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Posted By Discussion Topic: Carburetor Problems 1940-41     unclemark 07-28-2014 @ 8:00 PM reply profile send p.m. Member Posts: 84 Joined: Dec 2009 I have a carburetor that seems to have some kind of vacuum leak causing the engine to run very rough and rich. If I place something over 3/4 or more of the top the engine will run smoother and a bit higher idle. This would indicate a vacuum leak, however using either around the base and all surfaces no engine speed up can be found. (vacuum wiper port plugged/no leaks when running). No leaks anyplace around the intake manifold. There seems to be an internal leak of some kind. Throttle adjustment screw needs to be in almost all of the way in order to keep the engine running. Now here is the first kicker, I have 2 engines and the same thing happens on both, however I have another carburetor that works well on both engines seemingly eliminating any issues there. Next Kicker, I have close to $500 in various versions of these units that have been sent out for rebuilds and I still have the same problem. Bases and throttle plates have been milled, new throttle bars/bushings, power valves, you name it and I still have the problem At this point I just want a carburetor that works and may have to buy one at another $$$ but I am want to eliminate the engines and or vehicles further so I don't waste more money. I have been switching the one remaining unit from one vehicle to another when I need to drive either, this is a pain. Anybody out there have thoughts on this and or had this experience before? 41 panel & 41 1.5 platform pauls39coupe 07-28-2014 @ 9:11 PM reply profile send p.m. Member Posts: 205 Joined: Jul 2014 It seems you are running lean, which may not be caused by a vacuum leak. Partially blocking the air horn richens the mixture, same a pulling the choke. Use care blocking the air horn as you my rupture the diaphragm in the power valve. As you don't get any reaction by spraying ether on the outside, you probably don't have a vacuum leak. Most likely you have some crud in the jets or jets passages. Dirt/rust from the fuel tank or a flex line crumbling. The power valve might also be plugged, or incorrect for the carburetor. You will need to tear into it to be sure it is clean and that none of the passages are plugged. Return them to the rebuilder. If they were done by a pro he should make it right. supereal 07-29-2014 @ 5:07 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Look for a vacuum leak from a cracked or loose wiper hose or other post on the intake manifold, such as the line to the distributor, or the gasket under the lid of the snubber on the distributor. I've also seen problems when someone removed the piston from the snubber port in the distributor. By now, it seems you have eliminated the carb as the cause. unclemark 07-29-2014 @ 6:55 PM reply profile send p.m. Member Posts: 84 Joined: Dec 2009 Look for a vacuum leak from a cracked or loose wiper hose or other post on the intake manifold, such as the line to the distributor, or the gasket under the lid of the snubber on the distributor. I've also seen problems when someone removed the piston from the snubber port in the distributor. By now, it seems you have eliminated the carb as the cause. I plugged the wiper hose lead during the tests as well as the line to the distributor, (the distributor has been professionally rebuilt). This also does not explain why the same results happen on two vehicles and why when a good carb is put on both of those vehicles run very well. 41 panel & 41 1.5 platform This message was edited by unclemark on 7-29-14 @ 6:56 PM TomO 07-30-2014 @ 8:30 AM reply profile send p.m. Senior Posts: 7252 Joined: Oct 2009 Unclemark, Are you using a 91-99 Carburetor? Did you check the spark plugs for sooty black or wet deposits? On the 91-99 carburetor the most likely place for a vacuum leak is where the base mounts to the body. If you have a vacuum leak there, you will likely backfire under load. The fact that the throttle adjustment screw needs to be all the way in, leads me to believe that you re leaking gas past the power valve causing the mixture to be very rich and need to open the throttle plates in order to get more air. Tom pauls39coupe 07-30-2014 @ 6:20 PM reply profile send p.m. Member Posts: 205 Joined: Jul 2014 If you have a good carb that makes the engines run right, you have eliminated external vacuum leaks as a problem. Check the plugs to see if they are black from being too rich, or stone white from running lean. I would bet on it being lean as you say it runs better when you cover 3/4 of the air horn. As Tom said the power valve may be a source of your troubles, or the carb has picked up dirt or rust from the fuel system , and the jets or passages are plugged. Let us know what you find. If you have had them rebuilt, why not send them back to the rebuilder? They should correct the problem. unclemark 07-30-2014 @ 8:30 PM reply profile send p.m. Member Posts: 84 Joined: Dec 2009 Thanks guys, I am trying to reach the re builder now. I have some v/8 club members coming over to look at the situation this weekend, hopefully someone has a good answer to this strange problem. I will check the power valve again, someone stated that it can fail under the right conditions? 41 panel & 41 1.5 platform unclemark 08-03-2014 @ 7:26 PM reply profile send p.m. Member Posts: 84 Joined: Dec 2009 Go it figured out with the help of some v/8 members. Turns out that a phenolic plate I had installed has micro fissures/holes that open up and allow air to come in or a vacuum leak when using that carburetor. None of us new why the other carburetor did not cause any trouble. I pulled the phenolic plate off and put the unit on the way Ford intended and it works like a charm. I had assumed that the plate would last for ever but not the case, heat must have broken it down. Glad to have that problem solved. 41 panel & 41 1.5 platform ken ct. 08-03-2014 @ 10:46 PM reply profile send p.m. Senior Posts: 1513 Joined: Jan 2010 Thank you Mark. ken ct. TomO 08-05-2014 @ 9:33 AM reply profile send p.m. Senior Posts: 7252 Joined: Oct 2009 Another case of a modification causing more problems that it fixes. A properly rebuilt carburetor does not need the phenolic plate under it. If you are having "heat soak" problems, you need to recheck things like float level, power valve gasket and accelerator pump discharge needle seating. Tom

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