Tuning my 084 with the stock carburetor

[Corky]

I wanted to move this out of my build thread since that's coming to a conclusion and post up this info here for some reading material...
I've run the AFRs on the stock engine and here's the main event in a quick rundown But first a lesson on what the AFR readings mean...
A “stoichiometric” AFR has the correct amount of air and fuel to produce a chemically complete combustion event. By definition, stoichiometric is the calculation of relative quantities of reactants and products in chemical reactions. Which is a fancy way of saying it’s a mathematically derived “ideal” ratio of air to fuel. For gasoline engines, the stoichiometric AFR is 14.7:1, which means 14.7 parts of air to one part of fuel.
The stoichiometric AFR depends on fuel type—for alcohol it is 6.4:1 and 14.5:1 for diesel. For the purposes of our conversation here, we’re just concerned with a gas-burning engine, so 14.7:1 is the ratio that lies in the middle of a “rich” or “lean” mixture. A lower AFR number contains less air than the 14.7:1 stoichiometric AFR, therefore it is a richer mixture. Conversely, a higher AFR number contains more air and therefore it is a leaner mixture.

For Example:

16.0:1 = Lean

14.7:1 = Stoichiometric

12.0:1 = Rich

.
Leaner AFR creates higher temperatures as the mixture burns. Generally, normally aspirated spark-ignition gasoline engines produce maximum power just slightly rich of stoichiometric. In practice it is usually kept between 12:1 and 13:1 in order to keep exhaust gas temperatures in check and to account for differences in fuel quality. A 12:1 AFR is generally considered to be about right on a gas engine under full load (wide open throttle, hooked up and haulin’ butt), though there are certainly exceptions depending on a million different things.

[Corky]

Now, in regards to my engine here's what I'm seeing...The "rule" is 475*F is the magic number on cylinder head temps...I'm getting more than that with even a brief time up above 2500RPMs...I'm talking 510 to 540 on the gauge and climbing...No I'm not staying on it for long after getting there but I've been asking myself how to cure this...
Obviously I need to confirm that's the actual head temp so I need a infra red temp pointer to see where I'm actually at ...I see no calibration screw for the gauge..
I could richen up the mix but it's already where it should be for the most part... Could it be because the engine is new with only 2 hours on the meter ??? Possibly because it's sitting on the trailer and the air isn't moving like it will be on the water ??? These are some of the questions I'm asking myself..
the oil temps are steady at 175 for the most part and I can touch the oil cooler it's not really that warm as you'd expect but yet I see the CHT gauge and I get an uneasy feeling seeing the readout... Hmmmm....
Chuck had said to try and keep the CHTs around 450 or so......I'm past that the first 5 minutes even at the lower Rpms below 2000...It's 72* here glad I didn't fire this up in the dog days of summer !!! If I didn't have this gauge I wouldn't even know there was an issue I can touch most of the engine and it's not smoking hot like you'd expect with those readings..
So, OK...I know it's a 50 buck uncertified CHT gauge but I can't stop watching this thing climb like I'm sitting in front of a timebomb...

[bgmcl60]

check with a lazer and see if it is that hot. there cheap on ebay. new paint and all i'm sure something would be smoking at that temp.

[Bart]

which cylinder is the CHT gauge hooked up to?
somewhere i remember reading that other have stated that the back 2 cylinders, # 3 & #4, would run a little leaner, due to more of the fuel dropping down into the #1 & #2 cylinder intakes,
i just can't remember which post i read that on, but when they went to the Empi carb. they didn't have that problem as much, with the fuel running through a down draft, and not the side draft carb.

[Papee]

Keep in mind that your reading will be higher running it on the trailer. Mine gets warmer much faster on the trailer vs running on the water. You'll know when it gets warm, you'll smell it and you'll hear the tink tink tink when you shut it down.

[Papee]

which cylinder is the CHT gauge hooked up to?
somewhere i remember reading that other have stated that the back 2 cylinders, # 3 & #4, would run a little leaner, due to more of the fuel dropping down into the #1 & #2 cylinder intakes,
i just can't remember which post i read that on, but when they went to the Empi carb. they didn't have that problem as much, with the fuel running through a down draft, and not the side draft carb.

Yes I've mentioned this a few times. Part may have been because of the slang left from casting but mostly the design.

