Hey everyone, I’m hoping to take advantage of the collective brain power and experience of this group. I’m just getting back to building after several months of life getting in the way and man does it feel good! But I digress, I ran into a snag this evening while working on getting the mixture hooked up. It appears that I don’t have enough throw in the quadrant to get the mixture from stop to stop. When I investigated drilling a new hole in the quadrant, it appears that the standard Van’s green cable is running out of travel, so a new hole in the quadrant might not gain me much, if anything.
See the image below of the cable in the quadrant at full rich:
Then see the image below at the carburetor at idle cutoff:
When I look at the mixture lever, it appears I need about 1/4” more of travel from the cable to actuate the mixture stop to stop (not even including the standard ‘cushion’ in most engine control setups).
My next thought was to drill a hole in the mixture arm on the carburetor closer to the pivot point but the shape of it doesn’t really allow for that:
I don’t have an image on me, but the OP instructions from Van’s show a mixture arm that looks to be the same general shape as what I have, so it’s not like I have an oddball carburetor (well maybe I do, but it doesn’t seem like it). Furthermore, I found this Kitplanes article that specifically calls out the RV-8 as frequently having this problem in the ‘Controls’ section:
https://www.kitplanes.com/carburetor-maintenance/
So I’m kind of thinking this might be somewhat of a design flaw with the RV-8 quadrant.
Does anyone have any suggestions as to how to overcome this? Is there an aftermarket mixture control arm that I could buy with similar, but slightly different geometry that might work better in my application? The current mixture control arm appears to be made of brass or bronze or something similar, so without knowing the specific alloy, I’m apprehensive about any sort of bending/welding/modification that may weaken or break the arm.
Surely I’m not the only person to have taken on a carbureted RV-8 so I’m hoping this group can offer some advice.
Thanks!
See the image below of the cable in the quadrant at full rich:
Then see the image below at the carburetor at idle cutoff:
When I look at the mixture lever, it appears I need about 1/4” more of travel from the cable to actuate the mixture stop to stop (not even including the standard ‘cushion’ in most engine control setups).
My next thought was to drill a hole in the mixture arm on the carburetor closer to the pivot point but the shape of it doesn’t really allow for that:
I don’t have an image on me, but the OP instructions from Van’s show a mixture arm that looks to be the same general shape as what I have, so it’s not like I have an oddball carburetor (well maybe I do, but it doesn’t seem like it). Furthermore, I found this Kitplanes article that specifically calls out the RV-8 as frequently having this problem in the ‘Controls’ section:
https://www.kitplanes.com/carburetor-maintenance/
So I’m kind of thinking this might be somewhat of a design flaw with the RV-8 quadrant.
Does anyone have any suggestions as to how to overcome this? Is there an aftermarket mixture control arm that I could buy with similar, but slightly different geometry that might work better in my application? The current mixture control arm appears to be made of brass or bronze or something similar, so without knowing the specific alloy, I’m apprehensive about any sort of bending/welding/modification that may weaken or break the arm.
Surely I’m not the only person to have taken on a carbureted RV-8 so I’m hoping this group can offer some advice.
Thanks!