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Bad idle

R

rowdy

New member
Have a 2000 75hp Merc. thats h

Have a 2000 75hp Merc. thats hard to start when cold and when it starts idles rough.Plugs have been changed.Took it to a mechanic told him the problem. He immediatly told me it was low compression. The compression was checked and it was 100psi in all three cylinders. He said that was low and it needed a ring job.I am kind of leery of this fast diagnosis.The engine runs and idles fine after it is warmed up.So what I would like to know is what should the cylinder pressure be and what might be the problem.Is this guy trying to perform work that does'nt need to be done.Any help will be appriciated.
 
"William,

Most mechanics, m

"William,

Most mechanics, myself included, hesitate to get involved in an attempt to make an engine run properly when the compression is suspect. Frequently, the result is a lot of wasted hours, and little if any improvement in performance.

When compression declines, it is not a good sign, although an engine can run well with compression in the 100psi range. When new your engine probably had compression in the 120-130 psi range. The problem is that most times the compression will continue to decline and the wear can cause more serious problems to develop. Right now you might get away with a gasket set and piston rings, which is not too bad.

If there is an easy solution to your problem, I would guess that the fuel enrichment (choke) may be the cause of the hard starting; the rough idle suggests poor idle mixture, poorly adjusted throttle plates, or maybe even a clogged idle jet. You could do these things yourself with a little help from an engine manual (available here).

Tony"
 
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