Mercury 45 random idle issue

[sportsmanphil]

Once in a while this happens, did it again today.

Ive been running the boat several times a week and an issue came back up again today.

Motor runs 100% and then all of a sudden it doesnt want to idle low or in neutral. It stumbles and will die. Will not crank back. If I lift the fast idle it will crank and I have to drop the fast idle and push it into forward quickly. I have good spark. The prime bulb is tight.

When it done this in the past it was fine a few days later on its own.

Today, when I got it out of the water I took the lid off the engine and found a lot of fuel all over the carbs and even running down the LU.

Any ideas at what would cause a random low idle or low speed issue with the carbs and fuel coming out of the carbs?

 

[Laddies]

Re: Mercury 45 random idle issue

The inlet needles are leaking causing both problems

 

[sportsmanphil]

Re: Mercury 45 random idle issue

Thank you for the reply,

Are you refering to the needle controlled by the float?

The book I got with the boat is for a 1972 - 1987 and my OB is an 1989. There are several carbs listed in the book, one is close but has a integrated fuel pump (which mine does not have).

The carbs were went through last fall by some boat repair place. Guess he didnt do that good a job but the carbs were fitted with a rebuild kit at that time.

Let me know whats wrong in my thinking here: If the needle is sticking open, that would explain the excessive leaking fuel. But wouldnt the needle need to stick closed to cause the no start/idle issue?

 

[Laddies]

Re: Mercury 45 random idle issue

If the carbs are torn down and the float level are off and your sure that they were set to to proper height last fall, I will bet the inlet needles have black tips and the trouble is fuel not bad workmanship, If the needles are Mercury and not aftermarket you can reset the height and it should be fine, that also works on some aftermarket needles. The newest tips are almost the same color as the needle it's self and look like the needle is a steel needle. The silver needle has a different material on the tip and is more resistant to fuel additives. we went through the problem at a race last fall and changed 3 sets of needles on 2 different engines to get through the 1 day of testing and 2 days of racing. To make it even worst the fuel pasted the APBA Stock Outboard fuel test. So I think we all are in for problems this summer.

 

[sportsmanphil]

Re: Mercury 45 random idle issue

Interesting........


I wll pull the bowls & Floats and check the needle tips over the weekend.

Thanks for the help Laddies.

 

[sportsmanphil]

Re: Mercury 45 random idle issue **Update**

Re: Mercury 45 random idle issue **Update**

I pulled the carbs, floats and needles as Laddies suggested and they were the kind with black tips.

I picked up factory needles today (all silver) got home and installed them. One float was perfect and the other was a bit off. I set the floats as per the book.

Primed the bulb up tight, threw the muffs on it and fired it up. It ran for about 20 seconds and the RPM's started to fall to a base and it wanted to cut off again. I gave it a small bit of fast idle to help it warm up a bit but it never wanted to idle on its own.

Now most are going to suggest adjusting the carbs, but 85% of the time it runs like a sewing machine, just hums along perfectly. The way I see it, if it can run perfect as its set then I shouldnt start monkeying with the carb settings.

Any suggestions why this thing wont idle at random times? I am going to try to hit the lake for some high speed/load testing tomorrow, but as I stand now, the idle is still a random issue.

 

[sportsmanphil]

Re: Mercury 45 random idle issue

Anybody?

 

[matt9923]

Re: Mercury 45 random idle issue

sounds like an air problem? It runs fine everywhere except idle rite?
Does it caught or spit? You say it will run on the high idle but not low enough to shift?
You had the carb rebuilt so. Maybe the needle seats are leaking?
Ya the gas keeps causing more problems....
Matt

 

[sportsmanphil]

Re: Mercury 45 random idle issue

Its back and forth......no idle one day,,,, hard to get on topend the next. Then it might run 100% perfect for a week.

The inlet needles were replaced with factory needles yesterday......still dont want to idle.

 

[Mercitus]

Re: Mercury 45 random idle issue

Sounds to me like it's dropping a cylinder intermittently and it's hard to tell when it does because these older mercs run so smooth, especially if it's the 4 cylinder version. Mine did the same thing and it sounded like it was hitting on all four. Then I felt the spark plugs and one was barely warm while the others were hot. Run it until the water comes out warm out of the pee tube, shut it off and feel the spark plugs. I know this sounds simple but best to check these things first and to know which cylinder is effected.

Also, when you changed the float needles, did you go ahead and clean the idle mixture and main jets? A good indication is when there is no change in the idle when you adjust the air mixture screws when it's running.