stunthanger.com
Engine basics => Four strokes only => Topic started by: RC Storick on June 24, 2009, 05:01:31 PM
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This is a place to discuss four stroke set ups.
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Thanks Robert,
I have Saito .40 with stock C/L venturi modified per Bob Reeves articles with larger spray bar hole and nylon screw.
I adjust it on the bench and it runs fine for a period of time then starts running very ragged like it is lean, I richen the Needle valve and same thing occurs shortly thereafter. I am running Powermaster 20/20 fuel and a rev up 11x7
prop at around 8000 rpm. Any suggestions as it did the same thing in the air.
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Thanks Robert,
I have Saito .40 with stock C/L venturi modified per Bob Reeves articles with larger spray bar hole and nylon screw.
I adjust it on the bench and it runs fine for a period of time then starts running very ragged like it is lean, I richen the Needle valve and same thing occurs shortly thereafter. I am running Powermaster 20/20 fuel and a rev up 11x7
prop at around 8000 rpm. Any suggestions as it did the same thing in the air.
Hmmm, sounds like overheating (?)
Plan A - try again with a lighter prop - maybe an 11x6 and see if it will hold.
Plan B - and this might be more likely: are you using Uniflow? if not then consdier this: a standard vent tank always tends to lean out as the fuel burns off and fuel pressure-head decreases. Instead of 8000 RPM start it off around 7400. It should speed up some, but mabe will not reach the point of going lean and running rough...
Plan C - a Personal Message to Bob Reeves requesting help, as his Saitos run like watches!
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Thank you Robert..
Walter, That's a new one on me, out of 7 or 8 40's I've been involved with never had one that wouldn't turn an 11-7 at over 9 grand (RC carb wide open) and hold it. Am assuming you have checked the valve clearance and all the normal basic stuff.
I'm tending toward something too tight or changing in the engine, how much time is on it and are you seeing any black discharge from the breather?
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Walter
A few weeks ago I took my SA40 out to fly with a 11x5 zinger 15 % 18%oil at 9,000 RPM The engine easily turned 9,500. the plane flew great. My buddy Jim Welch uses 20 20 in his Saito 62 and wanted me to try some of his 20 20. I tried it on the next flight . The engine would not turn over 8,600 RPM . I let it go at 8,400 and had a flight of 10 min. on 2 1/2 oz of fuel. Landed and put my fuel back in the tank and the engine was back to normal. Who knows maybe it needs some castor. I got my old log book out and with a 11 x 7 on 10 % Nitro and 50 50 oil the engine turned 9,500 RPM
Willis H^^
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Saito is pretty explicit about not using Castor oil in their engines; something about varnishing up those little valve-thingies, I believe. My Saito .40 is very reliable with Pat Johnston's C/L mods. 1-flip starts, and turns an 11-7 APC at 9800. I launch at 9000, and it's like a tractor engine.
Edit: I should have added that I use only Powermaster YS 20/20 fuel, and the tank uses standard venting, not uniflow.
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Just wondering if that 40 was run on uniflow or muffler pressure?My 62's run great on muffler pressure but act the same as that 40 on uniflow.I don't think the fuel draw is the same all the way through a tank on uniflow as is the pressure set up.At the end there's no speed up or warning it just cuts off as if you flipped a switch.That takes a little getting used to but it's ok. Jim
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Thanks for all the replies,
I was using Powermaster 20/20 fuel with OS F plug. It will rev over 8000, however I adjusted the screw after
getting the rich lean setting for rpm, then setting the rich lean again etc. I am wondering if I have the venturi
chocked down too much with the adjuster screw. I have not checked the valves I will do that. I have another
Saito .40 I will also try with the same carb set up. What are the indicators of valves not properly adjusted???
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Thanks for all the replies,
I was using Powermaster 20/20 fuel with OS F plug. It will rev over 8000, however I adjusted the screw after
getting the rich lean setting for rpm, then setting the rich lean again etc. I am wondering if I have the venturi
chocked down too much with the adjuster screw. I have not checked the valves I will do that. I have another
Saito .40 I will also try with the same carb set up. What are the indicators of valves not properly adjusted???
Hi Walter, might check out the other threads started in this section.. Not sure if it will help but might give you a little more insight on how I'm running my 40's and if you follow the links you will see some of how I got where I am now. Can't answer your question about mis-adjusted valves as I've been pretty prudent about checking mine and have never had them far enough out to cause any problems.
Your problem is one I've never seen with a 4 stroke so just grabbing at straws. Doubt it can be caused by having the intake choked down too much, when I've don it the engine still ran fine just at lower power/rpm. This is leading me to believe something may be wrong internally with your engine. Bob Z tells about one guy that received a new 72 with the cam gear off by one tooth so stuff happens even with the best. Break in the other engine and if it does the same, think we need to start looking at your fuel and/or tank setup.