Replies to This Discussion

Permalink Reply by John Austin on August 9, 2013 at 9:16am

Ed,

I'm sure you know this, but rotating the carb is to balance the "swirl" of the mixture distribution between left and right cylinder banks, but of course does not overall enrich the mixture. I found that  by installing a smooth-bore 90 degree bend (rubber radiator hose) from the airbox and installing the vane insert, my EGT spread was extremely tight (usually less than 50 degrees over 6 cylinders!) and rotating the carb was not necessary. If you installed the vane insert after previously rotating the carb, I'd straighten the carb and see if it affects #5 positively. Also, Pete emphasized that the vane insert be installed with one of the internal vanes exactly vertical relative to the Bing's intake.

There are various after-market "Hacman" valves that can be used to vary the mixture on a
Bing carb (as I understand it, they alter the flow in the air balance tube between the airbox and carb and "trick" the Bing's altitude compensation), but I have zero personal knowledge and it would seem a questionable solution as it might introduce a new set of problems! The only way I know to richen the mixture would be to re-jet the carb. That might be a temporary solution to run a little cooler 'til the engine fully breaks-in, but if I were you I would consult with Pete about that. Of course, it seems problematic to deliberately run way over-rich just for the sake of one cylinder if the other 5 are "happy."

John

• ▶ Reply

Permalink Reply by Dr. Edward L. Olds III on August 11, 2013 at 6:45pm

John,
I've done exactly what you did, plus I did re-jet the carb at Pete's instruction. I have the smooth hose/vane, but still have the issue.
I flew today and had #5 running at 355 at 2800. The others were 50 to 100 degrees cooler.
I'm going to shave the last air dam over #3 down to nothing and play with the plate in front of #1. We'll see what happens.
Ed

• ▶ Reply

Permalink Reply by John Austin on August 11, 2013 at 7:54pm

I think one of the first tweaks I did was to aggressively shave the baffles above the cylinders of #! and #3. Both of them ran cool, so I wanted every bit of air going back to #5. Those baffles are totally shaved flush with the top of the duct in my engine. I "think" you've already done this, but I also extended the inboard end of the baffle above #5 to force the air down over the cylinder fins rather than let it bounce off the back of the ram air duct.

In cruise, my #4 is now usually the warmest (but normal). There is only a bit of baffle left above #4, so I'm tempted to add a little back to try get the CHT spread even tighter.

If you only got to 355, at least that was within continuous limits. If you keep running and breaking-in that engine, I'll bet it comes down. If that 355 @ 2800 remains stable, try cruising at 2900 or even 3000 and see what happens. I found that the cylinder cooling improved, but the oil temps would start creeping up. That was resolved with the oil sump duct, which of course, you already have installed.

John

• ▶ Reply

Permalink Reply by Dr. Edward L. Olds III on August 12, 2013 at 11:32am

John,

I agree with the shaving of the baffles.  I'll try it at 2900, but I'll have to have an air to air refueling:)

I have a fuel flow issue to work on today.  The right wing tank does not seem to feed equally?  Will do a flow test.

Ed

• ▶ Reply

Permalink Reply by John Austin on August 12, 2013 at 12:28pm

I'll try it at 2900, but I'll have to have an air to air refueling :)

It'll only be about 6 gph @ 2900 ... hey, after burning 14 gph at cruise with the 206's IO-540, anything in the single-digit range looks good to me! ;o)

I don't think any high-wing flows the tanks equally - I see about a 2 gal imbalance from full to empty, which I consider not that bad! 

John

• ‹ Previous
• 1
• 2
• Next ›
• Page