reinvented the choke

[rebuilder86]

been mucking around coz i was bored, its quite lonely here in the jungle.

i have forever been stuck with a 3k carby on my 4k, which had to hav its idle (slow) jet cut with an angle grinder to allow enough fuel to flow for a decent idle, and also required that the idle mix screw be wound out one turn further than factory PLUS also needed a customized PCV valve which provided perfect seal and no leak at idle for it to run without mucking with the base idle speed.

so i got to that point and realised that once hot, the engine would idle fine with the mixture screw back in abit, to half a turn from factory spec.

so i decided i wanted economy and clean plugs and set the mixture to this lean condition and i was, up until now, living with the fact i had to rev the engine when cold to warm her up before going anywhere.

this is very difficult when you don't have a handbrake and live on a hill in the jungle.

so yesterday i decided to make a lever in the car which operates the idle mixrure screw from the drivers seat hahah.

 

when cold, i push the lever forward to turn the screw anticlockwise half a turn, and then when its warmed up, i pull it back out and it idles slower and leaner where it should be.

 

i feel carburettor cold starting systems shouldve been designed like this in the first place rather than choking the air intake and opening the throttle at the same time like all conventional chokes do. i think the convential choke plate does sweet fek all and everyone who uses one is being fooled by the throttle cold idle link. 

in effect, i am manually doing what EFI vehicles do, enriching the fuel for the warm up period.

Edited October 3, 2017 by rebuilder86

[parrot]

I don't know what to say

 

[ke70dave]

What on earth.

You do realise that the choke flap creates a smaller opening in the carby, which speeds up the air as it goes past the venturi which sucks in more fuel and richens up the mixture?

The chroke flap does increase the fuel, automatically, just like an efi system.

[LittleRedSpirit]

Fuckin mcguyver over here

 

Edited October 4, 2017 by LittleRedSpirit
more memes required

[rebuilder86]

well u see, the choke was useless to me as i have no choke lever, or any ability to source anything that would do the job, so i simply removed the choke flap from the choke shaft 2 years ago. it never helped the engine start or idle at cold.

the only thing that helped was increasing the idle jet and idle hole via the idle mix screw.

but my point is, it is working so well, that i don't understand why engineers felt the need to choke the airflow to get more fuel.

also, dave, the air speeds up around the choke plate yes, but the choke plate is well above the primary venturi and completely out of the equation with the slow jet. it chokes the entire carby so that more suction, in the form of decreased static pressure, not as a reault of increased dynamic pressure, pulls more fuel, but with the throttle closed, this has next to no affect on the idle/slow jet.

remove your carbies cold idle connection, and id almost bet, that if you had the need for choke; that is,  the engine is cold enough for fuel to atomise on the manifold walls, the choke alone wont make the motor run propperly. its just the opening of the throttle plate that makes it run in my experience. 

not a conspiracy theory, its just a theory of mine that i have only so far been able to completely proove in my favour.

perhaps if someone can show me their motor running better in a choked configuration without the throttle opened by that linkage.

 

[rebuilder86]

in the chopper, piston powered robinson, we have a mixture control which sort of does the same thing, but to the entire fuel circuit of the carby. same with nearly all light GA aircraft with carbies.

this mixture control is to be in the fully rich condition for cold starts regardless of altitude.

aviation engineers had more brains than automotibe ones. the closest we came to this with carbies in cars, is the feedback carburettor by mikuni, which automatically adjusts the entire primary circuit, (slow and main jets on barrel one) by letting air into the fuel circuit to decrease suction applied to that circuit effectively by venting it through a solenoid to atmosphere which ticks open and closed very fast.

any other carby is stuck in a single fuel metering setting, but sometimes these are adjustable through adjustable air bleeds.

wasnt good enough for me anyway haha.

[altezzaclub]

Yes, the SU carbs also react to altitude as the thinner air can't pull the slide up as far.

Pete has found that the timing is the thing that starts an R44, it drives him mad that some aviaiton engineers can give him a freshly tuned helicopter back and it won't start on a cold morning at 3300ft.  It will crank on full rich until petrol drips onto the ground.  A different company will give it back and it starts every time.

A manual control on the 4AGE idle speed bleed screw has been on my mind..

