vsv123

Last summer I've tried to make a radio carburetor for my MK17, and that experience was quite succesfull, so I'd like to share it for someone who might consider to make a radio carb for their engines too (not only for MK17). So this is like another experience into an overall collection

The design is a typical two-needle radio carb. Overal dimensions of carburetor were designed as small as possible to fit between it's rear cap and plane's engine mounting frame. The diameter of ventury was taken from the stock ventury insert of MK17, and it is 4 mm. Using two cone drills straight cylindrical channel was shaped to match "ventury" shape


Into this carburetor case a typical rotating barrel with guide groove inserted. It fixed with machined 2 mm screw


At the opposite side of this barrel a nozzle inserted into carb on 4mm thread. Nozzle hole is 0.8 mm which is sufficient for 1.5cc diesel fuel feed


Two needles are inserted via 2.5mm thread


Both needles sealed tight with polyamide machined washers
So the final device looks like this:


This carb is inserted into MK17's rear tube for stock insert. The tube is cutted for as close as possible displacement of carburetor to crank case of the engine




After several improvements the performance is quite good and stable. Max RPM is ~11500..12000, idle 5000..5500 RPM. Transition between max and min is reliable (depends on needles setup)

The first long run
http://www.youtube.com/watch?feature=player_detailpage&v=BG1OgNoPTfE The first flight (max RPM unreliable because of muffler on MK17)
http://www.youtube.com/watch?feature=player_detailpage&v=jZ-ExXIQ6SA Intermediate results without muffler. This time MAX RPM is quite reliable. Also idle was setup a bit lean, and it sounds like a motorcycle
http://www.youtube.com/watch?feature=player_detailpage&list=UUjc-OpouW36kRi_WFGkxopQ&v=Tti28n44JTs So the conclusion I've got is MK17 is very reliable engine by itself (not taking into account stock nozzle). I've runned two different MK17 engines with this carb and the performance was almost the same on the whole RPM range. Also "carbureted" engine lifetime resource is at least doubled (runned already 9 hours without significant signs of engine wearing. However it depends on piloting style)
Next I'll try this (with reduced ventury) on my Cox049 diesel version

coriolan

Nice conversion and fine machining vsv123 !

vsv123

Thanks. It was really difficult to achieve these results on a cheap chinese lathe

MJD

My Feedback: (1)

This is the first DIY carburetor thread I have ever seen. Nice work!

I have a KMD 2.5 that I plan to fit a carb to some day - but I won't make it myself.

coriolan

vsv123
These Chinese mini-lathe are inexpensive but very usable for a knowledgeable machinist, is your the same as that?
http://www.mini-lathe.com/

vsv123

Actually no, I've got such "lathe": http://www.ebay.com/itm/Mini-Motoriz...-/221617086386
It is possible to machine small parts after strong tweaking this lathe, however, it takes a lot of time to produce with a suitable machining quality. And the spindle ball bearings are awful

The lathe you've shown is actually a pretty good lathe, comparing to what I own. However it requiries a garage or something, at least much more table space I can afford

coriolan

That looks like a copy of the modern 'Improved' Unimat3! Which makes your creation even more impressive!

vsv123

Yes, it's a bit improved version of Unimat MetalLine. Mostly connection pieces are improved (more tight connections of blocks).. I use collets and some other parts from Unimat as chinese version does not provide spares and tools.
This thing copes with aluminium 7075 (my carb made of) and brass pretty well, but I did not try to machine steel and other metals

wnewbury

Decades ago someone in Canada was advertising home made carburetors for the MK 17 in RC Modeler. I bought one, and the Russian engine worked very well with the Canadian carburetor.

coriolan

Must have been "Tarno" of Montreal which was making after market carbs during the 70's, still have one for Cox .049/.051!

MJD

My Feedback: (1)

Leads me to believe the current Cox .05 carb might work okay on a 1.5cc diesel?

coriolan

The Cox QB .074 might also be usable with minor mod.:
http://coxengines.ca/cox-.074-queen-bee-carburetor-assembly.html
http://coxengines.ca/cox-074/

Dan Vincent

Several years ago I adapted an OS Pet .09 RC carb to a MK-17.

It was a new engine and not broken in but managed to get down to 2,600 on a 9-3 white nylon Tornado prop.

earlwb

I found that a Thundertiger RC carb fits the intake spigot on some of my 2.5cc Russian engines. They have .07, .10 and .15 sizes that would work. If I remember correctly I was using the .10 size carb on one of my engines. I made a pinch bolt for mounting the carb in place of the OEM venturi.

I had been running this one for a while and it was accumulating a lot of messiness of course.

vsv123

With the same setup as shown on photo, the engine will not work properly on the maximum power output with stock 7x4 prop. I've got such insert as in the photo. It does not work at Max RPM and Min RPM without retuning needle. Either it will run too rich and stop working in idle, or it will not develop max power

Dan Vincent

A 7-4 is not much prop for an .09 diesel.

vsv123

It's not "not much" it is an air screw MK17 was designed for
Now take a look here


The manual says:
Max power output with 5mm ventury insert at 12000 RPM = 0.15 HP
Whatever prop. you set, power output (efficiency) will be lower at lower RPM and thrust will be lower as well

Dan Vincent

Sorry, my experience with diesels only goes back to the early fifties.

I usually run diesels with at least an inch larger prop than I would with a glo engine of similar displacement.

In the case of an RC carb equipped diesel I go with a larger club for a flywheel effect.

Please excuse my ignorance but my MK-17 with OS Carb ran pretty well on a larger prop.

fiery

My Feedback: (2)

My MK17 fitted with the nylon propeller supplied with it and an ENYA .09 air bleed R/C carb.

Fitment is reversible - no changes made to engine at all. Needle valve assembly removed and replaced with a plain stove bolt cut down to 7 mm length and a locking nut and washer to effect an air tight seal. The end face of the bolt presses upon and securely retains the carb spigot.

I could not get a reliable low speed under 5,500 RPM.

https://www.youtube.com/watch?v=T1hzKEfD4-0