Dave Larkin from Canada has been in touch with us about an article that appeared in the Aeromodeller section of June's Aviation Modeller International. Dave disagrees with some of the comments made by author John Stroud. If you have any comments to add please contact us at feedback@flyingsites.co.uk

Peter
Just received (here in Canada) my copy of the June edition of AMI. Good issue but the article on 'Dealing With Diesels' contains in my opinion, mostly misinformation. There used to be a myth that diesels would not idle. But this was de-bunked by Bob Davis when he started converting engines with decent throttles. To idle properly, a diesel (or indeed any other engine) needs to have the a decent carb and have suitable porting. Specifically the cause of poor throttling on many diesels was not the fact that they were diesels, but the fact that they used sub-piston induction. They were engines converted from free flight or control line use.

Modern diesels with variable mixture carbs like the Irvine 20D and 40D, the PAW 40, 49 and 60 and the Webra 28 idle beautifully. The smaller PAWs (down to 0.55cc/0.033 cu in)have a fairly simple carb (who said crude?) but though this isn't very linear it still gives a pretty good idle. However it is possible to misalign the spraybar when adjusting the throttle arm position. This can adversely affect the idle, but is easy to fix.

John Stroud's statement that PAWs can only be idled down to half speed is nonsense. It's not hard to get them all down to 3500 rpm.

Dave Larkin

Dave can be e-mailed by clicking here.

Peter,
I just saw your article about PAW diesel throttles, I have just made a carb for my PAW 80 diesel (.049ci), used a OS 4a carb as a patten (well they did copy all our best ideas!!) , & scaled it down based on the size of the 80's intake made one & it ran Ok.

Then made another which is a little larger but same internal dim's & it runs very sweetly esp as I have sealed the carb 100%! (Without a perfect seal only 1/2 throttle is the min) almost too slow to feel any airflow from the prop .If anyone wants a pic email me johnhugh.m@ntlworld.com

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