[rebuilder86]

so altezza what they needed to invent with su carbs, was a diaphragm with atmospheric pressure being sucked out of it at a predetermined force to vary the preasure based on altitude, instead of a spring which is a fixed total force.

this is how the pitot-static system works.

these su carbs are absolutely shit for me here where I'm driving over the 1500 ft hills every week.

i had problems finding a diaphragm for my old Variable venturi carb so ended up throwing it in the bin. i like the concept but i think it has been commonly proven to be a massive fail.

who is pete? another pilot on here? 

i was taught to slowly increase the mixture from cutoff while cranking when starting the r44 raven 2 which is EFI but not sure about carby, we were taught to always start carby full rich, however we have no airfields of an altitude greater that a 900ft over in WA so ive never seen that issue.

 bloody flat and boring place it is, geograpgically.

 

[altezzaclub]

Pete is Steve's dad, up in Walcha. He used to rally too, back in the '80s.   He's had R44s for years, but Raven 2s are still too expensive so all his have been carbed. I think the Lycoming is an outdated piece of crap, but you don't get any choice for personal helicopters really. The splash lube didn't do the job in the last one and it chewed a lobe off the cam, one that works two pushrods. I mean really?? Splash lube in the 21st century!!   At least Continental put the camshaft under the crank in the sump, not up on top!

The injection is a massive step forward from the 1930s, or whenever they designed it.

Anyway, the latest one seems pretty good at starting in temperatures under 5degrees.

[Banjo]

Quote

I don't know what to say

I’m speechless also.

However, I know where Jeremy is coming from.  If you go back through posts on this site, from Rolla owners looking for assistance with their K series engine, many involve the “car not idling properly”.

Carburetors, are mystery boxes to many people.  They are an important engine component, but tend to get overlooked & forgotten, hiding under the umbrella air filter.

We change our points, & clean & gap or spark plugs, but few give the same attention to the poor olde carburettor.  Now carbies are extremely reliable, but eventually, if left to their own devices, they will stop functioning, as they were intended.

I was brought up on English cars originally, like Morris & Hillmans, & 105E Harry Potter Anglias.

Many English cars used SU Carbys, & they were oh, so simple.  A bellows & a tapered needle that moved up & down. If you needed a different response, you just changed the needle for one with a different taper. They had a little oil dashpot, which worked like a shock absorber, where we mucked around with oil viscosity, to change the response time, when you flawed it.  Good olde days !  

However, in Australia the early Corolla’s had a C on the end of the engine model like 4K-C.  The C stood for California, which had the strictest auto pollution regulations in the world at the time.

Hence our early Aisan carbies, were surrounded by a large number of little rubber hoses & plastic valves & actuators, to implement the cleanest exhaust possible.  There are lots of little linkages that interconnected choke & throttle & the like.

 

There are some cut away diagrams on the web, that show the inside galleries, which are not obvious from the outside.  It is those tiny galleries in the idle circuit, that are so prone to getting full of “gunk”, especially if the engine has been left sitting for a long time.  This one below is from the Toyota Yellow K Series Engine Bible.

 

Only a couple of weeks ago, I started up my 5K that had been sitting for a long time. It ran great, but wouldn’t idle, so last weekend I dissembled the carby altogether, and after spraying with Throttle Body & Carby cleaner, down every little hole in the diecast body, I left it to soak in a plastic ice-cream container in Sulphamic acid. Sulphamic is not as dangerous as hydrochloric acid, and is readily available in hardware stores, as a toilet bowl cleaner, to remove scale.  Leave it submerged for about 20 mins, & it comes out, looking almost new.  Ferrous parts of the carby, like brackets etc. should only be left in the solution for about 5 minutes.

Anyway, I’ll reassemble it this weekend, with a new set of gaskets & accelerator plunger rubbers, & it will idle like new, I'm sure.

However, I can’t wait to get my full EFI going on the 5K, and have perfect idling control.

I often drive my daughter's Echo & my Wife's 2009 Corolla, and just love watching the tacho for the first couple of minutes after a cold start, as the ECU increases the revs with the air bleed around the throttle butterfly, and then gradually settles back down to around 900 RPM, once the temperature has reached a certain point. However, even EFI throttle body idle air bleed circuits should be cleaned with throttle & carby cleaner, every year or so.

