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Gas Saito Radial problems

Old 05-09-2021, 06:06 AM
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lazun
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Default Gas Saito Radial problems

I have a Saito fg-19 r3. Morris intake mod, Morris prop hub, timed correctly. Running Ethanol free 91 gas. Bench ran for two gallons, 16x8 prop. Runs perfectly on stand turning 7100rpm.

In airplane does not run at full throttle. It dies and starves out. Runs perfectly at idle and transitions great. But at full throttle it will run for a few seconds and then fades out and dies.

I thought it was debris in carb. Nothing.

I thought it was the tank or fuel lines rebuilt the tank. Nothing.
I thought it was air problems and made a hole in fuselage to channel air. Nothing.
In the stand it runs but in the plane it does not 100% of the time.
Whatís happening in plane?

Not a walbro carb. Saito pump carb.

No electric fuel pump.
It does it in the airplane static on ground.
Engine not cowled. Just carb in fus.


Old 05-09-2021, 07:59 AM
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The High speed needle setting is to lean, it needs to be richened, turn the HSN counter clockwise 5-10 minutes.
Old 05-09-2021, 10:59 AM
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I did open up the needle. No difference. Still dies as I come up to full throttle. But with it richer seems to last longer. So maybe fuel issue.

But the thing is that i keep taking the engine on and off the airplane to the test stand. I have yet to replicate this on the test stand. Only in the plane. 100% of The time same. All same components. Tank, ign, mount setup. Only difference was open in back of carb. So that is why I thought air. Made opening in fuselage to direct air directly to carb. No difference.

Yes thought it was air and ran a hole to duct outside air to Venturi. Now plenty of air to suck in at full throttle. Thought it was air. Now I have plenty to get in. Ran same with or without the cowl.

Also, not prop. Tried with many different props. Plus on stand with 16x8 runs flawless. Ran full throttle for 3 min straight no overheat issues on stand. Broke in on stand for 1 1/2 hours. In plane will throttle up to full but then in a few seconds starve. I thought air problems. But no. Maybe tank? I did rebuild tank. Tank about 4 inches back. 4 inch’s low. Yes taildragger.


Old 05-09-2021, 12:31 PM
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Originally Posted by lazun View Post
I did open up the needle. No difference. Still dies as I come up to full throttle. But with it richer seems to last longer. So maybe fuel issue.

But the thing is that i keep taking the engine on and off the airplane to the test stand. I have yet to replicate this on the test stand. Only in the plane. 100% of The time same. All same components. Tank, ign, mount setup. Only difference was open in back of carb. So that is why I thought air. Made opening in fuselage to direct air directly to carb. No difference.

Yes thought it was air and ran a hole to duct outside air to Venturi. Now plenty of air to suck in at full throttle. Thought it was air. Now I have plenty to get in. Ran same with or without the cowl.

Also, not prop. Tried with many different props. Plus on stand with 16x8 runs flawless. Ran full throttle for 3 min straight no overheat issues on stand. Broke in on stand for 1 1/2 hours. In plane will throttle up to full but then in a few seconds starve. I thought air problems. But no. Maybe tank? I did rebuild tank. Tank about 4 inches back. 4 inchís low. Yes taildragger.
It's still too lean, on Saito radials the high speed need has very little effect at full throttle. The low speed needle controls approximately 85% of the fuel delivered to the engine. Leave the HSN setting where you last richened it, now open/richen the low speed needle 5-10 minutes counter clock wise and do a full throttle run. The difference why it runs at full throttle without any problem on the test stand is the carburetor air is not restricted. With the carburetor inside the fuselage, even though you made an air hole for air, the fuselage still restricts the amount of air available to the carburetor, this causes the fuel mixture to become lean and starves the engine so it stops. I have several Saito single cylinder engines and two Saito radials, FG60R3 and a FG90R3 and from my experiences your problem points to fuel starvation due to needle settings being too lean. The clue to being still too lean is from what you wrote in your comments Quote "Still dies as I come up to full throttle. But with it richer seems to last longer" Unquote.
Old 05-09-2021, 05:54 PM
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Wow. Okay. Thank you. I will try.

However, I also did some more experimenting today before I saw your post. I ran a new fuel tank outside the plane to test. I dangled the new tank on the floor next to the gear. Choked it and the carb drew the fuel right up to engine mounted in plane. I started it and it did the same thing as always in plane. My son then raised the tank above the motor and it ran perfectly as on the test stand with the same needle settings as on test stand.

Can this be?

In the plane the tank is about 4in back and 4in below the Venturi centerline. On the test stand I used same tank as in plane and fuel line 4in behind as in plane but may have been only 2 inches lower than carb.

Can this be the difference in run?
Can this also be a pump issue?
How can I verify this?
I guess opening the low end compensates for this?


