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Old 10-08-2016, 02:57 AM
  #32351  
Hobbsy
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Think of kickback or backfire as we erroneously call it as the result of the over lean mixture being like tissue paper in your furnace, the burn is fast and super hot and obviously occurs way before tdc on the compression stroke. Kickback would be the correct term. The muffler having fuel in it makes it possible for the engine to run backwards a few seconds when it kicks back. Pictured is the result of one such kickback. This one occurred because when I set the timing so carefully at 33 degrees btdc it was actually at 43. The kickback from over rich is because the compression is increased by the greater amount of fuel. Some will argue that but I think that is the reason. Generally the lean kickback is more violent.

The term backfire is a holdover from carburetor days when raw fuel would flow into the exhaust system during deceleration and the hot exhaust system ignited it. Gasoline Farmall tractors were famous for this. Fire would blow out the top of the muffler.
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Old 10-08-2016, 03:08 AM
  #32352  
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Is this an engine brake in issue or could this be an on going problem? I have other smaller Saito engines that don't have this problem.
Old 10-08-2016, 03:27 AM
  #32353  
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If you have 40 minutes or more on the engine, it is as broken in as it's going to get. Saitos with their hard chrome bore and narrow ring do not need gallons and gallons of fuel to break in. I don't know why people say that.

Where is Hamburg, I grew up in Beaver County near the Ohio river.
Old 10-08-2016, 03:40 AM
  #32354  
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Got the engine used so don't know how much run time it has. The piston is clean the valves have some deposits on them.

Hamburg is west of Allentown about 40 minutes drive.
Old 10-08-2016, 03:59 PM
  #32355  
blw
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Dave, if that were true you could set the needles and forget them.....which you can't. Also, fuel economy would be fantastic which it isn't until some gallon or more fuel is burned. You just can't listen to any Saito with only 40 minutes on it and say that's a fine, well broken in engine. They fly well at 40 minutes if you keep some limitations in mind. I never advocate longer on the bench than 40 minutes unless you just like doing that. These Saitos aren't OS's, imo.
Old 10-08-2016, 05:03 PM
  #32356  
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We will never quite agree on that but that's A-OK, the OS's actually take longer and I've never seen one hold compression as well as a Saito. My only other brand fourstroke engine is an old Enya .80 and it's compression is surprisingly good.
Old 10-09-2016, 05:09 AM
  #32357  
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Smoker just tryin to help out here..you bought a second hand saito run in by somebody else you don't know,or even how old it is.If you are running it as rich as you say and it still backfires on the odd lean patch (inconsistantly) i'd pull some o rings or sit down and watch a re run of the movie dumb and dumber.Barry makes some good points about running in and tuning saito's plus he does'nt mention os's much
Old 10-09-2016, 04:09 PM
  #32358  
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Ge I will be carful what I say but I have issue with some of the miss information released above first lets look at what happens with a lean mixture . The fire starts with the glow of the plug when the piston is near at the top dead centre the flame front then burns the fuel in what is called a flame front across the cylinder. Now in the case of a lean mixture the flame front is slowed to such an amount that the fuel is still burning as it goes out the exhaust valve more than when the fuel mixture is correct (I think its around 14 ; 1 BY WEIGHT ) one part fuel by weight to 14 parts BY WEIGHT of air . Now the heat from the exhaust, which is now higher will ignite the fuel when the valves are on the rock at top dead centre (exhaust valve closing End of exhaust stroke and. opening of inlet valve start of the intake stroke.( this is known as valve overlap). AS the valve are both open the flame front which is still happening due to the slowed burning of the fuel ignites the fuel in the intake manifold. The motor can run back wards. it can spit out the carburettor and in do the prop nut. I hope I have a few friends after this.
Old 10-09-2016, 04:25 PM
  #32359  
Charley
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Quig;

I had backfire as you describe in a MOPAR 360 CID. It was caused by intake valve recession in the heads, allowing the flame to get back into the intake manifold. Had to find other heads.

CR
Old 10-09-2016, 05:43 PM
  #32360  
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I intend to finish wringing out the 1.25 as soon as we get Geri back to good health.

PS, the flame front may be slow but the kickback is caused by the ignition occurring too early. Way too early in fact. My 1.50 has been known to remove the starter stick from my hand. The starter stick is nearly worn out and it's made of some really tough stuff.
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Old 10-10-2016, 04:23 AM
  #32361  
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Hi smkrcflyer, it looks like your question was buried in all that talk about 'Truth Serum'. Yes, your timing could easily be off. It could be a bit tedious to reset correctly, but if you're familiar with disassembling and reassembling 4-Strokes, you can have it done in about 20 minutes, and then you just have to reset your valve lash.

You need a special 'tool' (see the attached pdf) but that can be easily made. I made mine out of clear tubing and steel rod. I can make one for you if you send me a SASE. Or, you can use any convenient piece of stock that you have lying around. It's a little bit finicky to do, but not hard. Just make certain that your crank is precisely at TDC when you do it.

