| sundog126 | -- 06-22-2020 @ 3:39 PM |
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I have a 53 ford flathead rebuilt ,but once I installed it i found out the engine runs real rough, i put a vacuum gauge on the manifold and the needle jumps all over the place and pops out the exh when stepping on the gas, i tried changing the timing, looking for air leaks, blocking each carb (2)and readjusting the valves, i have no problem starting it ,but the machine shop went out of business that rebuilt it so i am on my own on this one.It does have a 4 inch stroke crank, 3/4 cam and bored .040 over with 2 carbs and hot spark coil and dist., anyone run across this before? maybe keep advancing the timing ? This message was edited by sundog126 on 6-22-20 @ 3:42 PM
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| mfirth | -- 06-22-2020 @ 4:21 PM |
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Be sure your plug wires are in the right sequence. Are you confident the shop put the correct valves in it? Timing of the cam gear & crankshaft correct ? Had a shop put the wrong valves in once....irradic vacuum and missing like crazy. Others here much smarter than i will surely chime in . Be patient...God willing, you will get it runnung just fine. mike
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| sundog126 | -- 06-22-2020 @ 4:57 PM |
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all the above is correct
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| carcrazy | -- 06-22-2020 @ 5:08 PM |
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Which "3/4 cam" do you have? If it is an Isky, and it is a 77-B or a Max1 it can probably be made to idle well and will provide a little more power than the stock cam. These cams get their power increase by using more aggressive lift curves without severe overlap. If it is some other aftermarket cam, it may have too much overlap to be made to idle smoothly. Use the instructions which came with the cam when installing and timing it with the crankshaft. Which distributor are you using? The stock '53 distributor has no centrifugal spark advance mechanism and is dependent upon venturi vacuum signal from the stock carburetor to provide the proper spark advance. I would check the cam timing to make sure it is indexed properly with the crank in accordance with the cam manufacturer's recommendations. It may be retarded which would cause the popping out of the exhaust.
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| 40cpe | -- 06-22-2020 @ 5:51 PM |
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Popping out the exhaust indicates crossed wiring or a stuck valve. You say you have verified the plug wiring to be correct. I would check for a stuck exhaust valve. You can run a compression check, or remove all the plugs, turn the engine over with the starter, and put your thumb loosely over each plug hole to verify forceful compression. If you find one or more with little/no compression you have found the culprit. This message was edited by 40cpe on 6-22-20 @ 5:53 PM
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| sundog126 | -- 06-22-2020 @ 7:29 PM |
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I did a compression test, looks good 140-145 each, I had my cam grinded thru a well know shop up north, mild grind for my engine, re adjusted my lifters same vacuum reading, the shop said they had to weld a small crack from the bolt hole to one of the cylinders, sprayed carb cleaner around the intake, no change in speed
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| carcrazy | -- 06-22-2020 @ 8:03 PM |
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Once you have checked all of the easy things, if you still have the problem, you could degree the cam to determine exactly what the cam events are. It may have too much overlap or late exhaust valve timing.
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| sundog126 | -- 06-23-2020 @ 6:44 AM |
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thanks I will go over everything and check the paperwork from the cam, would the compression test show that the valves are not sticking and sealing ok ?
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| TomO | -- 06-23-2020 @ 7:15 AM |
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Do a cylinder balance test to determine if the problem can be localized to certain cylinders or if it is a general condition. You description of the vacuum gauge readings, leads me to believe that it may be able to localize the problem to certain cylinders. Cylinder balance test: set rpm to around 1,000 and sort out one plug at a time while watching the tach. Each cylinder should show about the same drop in rpms when shorted. What carburetors are you using and what intake are you using? Which spark plugs are you using and what heads do you have? Did the shop weld the block or stitch it? Welding old cast iron is pretty risky. Tom This message was edited by TomO on 6-23-20 @ 9:54 AM
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| carcrazy | -- 06-23-2020 @ 9:30 AM |
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What does your vacuum test show? A sticking exhaust valve should show up as a fluctuating needle.
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| sundog126 | -- 06-24-2020 @ 4:13 PM |
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i'm using new Offenhauser 2x2 intake, tried blocking off each carb holes, tried a couple of plugs and diff. setting,i believed the shop welded the small crack in the block, also running Offenhauser alum heads, and hot dist and coil from summit, I think there brand. i will try the spark test, I have a video of my engine vacuum and poping but don't know what website to show it on.
