It's me!!!

DavidBoren

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Let us begin with the fact that I do not currently have a go kart, nor have I ever owned one, and I probably won't ever...

I am here to pick your brains and study your habits... I am a "tinkerer" and I have this lawn mower... you can probably see where this is going....

My little Craftsman M250 push mower has a Honda GCV160 on it, and that particular GCV160 has a Keihin 18mm constant velocity carb...

The CVK18 Honda uses has a freaking emulsion tube!!! Weber uses emulsion tubes to regulate mid-range fuel curves... my lawn mower, and ever other lawn mower I know of, literally never operates in its mid-range... lawn mowers are at idle, or wide-open throttle (WOT), all day, all the time. There is literally NO mid-range.

So the use of this emulsion tube has to be for leaner overall jetting... literally any pre-mixture [emulsion] given by the emulsion tube will allow leaner main jet(s). And Honda, wanting decent fuel economy and emissions publicity/advertising has undoubtedly jetted these carbs/engines as lean as possible from the favtory...

Leaving literally no room to up the governor speed without re-jetting the carb.

I am here for your experience and collective knowledge for adjusting/tuning small, air-cooled engines from lean of peak to rich of peak operation.

Did I come to the right place?
 

DavidBoren

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To expand on my intentions...

I plan on increasing the governor speed of my 160cc engine to match the CFM demand of a 190cc engine... the next step up in displacement within my same engine family. It would require my 160cc engine to spin at ~4100rpms, in juxtapose to the 3100rpms the USA governor is set at from the factory to maintain "safe" blade tip speeds under 19,000fpm.

My willingness to exceed "safe" blade tip speeds need not concern any of you.

The blade is going to maintain an equal mass throughout all of the following tests... thus, my blade is my dynometer... my rpms will be my measure of "power"...

If that makes sense, we can continue...
 

DavidBoren

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18mm venturi is 'unchangeable'... even if I find the perfect 6* taper bore bit that I can jam into the ventrui to taper the bore a "perfect" 6* from its mouth to its throat and keep the exact same butterfly diameter... it is still not "meant" for anything resembling "performance".

But that emulsion tube... who else uses such a glorious device in their small engine carbs? This CVK18 intrigues me with its three separate emulsion tube part numbers, for the same family of carb... clearly they have designed purpose within the same carb family's operation parameters...

The GC160 uses a different emulsion tube, and different jets, but the exact same carb as the GC190. They both share #35 pilot jets, but use different main jets and emulsion tubes...

There is clearly room for adjustment/tinkering...
 

DavidBoren

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On my current lawn mower...

The displacement is fixed.
The cam profile is fixed.
The compression is fixed.
The ignition timing is fixed.

Literally the only things I can manipulate are fuel and RPM's... even RPM's are limited by fixed cam/timing profiles.

I just want to up the rpms and jetting of my current mower to operate rich of peak instead of lean of peak... and, yes, I am actually willing to get the full host of go kart measuring decives to tune my stupid push mower...

Let's talk in terms of:
Air Fuel Ratio
Cylinder Head Temperature
Exhaust Gas Temperature
and RPM's

These are things I can find the correct tools to measure... the go-kart community happens to offer singular interfaces that can measure everything I am looking for... nobody offers turn your push mower up to 11 kits, but plenty of companies cater to go-karts.
 

DavidBoren

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Not to single anyone out, but I prefer measurements based off of CHT rather than EGT.

EGT is just a measurement of heat expelled to atmosphere... I actually do not care about this statistic, but I can use these measurements if you do not collect or otherwise measure CHT data...
 

FlyFrog

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ok so, let me get this right, you are beefing up a push mower? or riding? and what exactly do you want, you have put down a lot of info to make a very vague question
 

DavidBoren

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It's a push mower that I will be working on. And I am trying to tune its engine to run rich of peak. As well as increasing the rpms it operates at. More of a learning experience than trying to accomplish anything "practical".

Companies like Alfano make data loggers that can measure cylinder head temperature, exhaust gas temperature, and other such things... so I was hoping like-minded tinkerers would be collecting data for $#!+$ and grins, if nothing else.

When tuning for rich of peak, the "peak" they are referring to is peak exhaust gas temperature... which occurs at stoichiometric air fuel mixture. Leaning the mixture lowers the EGT because there is less fuel to produce heat. And fattening the mixture reduces EGT because unburnt fuel absorbs heat.

Unburnt fuel absorbing heat is actually what got me started down this rabbit hole. I figured adding fatter jets to my carb might actually cool my engine... my theory was/is correct, and there's a term for it... rich of peak. Lol. It's actually an aviation thing, but it applies to most air cooled engines.

Honda, undoubtedly, has the leanest jets they can get away with for fuel economy ratings and environmental regulations... lean of peak will (or can) save you roughly 20% fuel at the expense of about 10% of your power. In juxtapose, rich of peak will burn that "extra" 20% of fuel to give you an additional 5% power.

Lean of peak uses 80% of your fuel and gives you 90% of your power, lowering EGT's by about 50*... in an aircraft, this equates to a 5% drop in air speed.

Rich of peak uses 120% of your fuel and gives you 105% of your power, whilst lowering EGT's by about 100*... in an aircraft, this equates to a 1% increase in air speed.

In terms of my lawn mower, it will cut grass good.
 

ezcome-ezgo

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I hope your actual intention is to build a flying car, since we are in desperate need of those, being in the future and all.
 

