| LTim1947 | -- 02-14-2012 @ 12:07 PM |
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My engine was rebuilt a few years ago and the car was wrecked with only 500 miles on the rebuilt. I have gone through the whole engine and confirmed all is good. The distributor was struck in the wreck and required a new cap rotor,condenser and points - all of these are fine. Problem is the engine starts and idles just fine, however it will not accelerate. It has dual Stromburg 97 carbs Finned alum heads etc and is 12 volt. I only have 3 lbs of vacuum and suspect this is why it will not acceletate. The compresion is equal on all cylinders. I need suggestions on what I might do to regain vacuum. This message was edited by LTim1947 on 2-14-12 @ 12:15 PM
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| Pauls39 | -- 02-14-2012 @ 2:23 PM |
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I am surprized that an engine with vacuum that low will even run! You likely have a leak in the distributor housing or in the line from the manifold, caused by the accident. Those aluminum housings bend and crack easily. Your mechanical advance may also be stuck which would further kill the performance. It is possible your exhaust is bent or plugged from the wreck which would also cause a low vacuum reading, but my bet would be on a leak up front on the distributor vacuum brake.
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| Pauls39 | -- 02-14-2012 @ 2:23 PM |
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I am surprized that an engine with vacuum that low will even run! You likely have a leak in the distributor housing or in the line from the manifold, caused by the accident. Those aluminum housings bend and crack easily. Your mechanical advance may also be stuck which would further kill the performance. It is possible your exhaust is bent or plugged from the wreck which would also cause a low vacuum reading, but my bet would be on a leak up front on the distributor vacuum brake.
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| supereal | -- 02-14-2012 @ 7:42 PM |
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If the car was hit hard enough to break the distributor, I'd suspect that the intake manifold is broken, causing the loss of vacuum. If the leak is in the vacuum line to the distributor, the engine would run well, except it would idle roughly. Fiddling with the timing won't raise the vacuum that much.
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| Old Henry | -- 02-15-2012 @ 7:14 AM |
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My vote would be for plugged exhaust. Old Henry (The older I get, the better old looks.)
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| supereal | -- 02-15-2012 @ 7:57 AM |
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Another possibility is that when the front of the engine was damaged, the timing gear was damaged, causing an out of time situation.timimg gears tend to be fragile, particularly the fiber variety. Being just a tooth off would allow idling, but change valve timing enough to affect compression enough to produce the problem you report.
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| TomO | -- 02-15-2012 @ 8:15 AM |
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Post your compression readings. It will help to know if they are equal, but low or if they are normal. To isolate the problem, Drop the exhaust manifolds, or headers and take a reading. Then try removing the carburetors one at a time and block off the opening. Then try replacing the intake manifold with a stock manifold. Then remove the timing gear cover and examine the timing gear. We could guess all day, but it is better to try one thing at a time to isolate the problem. If a step does not make a change, restore the engine to the previous condition. Tom
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| LTim1947 | -- 02-15-2012 @ 10:41 AM |
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Wow,thanks for the response. Most of your suggestions have been checked, but I still have the problem. 1. The exhaust is new, as are the headers and mufflers. The output of the exhaust is uniform, both sides. 2. The timing gear is new and aluminum and flawless. 3. Timing gear cover is without cracks or blemishes. 4. The low vacuum is measured at the base of the first carborator. I think this rules out any timing issues. 5. Compression on all cylinders is balanced and 60 lbs. 6. The intake manifold has been set on a surface plate and does not rock. It appears to be without cracks or problems. This could have a crack that I haven't detected. 7. Being that the vacuum is created at the base of the carburetor, do you think I could have a venturie problem with both carborators? I appreciate your response. LJT
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| supereal | -- 02-15-2012 @ 12:20 PM |
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Was your engine ever run with the current dual carbs? Lack of vacuum and poor performance off idle can be the result of a mismatch between the CFM (cubic feet per minute) rating of the carb(s)and the requirement of the engine. In short, it means that there can be too much opening to the intake manifold. Most flatheads run best with a single carb rated at less than 300 CFM. If you put two of these on the engine, it has the effect of quadrupling the venturi area (square law) and lowering the vacuum at the intake. The engine would idle, as it is fed by the air bleeds, but off idle, the engine usually coughs and dies. You can test this situation by uncoupling the throttle of one carb. Stock flathead intake manifolds are divided, and feed four cylinders from each carb throat. Many multicarb manifolds have a "plenum" that feeds all cylinders. Setting up a multicarb installation can be very difficult. Sometimes progressive linkage can help. We prefer a four barrel carb with a CFM front venturi rating of about stock. The rear barrels don't open until the engine is wound up fast enough to produce necessary vacuum, allowing good low speed performance. If you are using a non stock cam, the installation becomes even more critical. Admittedly, multiple carbs look "cool", but unless the car is used for racing or other high speed driving, they are often a real headache.
