Merc 4.5 lacks power

[marion]

I have a 1975 Merc 4.5 that runs fine, but lacks power. It seems to be putting out about 2 HP. I've got an Evinrude 3 that will run rings around it. I've checked the timing, cleaned the carb, etc. and am out of ideas. Any suggestions?

 

[sloopy]

Re: Merc 4.5 lacks power

your main jet is to lean, unscrew in a little bit until your normal! good luck!

 

[marion]

Re: Merc 4.5 lacks power

Good suggestion, but main jet is fixed.

 

[sloopy]

Re: Merc 4.5 lacks power

how positive are you? unscrew it all the way whenrunning (gas will poorout) and see if that makes a difference

 

[Bear]

Re: Merc 4.5 lacks power

Is it a one cylinder 4.5? Do you know the history of the engine, overheating problems and now less compression? Did this just start or has it been like this since you bought it? Do you have a good spark? Are the points set correctly?<br /><br />I think the air mixure screw might need some adjustment. But I don't know - yet...<br /><br />You should be flying past that Evin 3!

 

[12Footer]

Re: Merc 4.5 lacks power

If it acts like it's running normally, proper RPM and all, but doesn't seem to push the boat as it should, check that the hub has not "spun-out".<br />It will act like a car lossing traction on a slick road.<br /><br />Other than that, try switching gas tanks.Look for loose connections on the fuel line ,or other small cracks/holes in the fuel line. Check that the carb mo8unting bolts are tight. Also, if you didn't use a new gasket when R/R the carb, remove the carb and install a new gasket. You can make one from gasket material available at auto parts stores for a whole bunch cheaper.<br />But trust me, this is a common oversight,as the original gasket "looks fine". But they will rarely seat the carb properly a second time.

 

[rickdb1boat]

Re: Merc 4.5 lacks power

If it's a 2 Clyinder, you may be only running on one! Check for good spark on both cylinders, if it is indeed a 2 Cly.

 

[marion]

Re: Merc 4.5 lacks power

Thanks for all the ideas. Yes, it's a fixed main jet - I've had the carb completely apart and the jet in my hand. It's a single cylinder. I don't think it's an air leak/fuel problem as squirting extra fuel in the carb throat just bogs it down.<br /><br />It has a unique ignition system for a single cylinder motor in that there are high and low speed generating coils. Both test OK according to the manual, but it also says that poor high speed performance can be caused by a bad high speed coil. Anyone have any experience with this setup?

 

[12Footer]

Re: Merc 4.5 lacks power

Is that the stator coils? If so, the setup is very common.<br />And yes, it can cause the symptom.<br /><br />What was the compression?