Mercruiser 140hp not running right

[bmiszuk]

I've got a 1974 trihull with a mercruiser 140hp. Last year I could get 4000-4500 rpm wot depending on the prop. Over the winter I took the boat to the shop and had the timing and carb adjusted (it would not idle properly and was difficult to restart). I tested it on the muffs and found it to start and idle well.<br /><br />However, at the lake last Saturday I could only achieve 3000-3300rpm and at WOT I would get a clicking or pinging noise. (I know what a ping sounds like on a car, but not entirely familar with the boat engine noises yet.) If I backed off wot the noise would go away.<br /><br />Though the shop says that carb and timing are correct, I'm wondering if the timing could be incorrect and causing this loss of power and noise? Last year after I bought the boat I set the timing / carb by fiddling with it until it ran well. I figured that taking it to the shop in the wintertime so I'd "get it done right". Should I just set it myself again? Any other suggestions regarding this loss of power?

 

[sculbert]

Re: Mercruiser 140hp not running right

My old boat had the same problem, it is probably the timming. The system had a electronic timming advance unit under the back of the boat. It has to be disabled or bypassed sometime to set the timming correctly. <br /><br />The other time I had a problem the ignition coil was bad.

 

[anesthes]

Re: Mercruiser 140hp not running right

1974 ? electronic timing? I dunno about that.<br /><br />I've noticed the specific gravity of fuel has decreased recently.. WIth the same atmospheric conditions, things tend to be running a little leaner than they used to. perhaps the next grade fuel is in order for you?<br /><br />-- Joe

 

[bmiszuk]

Re: Mercruiser 140hp not running right

Used 92 octane fuel from Amoco, the highest octane that's available.<br /><br />No, it's not electronic ignition, it's points. The repair shop said they set all that.<br /><br />Am I risking a lot if I just set the timing so that it runs the best?

 

[sculbert]

Re: Mercruiser 140hp not running right

Actually If you read my post I said electonic timming advance not electronic ignigtion. I have a 1973 that I just took a 4 cylinder out of it, it had a electronic timing advance unit stuffed under the engine compartment. It is referenced in my Mercruiser Service manual also. Its soul perpose was to provide spark latency depending on the rpms that it monitors. This had a tendency of causing people to not get the timming right because they would not have the RPMS low enough when checking the timming; so you got gain from the weights in the distributor and also advance from this unit and it just made life tough.

 

[sculbert]

Re: Mercruiser 140hp not running right

You can adjust your timming by vacume by adjusting it to peak vacum then backing it off by 1.5 inches of vacume. that usually works for system that have timming problems. That is how I adjusted mine to get around the problem with the electronic timming advance unit. FYI mine had Points also.

 

[bmiszuk]

Re: Mercruiser 140hp not running right

Merc Blues, thanks, makes sense. Sorry I didn't read carefully about the electronic part. What do you mean by "under the engine compartment"? Sounds like you're talking about the prop Where was it mounted in relation to the engine?

 

[hoot]

Re: Mercruiser 140hp not running right

what do you mean by "fiddling with it"? timing needs to be set using a timing light, you can also check for advance with light. my boat would run fine up to 3200 rpm and then cut out. could back off throttle and it would run good again. replaced ignition coil, problem went away. i don't have an electronic timing advance unit on my '78 250 IL6, so it's not on all engines.