carburetor for 1 cc diesel engine

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carburetor for 1 cc diesel engine

This topic has 12 replies, 5 voices, and was last updated 27 March 2025 at 12:11 by jimbo7636.

Viewing 13 posts - 1 through 13 (of 13 total)

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26 March 2025 at 18:59 #790569
jimbo7636
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@jimbo7636
I found some great information on “fixed venturi” and “variable venturi” carburetors by George Britnell here: https://www.homemodelenginemachinist.com/threads/carburetor-information.8192/#post-90761

…but I have some questions. I’ve scaled his design to work with the Weaver 1 cc diesel engine. Please look over the photos here and let me know your thoughts. Id like to refine this one more time before I make chips… Thanks!
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26 March 2025 at 19:04 #790570
JasonB
Moderator
@jasonb
Most of these small compression ignition engines did not have a throttle, they just ran with the basic venturi as shown in the original drawings. As they tended to be fitted to control line aircraft or tether cars there was no way to activate the carb barrel anyway.
26 March 2025 at 20:17 #790581
bernard towers
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@bernardtowers37738
Beat me to it Jason ,overcomplication for no benefit.
26 March 2025 at 20:26 #790583
jimbo7636
Participant
@jimbo7636
here is another interesting bit. you guys might be right about overcomplication, but this video shows the carb is working. and this carb doesnt have an air bleed. In the video Jellyfish machine made a Weaver and then he made a 2 cc by basically mashing together two weavers! https://www.youtube.com/watch?v=c5ZdXl8KRs0&t=1733s
26 March 2025 at 20:39 #790592
JasonB
Moderator
@jasonb
He is running it as a glow engine so no need to adjust the contra piston as the throttle is adjusted.
26 March 2025 at 23:33 #790655
Emgee
Participant
@emgee
A 3 line control was sometimes used on control line models to operate engine speed so it is a possibility, but may prove difficult with a 1cc engine.

Emgee
27 March 2025 at 00:14 #790657
jimbo7636
Participant
@jimbo7636
I did find this article which talks about a diesel engine that also has an air-bleed barrel carb. Seems like it just lets the pilot basically switch between high and low RPM. https://sceptreflight.com/Model%20Engine%20Tests/Taifun%20Zyklon.html
27 March 2025 at 00:32 #790658
jimbo7636
Participant
@jimbo7636
Jason, what do you think PAW is up to with the PAW 06 BR and the PAW 06 BR R/C ? Seems like there is an air-bleed barrel carb on this engine which is a compression ignition diesel. https://www.eifflaender.com/engines

From other articles out there perhaps its just a way to idle the plane if you are using R/C. Not sure if having a low RPM and high RPM state is worth it. It would be great if you could also get a predictable transition from low to high.
27 March 2025 at 00:54 #790659
jimbo7636
Participant
@jimbo7636
here is another good webpage that shows multiple different diesels (compression ignition) with air-bleed barrel carbs. Seems like these are sold as “R/C” diesels versus “FF” free-flight diesels. So I wonder if they work? https://www.rcuniverse.com/forum/everything-diesel-87/11644355-whats-attraction-diesel-plane-engines-5.html

Id like to know your thoughts. Thanks,
27 March 2025 at 07:13 #790690
JasonB
Moderator
@jasonb
My gut feeling was that the contra piston would need some tweaking to correspond with changes to the throttle but seems it may be worth a try.
27 March 2025 at 08:08 #790698
Ramon Wilson
Participant
@ramonwilson3
Advice doesn’t come much better than from George Britnell but the only thing I can see wrong with the copied info is the statement that ‘when the engine is running it is always running at max speed‘ which could be a little confusing or misleading

The running speed of a fixed venturi equipped diesel engine can be varied by combinations of contra-piston position and needle setting from quite slow to indeed the max speed for a given prop/load. As such the revs are more or less constant for a given setting

Throttleable diesels have been around for many years and work mainly on varying the fuel/air ratio with a set compression though some have variable exhaust pressure as an additional means too

Some diesels perform much better than others when fitted with a throttle – I suspect that is much more to do with the internal timing set up than the carb.
27 March 2025 at 10:24 #790732
Ramon Wilson
Participant
@ramonwilson3
Further to the previous post – most small engine throttle carbs have a bleed hole that can be adjusted for slow speed running. The throttle closed position should also be able to be controlled – usually by an adjusting screw. A basic rotating throttle barrel, whilst restricting the air does not have an effect on the fuel setting so the mixture gets progressively richer as the air intake is reduced. This is usually overcome by having the throttle barrel move laterally as it is rotated to reduce the fuel input. Mostly achieved by a slot set at an angle or helical groove there are many good versions of this type – Super Tigre and OS spring to mind but many others too.
27 March 2025 at 12:11 #790757
jimbo7636
Participant
@jimbo7636
After watching this video on Youtube Im pretty sure a compression ignition diesel should be able to have an air-bleed barrel carb manage low, mid, and high RPM to a decent extent. check it out: https://www.youtube.com/watch?v=2jejCSZgq4E

It really looks like what I am trying to do. This guy has it working on various compression ignition engines. His carb has an airbleed hole but it doesnt look adjustable. It also has the barrel. Im going to study his videos a bit more. A commentor does talk about how sub-piston induction will cause the carb not to work but this engine does not seem to have sub-piston induction. they mention a chinese carb “CS Navo R/C carburettor”

Notes from the video and comments:

“In this video I let it idle for three minutes. I then commenced the video. No lag in pick up. Minimum safe idle is 3,800 rpm. Maximum rpm’s were 8,400. This engine, while not a show pony, has great fits where it matters. Piston and cylinder liner fit is particularly good. The throttle was supplied as an accessory by Aurora and some engines (such as this one) were sold with it instead of the usual intake tube with integral needle valve assembly and a fuel hang tank assembly . An 8 x 4 Master Airscrew gf3 black composite propeller is fitted and suits the engine perfectly. Fuel Composition: 35% Di-Ethyl Ether (Solvent grade) 38.5% F34 AVTUR (mil. spec. aviation turbine fuel) 1.5% 2-Ethyl Hexyl Nitrate (Amsoil Diesel Cetane Boost) 25% Castor Oil (first pressing cosmetic grade). For those who can’t buy a Aurora R\C carb… A PAW 100 r/c carb works just as good. You need to machine a aluminium 1/4″x40 adapter and epoxy the carb to it. Make sure there’s no sub piston induction on the engine, otherwise it will never idle.”
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