Tuning my 084 with the stock carburetor

[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.

[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...

[Bart]

for an reference, on an other post i put down an comparison of the 2 carbs the 084, and the 042. i used some small drill bits to try to get close to the size of the holes in the venturies and the fuel tubes. and put some pictures for the part together so some might see the comparison. i remember reading, on this forum about one, that purchased an new carb, and it would idle, but anything over 1500 rpm it would flood out. he came to find out he had purchased the carb for an 042 motor.
but at least with your O2 monitor you will be able to see when you drill it passed the point of no return.


http://miniairboatassoc.com/forum/at...1&d=1481481734

http://miniairboatassoc.com/forum/at...1&d=1481481549

[Corky]

for an reference, on an other post i put down an comparison of the 2 carbs the 084, and the 042. i used some small drill bits to try to get close to the size of the holes in the venturies and the fuel tubes. and put some pictures for the part together so some might see the comparison. i remember reading, on this forum about one, that purchased an new carb, and it would idle, but anything over 1500 rpm it would flood out. he came to find out he had purchased the carb for an 042 motor.
but at least with your O2 monitor you will be able to see when you drill it passed the point of no return.


http://miniairboatassoc.com/forum/at...1&d=1481481734

http://miniairboatassoc.com/forum/at...1&d=1481481549

Bart, thanks for the quick link to those findings I was going to try and find those for reference as to the hole sizes....The old threads have Chuck stating he drilled the "main jet" to .040 and the tube to .038 or something close to that and I couldn't figure out what he was refering to for those mods...Man, I got holleys and edelbrock/carter carbs down pretty good but this simple carb is new to me I just want to make sure of the correct mods before I need some new parts because I didn't ask the right questions...

[Corky]

OK here's what I've been working on...I know it's not exact but is this the basic theory for the fuel metering tube carb ?? The lower hole in the tube is submerged in fuel and the upper hole is at the carb venturi so the incoming air charge pulls the fuel from that upper hole ?? And in turn the carb "screw" as they call it has the holes around it's tube that let's a certain amount of fuel through into that well for the metering tube lower hole ??

[bgmcl60]

i think the fuel metering tube controlls the amount of fuel for the idle circuit and the jet that holds the float bowl controls the amount of fuel at high rpm

[Corky]

i think the fuel metering tube controls the amount of fuel for the idle circuit and the jet that holds the float bowl controls the amount of fuel at high rpm

Ok, so now I'm completely confused......Not by what you're saying...But how these circuits interact with each other and their carb routing in the body itself...I guess I need to disassemble it and educate myself instead of asking what might be obvious answers after disassembly...
EDIT: I may have it figured out before the teardown...judging by those pics provided by Bart...Seeing that O ring on the "screw" I'm assuming it's a sealed unit and that WHOLE WELL is exposed to the air charge...So at idle, only the metering tube has the ability to distribute the fuel at low vacuum...But when the RPMs go up{and more vacuum is created} that whole well will have the fuel pulled up into the venturi from below...Did I get it right ???

[bgmcl60]

the fuel metering tube meters the fuel for the idle circuit and part throttle. larger the tube the more fuel is sucked to the idle circuit but air gets mixed in that fuel. easy to get over loaded. the lower jet is enlarged to enrichen the high speed circuit. i had to almost close the mxture screw to make it idle when i used the large tube from the 042.

[Corky]

the fuel metering tube meters the fuel for the idle circuit and part throttle. larger the tube the more fuel is sucked to the idle circuit but air gets mixed in that fuel. easy to get over loaded. the lower jet is enlarged to enrichen the high speed circuit. i had to almost close the mxture screw to make it idle when i used the large tube from the 042.

OK here's a question regarding the mixture screw...Is that adjusting just an air bleed or is it adjusting a mix of air and fuel like a holley idle screw ??? I know the target is 1 1/2 turns out from bottomed out judging by my AFR meter the idle circuit is very rich without any mods.. EDIT: yeah, I know it doesn't really matter just do it.....But you guys know how I like to be thorough in the knowledge...