rumble when running
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From: hangtown
rumble when running
I have owned my '71 F100 for about 20 years. It is all original with 240/6 single bbl. carter. I have added electronic iginition and find it to be one of my better moves.
I have noticed since my recent tuneup that ol'blue seems to have a engine rumble when holding speed from 25-50 mph. I have replaced the dist. cap (thought it may have been cracked), rechecked plug gap (with age you seem to froget that they don't come from the store pre-gapped) and rebuilt the carb. Checked for vaccuum leaks (found none). I have messed with the idle screws so much that I think I wore off the threads. Any ideas where to look now?
I have noticed since my recent tuneup that ol'blue seems to have a engine rumble when holding speed from 25-50 mph. I have replaced the dist. cap (thought it may have been cracked), rechecked plug gap (with age you seem to froget that they don't come from the store pre-gapped) and rebuilt the carb. Checked for vaccuum leaks (found none). I have messed with the idle screws so much that I think I wore off the threads. Any ideas where to look now?
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Joined: Dec 2003
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From: hangtown
Wow, now this is help in buckets! I'll try to provide some answers. The rumble seems more like a miss rather than a thump. It is most noticeable when I step up the idle to around 1200 rpm and hold it there. The motor mounts are fine. The engine has around 100K since last rebuild. Please let me know what the vaccuum gauge should read when adjusting the curb idle. Again, thanks.
Post Fiend
Joined: Feb 2000
Posts: 5,130
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From: Brea CA
I had a 5.0 that did that and it was a burnt exhaust valve, try a compression test. It was like a lope, almost missing but not quite.
Barry
Barry
Last edited by BB; Dec 10, 2003 at 06:30 PM.
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From: hangtown
I want to thank all for suggestions. I started from scratch again and checked plug gap (ok) timing (only off 20 degrees!) and carb idle screws. After beating myself with my empty beer cans and resetting the timing to 6 degree BDC and adjusting the idle screw all seems in order. Its not too late to teach this old dog new tricks!
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