rpms drop, ...then hold steady

[jdcook]

I have a 1992 glasstream GXL 21', merc 4.3l 175 hp, my rpms only go to about 4000, then drop to 3500 and stay constant. Some times it does it and sometimes it doesn't. Also, shouldn't I be getting more rpms than 4000 at w.o.t. Thanks for any advice you can give me.

 

[pmgrape]

Re: rpms drop, ...then hold steady

I have a 1988 mercruiser 3.0L and had a severe RPM drop when the engine was warm last summer. I received some good advice and a lot of experience in engine diagnostics(I'm much better at diagnosing people than engines since I'm paramedic). My problem turned out to be major, a cracked head.<br />There are some standard things you could check. Since it's spring time I'd replace plugs @ wires, and if you have a distributor check/replace cap, points, and condensor and check timing. Check/replace fuel filter(s) and fuel/water separator. Another check for the fuel system,especially in older boats, is removing the pick-up tube from your fuel tank if it's accessable.<br />For your parts(plugs,plug wires,etc.)I've found NAPA to have great parts availibility for marine engines at prices that boat dealers cannot even come close to.<br />If none of this helps, do a compression check. I'm not sure the compression of your engine, but a little internet search or another post here should yeild results.<br />If you have low compression on one or more cylinders, it's time to pull the head(easy to pull and a pain in the butt to put back together) and send it to a machine shop for reworking.<br />Please keep us posted with this problem and good luck.<br />Brian

 

[Bondo]

Re: rpms drop, ...then hold steady

jd,<br />grape has the right Idea.....<br />Do a Full tune-up,+ engine Survey..... plugs, cap,+ rotor,+ timing.... you should have the T-boltIV on that motor.. No Points, or condenser....<br />check the Fuel system, Filters, Lines, Carb., etc... You need 5 to 6psi, At the Carb....<br />Compression check, should yeild 125lbs, to 175lbs... BUT, Not more than 10% to 15% difference between cyl.s.....<br />Your motor Should run 4400, to 4600rpms at WOT...<br />It Sounds like a fuel issue, But I could be wrong...