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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / December 2006Best way to find carburetor vacuum leak
Hi all -- I'm pretty sure my car has a major vacuum leak around the carburetor, as the car will start and only run for a few seconds and is impossible to keep running. In addition there is a whistling noise. I've checked the vacuum lines and they look okay; i'm worried though that a line that I cannot see may be leaking, though, or that the base gasket may be bad. What is the best way to find a vacuum leak? I thought using smoke would be good although having a lit match above a carburetor is a recipe for death. Is there any other good way to do this? I've installed a second carburetor with the same symptoms as the first, so i'm thinking its not an internal carb problem. Thanks, car is a 1986 Honda CRX 1.5. -J > Hi all -- > [quoted text clipped - 14 lines] > > -J Use an UNLIT propane torch. Just open the valve SLIGHTLY and move it around the area you think there is a leak. When you hear the engine rev up your near the leak.  SignatureSteve W. >> Hi all -- >> [quoted text clipped - 19 lines] > around the area you think there is a leak. When you hear the engine rev > up your near the leak. Thanks for reply. I can't keep the engine running long enough to do this, it dies within a couple seconds regardless if i'm giving it throttle or not. >>> Hi all -- >>> [quoted text clipped - 22 lines] > it dies within a couple seconds regardless if i'm giving it throttle or > not. First, determine if you do even HAVE an intake leak. Hold a piece of notebook paper over the carb--not air-tight, but just enough to 'choke it' a bit while someone else starts it. By varying the amount of air you allow into the carb, you should be able to keep it running if it does have that suspected leak.. IE, by letting in less air, you are making it run richer to compensate for any intake leak which makes it run too lean. Then, when you get it levelled out(assuming you find it to have an intake leak) , spray your wd-40 or whatever around possible-leak areas. When you reach the leak, as others have said, the engine will suddenly speed up (or if you now have correct flow of gas/air by use of paper, it may try to slow down from suddenly being way too rich!). Anyway, when the spray hits the leak, the rpm's will try to change quickly. HTH, s When was the gas filter last changed? You can spray WD40 around the seams in a running engine, otherwise folks use a smoke generator that blows smoke into it. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > Hi all -- > [quoted text clipped - 14 lines] > > -J Not sure when the fuel filter was changed...the car has 2 of them, i replaced one, the other is old. The float bowl seems to stay full of gas, though. I can't keep the engine running for more than a couple seconds so I can't really check for revving. I tried blowing smoke from a cigarette down a length of heater hose into the EGR port but couldn't see smoke coming out anywhere else. > When was the gas filter last changed? > [quoted text clipped - 26 lines] >> >> -J > Not sure when the fuel filter was changed...the car has 2 of them, i > replaced one, the other is old. The float bowl seems to stay full of [quoted text clipped - 37 lines] >>> >>> -J me thinks you have a problem not of vacuum leak origin. even with the brake booster vac hose open (large vac leak) you should be able to run engine with throttle opened up. BUT, a non flammable vac leak finder = shampoo bottle full of water, squirt it around suspect area and you will hear it start sucking water when you find leak.......whistling you mentioned may equal exhaust stoppage. all that goes in must come out grasshopper............... Your symptoms are more likely fuel starvation than a vacuum leak. Even with a vacuum leak, you should be able to make it run with throttle. I would change the fuel filter before spending any more money or time on it. Mike > Not sure when the fuel filter was changed...the car has 2 of them, i > replaced one, the other is old. The float bowl seems to stay full of [quoted text clipped - 36 lines] > >> > >> -J If you suspect a clogged fuel intake as some suggest you could disconnect the fuel line and crank the engine (mechanical fuel pump) or just turn the key in the ignition (electric fuel pump). You can also take off the air cleaner and look into the carb while pullign on the throttle control to see if a jet of fuel squirts into the trottle with every pull. Just for the record, another way to search for vaccum leaks is to use a water mist from opne of those house plant sprayers. That will slow the engine down if there is a leak. In your case you might try sealing all the hose connections with by wrapping them with masking tape to see if that stops the leak. If ti works then remove them one by one to see which causes the problem. Can we assume you'e done a carefull visual inspection of the hoses, pinching them between the fingers to check for cracks, and pushign each onto it's connector in case one is loose? I sometimes have hoses come loose when I'm working in the engine compartment. It's so crowded in there I don't notice if one has been jarred loose. I have checked the hoses and have not found any that are broken. I tried disconnecting the fuel line and cranking; a LOT of fuel came out. Its definitely not starving for fuel. I tried spraying both WD40 and carb cleaner around the suspected leak areas and did not find anything. I did try disconnecting the vacuum lines and taping them off and seeing it the engine would run better. There was one line that made the engine somewhat better (it could be kept running with