I remove my head & rocker arms as a single unit and put the pushrods and housing aside. Using a 1.5mm allen/hex wrench, remove the cam/gear (watch out for a spacer washer on either side of the cam and then push out the followers. AAMOF, on an engine the size of a 100, you might be able to push the followers out without removing the cam if you find something thin, flexible, and plastic (don't scratch anything). It takes longer to describe this than it takes to do it.


The file with the pictures was not done by me, it was done by someone else and posted online. I grabbed a copy.

Let me know if this helps you out,

Bob
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Old 10-10-2016, 04:27 AM
  #32362  
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Bob,
Thanks for the info its very helpful. I did reset the timing and hope to run it today.
Old 10-10-2016, 04:30 AM
  #32363  
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Bob, here's one most modelers have handy, a 2-56 stud and an inch of Sullivan Golden Rod
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Old 10-10-2016, 04:41 AM
  #32364  
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Jeez bob no need to get all uppity about truth serum dave's just explained why you see him smiling in every pic he posts,can you believe someone would name a place beaver?

Quigsy work on the Positive Side of mathmatics.If you got zero friends to start with you can't lose any..bang away buddy
Old 10-10-2016, 08:08 AM
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Got the engine running today. HS set at 2 turns out and LS 2 turns in. Ran 8oz and was a bit rich but no backfires. Will rum more later but I need a better spinner.

Thanks for all the help.
Old 10-10-2016, 02:23 PM
  #32366  
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You are most welcome, is the Short Brothers Aircraft maintinence center still in Allentown?
Old 10-10-2016, 03:45 PM
  #32367  
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Easy on the rum though, too much and you may not have fingers!
Old 10-10-2016, 06:11 PM
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The Rum is Pete's department.
Old 10-11-2016, 04:30 AM
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Originally Posted by smkrcflyer View Post
Ran it today at WOT and it ran for a few seconds then backfired and thru the prop nut. My setup is LS two turns in from outer edge of plastic arm, HS four turns out.
If the engine started & ran it isn't out of time. 1 tooth it is out 15 crankshaft degrees and the engine won't run that far out of cam timing.
Old 10-11-2016, 05:05 AM
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Exactly sr,they sound like a lazy 125 then.

Dave pour me a large glass of good navy rum and stand back..it's like puttin a fox in charge of the chookhouse
Old 10-12-2016, 01:58 AM
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Originally Posted by SrTelemaster150 View Post
I'm looking fore some input as to what would be an appropriate Saito engine for my latest project.

If it's got a Merlin in it, we could do the Mags for ya...

BJ
Old 10-12-2016, 02:02 AM
  #32372  
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Originally Posted by Dave, FormerDairyFarmer View Post
I intend to finish wringing out the 1.25 as soon as we get Geri back to good health.

PS, the flame front may be slow but the kickback is caused by the ignition occurring too early. Way too early in fact. My 1.50 has been known to remove the starter stick from my hand. The starter stick is nearly worn out and it's made of some really tough stuff.
That's a pretty bashed-up lookin Chicken you got there...

LoL

BJ
Old 10-12-2016, 02:07 AM
  #32373  
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Originally Posted by Charley View Post
Quig;

I had backfire as you describe in a MOPAR 360 CID. It was caused by intake valve recession in the heads, allowing the flame to get back into the intake manifold. Had to find other heads.

CR
I had a backfire on a Chev 454 due to a couple of plug leads in the wrong order - it blew a huge ball of flame back out through the Rochester 850 (?) carby.

Really lucky that my long-haired mechanic mate had just taken his head out from under the hood when it 'coughed'....

BJ
Old 10-12-2016, 04:30 AM
  #32374  
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Ok heres the plane. I don't know how to start. The saito .30 ran great the props recommended worked good. Did i say the little engine worked GREAT.
We had a hell of a time, we started out with the neatest little high speed boat you ever seen, could not get it off the water. After a couple of boat trips we took it in and made some minor changes and back to the water. (Armed with a trolling motor for boat, if you ever want to find out how out of shape you are try rowing a but ). So we try again plane takes off across water leaves water, stall splash. Out we go and back we get started back up little engine running great. Took off splash back out back in. We adjusted controls and tryed again. Little longer flight splash. Repeat this time it took off splash, floats break off. O NO PANIC. Jump in boat take off Frend shifts at same time i do splash. I am treading water frend still in boat full of water, trolling motor still going pushing boat in circles. With me hanging on the sid of boat and stearing boat back to shore, we dump water out of boat and back out to plane still floating with are dignity still intact sort of. We retrieve plane and back to shore, we decide that we were done. Plane needs some work and dryed out, it still was dripping water when i left for home next day. By the way little engine started ran great. I will have to say again that Saito makes one hell of of an engine.
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Old 10-12-2016, 05:20 AM
  #32375  
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Originally Posted by BJ64 View Post
I had a backfire on a Chev 454 due to a couple of plug leads in the wrong order - it blew a huge ball of flame back out through the Rochester 850 (?) carby.

Really lucky that my long-haired mechanic mate had just taken his head out from under the hood when it 'coughed'....

BJ

I don't know he might have looked good with the resulting Burr cut?!

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