Re: F-20 missing issue for you advance problem sol

Posted by lee on June 12, 2004 at 09:16:11 from (24.24.95.246):

In Reply to: F-20 missing issue for you advance problem solvers posted by Pete L on June 12, 2004 at 06:33:26:

Since you have swapped carbs and mags and the problem remains I will assume (and I hate to make assumptions) the problem is not there. You should pull the intake manifold and check it carefully for cracks and for uneven surfaces or leaks at the head and at the carby. This is easy and you need to be absolutely sure it is not leaking or cracked. Next I would do a very careful compression test, writing down the numbers, same number of strokes each cylinder, all spark plugs out, no leaks at tester, carburetor removed, or at least the air cleaner and throttle wide open, looking to see the compression is very good and consistent on each cylinder. Beyond that I'd be looking closely at the cam and valve train. You don't mention the cam at all. Have you inspected it closely? Are there any worn lobes. You can remove the valve cover and measure the lift at each push rod. I don't know the spec but they should all be the same. Verify each and every one.
Check all pushrods to insure none are bent.
Many times a head builder does not get the valve geometry correct and consistent when he grinds and replaces valves. If the head is not re-done correctly the valves can be too deep in the head. The stem will stick out too far on top side and the rocker will be rolled over to cam side too far. Valves will open too soon. There should be a spec for the correct dimension from tip of valve to spring seat surface or similar dimension for a rebuilder to make adjustments and get the head to spec on all valves. All the valves should be checked to be in spec and free of travel, no broken spring coils, etc., etc. At this point, with all the things you/ve done it's time to start from scratch and not assume you've done this or that and it can't be this or that.
You've got to re-verify everything. I did not mention cam timing. It doesn't sound like you
have been in there. Odds are someone else has
so it may not be right, who can say?

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