the throttle) but certainly not completely right. thanks for your input. I appreciate any and all help. -J > If you suspect a clogged fuel intake as some suggest you could > disconnect the fuel line and crank the engine (mechanical fuel pump) or [quoted text clipped - 16 lines] > loose when I'm working in the engine compartment. It's so crowded in > there I don't notice if one has been jarred loose. > I have checked the hoses and have not found any that are broken. I tried > disconnecting the fuel line and cranking; a LOT of fuel came out. Its > definitely not starving for fuel. It has never sounded like you have an engine that is starving for fuel so why do you have everyone looking for a vacuum leak? When you do get the engine started and running for a few seconds, Does it produce any smoke out the tail pipe when it does run? Does it rev up and cut off immediately or does it just sputter along and slowly die? Does it take a lot of cranking and charging the battery to get it started? Why did you just install a different carburator? I'm guessing it wasn't because the engine was running beautifully before. It's best to describe the symptoms of the problem clearly and completely rather than asking "why is my solution not working?" The reason you can't find a vacuum leak is probably because that is not what is causing your engine not to run. -jim > I tried spraying both WD40 and carb cleaner around the suspected leak > areas and did not find anything. [quoted text clipped - 27 lines] > > loose when I'm working in the engine compartment. It's so crowded in > > there I don't notice if one has been jarred loose. I was suspecting a vacuum leak based on simple troubleshooting charts, and based on the fact that the insulator did not seem to be making a good seal anymore. Another thing is that choking the carb further using a piece of cardboard allowed the engine to run instead of die, pointing to an overly lean mixture. If its not a vacuum leak, what could it be? There is no smoke out the tailpipe when I start it. The engine races to about 2500 rpm, runs for a couple seconds, and dies very quickly, and throttle does not help. It doesn't take that much cranking for it to catch, only a few seconds. I installed a different carburetor because the car would have trouble running when cold and failed emissions (NOx was over the limit). These two symptoms, along with a diagnosis from a auto clinic, made me believe there was some vacuum leak happening. Once i installed this carb, the car displayed the symptoms I listed above. Currently I put the original carburetor back in with a new insulator plate and the car runs but still isn't quite right. I had encountered a couple of broken hoses when i was removing the carb for the first time and was hoping that would account for the problems I was having. Unfortunately, now the car idles too high when hot (but at least it will idle) and adjusting the throttle does not help. i've been working on this car for almost a week straight and probably over 40 hours and thus have tried lots of things to fix the problem. >> I have checked the hoses and have not found any that are broken. I tried >> disconnecting the fuel line and cranking; a LOT of fuel came out. Its [quoted text clipped - 53 lines] > http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups > ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- > I was suspecting a vacuum leak based on simple troubleshooting charts, > and based on the fact that the insulator did not seem to be making a [quoted text clipped - 24 lines] > i've been working on this car for almost a week straight and probably > over 40 hours and thus have tried lots of things to fix the problem. Sounds like a plugged exhaust system. It would give similar symptoms to a lean mix because the air cannot get through the engine. Have a helper hold a hand over the tailpipe when you fire it. 2500 revs should push a good stream out the pipe. Does it have a heat valve in the manifold? Ran a compression test? SignatureSteve W. Near Cooperstown, New York > Another thing is that choking the carb further using a piece of > cardboard allowed the engine to run instead of die, pointing to an > overly lean mixture. If its not a vacuum leak, what could it be? BINGO! You have an exhaust system clog. Disconnect the manifold from the tailpipe and try again. When you reconnect it again, use stainless bolts and nuts and lots of copper gunk so it will be easier next time. --scott Signature"C'est un Nagra. C'est suisse, et tres, tres precis." >> I was suspecting a vacuum leak based on simple troubleshooting charts, >> and based on the fact that the insulator did not seem to be making a [quoted text clipped - 30 lines] > good stream out the pipe. Does it have a heat valve in the manifold? > Ran a compression test? The engine was rebuilt recently so I haven't checked compression, however it ran smooth on the highway when I had to initially drive it home. I'm not sure how much air should be coming out the tailpipe but its somewhat less than my 1985 Corolla. Thanks for the help. I will test this out today. -J > I was suspecting a vacuum leak based on simple troubleshooting charts, > and based on the fact that the insulator did not seem to be making a [quoted text clipped - 8 lines] > throttle does not help. It doesn't take that much cranking for it to > catch, only a few seconds. Ok That does sound like a lean condition. I assume this has a choke of some sort (besides cardboard) It sounds like you have not been able to run it long enough for it to run without the choke so if that is inoperative it could be the cause. Also if that was a carb from a junkyard where it sat and the gas was allowed