The International Cessna 170 Association

Hi All,

I purchased a 10-4895-1 (overhauled) to replace my 10-3237 and it came with safety wire where the throttle spring is on the old one. I saw something written about ensuring you safety the screw when removing the spring, but that was for a different model.

I remember during training being told if the throttle cable were to fail, the carb defaults to wide open giving full power, which I thought was the point of this spring.
Has anyone seen this on newer carbs? What would the throttle do in the event of cable or linkage failure without the spring?

Gareth.

I don’t have a perfect answer for you, but Service Bulletin A2-66 removed the throttle opening spring from certain other carb models…for example the 10-4439….which converted it to a 10-4895…. indicating (to my uneducated mind) that the spring was to be removed. It might be best to contact Tempest with your question for a more authoritative answer, but here is a copy of the SB which removed the throttle opening spring:

https://msacarbs.com/pdf/A2-66.pdf

Thanks George,

I continue to be amazed at the database of SBs, ADs, STC, etc. that you seem to have memorized!

I'm not concerned that the spring is missing - obviously it's in compliance with the SB. It's more I'm nosey and would like to know why it's been removed, what it's function was and why is that function no longer necessary!

Sometimes it's tough being an enginerd!

G.

gobrien wrote:Thanks George,

I continue to be amazed at the database of SBs, ADs, STC, etc. that you seem to have memorized!

I'm not concerned that the spring is missing - obviously it's in compliance with the SB. It's more I'm nosey and would like to know why it's been removed, what it's function was and why is that function no longer necessary!

Sometimes it's tough being an enginerd!

G.

Thanks for the complment …for which I am completely unworthy. It’s the “tribal knowledge” of the 170 Assoc’n that comes to the rescue of us all. People like Gary Friesen, Bruce Fenstermacher, Miles Bowen, Ed Booth, ….and geesh…I’d have to pull out the Directory and spend the day typing names…that really make this Forum and the Assoc’n so WorthWhile! (apologies to all those I didn’t have at the top of my small head)

I can’t answer they “Why” of your question…but I wonder if that throttle plate isn’t sucked wide-open by the manifold vacuum anyway if the engine is running. (Of course all that assumes the disconnect occurred at the throttle-arm… what if it was the cable itself which parted at some other point..?? Would the throttle-plate have sufficient influence to overcome the friction of a defective cable still attached..? I don’t know the answer.)

The better question is why the spring was ever installed in the first place. I can't imagine that it would have enough power to overcome the friction of the accelerator pump. This is a good reminder to pay close attention to the condition of the engine control cables and rod ends.

My guess is the spring is for hysteresis where vibrations if not attenuated, might lead to accelerated shaft wear but that’s a wag on my part