Update: RCM Article For Cox Engine Backplate Modification

I think there is a post about it on RCU's 1/2 spot. I have several Tee Dees will drilled venturis that are run on crankcase pressure. I also built a Sure Start will a drilled out intake than ran on crankcase pressure. I can take some measurements if you would like.

I will try searching RCU and see if it comes up. Also, thank you for your offer, but you do not have to go out of your way. It was just something I was trying to find. This article in question was for a Bee type engine.

The offer still stands. ask any time.

A Black Widow can handle opening the intake to .093". However, this isn't always without issue. Hard starting, fuel draw issues, and shorter run times, and difficulty getting a decent flying setting becomes a factor. .082" would be a better option because the power gain isn't as substantial as most claims. A product backplate can be successfully opened to 11/64". While the engine will run with a slightly larger opening, a too large venturi shows it's ugliness on launch when the engine just quits upon release like someone turned off a switch. This is where the need for pressure is required.

fit90 wrote:The offer still stands. ask any time.

Thank you.

Ken Cook wrote:            A Black Widow can handle opening the intake to .093". However, this isn't always without issue. Hard starting, fuel draw issues, and shorter run times, and difficulty getting a decent flying setting becomes a factor. .082" would be a better option because the power gain isn't as substantial as most claims. A product backplate can be successfully opened to 11/64". While the engine will run with a slightly larger opening, a too large venturi shows it's ugliness on launch when the engine just quits upon release like someone turned off a switch. This is where the need for pressure is required.

Hmmm. Kind of funny, but after reading your post, it almost sounds like you quoted the article in question. The numbers in decimal almost sound familiar as does your talking of fuel draw and starting issues, as I believe that that was also covered in the 'hint' I am looking for. Thank you.

Both Paul Gibeault and Rusty have had some excellent posts about mouse engines which probably cover all this information.

My little bit of experience with opening the venture on a reedie was to open it using an 11/64" bit, install a fine NVA and to use crank case pressure to eliminate fuel feed issues.

This shows where the pressure tap goes through the crank case:



This shows the opened venture:

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This shows the pressure tap exiting the crank case supported by a blob of J B Weld. The inside of the pressure tap was filled with solder and then a hole was drilled through the solder with a #80 bit

Here's a link to Paul Gibeault's Mouse Racing article.  It describes the modifications you refer to.

Rod.

https://coxengines.ca/files/MRP.pdf

Oldenginerod wrote:Here's a link to Paul Gibeault's Mouse Racing article.  It describes the modifications you refer to.

Rod.

https://coxengines.ca/files/MRP.pdf

Thank you. This is actually funny, as I was reading this article earlier looking for a part about sanding the tank back flat for another individual here asking about it. After quickly glancing through the article a few times, I did not see what I was looking for. But, now that you linked it to me on my question, the part I was looking for earlier is in the same paragraph!

I opened my baby bee tank venturi to 5/64, which is a couple thou off 2mm and it is a nice easy hop up that does not detract from operation... well, they run out of fuel quicker. Same starting, same running, more power. Does not work so well with an old single bypass cylinder (little to no performance change), but on the newer double bypass, and double bypass with boost it offers a few hundred rpm with little risk to the engine.

Phil

I'm not sure how far the Venom II venturis that Bernie is selling currently are drilled out, but mine so far has started easily, launched great, and makes significantly more power than the Black Widows I've tried on the same airplane(Sharkface).  Running it stock with no pressure taps or other mods.  It has had me thinking about drilling out one of the BW venturis to compare notes.  The only drawback I've noticed with the hotter engine is a shorter runtime, about 1.5 minute.