FrancisPerson

I am creating what may be the ultimate Davis Diesel conversion and like Frankenstein's monster I will pick and choose parts. Start with a MECOA .46 R/C engine in excellent condition, add a GMS/TOWER muffler a Davis Diesel conversion head, a MECOA .25 carburetor (.24" throat), a MAS 12x8 scimitar prop and some Davis plane fuel and I will report with pics, vids and numbers.

Testing Soon
Francis

AMB

Francis think the head for mecoa 46. OFNA 46, royal 46 , RJL 46 are all knockoffs of the OS46SF . You should have a nice conversion, I do not know if ultimate since you have OS ,irvine. STs ,TTs , which are great conversions too. you should be able to run the stock carb at 75% open and be fine, since you have a 25 carb you can do some comparisons
bottom line is you will have a good runner if its in good condition be interesting to see your revs martin

small correction the davis head is the same the engines are dups of the 46OS sf

FrancisPerson

I am trying the smaller carb as I have trouble peaking diesel conversions on engines with large carb bores. PAWs and LA/FP conversions are easy to tune but larger carbed engines especially ones where the low speed needle is effective above 1/2 throttle. And this .25 MECOA carb only cost $22.00

Will report soon
Francis

gkamysz

My Feedback: (19)

Martin, I have to disagree that running the stock carb at 75% open is acceptable. Most airbleed carb are on the idle circuit at 75% and many two needle carbs will be also. It can be done but for tuning it isn't always ideal. A smaller carb works much better.

AMB

Greg the only engine I have had a problem with the stock carb was the MVVS 40 and it resolved with a smaller carb (diesel conversion of course) martin
my irvine 53s all do fine and those are big (the stock jetstreams) but that may be the carb design also the Q40 conversions same thing also jetsream carbs
at 100% open they bog badly

AMB

The carb size thing seems to have a few variables and must be related to the carb design some seem fine at 75% wide open for decent running some do not any of the irvines with jetstream carbs my 25,36, Q40 conversions do, the MVVS NO needed smaller bore. I took a look at my Enya 25 diesel it appears
they are using the stock glow carb but just have inserted a brass restrictor ring in the carb barrel reducing its diameter clever solution. It follows that
the same amount of air being pulled thru if it has to go thru a reduced opening the velocity will increase and result in a better atomization of the mixture
Over the years Davis has stated that you do not have to buy a new smaller bore carb and this proves out. My PAW 40 does much better running a
MVVS carb on response and running at any speed. But also a better carb design my ST40 Davis head stock carb no issues . If you want to play and can do it make a small ring that
will fit the carb barrel it is drilled of course for the needle assemby to pass thru it and a press fit in the barrel ala Enya, you could of course just reduce the diameter of the carb intake body (easier) wonder if it would differ from the ring in the barrel in running martin

One thing I did do on my irvine 40 diesels was put in a pressure tap on the muffler and run tank pressure on the stock carb with constant pressure I think easier to adjust and idle to full speed more responsive on the one wearing the MVVS mufflers its already there so are the irvine glow mufflers in the conversions

Also going to run the ST-1 truck conversion this weekend under field conditions, just running up and down the street boring

FrancisPerson

I hope to have time to break in the engine on glow tomorrow morning.

Francis

lildiesel

I ran into that problem as well when I got a couple of DDD heads for larger glows in the early 90s. I had some success just choking down the intake area gradually by CAing in concentrically smaller rings of aluminum tubing until I got great fuel draw and good throttling with big props. If I had any machining skills I would have choked above and below the venturi (putting a kluged CA'd restrictor ring between carb and crankshaft didn't seem like good idea ) as well as experimenting with spacers adding distance between carb and the crankshaft. Notice that real diesels almost invariably have the carb higher above the crank than an equivalent glow?

Hobbsy

My Feedback: (102)

This is how I got my Fitzpatrick .61 to run, I Made a Delrin reducer, the carb blew out about as much fuel as entered the engine before I did this, even at part throttle. The Fitzpatricks have extreme timing being designed for 17,000 rpm. Claimed, anyway.

FrancisPerson

Ran great as glow with the smaller carb; next step is diesel

Francis

and buy a 12x8 prop