Merc 1000 revs to 3000+ RPM when should be idling

[Mercerman]

My 69 Merc 1000 hasn't been used for years. When I start it up, it revs over 3000 RPMs with the controls in the idle position. I rebuilt the carbs, but no change. The carb kits didn't have float needle seats. Could leaky seats cause this?

 

[Moody Blue]

Re: Merc 1000 revs to 3000+ RPM when should be idling

The problem lies in the throttle cable and/or throttle linkage. The throttle plates for whatever reason are not closing all the way. Could be the throttle cable is misadjusted or the throttle linkage is sticking after the years of sitting.

 

[Mercerman]

Re: Merc 1000 revs to 3000+ RPM when should be idling

The carbs are closed all the way. I have looked in the carbs and can see the flaps are completely closed where they should be at idle. The cable is disconnected right now and linkage is wired back, so it is not the problem. If I manually close the choke most of the way it will slow down, but runs rough.

Maybe I should say that I just bought this boat and have personally never run this motor. I was told it ran good a few years ago when it was last used. It started right up when I first tryed but ran fast like this. I then cleaned the carbs and put new gaskets in, but the kit I got, didn't have the float needle and seats (it's hard to find parts for this).

 

[daveswaves]

Re: Merc 1000 revs to 3000+ RPM when should be idling

If you are sure all three butterflys are closed at idle then it may be the distributor mechanism stuck. If for example it had been left sitting for those years with the throttle pushed forward, the spring loaded collar on the distributor may have stuck in the advanced position. Grease both grease nipples on the distributor and observe the action of the assemblies as you advance the throttle. Do not do this with the engine running.

 

[Crater]

Re: Merc 1000 revs to 3000+ RPM when should be idling

worn or sticky float needles and seats would either flood the carb or starve it either way they would have nothing to do with high idle rpms. Did you remove the idle adjustment jet(s) when you re-built carb(s)? If so you'll need to reset them to OEM specs then fine tune it to get the idle rpms correct. Could be a air leak in fuel line also. Dry rott of the fuel line is something to inspec for. Old fuel lines can look good from the outside but be shot in the inside, but that has nothing to do with the high rpms unless there's an air leak.

 

[Mercerman]

Re: Merc 1000 revs to 3000+ RPM when should be idling

It's not the distributor. I already took it all apart, cleaned and greased it because it was a little stiff (it had some hardened grease in it). All parts of the dist. work smooth.
The carb adjustment screws were set to specs but not fine tuned. Could be the fuel lines. I've never heard of air in fuel lines causing high rpms, seems it would cause the opposite, but I'll check it out since I'm out of other ideas.

 

[Crater]

Re: Merc 1000 revs to 3000+ RPM when should be idling

yea it's a guess but air in gas line could make the motor running leaner than it should so it's a maybe.
Have you done a decarb yet? Maybe some SeaFoam will clean err out.

 

[Moody Blue]

Re: Merc 1000 revs to 3000+ RPM when should be idling

What do you mean by "The cable is disconnected right now and linkage is wired back, so it is not the problem."

Are you checking RPM on a tach or "by ear"?

Can't see a lean fuel condition causing such high RPM at idle.

I would do a couple things at this point.

1) hook up a timing light and check ignition timing at #1 cyl.
2) screw the idle mixture adjusting screws fully in until lightly seated then back them out 1 1/2 turns.

Best approach would be to do a complete sync and link following the instructions posted in the FAQ section. That will address both ignition timing and carb linkage adjustments and set your motor up properly.

 

[Mercerman]

Re: Merc 1000 revs to 3000+ RPM when should be idling

Problem solved! I had been concentrating on a fuel/carburetion problem when it suddenly hit me. Slow idle is set by the distributor and not the carburetor and when I would back the screw out and turn the distributer as far as it would go it didn't slow down at all. So I threw a timing light on, turned the dist. idle screw out as far as it would go and put choke on enough to get RPM's down to 1000 and checked timing and it was at about 100 degrees btdc. So I checked the flywheel to dist. pulley marks and the timing belt was about 30 degrees off. How it even ran is amazing. The guy I bought it from must have put it on wrong or the bad fairies have been busy.
Anyway, thanks to everyone for their help.
Thanks Moody Blue, I figured it out on my own, but it seems you were onto it also I see.