[Corky]

I've got the thermocouple hooked up the the right rear cylinder {#3,second behind the oil filter} I figured this would be the hottest cylinder....On a side note on that plug,the sealing ring was oblong{that way when I took it off not from me overtightening} and not sealing too well so I took it off and just have the thermocouple ring as the washer.. It's sealed up but I guess I should have the compression washer there so I need some extra spark plugs..I did change the fuel back to regular instead of premium to help with the combustion and maybe help with the cooling.
The engine paint is discoloring close to the exhaust...Not burning off and flaking, just discoloring..This engine paint with ceramic in it is good to 500*{so they say} but no water cooled engine is getting that hot and living to tell the tale...And with 475-500 seemingly being the norm it's right there at the paint's limit..
I expected to see some lean readings from the stock carb then I could fatten up the mix to help with the cool down but as you see it's close I'd just be washing down the cylinders with extra fuel at the expense of the rings probably...
I did take the intake"joint" as they call it and debur/clean up all the casting flash so it's as good as it gets...

[Corky]

Well, I got my infrared thermometer now all I need is a nice day to continue the mission...I snagged it at lowes...I was going to get the harbor freight version but I was hoping this one might be a touch better quality...claims "accurate to + or - 2%" we'll see...It's got good reviews...
As I read more about the spark plug CHT gauge thermocouples in general...It's not the most accurate probe for it's intended use but if I can get a good reading using this gun I can possibly adjust the needle a touch and then know where it runs for a general quick check...
I have to wonder....Does anyone have an idea of just how the military read the CHTs and where they might have taken the readings at the head ????

[Corky]

So I had a chance to run this engine a little more today its 67* out...The engine is running fine....That number 2 cylinder is the cold one...20-30 degrees cooler than the rest...But still firing normally...It is the shortest/closest intake tube to the carb...As it turns out the number 3 cylinder{with the thermocouple} is in fact the hottest cylinder but not much more than the others...
After a brief warm-up I throttled it up to 3000 rpm...It runs fine, no miss and the hesitation from the carb really isn't that bad I could live with it to get on the water for now...But a few {2-4}minutes at 3000 rpm raises the temps to where its 500 plus degrees on the gauge...
And now I'm back to the same question I had before...Where do you take the reading for the head ??? If I shoot into the thermocouple/spark plug seat area I'm getting 40 degrees cooler than the CHT gauge reads...If I shoot the hottest head near the exhaust pipe I'm getting 500* and if I shoot the exhaust pipe an inch below the head it's over 600..This is with the oil temp gauge way below 175 and I'm not getting the hot engine noise papee is describing...The paint is discoloring a bunch now but if it's truly near the paints limit it will do what it's doing...
Do I have a hot running engine here?
Am I taking the readings incorrectly ?
Do I even have a problem and am driving myself nuts over nothing ???

[bgmcl60]

i would say where ever on the head surface that is the highest would be correct reading. when they say head temperature i think any where the hotest reading is taken. just me but i would run it just below 450 and let run there and maybe loosen up and fix the problem. unless you have way out of time. if you had to put a fan blowing on it to keep it cool at least run it and give it a chance to seat in and if it don't you have an internal engine problem. no telling what. broke ring to tight of piston. no telling what you will find. but most engines i rebuilt or even new short blocks i installed run hotter for a bit before they seated rings. if timing is set right and fuel ratio is close than friction is causing over heating.

[Corky]

Thanks Bobby...I've got a little over 3 hours on this engine just probing all running data of this new engine...Mabe I'm expecting too much too soon...I've never read what others have done with an NOS engine as far as a break-in time or routine...Here's some pics of the number 3{hottest probably the leanest} and the number 2 the coolest and the one that had trouble in the beginning..Also I moved the thermocouple thinking the exhaust was somehow throwing the reading off...But no change after the move...Note the discolored engine paint is this normal ??

[bgmcl60]

i would also do the mod to the carburetor an see if that helped no 3 is too lean.

