Can a carbie jetted too small get cold 100HP Chrysler

[MickLovin]

Just out of interest sake I want to ask a question about my carbie and what happened to it out on the water, firstly a bit of history, I put a 75hp 066 jet in my 100hp carbie when they should have been the 080, not knowing at the time it would or could make any difference, it was more of a mistake from having both sets apart. Anyway I was out on the water wondering why at WOT I was half pace when my friend and I stopped the boat to have a look at what may have been going on. I looked by chance down the throat of the carbies and it looked like water, but then for some reason I put my hand around the carbie and it was like it had been chilled in a fridge. This is the question, we have had rather hot days here nearly heat wave conditions, could the coldness of the carbies be from jetting the motor to low and the pressure from the motor is trying to force more through the jet??
Just so you know I realised what I had done to the jets, I re-jetted the carbs back to what they should have been and the motor ran fine with full power at WOT and no sign of water or condensation at the carbs. Where as with the small Jets in the carbs had a definite physical temperature drop.

 

[jerryjerry05]

Re: Can a carbie jetted too small get cold 100HP Chrysler

The cold is from the motor sucking in the air at an accelerated rate.
Try blowing across the back of your hand.It will get cold even though your breath is warm.

 

[Frank Acampora]

Re: Can a carbie jetted too small get cold 100HP Chrysler

No Nick! You were just seeing a natural physics law in action and the atmosphere may have been just right to prove it.

Here is the explanation: Your air conditioner (or refrigerator) works by compressing a gas (usually some type of Freon or fluorocarbon compound) into a liquid. Compressing it generates heat so it is run through an outside radiator to cool. Then the liquid is run through an orifice and expanded into a gas which cools it to a point where it is colder than it was originally (conservation of energy rule. Remember, we cooled it when it was hot). This gas is passed through the inside radiator where air is blown over it and cooled, then blown into the house or car.

Now, consider your gasoline as the already cooled liquid. When it is vaporized in the venturi of the carburetor it cools down more. Most times, the engine will be running hard enough that engine heat will overcome this cooling effect BUT given the correct conditions the carbs will become colder than surrounding air, sometimes (again given the correct conditions) cold enough to condense atmospheric humidity.

Because smaller jets will pass less gasoline at full throttle, they would--if anything--have less of a cooling effect.

By the way: Regarding your other post on the 100 HP engine. You would expect to use about 35 to 40 litres of gasoline per hour at full throttle. This is at the correct mixture for efficient combustion. Attempts to save fuel by modifying the carb or leaning are dangerous because lean mixtures can auto-ignite under compression, leading to detonation and massive engine damage. These engines are very old school design, about 50 years old, and there is not much you can do to modify them for better fuel mileage. Buy a bigger gas tank !LOL

 

[MickLovin]

Re: Can a carbie jetted too small get cold 100HP Chrysler

Actually Frank I don't agree with the smaller Jet theory you have, yes they would have less gas flowing through them but at a higher pressure due to the motor sucking for more and when you go from a low pressure to a high pressure doesn't this create the coldness I may have come across? I'm not an expert in refridgeration, but it works from changing from low pressure into a high pressure or vise versa?
This condensation has only happened when I put the smaller jets in, I haven't seen it happen since. Isn't it like when you let gas out of a bottle and inside is a high pressure releasing out to a low? and if you reduce the outlet size it increases the pressure?
I disagree with you Frank, but I am not saying you are wrong just unsure on this one due to experiences with refridgeration and a/c its doesn't sound right that increasing the orifice would cause the possible condensation, My arguement is, the higher pressure caused by the smaller opening with the same amount of pump pressure has caused the condensation. Can we talk more about this?

 

[Frank Acampora]

Re: Can a carbie jetted too small get cold 100HP Chrysler

Well, we would actually need a refrigeration expert to chime in on this.

My take is that fuel in the bowl is under atmospheric pressure only. The venturi can only generate a finite amount of negative pressure with any given air flow, that is why a smaller jet will deliver less fuel. Less fuel is less mass and cooling effect depends upon the mass of liquid being vaporized. As I sad, because this is not a closed system like an air conditioner, the effect would be subject to local atmospheric conditions and engine conditions and would be sporadic.

I could be wrong: I was wrong once before-- I thought I was wrong when I was actually right! LOL

 

[MickLovin]

Re: Can a carbie jetted too small get cold 100HP Chrysler

LOL someone told me I was wrong once , only once . I know and understand what you are saying but when you are running isn't the pump pumping all the time into your carbs at WOT and wouldn't this cause a constant pressure into the bowl and if you restict this pressure more wouldn't that cause the high to be higher forced through a small orifice?? not saying it is right or wrong just want a debate LOL not that I don't trust ya cause ur da man Frank but it'd be nice to get one on ya LOLOL

 

[Frank Acampora]

Re: Can a carbie jetted too small get cold 100HP Chrysler

NO! The pump does produce pressure all the time BUT the float and needle shut off fuel flow at a specified level in the bowl. The carb is vented to atmosphere to prevent any pressure build-up. This vent will be either a small hole in the side of one of the carb runners cast into the carb body. It will be seen as a hole about 1/8 inch diameter inside the carb above the float.THUS: the float maintains a constant level of fuel in the bowl and the vent maintains a constant pressure. These two things are very important because for a carb to meter correctly, fuel must remain at a constant level and pressure--in this case atmospheric or 14 PSI

 

[glennkil]

Re: Can a carbie jetted too small get cold 100HP Chrysler

I don't know why the carbs are cold but I know it is a pleasure to read a thread on a forum where people are not ramming their views down other people's throats. This forum has some people on it who have forgotten more about boats and engines that I will ever know however their ego always remains in check. The same people are always open to have their ideas challenged in the event they may be wrong and learn even more. Awesome forum. Thank you

 

[MickLovin]

Re: Can a carbie jetted too small get cold 100HP Chrysler

Don't you hate it when someone comes along with actual real facts and blows your stupid theory out of the water :facepalm: Ill get ya frank one day LOL thanks mate for your facts bugger ya thought I was on a good theory then