Hello, please let me respond to each post separately. Rob,
While rough running I have never experienced any detonations, just a serious drop in RPM and generally things seem to go out of whack. Ian Mc Phee, I believe mine are the old aviation leads (plugs were recently replaced). I did suspect they might have been broken so I borrowed a similar set from a friend who has FALKE. That other set did not seem to make any difference so I put mine back on. I am going to run the engine in the dark as you suggest though. The TUMA tap is no longer there. But I realize that it is high time for me to check up the fuel flow since I have still neglected this measurement and am still not even sure if that electric pump does or doesn't work. Ian Williams, A new throttle shaft is on its way to me. Since I am unable to lay my hands on any spare carbs the rebushing may become the only option. Your comment gave me some new hope. I am definitely going to share the results once things get done. Why should the red sillicon be kept 100 miles away from the fuel system? I hank you all very much. Best regards Jarek On Sun, 1 Dec 2019 at 00:45, Rob Thompson <[email protected]> wrote: > My experience with worn throttle shafts is that they cause an overall > leaning of the mixture but not sudden changes to rpm with the throttle > position constant. > What you are hearing can be a good indicator of what is going wrong. What > does it sound like when the RPM drops? > Rob > > Rob Thompson > 0429 493 828 > > > > On Sun, Dec 1, 2019 at 10:01 AM Ian Williams <[email protected]> wrote: > >> Hi Jarek, >> >> Just may be able to help you there, as I have had a similar issue >> >> I have just completed a 500 hr inspection of our Dimona. It is one of the >> early ones … (one of 10 bought by the Thai Air Force in the early 80’s) >> >> The engine was reconditioned in Germany about a year prior to all 10 >> being sold by the RTAF. However the aircraft did not fly again with them >> prior to being sold. >> >> The engine was half installed … ie refitted but not completed. >> >> One carb was new while the other had been used. >> >> The aircraft has done around 450 Hrs now in New Zealand. I have had a >> couple of engine problems … one where the magneto condenser became very >> leaky .. happened just after take off and the engine didn’t like it at all. >> The other was a fuel problem which as it turned out was self inflicted >> (note .. keep red silicon 100 miles away from any fuel system) >> >> >> >> So back to the present. Because of some corrosion around the engine and >> baffles, during the 500 hr inspection I took the engine out and corrosion >> protected everything. Then engine back in. >> >> The first test flight went well with no apparent problems … However the >> second and subsequent flights … not so. >> >> What was happening was at around 500 to 800 or so feet after T.O. the >> engine would loose about 400RPM for about a second, then pick up again. >> Later it would do the same randomly even in coarse pitch but a bit longer. >> >> I thought it was a fuel problem so took out the tank, flushed all the >> lines and checked the fuel flow (took off the fitting to the RHS carb and >> ran the electric pump for 30 secs) got 28 to 30 L/hr which I thought was >> OK. I have an MGL fuel flow sensor which has a small orifice so gave that >> a good clean as well. >> >> After putting everything back, another test flight … still the same >> Bugger. >> >> I did think it could be an plug lead problem but if a plug stops firing >> you sure do know about it so had to rule that out. >> >> So I took both Carbs to a bloke about 15Km from where we are. He is an >> EX Air Force engineer specialising in fuel systems. He took a look at the >> carbs and said that the throttle shaft of one carb … he wouldn’t allow that >> on a car. … the shaft was worn but didnt seem excessively so to my limited >> experience. >> >> Apparently there is available a kit to repair these. However also the >> bearing surfaces (just part of the carb body really) can be replaced with >> Teflon bearings he said … so basically quite repairable. >> >> It seems that even a slight leak around the throttle shaft can upset the >> operation of the plunger with the needle attached … which is quite >> surprising. >> >> I just happened to have a couple of “new” carbs in stock so installed >> them after checking the diaphrams condition. Did a test flight yesterday >> and all was good. I did lean the mixture a little as the CHT’s were quite >> low (100 to 120 degrees C). Of interest, the engine started a lot easier >> and in the past had a tendency to stop on roll out after landing (even with >> the idle RPM set to around 900 RPM) … but no issue now. >> >> So finally … yes, rebush the throttle shaft / bearings. Any leakage >> around them seems to have a significant effect on the operation of the CD >> control. >> >> Hope that helps >> >> >> >> Best regards >> >> Ian Williams >> >> New Zealand >> >> >> >> >> >> >> >> *From:* [email protected] *On Behalf Of *Jarek Steliga >> *Sent:* Saturday, 30 November 2019 10:30 a.m. >> *To:* Laurie Hoffman via dog <[email protected]> >> *Subject:* [DOG mailing list] Stromberg 150 CD3 air leak around the >> throttle axle >> >> >> >> >> >> >> >> Hello, >> >> >> >> I am still struggling with my Limbach rough run at RPMs around 3000. >> Since my max static RMPs are ca 2700 the problem only becomes apparent on >> take off (I actually had to abort one take off while being already ca 100 m >> above the ground - a rather hair raising experience). >> >> >> >> After having replaced a perforated metering needle piston diaphragm with >> a new one I am back to square one in my detective work of what gives. >> >> >> >> The next suspect I am zeroing in on is a badly worn out brass throttle >> axle combined with the visibly enlarged hole in the carby body this axle >> protrudes through. Can the air passing through this opening affect the >> formation of underpressure inside the carby to the extent of producing >> effects above described? >> >> >> >> Any comment will be greatly appreciated as always >> >> >> >> Regards >> >> Jarek >> >> >> >> >> >> >> >
