Straightleg

VERY interessting. What is the name of the carb, and where to buy?

/terje

Maxam

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It is an OS carb that fits the Gemini 120/160 and Pegasus FF240/320. You can get the carb from Advantage Hobby.com or Tower Hobby or a European OS engine supplier. This carb is for the 7-77 or 9-99 but not the 7-35.

Straightleg

Thanks! Tower has two almost identical carbs for these engines. One with 7 and the other with 8 mm bore. Both works?

chorner

Maxam, that's awesome news I would love to switch over myself! I wonder what crazy things this engine would do with the OS carb, plus my CDI setup. As it is, it pulls a 24x10 Mejzlik at 6,350rpm and will hold it there. I can't richen it up enough to even drop RPMS, never mind the overly rich bottom end.

I bet with a carb change I could push a really nice scale 3 blade for my Corsair easily. Good to know about the linkage too, I had redone mine already - good to know it will "translate".

Maxam

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Recall my corsair with the older 7-70 turns a 22x10 3 blade black Xoar warbird prop well. This 7-77 with the OS carb will easily turn a 23x12 3 blade well. Yes you can tune to slobbery rich on the top end with the OS carb.

BobH

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LXCA62
Max is that correct tower part number for the carb?
Thank you for the report!

Maxam

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Straightleg, go with the 7mm!

chorner

What's the original outer diameter on the OS carb if you don't mind me asking Maxam?

Maxam

My Feedback: (62)

It is 436". Trust OS but measure your engines dimensions! Look at my picture, it has the measurements. The OS part number is 46481000. During machining I made sure to constantly measure with a Sterret dial caliper. I made lapped piston fits so no gaskets or O-rings needed. When turning the carb you must take gentle cuts. The intake on the carb goes into the chuck and this portion is press fit in so you do not want to break that loose! Support the other end where the machining occurs with a live center. The carburation is much superior at all RPM's. There is no rough overly rich running anywhere in the throttle range. -Tom

Maxam

My Feedback: (62)

I just got back from the field flying my 50cc Yak 54 that has the 7-77 with the OS carb. The plane used to have a Saito 325 radial swinging a 20x10 prop. I have more power at less than 1/2 throttle than the Saito at full! The additional power with the 24x12 prop gave excellent pulling power and air braking like my Moki 215's with 33x16 props. The power is ridiculous at full throttle. From a hover the plane would pull out smartly straight up when floored. I have to say the 24x12 is too small. I need to get a 3 blade of the same dia and pitch. The OS carb has proven to be a great improvement even in 50 degree weather...burr. -Tom

Linkan2

Hi Tom
Glad to read that the engine is running so well.
I Changed carburetor on my 7-35 because it did not work out at high rpm.
The updated carburetor I can recommend to 7-35 are old.
Having looked a little on Saito's carburetor intresant is to Saito 90r3.
Lars

Maxam

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That is a good choice of a carb to use. That is the one I used on my Seidel 5-40 with great results. It should be ideal on the 7-35. -Tom

chorner

That's awesome Maxam - working on getting one of those carbs adapted Probably won't be able to fly at this point until next year, but I will be really excited to mount the engine up on a stand and let her rip!

P.S - let me know what 3 blade prop you try and the RPM. Once I get my carb adapted, I'd be interested in trying something like a 23x12, or 22x12 and see what it does - who knows, with the new carb maybe those will be too small...?

BobH

My Feedback: (2)

I ordered my Carb yesterday from Tower. I already knew that the supplied carb was insufficient. Can't adjust it properly as it's a poor design.
I would recommend to Horizon that they talk with the Indian designers and suggest/insist on a better carb for future productions of the engines.

Maxam

My Feedback: (62)

I actually got three carbs. Next engine, my 9-90 in the Robinhood 99 and then the 7-70 in my Corsair. Maybe I should get two more for the future. I could just see OS stop making them. They make far fewer 4 cycle engine models than they used to. It seems many modelers are running away from glow fuel to gas and electric. -Tom

Does anybody know someone who has the OS FR7 radial?

chorner

It's a shame actually. I love the glow engines; gas is too messy to be used for modelling unless you do all of your work outside in a shop. Even then, transporting them in your vehicle smelling of gas isn't exactly a great idea either. Huge fan of glow over gas, but I personally convert all of my engines over to CDI spark ignition for better running.