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| LTim1947 | -- 02-15-2012 @ 1:24 PM |
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Thank you your response it is along with my line of thinking. I plan to block off one carb to see if this gives new clues. This car ran well prior to the wreck, with all parts being the same I have not looked for anything but the obvious. The fan bracket waw damaged in the wreck and could have sustained damage to the threaded hole in the manifold,I havent checked that. Thanks Lee Taylor Az LJT
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| supereal | -- 02-16-2012 @ 7:18 AM |
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Lee: if you bought the car wrecked from an insurance company, did they tell you that it ran well before the wreck, or do you actually know that it did? T here is something here that is odd.
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| TomO | -- 02-16-2012 @ 7:36 AM |
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60lbs of compression is very low, along with your dual carb set up,could account for your low vacuum. Valve timing could account for your low compression and vacuum. Make sure that the timing marks line up when no1 piston on the passenger side bank is at TDC. Tom
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| LTim1947 | -- 02-16-2012 @ 11:07 AM |
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supereal. No data available as it was bought at auction. This is a frame off resto. The chassis is completely refurbished and made as new as possible.I have removed all damaged engine components, It has new Bob Drake water pumps. Oh the rotating assemble is bright like new top and bottom. I did check the timing gear marks and they were aligned. I rebuilt the dist,after disassembly and cleaning,checking the bearings,etc and put in new points,gapped at 15 and reassembled with new rotor and condenser (cap), new crab cap,new wires. you name its got it. The carbs only appeared dirty,cleaned,checked the float and other obvioua things, new gaskets here also. Could I have put in a incorrect gasket blocking gas flow to the venture? This vehicle is stunning with a black chassis,aluminized high temp exhaust paint,red engine and gobs of chrome,finned heads etc. I am going to reconfirm the timing marks,recheck the dist and go to the carbs to see if i missed something. Thanks for your help I'll let you know what I find Lee LJT This message was edited by LTim1947 on 2-16-12 @ 2:36 PM
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| LTim1947 | -- 02-16-2012 @ 11:08 AM |
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No data available as it was bought at auction. This is a frame off resto. The chassis is completely refurbished and made as new as possible.I have removed all damaged engine components, It has new Bob Drake water pumps. Oh the rotating assemble is bright like new top and bottom. I did check the timing gear marks and they were aligned. I rebuilt the dist,after disassembly and cleaning,checking the bearings,etc and put in new points,gapped at 15 and reassembled with new rotor and condenser(cap), new crab cap,new wires. you name its got it. The carbs only appeared dirty,cleaned,checked the float and other obvioua things, new gaskets here also. Could I have put in a incorrect gasket blocking gas flow to the venture? This vehicle is stunning with a black chassis,aluminized high temp exhaust paint,red engine and gobs of chrome,finned heads etc. I am going to reconfirm the timing marks,recheck the dist and go to the carbs to see if i missed something. Thanks for your help I'll let you know what I find Lee LJT This message was edited by LTim1947 on 2-16-12 @ 2:52 PM
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| supereal | -- 02-16-2012 @ 3:20 PM |
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That still doesn't account for the low compression. I've seen some beautiful engines and cars that couldn't pull their own weight, Lee.
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| LTim1947 | -- 02-17-2012 @ 1:14 PM |
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Supereal: The car was being driven when the driver hit another vehicle in the rear. READING through the responses I am going to take the Dist and timing gear cover off and confirm again TDC and tinimg marks are alligned as well as the dist set ro fire cyl 1 at the right time. Stroker: The intake manifold is a Eddlebrock "SUPER' as it is embossed on the manifold. It does have a slot on the front for the fan bracket to slide into. If the timing search dosent cure things I then will remoce the intake and check again to ensure its flat and without any cracks or holes. I have never had the heads off as it has never seemed necessary (to date). I'll get this done on Sat with my fingers crossed LJT
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| 40cpe | -- 02-17-2012 @ 2:15 PM |
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One of these threads on the same subject needs to be deleted or abandoned
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| supereal | -- 02-17-2012 @ 8:23 PM |
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Lee: when we find a modern car with low compression that is fairly evenly distributed between cylinders, it is most often the result of the timing belt skipping teeth. Only one or two teeth can cut the compresion by half or more. Given the your car took a big hit on the front, probably when it was running, it is possible that either the timing gear, or the crankshaft gear, or it's key, was affected. That is why I suggested it several posts ago.
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| TomO | -- 02-18-2012 @ 7:52 AM |
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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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| shogun1940 | -- 02-18-2012 @ 6:43 PM |
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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???????
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| supereal | -- 02-18-2012 @ 7:01 PM |
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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
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| LTim1947 | -- 02-21-2012 @ 4:59 PM |
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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
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| TomO | -- 02-22-2012 @ 10:33 AM |
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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
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| supereal | -- 02-22-2012 @ 10:40 AM |
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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.
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| Stroker | -- 02-22-2012 @ 12:32 PM |
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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".
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| Pauls39 | -- 02-22-2012 @ 4:59 PM |
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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.
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| shogun1940 | -- 02-22-2012 @ 5:55 PM |
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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
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| 40cpe | -- 03-03-2012 @ 11:14 AM |
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Any updates on this engine problem?
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