine wants clean filtered air, if there is a leak the air can come in much faster than normal, thus leaning out the mixture. The air filter retards the air flow down to normal settings, so it is important for all air to travel thru the filter first or else it will run lean.

[vasylivy]

@mrmaxstorey more air traveling in will create a bigger drop in pressure as the air passes through the venturi, pulling in more fuel from the floats..so the mixture would not lean out because of leaks in the airbox(assuming you adjusted the carbs with the leak present). the mixture will only lean out if the air is added down stream of where the fuel was added right? which would be at the connection between carb and manifold.

[mrmaxstorey]

@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

[vasylivy]

@mrmaxstorey Makes sense. I actually have a question i will message you about vacuum leak on my bike/high idle. Too many characters to post here. Seems like you know a good bit and i could use any help!

[mrmaxstorey]

@vasylivy OK send away

[lauriejennifer]

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.

[mrmaxstorey]

@lauriejennifer Thanks hope you figure it out

[lauriejennifer]

@mrmaxstorey Me too! If you watch the carb at idle, it's vibrating like crazy and I just did a track day yesterday. I am betting something just got rattled loose or got a nice little rip or tear. *sigh* Right now I am grateful for having *one* carburetor. If I ever had a multi-cylinder bike again, it would be FI.

[mrmaxstorey]

@lauriejennifer They really arent that bad if you follow a couple of important guidelines for maintaining them. Most of my bikes are 4cyl carbed bikes between 20-40 years old, and I usually don't have much trouble getting them running well, however yeah carbs can take some work which is why so many of my videos are dedicated to carb maintenance.

[lauriejennifer]

@mrmaxstorey They are much cheaper to modify and fix yourself than FI, I'll grant you that. And if you take the time to tune them well, you won't hardly be able to tell the difference between a well-tuned carb bike and a FI bike. However, this little single is my only vehicle, so the simplicity (and, therefore, time-saving) of only ONE carb is a beautiful thing.

[mrmaxstorey]

@lauriejennifer Haha I hear that, sometimes the simplicity of these old engines really impresses and amazes me

[lauriejennifer]

@mrmaxstorey I think that's why a surprising number of them are still around, and with such high mileage. Plus, Kawasaki is pretty good at not adding frivolous complications. They don't tend to have electrical problems, etc., as a result. I may be biased, though. ;-)

[mrmaxstorey]

@lauriejennifer No,I definitely think you are right about that. I have lots of respect for Kawi products

[lauriejennifer]

@mrmaxstorey Well, it wasn't the vacuum leak. Just checked. And I even tried opening the gas cap, as a shot in the dark. No change. Idle still wanders. Races, then doesn't, then does again, etc. Eventually, if i leave it idling, it will bog lower and lower until it dies. This happens sooner once the engine is warmed up. Almost as soon as I pull the clutch in to coast, it will bog and die. Frustrating. Praying it's not electrical...

[mrmaxstorey]

@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?

[lauriejennifer]

@mrmaxstorey KLX 250 (actually, a 350 now). Not sure how to check float. Had a pinched fuel line before from the reserve tap, so it would die when switched to reserve. I already replaced and double-checked that fuel line and it is flowing properly. Not sure how to check either float or petcock. I use opaque fuel hose. How do you see if it's running without spraying gas everywhere? lol

[mrmaxstorey]

@lauriejennifer Well pull the line and make sure it flows well. To check fuel height see my video on that topic. Im not sure if you have to rejet the carbs since boring the motor or not, get on the kawasaki forum and ask other guys who have done the same procedure.

[lauriejennifer]

@mrmaxstorey Oh, already rejetted. It was running like a freakin' champ after the bore and rejet for the first 600 miles or so. (300, then oil change, then another 300).

[mrmaxstorey]

@lauriejennifer Welp sounds like you did most of the good work, how about a compression test to see if those valves are any good?

[gjstroudify]

Brilliant! Thank you for the help!

