mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

[dennisvandiermen]

Here's a question from Holland. I bought an other boat with a 3.0 140 hp mercruiser 1981. The first time i went out the engine started perfect. When i went out of the harbour and the engine was on temp. i put the throttle down. The engine went out and after many starts it started. Then after a few minutes i put the throttle again open and it came in plane. But when the rpm reaches the 3000 it stucks and it looks like it's holding.<br />I replaced the sparks,ignition e.t.c. The engines runs better now on low rpm's but still i got problems with exceeding the 3.000. It looks like it won't get enough fuel.On full throttle it's holding back. I'll hope that someone can give me a few tips.<br /><br />Greetz from sunny Netherland !!!

 

[Wakeboarder141]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

If you have already done the tune-up stuff I would consider rebuilding the carb and check to make sure your propeller is the correct one for your application. When I purchased my boat it was severely over-prop'd and I couldn't even get up on a plane.

 

[dennisvandiermen]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

It's a 17" prop. When it's in plane the rpm goes up but will stock at 3000 and it's holding back. You get the feeling that the engine will run more rpm's but is just holding back.<br /><br />Let me know why you think the carb is in for a rebuild. Is there a way to check it ??<br /><br />Greetz Dennis

 

[cobra 3.0]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

Does the throttle cable activate the carb completely?

 

[dennisvandiermen]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

No, i did not check the cable yet. I will check it this week, because the boat is somewhere else. Also i'll check the compression so that i know if that's alright. On full throttle it's turning 3000rpm but the engine is not running fine. Below the 3000 no problems and running smoothly.

 

[John Boelte]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

I'm having the same problem (or similar at least); I'm leaning towards the wrong propeller....

 

[goodtimeguy]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

i'd check the points gap to make sure that you have the proper dwell, it should be listed on flame arrester cover. also check you fuel pump+the fuel filter. a plugged filter with do all sorts of bad things

 

[dennisvandiermen]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

We set the points on 0.2 and we have tryed 0.25 and 0.30 There was just a little difference between the settings and than most in the lower rpms. The problems always occure by 3000. The only thing that maybe wrong is the gap between the sparks. The guy which i bought it from said that the gap was already the right one. After messuring the gap it was 0.60. The cover says it has to be 0.35 so maybe that's also a problem. I'll also check the fuelline+pomp. Some tips were i have to look for by the pomp should be great.

 

[cobra 3.0]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

.60 gap is way off! .35 will definitely change things. I'm surprised it runs at all with an overly large gap like that!

 

[hoot]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

from other postings with related symptoms; check volts on ignition coil/replace ignition coil, these things break down with heat and a lot are being replaced this year. check output of alternator. check for exhaust restriction.

 

[dennisvandiermen]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

Today i talked to a car mechanic and he was also saying that the gap between the sparks to big is. He says that if the gap is to big it will run on low rpm but when you accelarate then you''ve got a problem. Wensday i'll go out for a test and check everthing. Also the dwell. I've got the special tool to test it. I put the sparks to 0.35 and see what happens. I'll let you know !!

 

[Boatist]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

Spark plugs should be .035 inches as you know and the points gap should be .018 inches. Also make sure the points spring is installed in the right way to give more pressure to the points to close, Or better yet hook up a dwell and make sure the dwell does not change as RPMS go up.

 

[dennisvandiermen]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

Now i see the problem. I'm from the Netherlands and we are using cm/mm. The tech. details on the cover are in inches......I've converted them to mm and now i'am seeing that the points have to be .04 MM and the sparks .08 MM. Hoping that it solves the problem.

 

[cobra 3.0]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

Actually, multiplying by 2.54, it's closer to .09 mm (exactly .0889) and .045 mm (exactly .04572). Engines using points and condensor are pretty picky about gap sizes.<br /><br />Come to think of it...so was my old 1989 Volks Jetta that had electronic ignition. Once the plugs were worn and the spark plug gap had increased from normal use, the engine wouldn't idle as well or accelerate smoothly until I reset the gaps...

 

[John Boelte]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

I just discovered that my tachometer is inaccurate. I've got a 17 inch pitch propeller, and top out at 35 MPH; going to get a 19 inch and see what happens! Check your tahcometer!

 

[glenn w]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

you need to set your points at .18. i had the same exact problem wouldn't get past 3000,repair manual told me to set points at .22 then found a website that said .18 boat now runs at 5100 rpms and screams across the water

 

[Rhadley]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

Be careful of your units. You don't mean .18 inches, and it can't be .18cm. You probably mean .018 inches.<br /><br />I will have to try the .018 setting on mine also. Book calls for .022" (.56mm).

 

[glenn w]

Re: mercruiser 3.0 140 hp won't exceed 3.000 rpm ??

i stand corrected , it is .018,forgot the o.and the manual does say .022 but ran across a web site that said it should be .018 so i tryed it and it worked,let me know if it does the same for you