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Hi,

I am trying to get my carbs synced & having issues. I replaced the diaphrams in both carbs. Went through & made sure the jets matched on both carbs & that the needle clips were in the same position. 

With the carbs on the engine I set both idle screws to the same position & also set & checked the throttle cables start opening at the same exact time. I also checked that the mixture screws were both set at 1.5 turns out. 

 

With the air filters off & the engine running, as the throttle is slowly increase I can clearly see 1 slide opening before the other. 

Is the fix as simple as adjusting the slow opening side more on the throttle cable adjustment? 

I would think that if the throttle levers on the carbs start moving at the same exact time then the vacuums would be identical........ 

I also held the slides open (engine off) & verified that the butterfly valves move at the exact same time when advancing the throttle. 

Any suggestions......? 

 

Note: I can't do an intake/vacuum balance of the carbs without some fabrication on the crossover tube. The crossover tube was modified by the previous owner & is now a 1" tube with only 1 sync port on the right bank. There is no port on the left bank for hooking up vacuum gauges. 

 

Thanks,

Jesse 

  • Re: 912UL Carb sync

    by » 5 months ago


    Does the modified crossover tube have a removable center section?


    Walt

    my blog; waltsrv12.com


  • Re: 912UL Carb sync

    by » 5 months ago


    You will have to find a way of attaching the vacuum gauges to each cross over port (remove the balance tube). This is what I did on my first Rotax 912 ULS, a 1999 model without the small vacuum ports.


  • Re: 912UL Carb sync

    by » 5 months ago


    Yes, but its a 1" tube. I would have to make adaptors to choke it down small enough to hook smaller vacuum lines to it. 


  • Re: 912UL Carb sync

    by » 5 months ago


    Jesse Ringgold wrote:

    Yes, but its a 1" tube. I would have to make adaptors to choke it down small enough to hook smaller vacuum lines to it. 

    I have never seen a balance tube modified to 1in, so am having difficulty in advising beyond what I have already said.

    With my last 912 I just made up an adapter/reducer out of different pieces of hose, so that each vacuum gauge tube could be attached - worked just fine.


  • Re: 912UL Carb sync

    by » 5 months ago


    That's likely what I'll have to do is have to custom make adaptors to fit the 1" fittings. 

    This setup is odd & custom. The guy who did it claims that it smooths out the low end. I can't confirm or deny that it works. 

    Here is a pic that I tried to zoom in on. 

    37726_2_Screenshot_20231014-191109_Gallery.jpg (You do not have access to download this file.)

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