[justinchaffin1013]

i had the same problem with a dirtbike i just turned the idle down alot(:

[mrmaxstorey]

@justinchaffin1013 Lol whatever works for ya

[justinchaffin1013]

@mrmaxstorey it saved me from getting a ticket too i usto ride like a mile from my house not even i think i usto go to this abandon golf course and the bike started revin so high i shut it off turned and looked cop sittin right there didnt see me he was lookin for speeders in the thing right next to a road in the parking lot it was so lucky

[bghauck]

Haven't watched your video yet on carb syncing but will shortly as I'm going through a number of them. Have had this bike about 8 years but just starting to do all of my own work recently. Have no idea where to find the idle adjust knob.

[mrmaxstorey]

@bghauck If I recall it should be located between 2 of your carbs, either pointing front or back, a small knob about the size of a nickel. But I could be wrong, I sold my v65 over a year ago. Go to bikebandit and look up your bike, if you click on the carburetor schematic it will show all of the individual parts to your carbs and you should be able to identify it for your bike.

[bghauck]

@mrmaxstorey Thank you - I'll add that to the top of my list before I begin disassembling. Your videos are fantastic. They have taken a lot of the "mystery" out of repairs, and helped save money. 

[mrmaxstorey]

@bghauck Thanks, glad to help

[ilikesuzuki]

@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.

[mrmaxstorey]

@ilikesuzuki There are a couple of ways to tell. You can look for some thin black smoke out the tailpipe, that indicates a lean mixture, as does black sooty deposits on the spark plug, or if when you put on the choke the bike dies. If you are burning too lean, then your spark plug will look ashy an whiteish. Its possible you may have a fuel flow problem, partially clogged main jets, carb slides that dont go up all the way, some small vacuum leaks, or other problems.

[bghauck]

I have an '84 Honda Magna V65, 24,500 miles, which has similar operating problems. It will not idle without the choke on with rpms about 2k. It runs well, hot or cold, but whenever I come to a stop the choke needs to be on to keep it idling and from not shutting down. My thoughts are to replace fuel filter and air filter, and clean the carbs. I don't think it has a vacuum leak, but just watched this video and will check that too. Any other thoughts or suggestions?



[mrmaxstorey]

@bghauck Sounds like you are on the right track. Have you tried syncing the carbs? And might be a simple suggestion, but have you tried just increasing the idle via the idle adjust knob?

[rkamphowe]

I have a 1980 suzuki GS550L It is hard to start and won't idle below 2- 2.5 grand, if you adjust idle below that it dies. Runs fine up and down the road and has plenty of power, but is hard to start even when warmed up. I watched your carb rebuild video and changed all the jets and adjusted the float heights, could the carbs just need synced or could this be a vacuum leak?

[mrmaxstorey]

@rkamphowe Either could be causing your problem. Check for vac leaks, sync the carbs, and make sure your slow jets are not clogged. Good luck!

[edempsey3]

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!

[mrmaxstorey]

@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!

[513mccreary]

Do you know why the vacuum pump goes out on the air intake system? I checked the diaphram on the hypercharger and it works fine however, vacuum on my bike bearly works...

[mrmaxstorey]

@513mccreary Could be any number of reasons, check out my other videos on bike diagnostics too much to go into here

[jthuggamk3]

won't the carb spray eat away at the rubber and cause a leak?

[mrmaxstorey]

@jthuggamk3 Not if you spray just a little, even hydrochloric acid cant corrode rubber that quickly.

[jthuggamk3]

@mrmaxstorey but the condition of the ones in the vid it would be best to just replace them

[mrmaxstorey]

@jthuggamk3 Obviously and I say that in the video, but I also said that this wasnt a keeper bike I was just fixing for resell so I didnt want to spent the money on new boots, plus I just wanted to diagnose the problem so a semi-permanent fix of gasket maker was the right choice in this situation.

[Michiganborn1969]

Hi Max. I was curious if you do video replies? I think I found part of my acceleration problem & it would be easier to show you what I found.

[mrmaxstorey]

@Michiganborn1969 Sure, go for it. Or put it on youtube and send me the link

[lynette1953]

@mrmaxstorey hey man one of my carbs is leaking fuel outa the drain , whats the problem here?

,jon

[mrmaxstorey]

@lynette1953 Sounds like it is a sticky float or needle, check out my video on leaking carbs that explains how to fix it.