Last edited by lazun; 05-10-2021 at 03:18 AM.
Old 05-09-2021, 05:56 PM
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Old 05-13-2021, 04:59 PM
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First thing that came to mind is tank location so based on your experiment you answered the question. The tank position should also be covered in the Saito manual. The tank should be even with the carb not below so it can draw fuel.
Another thing to check is back pressure from the exhaust to the tank. I run this on the FG60 radial and itís pretty much required for smooth operation. I tried it w/o and had poor results.
The FG90 doesnít seem to need this. Iíve run the FG30 as well and it didnít have the back pressure line, sure enough in flight it lost power.

Also now that you have some time on the engine you might want to check the valves and adjust them as needed.
Old 05-14-2021, 04:55 AM
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Originally Posted by Chris Nicastro View Post
Another thing to check is back pressure from the exhaust to the tank.
Gaps all done. I am trying to move tank upwards and closer as we speak. Sounds like a plan on the pressure from exhaust.

So tap into exhaust ring and run to vent line of tank? Does this create problems with the dirty oily exhaust to the tank? What do you do?

Also how do I know the pump works on this carb? It should do something to help with flow? But how does it work on Saito and how can I verify it’s working? As you can see it’s a Saito pump system carb.
Old 05-14-2021, 11:44 AM
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The Keleo pipe had a tube for the 60 but if yours doesn’t then you can probably use a Dubro brass fitting. For the dirty oily residue I just put an in-line filter but after some time running this it didn’t seem to be a big deal so I removed the filter. The residue was minimal. The location is at the 12oclock position for max back pressure but you can be left or right of that as needed in case the exhaust port fitting is in your way.
Worst case if it’s not helping you can plug it but most likely it should help keep positive fuel pressure.
Old 05-15-2021, 08:01 PM
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Originally Posted by lazun View Post
Wow. Okay. Thank you. I will try.

However, I also did some more experimenting today before I saw your post. I ran a new fuel tank outside the plane to test. I dangled the new tank on the floor next to the gear. Choked it and the carb drew the fuel right up to engine mounted in plane. I started it and it did the same thing as always in plane. My son then raised the tank above the motor and it ran perfectly as on the test stand with the same needle settings as on test stand.

Can this be?

In the plane the tank is about 4in back and 4in below the Venturi centerline. On the test stand I used same tank as in plane and fuel line 4in behind as in plane but may have been only 2 inches lower than carb.

Can this be the difference in run?
Can this also be a pump issue?
How can I verify this?
I guess opening the low end compensates for this?
Sorry lazun I've been away this past week. Did you open/richen the low speed needle 5-10 minutes as I suggested and run the engine to full throttle with the fuel tank in the fuselage location? If you did, did the engine run at full throttle longer than it did before, then the engine stopped? You proved the the pump is working by what you wrote :above " I dangled the new tank on the floor next to the gear. Choked it and the carb drew the fuel right up to engine mounted in plane". The Saito carburetor pump operates by using the vacuum from suction caused during the intake stroke of the piston to actuate the pump diaphragm, then the pump spring returns the diaphragm to its resting position. This pump diaphragm sequence repeats on every intake stroke of the piston to draw fuel from the tank to the carburetor.
Old 05-20-2021, 10:49 PM
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Finally got to it. I did a lot of things that was suggested, and I think they will all help. I may not know what will cure it exactly.
1. Rebuilt new tank with XL fuel line, recommended on Saito website. Canít hurt.
2. Raised tank as high as possible in airplane. Canít hurt.
3. Brought tank closer to firewall. Canít hurt.
4. Made an intake scoop for carb air. Canít hurt
5. Opened low and high end needles.
6. Gaps all done, plugs and carb is clean and working correctly.
All this took a while to rebuild around my days off from work. Mounting everything back in plane and will be ready to run in plane on my next day off. Thanks for all the help.
Old 05-23-2021, 05:42 PM
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I finally got to run the motor in plane. It took different needle settings to run correctly. 1 3/4 high end 5 7/8 low end. You are correct that the low end also affects the high end significantly. Both needles run on the same tube like a glow engine. The pump sucks. Motor transitions good. Runs if I point it straight up or down. But sometimes quits at full throttle instantly if I lower nose too fast from a nose high attitude.
Old 05-25-2021, 08:08 AM
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Originally Posted by lazun View Post
I finally got to run the motor in plane. It took different needle settings to run correctly. 1 3/4 high end 5 7/8 low end. You are correct that the low end also affects the high end significantly. Both needles run on the same tube like a glow engine. The pump sucks. Motor transitions good. Runs if I point it straight up or down. But sometimes quits at full throttle instantly if I lower nose too fast from a nose high attitude.
When you go flying avoid pulling negative G's, the engine will stop due to fuel starvation. You will be fine if you fly normal routines such as straight & level, banking, aileron rolls, loops etc. but avoid pulling negative "G" maneuvers. If you want to do negative G's you will have to slightly re-adjust the needle settings which will be a bit tedious and sometimes frustrating if you're not a patient person with this type of Saito gas carburetor.

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