DavidBoren

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I do not think the general populous is nearly responsible enough to drive in a 3-dimensional environment... people can barely drive on a fixed surface. The last thing I would ever willing work on is a flying car intended for public distribution.

You have @$$clowns taking cars and trucks into crowds of people... now you want them to be able to go all 9/11 on a whim? No way, not me... I'm not willing to hand people that sort of destructive power. If anything, I think the minimum age to get a driver's license should be raised to 21+... the fewer morons out there driving at any given time, the better.
 

FlyFrog

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so i did a bit of looking around on the gc160, you can port match, advance the timing a bit 16-18 lbs valve springs and up the jet size 1 or 2 if you want you can switch out the carb from one that is made for mutiple speeds, it probably only has 1 jet, you would want 2 and after that adjust govener, if the "emulsion tube" your talking about is a crank case vent that keeps polution down, just disconnect it from the carb and cap that off on the carb
 

DavidBoren

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How would one advance the timing a little bit? Slot the screw holes on the pickup, just physically shift it a little bit? Or were you talking about installing the cam gear advanced by a tooth or two? For increasing rpms, wouldn't I want to retard cam timing?

I am going to disconnect the PCV hose from the airbox, and will be running a little valve cover vent filter in its place.

The emulsion tube is inside the carb, between the main jet and the venturi... fuel exits the main jet, and goes through the emilsion tube on its way to the venturi.

Well, that might be oversimplifying it... the fuel exits the main jet and actually goes around the outside of the emulsion tube... the fuel actually travels between the outside surface of the emulsion tube and the inside of the bore that the emulsion tube sits in... air is drawn down the inside of the emulsion tube, and that air mixes with the fuel via a series of ports in the sides of the emulsion tube.

Weber has dozens of emulsion tubes with different porting arrangements, different diameters at different heights on the emulsion tube, all sorts of different depths, every which way you can possibly manipulate this tiny little tube... Weber has a version of it... They have "perfected" the use of emulsion tubes to modify mid-range fuel curves.

Honda using a carburetor on a push mower that uses an emulsion tube is strange, isn't it?

And, this CVK18 carb Honda is using does, in fact, have an idle circuit... a replaceable pilot jet, too. There are almost a dozen different pilot jet sizes available ranging from #35 to #45. It does have this stupid pilot screw that snaps in half if you mess with it, but I am relatively certain I can find an adjustable fuel screw for it. Keihin carbs are quite popular...

Main jets range from #45 to #150, and there are three different emulsion tubes available... I feel I have an incredible amount of tunability available with this carb... which is hilarious because the mower only has one operating speed.
 

FlyFrog

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it has all those possibiltys because its not just used on mowers, to advance timing you can by a advance timing key pull the flywheel off take out the old put in the new,
 

DavidBoren

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Thanks for pointing me towards those advanced timing keys... seems simple enough.

Heavier valve springs, huh? Is valve float a thing at 3100-4100rpms? I have always told people that the valvetrain is definitely not the area to start pinching pennies, so I have no problem throwing stiffer springs in there... but a go kart or pit bike spinning at 9500rpms is a completely different animal than my mower at 3500rpms.

I think this CVK18 would be an excellent carb for a scooter or pit bike. It seems like overkill on a push mower or generator, though. The only thing this carb is really missing is an adjustable float/needle valve... there is only one position available with this particular carb. And, I guess, an adjustable fuel screw... they come with an anti-tampering fuel screw installed (probably for emissions regulations).

I wonder what else out there uses this style of CVK18.
 

DavidBoren

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Takes special talent to answer your own posts with more posts🤭, but you're spinning your wheels and not getting traction in the Intro forum.

I'd move this to one of the real subforums, maybe "More Builds" ...https://www.diygokarts.com/community/forums/more-builds.27/
My bad... if mods can move this thread to the more appropriate section, I will not complain.

If not, well, this is me... sometimes I come back with more or new information. Sometimes I post questions whilst I am actively seeking answers to those questions... sometimes I find my own answers elsewhere... I continually update my posts with the information I find, just in case others randomly stumble into the thread via searching.
 

DavidBoren

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If people want to actively talk about tuning air cooled engines rich of peak... this thread is as good of place as any other...
 

landuse

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My bad... if mods can move this thread to the more appropriate section, I will not complain.

If not, well, this is me... sometimes I come back with more or new information. Sometimes I post questions whilst I am actively seeking answers to those questions... sometimes I find my own answers elsewhere... I continually update my posts with the information I find, just in case others randomly stumble into the thread via searching.
I have moved your thread to the More Builds section
 

DavidBoren

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Thanks for moving the thread.

I found another emulsion tube for my particular family of CVK18 carburetor... that brings my current 16166-Z8B- family of Honda "main nozzles" to four:
16166-Z8B-841
16166-Z8B-901
16166-Z8B-911
16166-Z8B-WA1

That is a similar variety of emulsion tubes readily available for a lawn mower engine than that of the CVK's found on older Harley Davidsons. Lol. Am I the only one that finds this odd?

I ordered all four of the ones I have found... in the name of science I am intrigued to see the actual difference.

Whichever one of them ends up being a duplicate of the one currently installed in my lawn mower's carburetor will become a test mule for any mad scientist modifications I might want to try... I have heard about people drilling certain Weber emulsion tubes (F11's?) all the way through, or something like that. I don't know exactly how Honda makes their emulsion tubes, honestly... I haven't taken my current carb apart, it's practically brand new.

If anyone is interested, I could probably post dimensions and crappy cell phone pictures detailing the different tubes when they come in.
 
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