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1999 F100 Tapping Noise top end

B

big_rig

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"Having a tapping noise, sound

"Having a tapping noise, sounds like a stuck lifter. When first startup, something taps for about 5-10 secs then quits.

After running down lake, fish awhile, start engine, same tapping for about 5-10 sec then it quits.

Pulled the cowl, it sounds like it's coming from the top end. Am I on the right track.... Valve adjustment, stuck lifter??????

Which service manual would you recommend?"
 
"Try the fuel pump on the rock

"Try the fuel pump on the rocker cover, they seem to knock when there is not enough fuel in the system, normaly on first stat up if you have not primmed thr fuel bulb. The valves are shims on that model and a mission to adjust"
 
"It seems to tap at different

"It seems to tap at different times. It doesn't always start tapping when first started, maybe 5 sec after. Then will tap for different lengths of time. I tried decarbing the piston/valves through the spark plug hole, didn't help.

Somewhat sure the tap is comming from # 1 exhaust valves (steth-a-scope trick). I'm beginning to think its a weak valve spring. Any advice an this, the chances of a weak spring, how hard to change out?"
 
the odds of a yamaha having ba

the odds of a yamaha having bad or weak springs are very rare. the fuel pump is the first place to look if to much vaccum will make the engine tap its pretty cool to see. next time running the engine pinch off the fuel hose after about a minute it will start tapping and will get louder.see if this is the sound u here.
 
"JUSTIN - You nailed it. Afte

"JUSTIN - You nailed it. After many, I mean many trial and errors, I found the problem. The simplest things are often overlooked.

If I squeeze the primer bulb every time before start up, the tap is gone. If I forget the bulb, the tap reappears.

Amazing how the simplest things seem to be the hardest to find?????????"
 
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