912 carb position switching

[Birdseyeview]

My build manual showed the installation of my Bing 64 carbs with their throttle and choke cable interfaces positioned inboard on the manifolds and with the manifolds bending towards the outboard positions. This is the way I assembled the carbs on the engine originally but I was dissatisfied with the accessibility of the throttle and choke cables and return springs and I had some photos of other builders carb/manifold installs and their cable interfaces were positioned on the outboard sides. As a result, I recently switched my carbs positions so the cable interfaces are now both positioned on the outboard sides too. I left the manifolds in their current outboard leaning positions. This position now makes all the interface points easy to check and adjust. This might have impacted the length of my existing throttle and choke cables but I drilled a new hole in the firewall for the left throttle cable and used the original hole for the right cable and they both just reached their respective carbs. Since I was changing my choke cable to a new T handle turn-to-lock version anyway the choke cable length was a non-issue. However, I did redrill the firewall holes for the new choke cable to optimize the cable routing. See the before and after pictures below of the right side carb:

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In the process of the changes described above I have been having some issues with hard starting and fuel venting and rough idle and as I was searching the Rotax heavy maintenance manual for information I noticed the following figure on page 33 of section 73-00-00:

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Now I'm wondering if by moving my carb positions I should also be swapping the guts of the choke mechanism to match the figure above. The last time I started the engine I had to use some starter fluid to get it started and I'm not sure if its related to the carb move or not. I'm believing my on-going carb venting issue is unrelated to the carb position swap and I'm chasing other ideas to solve that issue. Any thoughts / suggestions on the figure above? Did any of you have to swap out these choke parts to get the choke to function properly?

[avidflyer]

I put a factory new set of carbs on my Kitfox 912 a few months ago, and didn't do anything with the choke/enrichener. Starts just as good as always. JImChuk

[Dave S]

Larry,

A couple things that came to mind from the photos you showed - don't know if this will help or not but thought I should mention.

The little tygon hose coming from the inlet end of the carb looks like it may be pinched off - rotax does tuck the end into the bail for the carb bowl during shipment to keep it from getting lost and to keep crud from entering through it in transit. The vent does affect how how the engine may run and can affect fuel bowl venting.

A person could check having a second person available to make sure both enrichment vanes (choke plates) close completely when the choke is activated from the cockpit.

Unrelated; but, might be worth considering, to save some grief down the road or with the airworthiness inspection, is the ground lug attached to the engine mount - don't know what the 6 manual says, however, since the lug is tin plated copper and pretty soft; it is a setup for vibration wearing in the copper and causing the bolt to lose torque which can interfere with both the electrical ground and the integrity of the mounting point. The later model engine mounts have ground lugs welded to the engine mount tubing; but, I don't see any lugs on this mount???

My apologies if my suggestion is not very complete but you might want to check the little tygon hose

[Birdseyeview]

Dave,

Thanks for the suggestions - I didn't think about the soft copper ground lug on the engine mount bolt losing torque over time - sounds like I should at least add a check to my annual condition checklist to look at the grounding bolt for tightness. I will also check to see if I sandwiched the copper lug in between some steel washers to spread the load better.

The vent lines terminating under the bowl retainer clip does really seem optimum and I have added a 6" length of tubing to each side temporarily so I can better see from the cockpit if gas is leaking out the vent tubes. Once that leakage issue is resolved I plan to route the vent tube into the lower back side of the air filter as others on this forum have done.

I checked my carb's choke disc set up today and it reflects the figure I was wondering about and it started good today so I was probably concerned for nothing.