to evaporate in the carb it could be pretty gummed up inside which might be the cause of the lean condition. > I installed a different carburetor because the car would have trouble > running when cold and failed emissions (NOx was over the limit). These > two symptoms, along with a diagnosis from a auto clinic, made me believe > there was some vacuum leak happening. Once i installed this carb, the > car displayed the symptoms I listed above. Your original problem could hve been timing and/or bad EGR now it sounds like you have messed up vacuum hoses and possibly messed up carburetor and possibly fouled spark plugs to also contend with. A vacuum leak could have been the original problem, but its doubtful that was the problem with the replacement carb. At this point you need to get everything back to where it was. If the the emissions were good all except the NOX that was most likely a plugged EGR. The problem running when cold is likely a completely separate issue. -jim > Currently I put the original carburetor back in with a new insulator > plate and the car runs but still isn't quite right. I had encountered a [quoted text clipped - 61 lines] > > http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups > > ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- >I have checked the hoses and have not found any that are broken. I tried >disconnecting the fuel line and cranking; a LOT of fuel came out. Its >definitely not starving for fuel. >I tried spraying both WD40 and carb cleaner around the suspected leak >areas and did not find anything. Whose idea was it that WD40 was a good product to use? It'll leave an oily residue everywhere you use it and that residue will be flamable. Use carb cleaner instead. It'll evaporate and leave no bad residue. Umm, we 'regularly' have to spray the 'insides' of our distributor caps when off roading in the Canadian bogs with a good 'water displacement' fluid and we use WD40. If it left a flammable residue, our distributor caps would explode. It 'does' have a flammable carrier when in spray mist form, but not once on the surface and liquid or evaporated leftovers, hence folks using it for vacuum leak detection. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > >I have checked the hoses and have not found any that are broken. I tried > >disconnecting the fuel line and cranking; a LOT of fuel came out. Its [quoted text clipped - 7 lines] > > Use carb cleaner instead. It'll evaporate and leave no bad residue. it will only be used for a diagnosing purpose... your not obviously going to find the leak and leave it there no!! your going to find it and properly repair it oily residues are normally cleaned after a repair.. why because we are professionals and we want the customers to keep coming back and a clean job is a good job. >>I have checked the hoses and have not found any that are broken. I tried >>disconnecting the fuel line and cranking; a LOT of fuel came out. Its [quoted text clipped - 7 lines] > >Use carb cleaner instead. It'll evaporate and leave no bad residue. >it will only be used for a diagnosing purpose... your not obviously going to >find the leak and leave it there no!! your going to find it and properly >repair it oily residues are normally cleaned after a repair.. why because we >are professionals and we want the customers to keep coming back and a clean >job is a good job. I'd rather not make the mess in the first place. I tried disconnecting the fuel line and cranking the engine and a lot of fuel came out. I dont think its starving for fuel. I also tried putting some cardboard above the primary barrel and effectively choked the intake while a friend cranked the engine. it started and ran much better, it was racing at idle and didn't quit. So im thinking that points back at a large vacuum leak? Thanks -J > Your symptoms are more likely fuel starvation than a vacuum leak. Even > with a vacuum leak, you should be able to make it run with throttle. [quoted text clipped - 44 lines] >>>> >>>> -J That would almost have to be the brake booster blown or it's line with a hole in it. Maybe the charcoal canister if it has it or PCV line open also. Mike > I tried disconnecting the fuel line and cranking the engine and a lot of > fuel came out. I dont think its starving for fuel. [quoted text clipped - 55 lines] > >>>> > >>>> -J >That would almost have to be the brake booster blown or it's line with a >hole in it. Maybe the charcoal canister if it has it or PCV line open >also. Take some clamps and clamp the hoses down. Does it start? Now start opening 'em. --scott Signature"C'est un Nagra. C'est suisse, et tres, tres precis." using wd-40 or starting fluid spray around throttle body and where carburator sits and where there are vacum hose connections.. if vaccum leak present engine should accelarate and rpms should go up, where ever it is that this happens thats where your leak is >Hi all -- > [quoted text clipped - 14 lines] > >-J Honestly, reaching here, but does your carb have a fuel-pump mechanical spring operated, mechanically [throttle pressing] activated feed system? I realize I am reaching , but do you have a pump plunger? Or a fuel shut-off valve? It is mounted on the carb, a diaphragm and spring inside a plate, that is activated [pressed] by a mechanical rod or lever when you press the throttle pedal. http://tinyurl.com/yxc878 SignatureKnifeblade_03 http://www.automotiveforums.com carb cleaner is best way to find vacuum leak..just don't spray on exhaust...unless you got a vacuum guage..if idles up when spraying you'll know your getting close too leak...... SignatureScrapper http://www.automotiveforums.com |
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