[kent]

I read through the o84 engine manuals (pdf) that are listed....
no where, that I read, does it state the gasoline spec or a minimum octane level...
anybody know?
higher octane burns slower and cooler.... Corky, do you want to try some of my 100LL av gas?
kent

[Corky]

Kent, the 084 has a low compression 6.9 to 1...I originally had some high octane in it then switched back to regular thinking the fuel was burning too slow and might have been going out the pipe more so than completely burning..So we were both thinking the same on that one as far as some type of fuel issue...But here's what I've been waiting for Bobby and others to call...
I too thought the number 3 is too lean by reading the plug...The strap is completely white and there's absolutely no color on the plug almost like it's too hot...And here's something else I've noticed...
As we've brought up earlier, the front two cylinders are the ones getting most of the fuel...You can see number two and on the other side number one is "wet" around the thread ring every time I pull it...But the back two cylinders plugs read both lean when I pull them...
So even though my AFR reads close to perfect I'll bet those back cylinders aren't getting enough fuel and the front ones are getting much more of the share...I was thinking today everything points to the engine running lean regardless of the AFR on the meter... But I didn't want to mention this and influence other's findings...

I've got another NOS carb coming so I'll go ahead and drill out the jets a few thousands and then see what I've got...I'll tune it by the plugs then see where the AFR readings are in the end...As long as those front two cylinders don't end up too rich I should be fine..I'm betting as the RPMs go up the distribution gets better with velocity but at this point I can't run it up and keep it there long enough to get a good plug reading....There's really no way out of this except just dumping the original carb and intake joint but I'm not ready for that quite yet...

I'm still going to get the compression for each cylinder just to be sure and in the process check for any intake runner leaks using a spray test...

[Corky]

i would run it just below 450 and let run there and maybe loosen up and fix the problem. unless you have way out of time. if you had to put a fan blowing on it to keep it cool at least run it and give it a chance to seat in and if it don't you have an internal engine problem. no telling what. broke ring to tight of piston. no telling what you will find. but most engines i rebuilt or even new short blocks i installed run hotter for a bit before they seated rings. if timing is set right and fuel ratio is close than friction is causing over heating.

Yes I know what you're saying about the first few hours on a new engine..This is the crucial time for break-in with the friction...I've added an oil additive with ZDDP to help the lifters and cam, etc... The oil cooler is doing it's job it's a good 20-30 degrees cooler than the oil temps at any given time..
Yes, I can run the engine and get some hours on it...It runs fine and there's really no cooling problem to speak of I was just wondering why it heats up so quickly... It cools down fast into the 400-425 range as soon as you drop the RPMs...
I realize in summary the engine is new, running a touch lean, and it's on the trailer while I'm tuning it..Now it's time for the next stage from the stock configuration and that's the factory carb mods...

[bgmcl60]

do you know what your max rpm's are?

[Corky]

Yes, the prop is limiting RPMs to 3000 at the pitch it is set at... I've read where the IVO prop on some of the airboat pros builds were spinning to 3700 ..

[Corky]

I've read so many different descriptions of the carb parts on this site I want to post a breakdown of the parts so everyone can identify them as originally named...I'm guilty of this also so now we can all be on the same page...Literally......
Okay,the parts that get modified are highlighted in red...Anyone care to explain how to go about modifying these two components to richen up the mix ??? Papee ??? Bobby ???

[bgmcl60]

if you have the rpm's maxed out to 3000 then when your anything over 2000 rpm's your engine is working full power set by prop pitch. with the belt drive that should be 3600. on a direct drive it should be at 3000. so what i'm trying to say is your loading the engine down before it makes its power and overheating. probably nothing wrong with the engine if the prop was set to 3600 and it would be working a lot less and not lugging down. if you had the power to plane out at 3000 rpm then you would be putting the prop under the rpm's it should be set for' my razor works best at 3600 to 3800 but i don't run it long at 3800. if i run it hard its just for short burst to get on plane faster. drill out the tip of the fuel metering tube also the side holes can be drilled out to but not a lot.the bottom jet that holds the float bowl on is the high speed jet the holes you drill out are above the gasket. you can drill out only one or both holes next to gasket. the 4a042 carb has a larger fuel tube and i think the venturi is a bit larger. i would start by drilling out the bottom holes on the high speed jet a couple thousandths.

[Corky]

Now that's what I was looking for thank you very much !! And it makes perfect sense...I'll check the pitch{I have a digital angle finder for the job} and keep bumping the degrees until I'm there at 3600..I would assume this is the first step before any mods are done...I have a diagram I'm working on I want to show you give me a minute...