OS 9B Carby Issue

[Wayne Johnstone]

Hi all, I am currently having some issues setting up my 9B carb. My main issue is getting the set screw tight enough on the carby rotor, at the moment no matter what I have tried the throttle lever is spinning on the rotor which results in no throttle control. I have tried doing it up as tight as possible - still slips, do it up tight plus a loctite product - still slips, grind a flat spot on the rotor do it up as tight as possible plus loctite - still slips. I am currently out of ideas on how to fix it so that the throttle lever/arm doesn't come loose. Has anyone else experienced this or have any suggestions on what may work? Any help is greatly appreciated.

 

[Tom Foley]

Sounds like the arm has become dished or recessed in the center where the screw tightens on the arm . I would get /make a new arm with a heavier washer installed on the outside under the fastener . There should be very little resistance to turning and make sure it does not bottom out at either end of throttle throw . post a photo if you can .

 

[Wayne Johnstone]

I have attached some photo's. The "Carby 2" picture has the standard carby on the left and my modified (grinded flat section) on the right, I have also attached pictures of the throttle arm (not real good quality, sorry). The arm I believe is made out of aluminium. On inspection I noticed that groves, matching the thread on the rotor, have been made on the inside of the arm housing, could this be part of the problem? Also, I fired the motor up today to see if it would last, whilst it was running it was ok, every small movement on the controller resulted in an equal movement of the arm. When I then checked it after the motor cooled down, the slipping had returned, could the expansion / contraction of the 2 different metals be an issue? Thanks for the reply Tom.

 

[ids987]

The O.S throttle arm is steel, much thinner than yours, and sits on the plain section before the start of the thread. O.S use a star washer with a nut, to retain the throttle arm. If there is enough thread left (and enough to hold the nut), you may be able to revert to the original arrangement; Tower Hobbies may have parts. Loctite will not hold a plain arm on a thread, but could be used with the nut; if the thread is still good enough.

 

[ids987]

Original equipment parts: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCW23&P=Z

 

[Don Ferrette]

The O.S throttle arm is steel, much thinner than yours, and sits on the plain section before the start of the thread. O.S use a star washer with a nut, to retain the throttle arm. If there is enough thread left (and enough to hold the nut), you may be able to revert to the original arrangement; Tower Hobbies may have parts. Loctite will not hold a plain arm on a thread, but could be used with the nut; if the thread is still good enough.

Yup what Ian said.

 

[Wayne Johnstone]

Thanks for the info guys, so very much appreciated.

 

[Tom Foley]

Upon looking at your photos you could drill and tap for 3 set screws 4-40 , if you cant easily get new parts . I'm pretty sure it would not move .

 

[dwilfong]

I had problems with the 8AA carb same carb as 9B just a bigger bolt pattern.

The metal arms would break. I made a arm out of 1/8" aluminum plate and used the nut and washer to attach it .

Problem solved.

David

 

[Tim_Duggan]

There should be very little resistance to turning and make sure it does not bottom out at either end of throttle throw .

I agree with Tom. The linkage continuing to move the arm when the barrel is hard up against the barrel retaining screw, + movement in the engine mount when the engine is running will be the likely culprit. Many carbs with no "stopper" in the barrel use the grub-screw method to secure the arm with little to no issues because the barrel can move beyond fully open or fully closed.

Does your throttle servo mount have the rubber grommets and brass inserts on the mounting lugs? If not it will be very hard on the servo if you fix the carb arm movement without fixing the travel limit.

 

[FloridaScaleBoater]

I had problems with the 8AA carb same carb as 9B just a bigger bolt pattern.

The metal arms would break. I made a arm out of 1/8" aluminum plate and used the nut and washer to attach it .

Problem solved.

David

I run, and have run for quite some time, the 9B carb on everything 67 that I own. I have never broken an arm!

 

[Ray Sametz]

I had problems with the 8AA carb same carb as 9B just a bigger bolt pattern.

The metal arms would break. I made a arm out of 1/8" aluminum plate and used the nut and washer to attach it .

Problem solved.

David

I run, and have run for quite some time, the 9B carb on everything 67 that I own. I have never broken an arm!

Well RRRick, just screwed yourself. I say 3 broken carb arms next season. RRRay........==={}

 

[FloridaScaleBoater]

I had problems with the 8AA carb same carb as 9B just a bigger bolt pattern.

The metal arms would break. I made a arm out of 1/8" aluminum plate and used the nut and washer to attach it .

Problem solved.

David

I run, and have run for quite some time, the 9B carb on everything 67 that I own. I have never broken an arm!

Well RRRick, just screwed yourself. I say 3 broken carb arms next season. RRRay........==={}

Guess I should order a few Huh???

 

[Wayne Johnstone]

I have had a look and it appears to have the rubber gromet / brass inserts are in place. As far as the throttle travel I have tried a few different positions / servo arm combinations and I have it close to where it achieves wide open throttle at the end of the servo travel (I think).

 

[Wayne Johnstone]

I have just received the standard arm for the 9b Carby, I have tried to find some technical diagrams to answer the question I have but no luck as yet. The star washer, is that placed between the arm and the carby or between the arm and the nut?

Thanks again for all the assistance with this matter, very much appreciated.

 

[SayMikey]

I have just received the standard arm for the 9b Carby, I have tried to find some technical diagrams to answer the question I have but no luck as yet. The star washer, is that placed between the arm and the carby or between the arm and the nut?

Thanks again for all the assistance with this matter, very much appreciated.

between the arm and the nut Make sure you dont have too much servo throw or it will bind up and break the arm,servo or shear the stop pin in the carb