Cheers Banjo

Edited October 5, 2017 by Banjo

[rebuilder86]

interesting about sulphamic acid, never heard of it, and ill probably be shit outa luck ever getting it on my carb.
No hardware stores here in philippines would even know what anything about the subject other than the word acid and would have no idea there are different types.
Toilets here are cleaned with chlorine., so everyone's toilets smell like a public swimming pool haah
And I'm sure airlines would be super happy about seeing it in my baggage, so flying it over is out of the question.

for all those out there with the idle problem, my experience shows thus.
The kp61 and KM20 series carb by asian, that is the one with a vacuum diaphragm operated secondary throat, and all the complicated vacuum hoses everywhere, come with a 0.45 or 0.48 mm slow idle jet. this is simply too small and is a cock up and no engine with a functioning stock PCV valve will idle in this configuration at anything less than 900 rpm, by opeing the base idle screw.
The other carb, as illustrated in your scan, of the one where the secondary throat is governed (allowed to be operated) by a mass air flow valve inside the throat, comes in slow jet sizes: 0.45, 0.47, 0.5 and 0.53 mm with the latter being the jet size for the 4K-C. This 0.53mm is getting close, but to idle at 800 rpm the pcv will need to be almost blocked and your hot idle compensator valve must be in pristine working order and not leaking at all.

For me it had to be ground open to about 0.6mm and then regulated by the mixture screw.
To repair the hot idle compensator, just take the cover off, pull the valve assembly out, and spin the little rubber seal block around and it should be good for another life.

interesting also to note that the factory manual states, for this mass air flow valve carby, as illustrated in your pic, the mixture screw setting ranges from:
1-1.5 turns from seat \ (4k-C)
2-2.5 turns from seat  \ (2k and 4k)
3 turns from seat \ 3k-c and 3k-H

The 3 turns is because of the smaller displacement of the 3k motor, which at idle, is not enough suction to suck out the fuel from a 0.47mm jet.
But then again, the larger 4k motors require more total fuel at idle, hence the larger slow jet and smaller mix screw opening. This setup is the best, as more fuel is allowed to the point of atomisation where it is restricted only for the purpose of atomisation. The smaller jets restrict the flow with no benefits of aiding in atomisation. they in fact decrease the atomisation because less fuel is allowed to flow through the opening.

In short, reveres the idle circuit setup, because the engineers cocked up. the biggest restriction should be at the exit point, the idle port.

[Banjo]

Hi Jeremy,

                   Sulphamic acid is good, because it attacks & dissolves nitrates, which is what those crustations are that build up inside the carby galleries. Although safer than hydrochoric acid, to use, you should still wear gloves, and not get it on your skin, or face.  Some people say, it even works better, if you mix a little water with it, rather than use it neat.  I haven't tried that myself, & I'm not a chemist. ( just got a "B" in chemistry at high school ) 

If you can't lay your hands on sulphamic acid, may I suggest you just use citric acid, (lemon juice).  Again you can use it neat or make a diluted solution.  I noticed in the supermarket here in Brisbane, recently, that they sell neat lemon juice in plastic bottles.  Lots of people swear by it.

$ 1.65 for 500 ml.

Whatever you use to clean your carby body & galleries, it is imperative that you wash all residue of the cleaning fluid, out of the carby, & blow it with compressed air, down any hole you can find in the body.

With carbies, it doesn't matter how dirty they are on the outside.  It's how clean they are inside, where you can't see, that makes the difference between good results, & an average performance.

However, despite how much time & effort you put into producing a clean carby, it will not provide good results, if the carby is olde & worn, and sucks in air around shafts that have worn the body pivot points.

An olde mechanics trick, is to spray some starter fluid, on the outside of the carby body at the butterfly pivot points, with the engine running at a fast fixed idle. If there are worn gaps at the pivot points, you will hear the engine speed change, when you spray the fluid, as it would be sucked in through the gaps.

If they are worn, you could get them rebuilt, but the cost would be pretty frightening, & maybe a better option would be to just buy a reproduction Aisan carby on the net.

I've seen them complete for around $ 100.00.  

If any one has bought one & fitted it to their Rolla, I'm sure we like to hear how it performed.

Cheers Banjo 

 

 

 

  

 

Edited October 6, 2017 by Banjo

[rebuilder86]

i already replied to a topic about the hunjy dollar aisan china ebay carby.

it works, but the accelerator pump died very quickly as it was not kept wet with fuel. thr leather just broke apart.

the screws on the top have all rusted and all were destroyed even when using an impact screwdriver :( so getting to said accel pump plunger was a cunt of a job.

and finally, the air horn gasket it comes with fell apart completely upon opening so fuel squirts everywhere when the bowl sloshes around.

 

however, when it ran, it ran fine.

i purchased the non diaphragm operated one, the simple looking one with no hoses.