To lean or to rich

[stevehendo34]

My 90hp tower won't start well when cold. Will if I spray forging oil in cylinders. Willl idle fine when cold, but extremely low idle when warm and kill. Pumping bulb dose not help.. Would you guess it is set to run too lean or too riich with idle screws two carbs.Timing OK.

 

[Chris1956]

First of all, all towers are hard to start when cold. Set the cold start lever all the way up, hold the choke button down and crank her until she fires. It makes sense to make sure the choke is working.

Is your idle speed set to spec? I would expect that motor to run at about 900 - 1000 RPM in neutral, when warm. You can turn the idle stop screw a bit to achieve that. You do have three carbs, right?

 

[stevehendo34]

My choke are working, I know how to take cowling of the motor.

I stated it has 2 carbs in the first post. It also has a distributor.

The question was meant to be if it idles OK when cold and dose not idle when hot and you must pull up on the lever to keep it running is it running lean or rich at idle when hot?
Both times while idling in neutral with chokes off.

"Not the idle stop screw to achieve the idle.
The mixture screws on the carbs them selves
That'the question which direction CW, (leaner) or CCW, (richer) depending on the lean rich answer.
I know you try the top carb first.

Forget the fuel pressure, linkage, timing and idle stop.
If I know if is running lean or rich when hot I can make adjustments to these to help eliminate my problem!


"Set the cold start lever all the way up, hold the choke button down and crank her until she fires"
Forget that it just complicates the issue I am having.

 

[Chris1956]

OK, sounds like an inline 4 cylinder motor, older than 1976. On a normal engine, if she idles when cold but not hot, the idle mixture is too rich, however, Merc Inlines usually do not have this issue, as they like an overly rich idle mixture.

Set the idle mixtures 1.5 turns CCW from lightly seated. CCW turning richens the mixture. Now warm her up and water test her acceleration. If she stumbles, open the top carb 1/8 turn and retest. Follow with bottom carb, and retest. When you have reasonable idle, and smooth acceleration you have them adjusted properly.

My advice on how to start that motor is based upon experience. I did not make it up.

 

[stevehendo34]

OK thanks the 90 is a pre 78 inline 6 with 2 carbs. They are just detuned 115s with one less carb.
"she idles when cold but not hot" the idle must be the idle mixture is too rich if that's what you think.
First I'll try and run the top carb screw a 1/8" inch CW, (leaner) to see if idle improves or gets worse.
You never know I guess if the last mechanic set up the idle screws when cold.
It dose not stumble now at all when warmed up just won't idle.

Thank You For Your Answer

 

[Chris1956]

I never heard of an inline 6 Merc with two carbs. I sure would like to see a picture of it...

 

[stevehendo34]

https://www.youtube.com/watch?v=t9uGC8GwowcIt's 2 ours away possibly has 3 carbs, but I remember 2
https://www.youtube.com/watch?v=MW-jxQgUyjA
Dose not really matter much the fact that you said its running rich if doesn't idel when hot is what I wanted
Thanks again

It dose have 3 carbs
https://www.youtube.com/watch?v=t9uGC8Gwowc

 

[emckelvy]

90hp Inline distributor model has smaller ports than a 115 and should idle really good. Just get all 3 carbs synched and run either in the midrange of the idle mixture adjustment, or as lean as possible while still maintaining a hole shot. Another good tip for starting these is to make sure the primer bulb is pumped up HARD and upon cold start, hold the choke in until the motor starts.

Note that the only way to adjust idle mixture is to get the motor warmed up in the water, and adjust in gear. Adjusting with no load on a flusher will not even be close to what it needs in the water.

HTH..........ed