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| sundog126 | -- 07-01-2020 @ 10:33 AM |
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shouldn't a compression test show if the exhaust valves are sticking ? i have good compression
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| carcrazy | -- 07-01-2020 @ 11:37 AM |
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Yes, a compression test should show if you have a valve sticking. I would focus on checking the timing. If you are sure you have the correct ignition timing then you will have to get into the valve timing. I suspect your 3/4 cam has too much overlap to allow the engine to idle correctly. Does the engine smooth out and run better once the speed is increased to 2,500 RPM or more?
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| 37RAGTOPMAN | -- 07-01-2020 @ 12:09 PM |
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Hi Recheck your ignition wires if are on right, condenser and point wiring tight,? wobble in distributor plate , or play distributor shaft ? is the dwell steady ? did you check if the timing is advancing , with a strobe timing light, if running dual carbs you might have to try different springs on the vacuum advance, a ball point spring is what a friend of mine had to do with dual carbs, and it worked on his 1950 FORD, not enough vacuum to advance the plate. with dual carbs, hope this helps, 37Ragtopman
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| sundog126 | -- 07-18-2020 @ 8:03 AM |
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I did a cyl. leak/bleed down test ,each cyl showed in the green 18-20% leak out of the dip stick hole which isn't much, like I said before compression test showed 140-145lbs on ech cyl ,still not sure why the vacuum test shows the needle vibrating 3-15 ins and still pops out the exh when rpms are increased,now i'm thinking bad cam grind or cam was put in off one mark. This message was edited by sundog126 on 7-18-20 @ 8:44 AM
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| sarahcecelia | -- 07-18-2020 @ 11:55 AM |
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My friend Bruce had a similar problem. Poor idle and vacuum bouncing all ove the place! He brought the car to me. I found out by finally taking the top off of his carbuetor, that one screw that holds the "pee" tubes was stripped, among other things,and the idle mixture adjustments would not respond correctly. I sold hom a perfectly good carburetor for $50, installed it, and adjusted the idle mixture screws,and idle speed. Vacuum is steady now, and It runs like "new" and I have fixed a lot of problems for a lot of Flat head owners; They nick named me "The Man." They say that I can fix any problem they have, and when I do; They say, "Your the man" Steve. I am just getting back to speed on these, as I haven't messed with a flattie much since was in my 20's, and that was 60 plus years ago!! I had a '50 in 1955,and fixed it all. I didn't have the cash to pay a mechanic! Regards, Steve Lee
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| 40 Coupe | -- 07-19-2020 @ 5:07 AM |
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A compression test will not always show a sticking valve. Big difference between starter motor RPM and idle RPM .
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| TomO | -- 07-19-2020 @ 8:23 AM |
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You need to do the cylinder balance test to see if the problem is isolated to one or more cylinders or is a random miss. Once you know that, it will be easier to isolate the cause of your problem. Compression vacuum and leak down tests all have their uses, but you should have an idea of what you are looking for before doing the tests. Your description of the vacuum test indicates the problem may be isolated to one or more cylinders and not a random miss, but you won't know until you do the cylinder balance test. Tom
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| sundog126 | -- 07-19-2020 @ 1:19 PM |
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that's for your input Tom, I am running 2 carbs, I removed and blocked off one at a time seem to make no difference, I did the cyl bleed down test on all cyl. 3 times to see if one of the valves were sticking, all cyl had the same loss ,that's why I am going to remove the front gear plate to make sure the cam is lined up with the gears ok ,sense the machine shop that did my engine is shut down I am on my own doing this.
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| TomO | -- 07-20-2020 @ 7:00 AM |
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A cylinder balance test is not a bleed down test and will give different results. You can tear down your engine to try to find the problem, but I am trying to help you get to the area of the problem faster. Tom
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| sundog126 | -- 07-20-2020 @ 7:54 AM |
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Thanks Tom ,I thought they were the same, I will look up a balance cyl test
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| JayChicago | -- 07-20-2020 @ 6:06 PM |
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Re-read TomO's post of 6-23-20. Tells you how to do the cylinder balance test.
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