I may order another carb as well as I actually have two 7-77's.... although one of them has become strictly a parts engine. I'd like to buy an FR7 radial as well one of these days before they stop making them!

... on another note, I'm hopefully going to be able to adapt the carb to the 7-77 without hacking the mounting "lugs" off the OS carb. I'd like to still be able to use the bolt holes, to attach an OS choke mount on it versus using the stock EVO choke setup.

Two possible methods:
1) make a round adaptor, that can be 'locked' in place using the existing grub screws and same position on the backplate, and then on the front lip of the adaptor, drill down and use two more grub screws to secure the carb to the adaptor.
2) make a round adaptor, locked in place with original grub screws - and design a plate on the end of the adaptor that fits over the top of the two bolt holes, so you can use the bolt holes on the OS carb to use as a mounting point to the adaptor.

No carb hacking required, and should be no need to exactly match the distance from the carb inlet to the backplate as long as it's not way off. Going to try to get Adrian from CH to make me the adaptor as unfortunately I don't have the equipment to do so myself. If I did, I'd have one made up already!

kiwirob

Hi All,

I'm researching a possible next build project which will be a Hughes H-1 Racer 1/5 with an 80" wingspan (long wing version). I now have the Pepino plans and a cowl and thinking about engine possibilities - i'm a glow fuel baby

https://en.wikipedia.org/wiki/Hughes_H-1_Racer

I would really like a scale flying 7-cylinder radial and think the Evolution E735 or E777 could be a great match.

I have measured and both will fit within the cowl, the E735 with 1" clearance and the E777 with 1/4" which is tight but it would look very scale.

My preference is the E777 but i'm just worried it might just be to much weight and power, but it sure would look good in that cowl and it is a "racer" after all. The H1 has much lower drag compared with a war bird or a bi plane.

I plan on using Flite Metal, a scale solo prop, custom built scale landing gear which feature struts built into the gear doors, and a fully detailed cockpit. I estimate the model would end up in the 20-26 lbs range.

Any advice much appreciated

Rob

CH Ignitions

My Feedback: (11)

Hi Cody,
I have design the parts. It is a 2 part assembly.and I will have them shortly for all people that will like to try my design.
My try to carry OS carbs as-well and have as a kit.
Did not had time to build it for you this weekend, but I will try next weekend.

Thanks
Adrian

Do not reproduce for commercial purpose !!!

chorner

Adrian,

Awesome Can't wait to try it out. Looking forward to finally retiring the terrible stock carb. Exactly the design I had hoped for - being able to use the bolt holes and not having to cut into it or modify it in any way. The OS carb is beautifully made compared to the UMS stock carbs. Night and day just holding it in your hands

chorner

Rob, I think the Evo 35cc engine would for sure be under powered for a 20-26lbs plane. With that engine you're looking at an 18x8 prop at the large end for thrust swinging less than 6,000rpm stock. That translates roughly to 9 and a bit lbs of thrust. Think of the Evo 35 like mounting a 1.20 4 stroke single cylinder engine, with lower rpm and more torque. (Slightly larger props a bit slower).

The 7-77 would be right at home there, all the way up to a ~30lbs plane.

Maxam

My Feedback: (62)

I concur with chorner Rob. Definitely the 7-77 for this plane. -Tom

To Adrian, are these for sale? If so I will take two, if they are a piston like fit!

BobH

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Adrian, me too. I'd like one too.

Maxam

My Feedback: (62)

Adrian, are you planning on making this adapter? -Tom

CH Ignitions

My Feedback: (11)

Hi guys,
I will have the parts I think by Thursday.
Have to check the fit , to mount the carb on the adapter and on the engine.
I will let you know how it fits and if I did all right then I will make them available for you, I will post a picture.
I made only 25 of them, if more will need...then I will have the CNC shop to make more.
Price will be $30-35 have to see the final invoice with shipping .
Thanks
Adrian

Maxam

My Feedback: (62)

OK Thank you Adrian!