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Posted By Discussion Topic: Engine with low vacuum -- page: 1 2 3     40cpe 03-03-2012 @ 11:14 AM reply profile send p.m. Member Posts: 473 Joined: Jan 2010 Any updates on this engine problem? shogun1940 02-22-2012 @ 5:55 PM reply profile send p.m. Member Posts: 464 Joined: Feb 2010 do you know how to do a cylinder leak down test?? put each cyl. on top dead center then pump shop air in. if you have a guage set up your allowed 10%, if you do not have a guage listen to where the air leaks out. oil fil= rings, intake valve leaks out the carb, ex. valve the exhaust, bubles in the rad. cracks or gaskets. I still question the sudden stopage of the enghine maybe which could twist the cam but we donot know what happened in the crash Pauls39 02-22-2012 @ 4:59 PM reply profile send p.m. Member Posts: 81 Joined: Oct 2009 Lee, I don't know which type of cam you have in your engine, but many early V-8s used a pressed on cam gear. You need to check the mark on the cam as it relates to the cam gear. Your cam and crank may still be in alignment, but the cam itself may have slipped inside the cam gear. Stroker 02-22-2012 @ 12:32 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 Lee: I believe the carburetor balancing device you described is probably a Uni-Syn. I don't believe it is necessary for you to need them to set your dual Strombergs. They were absolutely necessary to balance the "constant velocity" or "constant depression" variable venturi carbs used on many foreign makes, such as SU's, Solex's, Mukuni's etc. For your Stromberg carbs, basically all you need to do is make sure they are opening exactly the same. Start by backing-off the idle speed screws so the throttle plates are completely closed, and verify that by observation through the air horn. Adjust the throttle linkage so that they "crack" open simultaneously. Now go back and set your idle speed screws to provide the same opening for both. You stated early-on that the motor idles fine, but you can tweak the mixture screws by ear, or vacuum gage connected to the appropriate carb base. I don't believe your lack of vacuum is related to your manifold or carb adjustments. You cannot have good vacuum without good compression. True, a radical cam grind will kill both at low speeds, but unless you are running something like an Isky 404, or Potvin Eliminator, that shouldn't be the case. If your compression readings are severely low, you either have very poor cylinder sealing, or a badly out of time cam. I'm kind of running out of ideas here; but let me pose a couple of hypothetical questions. When the car was wrecked, your description stated front-end damage. Is it possible that the engine continued running (or was driven)after the accident? Is it also possible that due to loss of coolant, the engine severely overheated? Doesn't take too long to take all the temper out of the rings under these conditions, which might explain the low compression. I know I'm "grasping at straws", but I think we have to trace the problem back to the "event". supereal 02-22-2012 @ 10:40 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 If you haven't solved your low compression problem, it is likely that all the fiddling with the carbs won't help. The formula for determining carb size is as follows: engine cubic inches X highest RPM divided by 3,456= cubic feet per minute air. Thus, a flathead of 239 ci x 2,500 rpm div. by 3,456 equals a cfm of 173. Dual stock carbs will furnish a capacity of 692 cfm, far in excess of the capacity necessary for operable vacuum. As said earlier, I find it hard to believe that your engine ever ran well, if at all. TomO 02-22-2012 @ 10:33 AM reply profile send p.m. Senior Posts: 7253 Joined: Oct 2009 Your low vacuum reading is probably not the problem with the car not being able to accelerate. With your manifold, you are only reading vacuum from half of the cylinders. You have low compression and likely have a performance camshaft. If you are using a stock distributor, your vacuum brake will be active all the time. This will make your timing retarded when you start to accelerate. Have your distributor set up on a distributor machine and set the vacuum brake so that you have 32 degrees advance with 1" of vacuum. Maybe Stroker can help on the balancing of the carburetors. I am not familiar with the Edelbrock Super manifold. You could also check with Edelbrock about the distributor set up. http://www.edelbrock.com/ Tom LTim1947 02-21-2012 @ 4:59 PM reply profile send p.m. Member Posts: 11 Joined: Feb 2012 TomO Well I went back in and took off everything. The timing gear cover is perfect,no cracks,etc The timing marks line up at TDC on cyl 1. The timing gear and crank gear are like new and have no missing teeth or chips. They look perfect. The plug wires go to their proper plugs. I took the dist down to its simplest component. The counter weights work like they should and the springs are fine. The intake manifold is flat,starter spray did not cause any response. The float bowls are full of gas,the accelerator pump squirts gas into the throat. I have ordered a new timing gear gasket to reassemble these parts. I have had a friend who give me two carb top balance gauges.They have a glass vertical cylinder with a red ball in the cylinder. The throat is adjustable. How ever he has never used them and dosent know how to use them. Neither do I. What do adjust and for what are you adjusting. The only adjustment on the carb is the idle screws,is this what you adjust to achive a balance of the two red balls? I wont get my parts until next week. Mac says the are swamped with orders and are hiring. So for now Im off working on other parts of the restoratiion. Get back to me on these calibrators if you can. The intake manifold is a eddelrbrock super and as such it precludes me fron blocking off one carb as each carb feeds four cylinders. This is just more data about my low vac problem, Wnen I get this put back togther next week I'll see where I am then. Thanks Lee LJT supereal 02-18-2012 @ 7:01 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 True, but that wasn't the point of my example. I have seen damaged fiber timing gears skip, but if the coliision jammed the crank pulley, a sheared key is possible when the inertia of the crank twisted it, allowing the crank gear to move. We see those on modern cars when we have a timing problem. A partially sheared key throws the crank position sensor off. A vacuum leak would not account for the low compression reported. This message was edited by supereal on 2-18-12 @ 7:03 PM shogun1940 02-18-2012 @ 6:43 PM reply profile send p.m. Member Posts: 464 Joined: Feb 2010 you can check for a vacuum leak by using a propane or acetlene torch UNLIT any where a leak may occur. Your compression sounds low on a good eng.,, usually low compression across the board is timing , cam to crank.,. chains and sprockets jump but gears do not , that leaves twisting,,are you sure the timing is correct??????? TomO 02-18-2012 @ 7:52 AM reply profile send p.m. Senior Posts: 7253 Joined: Oct 2009 Lee, while you have the cover off, check the crank gear for wear. I have seen them where the front of the gear looks OK but there is quite a bit of crank movement before the cam gear moves. Tom

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