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Author Topic: Geometry of Reeves' Saito 62 Carb Screw?  (Read 286 times)

Online Dave Hull

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Geometry of Reeves' Saito 62 Carb Screw?
« on: September 03, 2018, 07:40:05 PM »
Working on a plane for a friend. The first 4-stroke I've dealt with and learning a few things....

It has a Reeves' carb mod according to the graphics on the plane. The tip of the nylon screw is distorted/melted, probably from running backwards. What shape should the tip be, or does it make any noticeable difference?

Since this is mounted inverted in a Legacy, it places the intake quite close to the cross-grain filler between the engine mounts. There is some charring and erosion. I was thinking about bonding in some type of heat shield to maybe make things less fire-prone. The first thought was a small piece of tin-plate material.  Anyone else doing something similar?

Thanks for the help,

Dave


Offline Bob Reeves

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #1 on: October 02, 2018, 04:08:22 AM »
Been a while since I have visited the forums..

The nylon screw should be as new or as cut to length with dykes, no issues with messing up the threads, just makes it stay put at the setting better.
Use a starter, prevents starting backwards, charring is due to engine running in reverse, never had one do that because I always use an electric starter..
I put an air scoop on the inside side of the fuselage to force clean cool air into the intake area. Never had one mounted other than on it's side. In your case I would put the scoop on the top of the nose and create an air path through the cross-grain filler to the intake.

Offline Vitalis Pilkionis

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #2 on: October 02, 2018, 04:39:00 AM »
Hi Bob,
can you please post an image with the inside side of the fuselage showing all the route of clean air to the intake.
And what effects can one expect in flight while flying without this fix?
I'm going to maiden my new ship with Saito 72 in a few days.

Regards,
Vitalis

Offline Bob Reeves

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #3 on: October 02, 2018, 02:05:43 PM »
Pictures in this thread show the nose of the Latency with the air scoop.
https://stunthanger.com/smf/building-techniques/functional-4-stroke-nose/msg100873/#msg100873

The scoop is just 1/16 balsa wetted then wrapped around a dowel. After it was dry I cut it on an angle with my band saw. Under the scoop is a hole that channels the air into the engine compartment. Hard to see in the photo but the hole through the fuse side is angled back.

Online Dave Hull

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #4 on: October 02, 2018, 09:27:29 PM »
Bob,
Thank you for your reply. It definitely helps.

This engine is set up as a OTIAS 62, and I didn't realize (I was the guy holding the plane) that the engine was being started "backwards" until I felt the air going the wrong way.... I also did not realize that they would run backwards continuously, or that the intake  becomes the exhaust and vice versa. With what I have heard since then, I would probably just stick my finger over the muffler to shut it down quickly, or maybe pinch the muffler pressure line to cut off the fuel?

We used a starter, but red to red doesn't work if the engine is set up for reverse rotation.... We will add that to the preflight prep list as well.

I will go ahead and just square up the end of the choke screw, since you are suggesting that a standard screw is preferred. I didn't know if it was supposed to have a taper on it or not. But now we will have to find the right position for the screw all over again. Is there a thread on how to do this?

I made a heat shield out of tin plated steel to screw down on the bearers that covers the wood around the inlet in case there is another mistake. No need to burn the plane up....

As far as the air scoop, I guess I am going to suggest to the owner that we try it out as is, with the air coming in via some really big cutouts in the Legacy cowling. I moved the bulkheads around, so there is now one right behind the intake, which should add a bit of cowl pressure. Rear intakes have worked well for me on racing planes, including B-TRs and F2C planes, so it is worth a go. It tended to stabilize the run and settings. Hopefully the big 4-stroker will do the same. If not, then a top-mounted air intake scoop lurks in the future....

I wanted to rebend the exhaust pipe per recommendations in a prior thread, but since it is not my engine, I didn't want to experiment with that process. I will rotate it so that a nose-over won't knock it off the plane--hopefully.

Thanks for the photos and the information,

Dave

Online Dane Martin

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #5 on: October 02, 2018, 09:45:57 PM »
I'm not a fan of starters on 4 strokes. 3 choke flips and clear it 6 times. One good strike backwards and it should fire right up. If it typically starts backwards, it's too wet. Adjust the choke / clearing flips from there.
Also! With that big engine, don't flip through like we do on 2 strokes. If it's too wet and kicks back, well, you know. I was starting a 72 with a finger guard. Not following my own advice, I attempted to start it with a fast flip through. It threw that finger guard across the runway!

Online Dave Hull

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #6 on: October 02, 2018, 10:10:23 PM »
Danish,

Can you be less cryptic about finger flipping methods for large 4-strokes? I'm beginning from zero here....

Do you mean that you slowly or gently flip backwards and expect it to kick forwards, knocking your finger out of the way, and starting? I know that works great on Mongo-compression engines like the Supertigre C35 if you get it wet before flipping. Safest method. On the other hand, I whack a K&B 40 pretty hard forwards (Dykes ring). Not much experience yet with 60's, but have an Enya CXL 61 Pro going into something soon and a rebuilt (sort of) K&B 61 that needs test running. Since these are 2-strokes, I'm pretty confident I can figure them out pretty quick. No such illusions about the Saito....

I use a glove anytime it is not a wood prop. I use a glove on a wood prop if I am unfamiliar with an engine's eating habits....

McDivot

Online Dane Martin

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #7 on: October 02, 2018, 10:16:12 PM »
3 Choke flips forward, no battery connected. 6 fast flips forward, no battery. Spin it to compression and connect the battery. Then a good strike or flip backwards. It should fire right up.

So yes, if you try to flip start it forwards, it'll usually fire backwards with your finger in the way!

Online Dave Hull

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #8 on: October 03, 2018, 12:29:28 AM »
Ok, I think I get your method for hand propping the beast. Thanks!

I just cut down the melted screw. It was plenty (too) long, so I knocked off a bit on the bandsaw then took it to the belt sander, and finally broke the edge with a file. Pretty much a flat tip.

If I can get the final trim colors on it, we can test out the engine again.

Dave

Offline Bob Reeves

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Re: Geometry of Reeves' Saito 62 Carb Screw?
« Reply #9 on: October 03, 2018, 12:24:18 PM »
Setting the needle and choke screw are discussed at the end of this article.
http://www.tulsacl.com/SaitoCarb.html


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