I have a very general engine tune up question. My 250 has a 'miss' in it. I used to think it was only at idle but last night I ran it at high rpm and noticed it then also. I have done a complete tune up plugs/wires, points, dist cap, rotor. Also has a rebuilt carb. I checked the timing and its good. Dwell is within spec., replaced all the vacuum lines. The engine only has 40k miles on it. The only thing I have not replaced is the coil but I don't see how it could be at fault. Any suggestions?
Probably not the coil. I'm assuming you had the miss and then replaced all the listed components in an effort to eliminate the miss? Where can you find an old oscilloscope when you need one? With a tachometer connected and the engine running at idle, I would begin diagnosis by pulling one plug wire at a time and watch which cylinder has the least RPM drop. The cylinder with the least drop is your cylinder with the miss. You can then begin diagnosing that individual cylinder.
It ran pretty bad when I first got the car back in May, so I jumped right in and did all this tune up work but it turned out that the carb was the main problem, so I installed a nice rebuild and it then ran nice except for the slight miss. So its hard to say if it was there before the tune up or not. Your plan sounds like a great place to start, I will try that on Monday when the rain stops around here. Also, I have a very old O-scope at work that I can borrow and maybe give that a try as well. Thanks for the help.
another possibility though with the mileage I doubt it but anything is possible you could possibly have a weak valve spring or a rocker loose just a hair good luck
You didn't mention if you performed a compression check. 40K miles and over 40 years, check the basic parts condition, think simple, have fun ... The 250 is the stroked version of the 200 small block six with more available (low end) torque than typical stock 302. The inline 250/C4 was 70's Ford 'replacement for displacement' in the durability and MPG challenge with TB3. With a little help, the anvil-strong 250 easily can handle additional power adders.
Powerband, A little off topic. I thought the 200 was a bored out 170. The 250 was a different block with a taller deck height to get the added displacement. Fillcm, How are the fuel filters. An old tank may be sucking up a little junk. Test the fuel pump output and pressure also. Micah
Actually the 170 is a bored out 144 with only 4 main bearings. The 200 has 5 freeze plugs on starter side (right) of engine and 170 has 3. I had a 71 Maverick with the 170 and 3 spd toploader. The 200 starting @1965 has 7 main bearings allowing large increases from stock power with a rock solid bottom end. The 200 and 250 share same Cylinder head and most reciprocating parts except longer rods for the taller block deck (@1-3/4").The 250 is same as 302 V8 for Flywheel, Bellhouse, Starter, Clutch, Tranny, etc have fun 250
