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Posted By Discussion Topic: advance timing -- page: 1 2 3     sundog126 06-22-2020 @ 3:39 PM reply profile send p.m. Member Posts: 22 Joined: Mar 2018 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 mfirth 06-22-2020 @ 4:21 PM reply profile send p.m. Member Posts: 205 Joined: Nov 2017 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 sundog126 06-22-2020 @ 4:57 PM reply profile send p.m. Member Posts: 22 Joined: Mar 2018 all the above is correct carcrazy 06-22-2020 @ 5:08 PM reply profile send p.m. Senior Posts: 1587 Joined: Oct 2009 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. 40cpe 06-22-2020 @ 5:51 PM reply profile send p.m. Member Posts: 472 Joined: Jan 2010 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 sundog126 06-22-2020 @ 7:29 PM reply profile send p.m. Member Posts: 22 Joined: Mar 2018 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 carcrazy 06-22-2020 @ 8:03 PM reply profile send p.m. Senior Posts: 1587 Joined: Oct 2009 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. sundog126 06-23-2020 @ 6:44 AM reply profile send p.m. Member Posts: 22 Joined: Mar 2018 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 ? TomO 06-23-2020 @ 7:15 AM reply profile send p.m. Senior Posts: 7243 Joined: Oct 2009 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 carcrazy 06-23-2020 @ 9:30 AM reply profile send p.m. Senior Posts: 1587 Joined: Oct 2009 What does your vacuum test show? A sticking exhaust valve should show up as a fluctuating needle.

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