[Michiganborn1969]

@Michiganborn1969

Cool, I'm editing it now

[Michiganborn1969]

Yeah I think you would have a tougher time. Its been said that the weight & the wheelbase on the bike is an important factor taking the test. My Maxim with me on it weighs in the neighborhood of about 760# but I guess the Maxim was designed as a cruiser with almost. 6 1/2' wheelbase. I have a YT video on here "how to change a motorcycle air filter" its normally a great running little rocket with the inline 4 cylender & DOHC putting out a rated 87hp @ 9k rpm.

[Michiganborn1969]

Lmfao. That's kinda funny & scary at the same time especially when it comes to the DMV's test course where you gotta weave back/forth around the outside of the of the cones then you got to go around a very tight circle about 12' in diameter where the tract is barely 18" wide & if your front tire touches the painted line or you put your foot down, you fail. I have a CDL & if I have to take the written test again I must retake the written for all my endorsements. That would totally suck sideways.

[mrmaxstorey]

@Michiganborn1969 Yeah the MD test was kinda like that, we had to go uphill and accelerate to 30mph and then brake before these striped lines ended and all, make a u-turn in 2 standard size parking spaces without putting a foot down, actually pretty challenging. I passed it 2nd try on my kz305, not too sure I could do it now on my GV1200 tho, haha.

[Michiganborn1969]

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.

[mrmaxstorey]

@Michiganborn1969 Haha thats what happened to me when I took my test in MD. My clutch cable snapped and I couldnt do the 30ft start-stop without stalling out, had to take the test again after I fixed it. It was then that I resolved to take matters into my own hands and learn everything I could about my motorcycle.

[Michiganborn1969]

Subscribed :) I've only had this bike since last October & my 1st street bike since 1993. I'm still learning where everything is at & how to fix/replace things. I don't want to sound like a dummy, but is the coil located where the other end of the plug wires go under a silver casing mounted on the head tube under the gas tank?

If it

s the silver box then I should also replace the plugs/wires while I'm at it b/c of mismatched plug wires.

[mrmaxstorey]

@Michiganborn1969 No worries dude, I was in your position once. Good for you for trying to learn it on your own. Your coil is on the other end of your spark plug wire, yes typically underneath the tank. And if you have old crappy wires that could definitely be a part of your problem.

[Michiganborn1969]

@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

[mrmaxstorey]

@Michiganborn1969 Well those numbers sound about right, but they do not test the coil. You can use your multimeter to test the ohm resistance in your coil, check out your owners manual for the specific ohm readings you should experience. It can be difficult to assess for this problem with the bike warm, unless you warm up your bike and then real quick check continuity with the coil hot. What I do tho is just keep a bunch of spare coils on hand to swap out and see if the problem improves.

[Michiganborn1969]

I wonder if this little test will help with the idle issue I'm having on my 85 Yamaha Maxim XJ700? Its starts ok sometimes even w/o the choke but once it warms up it wants to die & sometimes get hesitation on acceleration. Btw it only has 20k miles.

[mrmaxstorey]

@Michiganborn1969 It couldn't hurt to test it out, perform the test twice once with the bike just started, and once while warmed up. Also consider looking to your electrical system, especially coils. Old coils can develop hairline cracks which are not so much of a problem cold, but they expand when the bike warms up, and the spark cannot arc the fracture, grounding out. Check out my other videos for more diagnostic ideas.

[YoshiMan246]

Curious, What do you do with all these bikes after you fix them up? lol i mean shit id sell a few, buy one for around 300 -400 well that's what i paid for 87 honda cbr1000, once i repair it im going to order new plastics from ebay then hopefully sell it for around 1,300 make a good little profit.

[mrmaxstorey]

@YoshiMan246 Hey man your bike is worth more than that! I don't really buy bikes for profit, altho sometimes it does turn out that way. I kind of think of myself as a collector, but what I really like to do is work on bikes, pull them out of their sheds and barns and breathe some life into them and get them out on the road where they belong. But yeah, I don't work for free.

[HOPPERFZR]

that seat has to go 

[mrmaxstorey]

@HOPPERFZR Haha you got that right

[mrmaxstorey]

Yes vacuume leaks around the boots were the problem, I filled them up with a little gasket maker. Not a very good repair, but good enough. Best to replace the boots.

[awesomeelmo]

did you ever figure out the problem? i have the same bike with a similar issue just seeing if you had any tips