Idle Problem - 77' 1150

I've posted about this before so this may seem familair to the regulars. The problem I am having is that the engine starts beautifully when cold, and idles great for a while. When I take it out and run it, it doesn't want to idle anymore. The motor will only run in fast idle, and when I put it into gear, it dies. Otherwise, at all other rpm ranges, the motor runs perfectly when hot. It is extremely fast and smooth at wide open.

After thinking about it for a month, and processing all of your ideas, I believe I have a clue. I think that when it gets hot, the idle mixure no longer works. This tells me that it may be running too rich at idle (this is why it starts and runs when cold so beautifully).

It appears as though the idle screws allow air to enter the carb as apposed to fuel, yes? So, by turning the idle screw CCW, we will be letting more air in and, thus, leaning out the air fuel mixture. This should allow it to run better when hot, but not as well when it's cold. Sound good so far?

So, maybe I should back each screw (3 carbs) out half of a turn and see if it idles better when hot?

Is there a point where I could set it so lean that it burns up the pistons?

Thanks again all of your thoughts.

Re: Idle Problem - 77' 1150

Check the FAQ section of the forum. Go to the bottom and there you will find the link and sync for mercury inlines. I think this will help. Yes you can burn a piston if one carb is set too lean.

Re: Idle Problem - 77' 1150

Timing and Sync of Merc Inlines (to 1988) Read this post in the FAQ section

It is a good explanation and will help you along. I doubt you will set it too lean to burn it up at an idle however at high speeds it will cook.

Re: Idle Problem - 77' 1150

Pfoley, The idle screws are gas screws. CCW turns richen the mixture. BTW, I have had the same symptoms you have now. You need to lean out the mixture slightly. This adjustment will have no effect on the high speed mixture, since those jets are fixed. I would start with the bottom carb. Remember, it may only be the bottom carb that is necessary to adjust, since it (on my '77 1500) always runs a bit richer than the others.

Re: Idle Problem - 77' 1150

put it on the muffs in the driveway . adjust all 3 carbs at 2 3/4 turn out .even look into the cab barrels and see if the plates all open close to even . set the timming . use 40 t0 1 mix .make sure your carb jets are tightly screwed in . fuel pumps are good and a quick ohm reading on your spark plug wires , and a good clean fuel flow to the engine . should idle @ 800 rpm or so .

Re: Idle Problem - 77' 1150

Thanks everyone. I have read the lync & synch post many times. Unfortunately, it's beyond the level of my expertise and I don't have a tach or a timing light. If I had a tach, I would probably buy a timing light. Can I set the timing without a tach?

Chris, somewhere in my manual I read that the idle screws were air screws as apposed to gas screws. As you are a "Lieutenant Commander", I must assume you know what you're talking about so I will turn them clockwise to lean it out.

Somebody mentioned 40:1. Why 40:1?

Re: Idle Problem - 77' 1150

Your problem sounds as if it is in the first timing event. A linc & sinc will cure it. My engine would die while shifting and it turned out to be a timing issue. Once the timing is set and the carbs are set (roughly) then you can procede with the correct carb adjustments.

If you are trying to adjust the carbs and the timing is not correct the problem will not straighten out.

Timing lights are cheap at walmart and tack on another 10 bucks to buy a good friend lunch and you can get it done. It really is a 2 person procedure.