Neil67 Posted April 21, 2023 Share Posted April 21, 2023 I recently acquired a standard Balsa Acrowot with a Saito 82 engine. The previous owner, a very experienced pilot, has configured the engine with the line to the silencer simply mounted under the engine (as apposed to being fitted the the top of the silencer) i.e.. open to the general airflow. He has advised that the engine runs better as no gunk from the exhaust will be fed back into the fuel tank. I am confused as the Saito instructions say, as all IC engines I have, that it should be connected to the nipple on the silencer. Will an open tube work or am I missing something? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted April 21, 2023 Share Posted April 21, 2023 (edited) The outlet on the bottom is the crankcase oil drain Neil The tank pressure pipe goes to the silencer nipple You can put a small pipe on the bottom drain if you need to clear the cowl Edited April 21, 2023 by Denis Watkins Quote Link to comment Share on other sites More sharing options...
J D 8 - Moderator Posted April 21, 2023 Share Posted April 21, 2023 I think Neil is asking if it is ok to run engine without muffler preasure. Some engines are run without pressure like laser,older engines without mufflers the same. Running with preasure alows the carb to have a larger ventury letting in more air to wich you can add more fuel for more power. Downside is there may be times when the engine can not draw enough fuel to keep up with the air and goes lean enough to stop. This is more of a problem for two strokes that fire more often. Four strokes tend to be less affected. Could be previous owner has found the Saito is happy without. Quote Link to comment Share on other sites More sharing options...
Torsten Spitzner Posted April 22, 2023 Share Posted April 22, 2023 My Saito 82B's manual specifically states "Muffler pressure must be used without fail" Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted April 22, 2023 Share Posted April 22, 2023 Laser Engines run just fine without exhaust pressure, but most (all?) unpumped Japanese 4 stoke engines are designed to run using exhaust pressure. I have a Saito 40 which uses exhaust pressure and haven't noticed any gunk in the tank, bear in mind their is very little exhaust gas flow from the silencer to the tank as it's a closed system. so any "gunk" is absolutely minimal. Maybe he was running a high content of castor.................. But there's no real reason why you couldn't run the engine without exhaust pressure, as long as the engine can still draw sufficient fuel. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 22, 2023 Share Posted April 22, 2023 In many years of running 4 strokes with tank pressure, I’ve yet to find any problems with “gunk” in the tank. This is despite running on Southern Modelcraft fuel with 2% castor as standard. Two of my non-Laser engines run without pressure - a tiny OS 20F and an ASP 160FT. The first as it didn’t have the option and the second as I’d fitted a fairly restrictive home made silencer and it cured an over sensitive mixture needle. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted April 22, 2023 Share Posted April 22, 2023 Never had problem with gunk in tank with pressurised system . I have modified an old saito 45 that had open exhaust to have a pressure nipple for fuuelcsystem as it would cut intermittently ehen fuel was getting low. Never had issuse after that and always run tank dry . The only engines that i know of that d9nt require a exhaust pressure are Lasers as tgey draw fuel extremly well and pumped engines like YS, some OS and petrol engines with pumped carbs. Quote Link to comment Share on other sites More sharing options...
Jon H Posted April 22, 2023 Share Posted April 22, 2023 Muffler pressure will return some contaminants to the tank but it should not be that serious. As a general rule all of my engines intended use pressure do, and all those that are not intended to dont. The exception is my Enya 155 which ran far better without it. However, this engine is now running a laser carb and exhaust due to it being a bit of a mod platform for a number of years. Other than my Laser engines my others not running pressure (some in service and some not) are ASP160T, ASP400 radial, OS FF240/320, FT300, Magnum 240v and Enya VT240. In the past my Saito 450r3 also did not use exhaust pressure. The common theme is they are all multi cylinder engines and these tend not to use it as they are rarely supplied with anything more than a straight pipe for exhaust. In any case your saito will not randomly explode if you do not use it. If the tank is in the right place (top of tank, centre of carb) and its all tuned up correctly it should run just fine without it so i wouldnt be too concerned either way. Quote Link to comment Share on other sites More sharing options...
Neil67 Posted April 23, 2023 Author Share Posted April 23, 2023 Many thanks to all for your respones, much appreciated. Neil Quote Link to comment Share on other sites More sharing options...
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