stuck at 3k rpm (merc 3.0)

[slag]

I'm at a loss. I've rebuilt my carb and it idles perfectly, gone through a couple tanks of fuel, rechecked the carb, changed my fuel filter down by the oil filter, cleaned my points, set my dwell and timing, and still, I'm stuck at 3k rpm and about 30 mph on this 1989 Regal Medallion boat. Using a 17 or 19 degree pitch prop makes no difference, rpm stays the same. It will get up to around 3100 rpm when trimming, but no more.

Ideas? I'm stuck. The boat is firing on all cylinders and all plugs look good, but I'm about to change out the plug wires and plugs just because I can't figure it out. It runs smooth at idle and up to speed but stops short at 3k rpm. When looking down into the engine, the throttle plate is fully open.

Distributer cap and rotor look good as well.

EDIT: Two people or 5 people, it doesn't matter. RPM stays the same.

 

[EddiePetty]

Re: stuck at 3k rpm (merc 3.0)

(A) Check your tach with a portable unit

(B) Verify your speed with a GPS

(C) Verify full mechanical advance and correct initial advance

(D) Verify full fuel flow

(E) Check compression

(F) Don't forget to wipe your bottom!!

 

[Alpheus]

Re: stuck at 3k rpm (merc 3.0)

You didnt mention anything about the fuel filter in the carb inlet.

 

[slag]

Re: stuck at 3k rpm (merc 3.0)

You didnt mention anything about the fuel filter in the carb inlet.

That's part of rebuilding the carb (it comes with the kit)

 

[Don S]

Re: stuck at 3k rpm (merc 3.0)

Has it ever run at the proper rpm?

 

[slag]

Re: stuck at 3k rpm (merc 3.0)

Has it ever run at the proper rpm?

Not since I've gotten it. Weird, I know.

 

[amdburner]

Re: stuck at 3k rpm (merc 3.0)

I believe you have a tired engine. I am suffering the same problem with my 85 3.0L. The compression is between 120 and 130 across all 4 cylinders and it is blowing by badly as evidenced by the amount of pressure coming from the breather in the valve cover. The engine runs great but will not rev beyond about 3600 rpms regardless of prop pitch. Check your engines vent while it is running. There should be little or no pressure. Mine is bad enough that I could inflate a balloon with it if I tried. Hope this points you in the right direction.

 

[slag]

Re: stuck at 3k rpm (merc 3.0)

Heading out to the lake here in a bit, I'll do just that. Tired or not, it doesn't smoke or anything else and just plain runs well aside from not reaching max rpm.