78 Merc 140 missing on load

[LongLaker]

I've inherited a 1978 Mercury 1400 140hp in-line 6 engine. It seems to idle fine (I can get it up to about 2000 rpm using the idle lever). However, when I put it in gear I can certainly tell its missing on at least 2 cylinders. It boggs down and certainly does not have enough hp to pull skiers. I can only get about 1000 rpm under load in this condition.<br />I've cleaned up the carbs and checked all the fuel lines and that all looks pretty good. It starts really well on the first crank all the time.<br />I've changed the spark plugs as well with no luck.<br />I'm starting to think it may the timing, but I've never adjusted it on these motors before. It looks like the distributor cap actually moves as you throttle up/down.<br />I've heard about carburetor sync may be the issue as well. This motor has 3 of them servicing the 6 cylinders.<br />I'm not sure what other electrical components may be causing this issue. I've looked at the spark plugs wire and a few may be questionable at the distributor end. I may try and fix those next.<br /><br />Any help/hints would be appreciated.

 

[crazyray2]

Re: 78 Merc 140 missing on load

1st you need to check compression on all 6 cylinders....if good you can try to isolate which cylinders missing by pulling plug wires off one at a time and see if makes difference in running of motor.. then you know where to concentrate.<br />good luck

 

[LongLaker]

Re: 78 Merc 140 missing on load

Thanks for the input. The person who loaned me the boat for the summer assures me that he had the compression checked last year and that it was O.K.<br />I tried the spark plug wire trick and I know from first hand experience (don't ask) that we are getting spark to all the cylinders but no power from at least 4/6 cylinders under load. When I changed out the spark plugs the top 4 plugs were "wet" you could see gas/oil mix residue on the plugs in those cylinders. The bottom 2 plugs were "dry".<br />For an experiment I sprayed in some starting fluid into each carburetor. When I shot some in the top carb (for top 2 cylinders) it immediately flooded out and the engine stalled out. When I did the same thing on the middle carb it little effect under idle. When I tried it on the bottom carb/bottom cylinders it really fired up the cylinders like it should with a shot of starting fluid.<br />Any insight would be appreciated.

 

[Yepblaze]

Re: 78 Merc 140 missing on load

Pull the lower carb again. Get in there and really clean out the jets. Unscrew them and look through them and make sure they are open. Spray some carb cleaner through them and see that it flows well before reinstalling the jets. Sometimes above the main jet is another brass section that unscrews called an emulsion tube with holes around it's sides that needs to be checked.

 

[LongLaker]

Re: 78 Merc 140 missing on load

Thanks for the tip Yepblaze. I followed your idea and cleaned out the jets in the bottom carb and she's firing on all cyliders now. Its hitting top RPM around the lake now.<br />I think I still have a little work to do though. After cruising around the lake a couple of times at almost full throttle, when I slow down back to around idle speed and then try and take off again it seems to take quite a while to get back up to high RPM. Definately not good enough out of the hole for skiing. It sounds/feels like its running really rich at this point. Eventually it does wind up back to high RPM. I know I need to adjust the idle mixture screws because it idle's pretty rough and slow. My thought is that the idle mix is too rich and when I slow down from full throttle it gets a bit flooded because of this and takes a while to air out to get back up to cruising speed.<br />Another issue may be the Gumout I put in the gas tank last week to try and clean out the systems or perhaps I'm still running on some old/poor gas which is not letting the engine fire well as lower speeds. <br />Thanks again for your help.