Mercruiser 120, will not idle

[dugaloni]

I just bought 23 ft formula with twin mercruiser 120's. One runs sweet. the other has troubles. First fire up she would not idle. I did tune up. Still no idle (sni). Rebuilt carb., sni. Found water in oil. Replaced cracked head, and now have good compression, sni. Switched carbs, sni. Switched carb. and intake, still no idle. Now what, pull and rebuild? Possible water damage to camshaft or lifters?<br />Thanks for input,<br />Doug

 

[Ryoken]

Re: Mercruiser 120, will not idle

probably gonna need a more descriptive explanation of the prob. cold, no idle issue could be as simple as a choke prob or carb issue.. if it just falls off from a 1000 to 0 quickly, a vacuume leak might be the culprit. <br /><br />does it runs ok in the upper rpms? will it spin 3500?

 

[dugaloni]

Re: Mercruiser 120, will not idle

I checked with a vacuum guage, and there was no leak. The engine was warmed up (155), and will run a little rough above 1500 rpm. I have not run it up to 3500, So I can,t answer that one. When it dies it sounds like it is drowning out on fuel. When I did the vacuum test at one point I created a leak by pulling the hose off and it ran a little better but still died.<br />Totally baffled,<br />Doug

 

[Walt T]

Re: Mercruiser 120, will not idle

Does the boat have two fuel tanks? I'd double check the ignition points and timing and firing order. Go over basics first.

 

[dugaloni]

Re: Mercruiser 120, will not idle

Both engines are on the same tank. As soon as it stops raining down here in LA I'll go check all again. <br />Thanks,<br />Doug

 

[daveswaves]

Re: Mercruiser 120, will not idle

Hey Doug, the fact that it tended to perk up a little bit when you disconnected the vacuum line may indicate that it is getting raw fuel into the venturi, could be power valve in the carb. In your rebuild you should have had to replace a small ball bearing and spring in the carb. If you don't remember the spring and ball there is a good chance that corrosion has prevented it from falling out of the carb body.

 

[dugaloni]

Re: Mercruiser 120, will not idle

I have eleminated carb problems, because I have taken the the one off the engine that runs perfect and put it on the troubled engine. It still won't idle. The carb. I thought was bad works fine on the good engine.<br />Doug

 

[K Hultgre]

Re: Mercruiser 120, will not idle

What are the compression #'s (cold,hot)? <br />What do the spark plugs look like after it has been run, any of them wet or cleaner than the others (water in cylinder)<br />How old are the engines, how many hours, and has the manifold or riser ever been replaced or recently pressure tested.<br />Did you use marine gaskets when reinstalling the head, manifold, carb, etc.? (it does make a difference)<br />How did the timing chain look? Have you tested for excessive slop?<br />Did the tune up include points,cond.,cap,rotor,wires,plugs ?<br />Rechecked rocker adjustments?<br /><br />Sorry for the ? but trying to get a better idea of what is happening.