Merc 140 with bad idle

[bmiszuk]

I've got a 1974 Mercruiser 140 that I need to set properly, but I've got questions about the specific techniques for doing this.<br /><br />I set the dwell using a dwell meter while cranking it over with cap/rotor removed. Is this sufficient or do I need to somehow check it with the engine running also?<br /><br />I set the timing to 6 degrees btdc (it was at 0). I assume I should recheck the timing after I set the idle, right?<br /><br />Now I see that idle speed is supposed to be set with the boat in the water, engine hot, in gear and idling. Am I just supposed to anchor it somewhere while I fiddle with idle speed and the idle screws? Seems a bit dangerous. Or I suppose I could just point her in a direction and set the carb before I hit shore! How do people normally do this? Too bad I can't set it on the muffs.<br /><br />Thanks.<br /><br />Bob

 

[jeff13601]

Re: Merc 140 with bad idle

Do you have friends or family? Take one of them with you. If you dont you could send me a plane ticket and I can steer the boat while you set the idle

 

[Don S]

Re: Merc 140 with bad idle

You can set the dwell while cranking, but it may not be the same when you start it. But at least you will know where to go and by how much for the next adjustment. The timing must be set after the dwell has been set, it also must be set at idle rpm.<br />After the timing is set, idle mixture and speed are set to specs. Timing and dwell will not change with carb adjustement. But the advance will cause the timing to be off if the engine is idling too high when you set the timing. Make sure the timing is set at the proper speed.<br />Also check the advance timing to make sure it's where it should be.<br />If you set the rpm in neutral at 700 to 750, you can check the idle when you take the boat out. If it's 50 rpm too high, go back to neutral and lower the rpm by 50. It's that easy.

 

[bmiszuk]

Re: Merc 140 with bad idle

Thanks, Don, that helps a lot. The book says it's best to set the idle using a vacuum guage. Where's a good place to hook it up? Or is it good enough just to turn the screws each way until the rpm's change and set them to the middle point. How critical is this setting?<br /><br />I already see that my idle was set too low. It was at 600rpm in neutral in the driveway, but a shop set it that way. It explains why it won't start when it's on the water unless I bypass the neutral start switch and give it gas.<br /><br />Sorry, Jeff, I'll have to decline your offer! I'm sure I can find a friend to drive it.

 

[jeff13601]

Re: Merc 140 with bad idle

I thought Id try. Good luck

 

[Don S]

Re: Merc 140 with bad idle

It explains why it won't start when it's on the water unless I bypass the neutral start switch and give it gas.

Now, we are getting to the real problem.<br />Hard to start is what your problem is right?????<br />Sounds to me like you don't realize you have a neutral only option on your controler.<br />You may have a seperate button that you pull out when in neutral, then move the throttle forward without being in gear. When you pull the lever back to neutral it automatically goes back to shifting the outdrive.<br />Depending on your shifter, you may have a button next to the control lever, or even a push button in the center of the pivot of the shifter.<br />When in the neutral only position you can pump the throttle to squirt some gas in the carb and also allow the choke to set. Without it, you may have an almost impossible time getting the engine going.<br />600rpm might be ok for an EFI engine, but it ain't gonna work on an old carbed 140.

 

[bmiszuk]

Re: Merc 140 with bad idle

Hard to start is what your problem is right?????

Yes. When it's cold, it will start easily but idle poorly. When it's hot, it will never start without me being on the throttle. When hot in neutral it gradually idles worse and worse until it dies. If I give it a little gas (and therefore shift it into gear) the idle smooths right out and it runs well.<br /><br />

Sounds to me like you don't realize you have a neutral only option on your controler.

You're right, I don't realize it! Tell me a little more about what I'm looking for. The handle for the shifter has no button on it, just a round ball. The center of the pivot appears to be a screw thread with a generic knob screwed onto it.<br /><br />I replaced plug wires this morning and should be able to get it on the water tomorrow night to finish adjusting it.<br /><br />I suspect the repair shop turned down the idle in response to my complaint about it running-on when hot. It helped the run-on but made it hard to start. And I had bad plug wires, incorrect timing, etc. Time for a full tune-up.

 

[Don S]

Re: Merc 140 with bad idle

Can you post a picture of your controller? Or email me one?

 

[Don S]

Re: Merc 140 with bad idle

Check the choke, if it's too tight, it will cause problems starting hot.

 

[bmiszuk]

Re: Merc 140 with bad idle

I'll take a picture tonight and send it to you or post it.

 

[bmiszuk]

Re: Merc 140 with bad idle

You may have a seperate button that you pull out when in neutral

Maybe a picture isn't even necessary. The center pivot of the throttle pulls out, apparently allowing me to give it gas without putting it in gear. I did not know this was possible. Should I need to do this commonly, in order to restart it?<br /><br />Thanks for all the help!

 

[Wotknot]

Re: Merc 140 with bad idle

After it's warmed up and providing everything else is in working order.....no.