- #1
Neil Spooner
- 2
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Hi Guys/Girls,
Please may I seek your collective minds for help?
I have an issue with poor mixture distribution from a carburettor that uses a spray bar and throttle slide (known as a Throttle Body Injector TBI) The holes in the spray bar are at the side of the spray bar in full rich, the spray bar is rotated so the holes progressively face the airflow to reduce fuel flow and lean the mixture.
The device matches fuel flow to air flow as the slide is opened by having a greater population of holes in the spray bar toward the full throttle end. This is fine except that if there is insufficient turbulence downstream of the TBI there is a bias of fuel toward one side of the intake duct. In my case this is leading to some cyl's running rich whilst others are lean only when at Wide Open Throttle (WOT).
The TBI is bolted to the bottom of the engine sump, the airflow goes through the TBI, into the ducting in the sump and then branches out in 4 directions to the individual cyl's. The two cyl's closest to the full throttle end of the TBI run rich, the other two lean, but only during WOT operation.
My question is this: How do I create an effective turbulent mixing without reducing airflow? (A contradiction I am sure!)
The possibilities as I see them are:
1-Fit a lip between the TBI and the sump flange that projects into the airflow creating turbulence.
2-Offset the TBI to one side of the inlet duct which creates a duct mismatch.
3-The sump inlet has a conical adaptor fitted to allow the use of larger carb' throat dia' of 50mm, I could remove that adaptor.
4-Modify the adaptors shape by cutting some away only on the WOT side, or the idle side.
5-Adding to the adaptor on either side.
6-Fit an aerofoil shaped fin in the sump entrance attached to the conical adaptor. If I go down this route what dimensions should the aerofoil be? And what should the "angle of attack" be?
Here is a link to a Flikr photo album which has pictures of the installation (the pertinent photos are at the end):
https://www.flickr.com/photos/62722241@N00/sets/72157647983156255/
Any suggestions or guidance would be very gratefully received thank you. I have roughed out some options that I think may be viable and are shown in the Flikr album.
TBI throat dia': 40mm
Turbulence before and after the TBI can affect its performance, that is why I have fitted a honeycomb air flow straightener before the TBI.
Best wishes,
Neil
Please may I seek your collective minds for help?
I have an issue with poor mixture distribution from a carburettor that uses a spray bar and throttle slide (known as a Throttle Body Injector TBI) The holes in the spray bar are at the side of the spray bar in full rich, the spray bar is rotated so the holes progressively face the airflow to reduce fuel flow and lean the mixture.
The device matches fuel flow to air flow as the slide is opened by having a greater population of holes in the spray bar toward the full throttle end. This is fine except that if there is insufficient turbulence downstream of the TBI there is a bias of fuel toward one side of the intake duct. In my case this is leading to some cyl's running rich whilst others are lean only when at Wide Open Throttle (WOT).
The TBI is bolted to the bottom of the engine sump, the airflow goes through the TBI, into the ducting in the sump and then branches out in 4 directions to the individual cyl's. The two cyl's closest to the full throttle end of the TBI run rich, the other two lean, but only during WOT operation.
My question is this: How do I create an effective turbulent mixing without reducing airflow? (A contradiction I am sure!)
The possibilities as I see them are:
1-Fit a lip between the TBI and the sump flange that projects into the airflow creating turbulence.
2-Offset the TBI to one side of the inlet duct which creates a duct mismatch.
3-The sump inlet has a conical adaptor fitted to allow the use of larger carb' throat dia' of 50mm, I could remove that adaptor.
4-Modify the adaptors shape by cutting some away only on the WOT side, or the idle side.
5-Adding to the adaptor on either side.
6-Fit an aerofoil shaped fin in the sump entrance attached to the conical adaptor. If I go down this route what dimensions should the aerofoil be? And what should the "angle of attack" be?
Here is a link to a Flikr photo album which has pictures of the installation (the pertinent photos are at the end):
https://www.flickr.com/photos/62722241@N00/sets/72157647983156255/
Any suggestions or guidance would be very gratefully received thank you. I have roughed out some options that I think may be viable and are shown in the Flikr album.
TBI throat dia': 40mm
Turbulence before and after the TBI can affect its performance, that is why I have fitted a honeycomb air flow straightener before the TBI.
Best wishes,
Neil
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