| nelsonford | -- 10-07-2017 @ 12:31 PM |
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My 48 Merc still runs rough, surges and bucks in lower gears and runs rich. Plugs carbon up. Adjusted carb many times. Lowered fuel level twice after adjusting to spec level. Rebuilt disributor. Rebuilt coil from Skip Haney. Vacuum is plugged to wiper motor. Runs at 180 degrees. Didn't check compression yet but was rebuilt at some point. Has updated oil pump. My uncle's original low mileage 40 Ford convert runs so nice and smooth . Merc used to run great when I had dual carbs on it. But took them off later after problems started. Carbs also leaked but now fixed that. Any ideas would be appreciated. Thanks, Jeff
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| supereal | -- 10-07-2017 @ 1:05 PM |
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Test with a vacuum gauge. It is the quickest and most reliable diagnostic tool. If it shows repeating drops, then a return to normal, it can indicate a sticking valve, fluctuating fuel/air mixture, head gasket leak, weak or broken valve springs, exhaust restriction, or incorrect valve timing, and other related causes. If you don't have the chart, I can post one.
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| nelsonford | -- 10-08-2017 @ 7:17 AM |
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Hi Supereal' I found a chart in a 1949 Autos repair manual and and a copied Article "Tune-diagnosis by vacuum Gauge" by Joe Petrovec" ( a hot rod guy) each having a dozen or so different tests. Some being what you have mentioned like most of the leaks and valve timing and ignition timing. These are not relating to Ford v8s if that makes a difference. Thanks very much, Jeff
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| shogun1940 | -- 10-08-2017 @ 10:16 AM |
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Start with the vacuum guage, 18 to 20 inches at idle, drops down when you open the throttle and comes back up to steady reading at 1500/ 2000/2500. Now put a long hose on it and go drive it. The readings should be close to the same. To find a vacuum leak use an unlit propane or acetylene torch, wave it over the carb and then along the manifold to find any leaks.
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| nelsonford | -- 10-08-2017 @ 7:05 PM |
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Thanks very much shogun Jeff
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| TomO | -- 10-09-2017 @ 7:41 AM |
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Jeff, If you are running rich and your plugs are fouling, have your carburetor rebuilt by Charlie in NY. Contact him at: cas5845@yahoo.com Your Merc has all of the symptoms of a leaking power valve. This could be because the power valve gasket is leaking, the power valve is leaking or the vacuum chamber for the power valve is leaking due to a warped casting. Tom
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| nelsonford | -- 10-10-2017 @ 3:22 PM |
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Hi Tom, I was very careful trying to insure (visually) that I had used the best washers and correct fitting power valve and even changed to the triangular id as was suggested to me. But I will be happy to go through that exercise again hoping you are right. Thank you Tom. Jeff
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| TomO | -- 10-11-2017 @ 7:35 AM |
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Jeff, you may have problems with the casting for the bowl or base. Charlie NY checks these out and makes sure that there is a good sealing surface for the power valve gasket and the base gasket. The carburetor needs good vacuum in order to keep the power valve closed at steady speeds, so the bowl to base gasket sealing is important. It is also important that you have the correct power valve. If you have a racing cam, you will have lower vacuum than stock and need a valve that will stay seated at the lower steady vacuum. If you have a racing cam, look for a 5.0 or 5.5 power valve. With a stock cam, I like the 6.0 or 6.5 valve. A lot of the kits come with a 7.5 or 8.0 valve and they can open under steady engine rpms and give you an unwanted rich condition. Tom
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| nelsonford | -- 10-11-2017 @ 5:39 PM |
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Hi Tom, I checked out the Merc tonight so I could tell you the latest situation with the car. The power valve I had in the carb says on it 145 (it was supposed to be 45 or 4.5. I put clean ngk plugs in the motor prior to a driving the car on Saturday. I checked out a couple of plugs tonight and found them clean after driving about 6 miles on sat. I guess I should get a new 6.0 or 6.5 p valve and try it again. If I were to put the Dual carbs back on would the 6.0 or 6.5 be good for the carbs? Thank you Tom, Jeff
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| TomO | -- 10-12-2017 @ 7:10 AM |
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If you have 4.5 power valve in your carburetor, you should not be seeing it open at steady speeds, unless there is something wrong with the power valve or the carburetor. All my experience with multiple carbs was in the 1950's and we used Stromburgs then. Here is a link to a good vacuum gauge chart. http://www.secondchancegarage.com/public/186.cfm Scenario 15 can also be caused by fuel leaking into the venturi. Tom
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| nelsonford | -- 11-05-2017 @ 7:03 PM |
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Tom, Still working on the 48 Merc coupe got a 6.0/6.5 power valve as you suggested from Napa/Echlin. I found the Echlin part no 2-42266 in Dick flynn's Tech Tips book and have it installed. Motor runs a little better I think but had a hard time starting it later. I might have flooded it because it started right up a couple of hours later. I also bought a vacuum gauge to do some testing as Supereal suggested. I will give Charlie in NY a try next. My appreciation to all you guys. Jeff
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