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May 08, 2021, 09:25 PM
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lazun's Avatar
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Discussion

Saito radial problems running


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.
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May 08, 2021, 09:30 PM
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lazun's Avatar
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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.
What’s happening in plane?
May 09, 2021, 06:18 AM
Still gassin' it.
I assume, it has a Walbro carb? Does it have the electric fuel pump?

When you say "in the airplane", do you mean "flying"? or does it allready die while still only standing still in the pitt?

Is the engine cowled? (cooling)

If it dies when flying, my thought is fuel starvation due unloading in the air, in that case just set it a bit richer.
May 09, 2021, 06:57 AM
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lazun's Avatar
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Thank you so much for the reply.
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.
May 09, 2021, 11:19 AM
Still gassin' it.
Taildragger plane? Where is your tank located? Directly up against the firewall, or further back? (The Saito carbs have weak pumps according to Saito themselves).
May 09, 2021, 11:58 AM
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Bone's Avatar
I reckon the 16x8 prop is too big causing the engine to overheat and slow down. The manual for the engine recommends a max prop size of 15x6.
Last edited by Bone; May 09, 2021 at 11:58 AM. Reason: Text layout
May 09, 2021, 12:23 PM
No more wasted spark 😉
ClubFlyer's Avatar
It could be caused by the prop wash / air pressure fluctuations inside that short cowling where the carb is protruding into, and air pressure fluctuations inside that area are acting on the metering diaphragm atmosphere vert.
May 09, 2021, 12:45 PM
Still gassin' it.
Quote:
Originally Posted by Bone
I reckon the 16x8 prop is too big causing the engine to overheat and slow down. The manual for the engine recommends a max prop size of 15x6.
Hmm... Missed that... that might indeed be a bit large, although 20 cc singles usually run well enough on a 17 x 6 (approximate equivalent) a radial might not.
May 09, 2021, 01:13 PM
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lazun's Avatar
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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.
May 09, 2021, 01:15 PM
Still gassin' it.
Quote:
Originally Posted by lazun
In plane will throttle up to full but then in a few seconds starve.
Did you try setting it a bit richer?

Quote:
Originally Posted by lazun
Tank about 4 inches back. 4 inch’s low.
Tail dragger or trike?
May 09, 2021, 01:17 PM
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lazun's Avatar
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Yes thought that 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.



Quote:
Originally Posted by ClubFlyer
It could be caused by the prop wash / air pressure fluctuations inside that short cowling where the carb is protruding into, and air pressure fluctuations inside that area are acting on the metering diaphragm atmosphere vert.
May 09, 2021, 01:17 PM
Still gassin' it.
Quote:
Originally Posted by lazun
Just carb in fus.
Possibly altered airflow affects air pressure sensing hole.
May 09, 2021, 01:19 PM
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lazun's Avatar
Thread OP
Quote:
Originally Posted by ClubFlyer
metering diaphragm atmosphere vert.

Can you tell me more about the metering diaphragm? Where is it? How can I test?
May 09, 2021, 01:25 PM
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lazun's Avatar
Thread OP
Quote:
Originally Posted by 1967Brutus
Did you try setting it a bit richer?



Tail dragger or trike?
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.
May 09, 2021, 01:34 PM
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lazun's Avatar
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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, it’s the 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.
Last edited by lazun; May 09, 2021 at 02:02 PM.


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