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I have now tried three different sets of carbs including a new set on this under 100hr 912 and The same behavior with all of them when trying to pneumatic sync.

Left side makes good vac at idle but right side is will not. To get them close, throttle positions are very far apart. (3/16”+) And egt’s are then very far apart as well so that feels like a bandaid.

Direct Compression test shows 135psi on cyl 1 and 2
155psi on cyl 3 and 4
Diff compression test shows all within 2 psi. 82/85 etc.

I have done the intake leak test spraying starting fluid while at idle and no change in rpm.

New plugs, Also dee no change in right/left relationship during mag check.

I have replaced fuel lines and blown out banjo Tee fitting.

I have removed valve covers to confirm that all valve are opening completely and no rocker play is present at any point.

I am now 2 months in trying to find the issue with no resolve.

Please help.

Is there any possible ignition issue that could effect right/left?

They will not sync and the egt’s are 350 set apart in cruise rpm.

Engine does not run rough though.
  • Re: Cannot sync with new carbs

    by » 6 years ago


    Did you try changing your gauges between carbs to see if the reading would swap sides?

  • Re: Cannot sync with new carbs

    by » 6 years ago


    Yes, I swapped the complete vacuum setup between sides to verify it is not a tool issue.

  • Re: Cannot sync with new carbs

    by » 6 years ago


    Then it is a throttle issue or a fuel delivery issue.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Cannot sync with new carbs

    by » 6 years ago


    I went up today and went through the throttle linkage to make sure. I also changed the EGT sender again. Still, 300 degree difference in cruise flight and about 150 degree difference at idle. The right side is always the lower temp side no matter what I do.

    Again, I have had three different pairs of carbs on it including a brand new pair and always the same behavior. I have blown out the fuel lines from the banjo tee to the carbs.

    My next question is, If the fuel pump is failing, should I expect one side to be consistently effected over the other?

  • Re: Cannot sync with new carbs

    by » 6 years ago


    I doubt it is the pump. How many inches of vacuum difference between carb? Don't worry about the temp. Just get the vacuum equal. Are the EGT probes the same distance from the head flange?

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


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