Rotax 912 carb sync.

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fusionfab

Well-Known Member
Joined
May 16, 2012
Messages
87
Location
southern ontario canada
Well, after some down time with the plane over the winter and redoing cooling issues etc. I'm just about to wrap up it all up once the plumbing is done.

This weekend I will be running and syncing the carbs. The previous owner installed this freshly rebuilt stratos EA81 and encountered loss in power and engine wouldn't reach high rpm's. I purchased the plane, rebuilt the ridiculously dirty and clogged carbs and re did throttle linkage so they were pulling equally and a huge difference in power gain and rpm range. Now I am confident the issues were fuel and intake.

So here are my questions:
1. What are your thoughts on this cross section hose that leads from one carb manifold to the other, is it some sort of vacuum balancer?
2. On the one manifold theres this press in fitting thats loose and seems to me like it would be a huge vacuum leak, is that supposed to be like that?
3. Lastly, with no ports on these intakes and just this connecting hose, how do I go about syncing the carbs? Or am I bench top syncing them equalizing all set screws?

This is a freshly rebuilt subaru EA81 engine with the dual 912 carb conversion.

Here is the link to the video showing what I mean and I appreciate any help.

https://www.youtube.com/watch?v=6UMNsQza-v4
 

Richard6

Well-Known Member
Joined
Aug 14, 2010
Messages
721
Location
Plymouth, MN USA
Wow, that looks bad.

Typically the crossover tube is used to reduce intake noise. However I don't know what the small tube into the intake manifold is for. I'm guessing it was used on the car as part of the engine control system. I see that it was supposedly plugged with a short capped off tube. Now I'm not an expert on Subaru engines, but I'm guessing that you don't need this and it diffidently will present a air leakage problem. I would suggest that you get it welded shut.

Good luck,
Richard
 

fusionfab

Well-Known Member
Joined
May 16, 2012
Messages
87
Location
southern ontario canada
I agree I noticed this was loose and was like what the hell. Just as you said it looks bad so j think I'll be tig welding it closed. Would I install two new ports for syncing the carbs or no?
 
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