Front cylinders super rich

[bodex1]

I have a 1600 single port in my aircraft and after high power runs I'm finding the front cylinders are super rich but the rear ones are perfect. If I hit both cylinders with an IR gun there is very little temp difference. I have a long unheated manifold and I think the fuel is condensing an as the last part of the manifold is curved, centrifugal force is pushing the fuel drops into the front cylinders via the single intake port.

Anyone have similar issues?

 

[Todd Loes]

It might be due to the shape of your induction system. If there's non-evaporated fuel in the system, it'll stay on the "outside" curve. Since your outside curve would dump to the front cylinder, it's a feasible explanation. A perpendicular entry might be less efficient but distribute more evenly. Photo attached of "HAPI" single-port adapters. Notice how the bend is 90-degree offset compared to yours.

 

[Steve Stephenson]

tloes solution above is elegant.

 

[DeadRinger]

I agree with post 2 that's why VW laid the intake bends out to follow the port shape and hit the flow divider just right. Honda had the same issue on some of there engines with one injector and two intake valves. also with the dual port intakes if you try to port them lots of times you just make things more unbalanced because of all the curves. on single ports if I remember correctly there isn't a good balance in flow from one side to the other. You may be able to fix that with a log type plenum at the intake mounting area. Port balancing wouldn't be worth the money and you'll still need a new intake.

 

[Pops]

This is what it takes. 1.25" dia, Stainless Steel bathroom handrails from the aviation section of Lowe's Box store.
Hot oil box at base of carb to stop the charge from condensing . Engine much smoother and more power.

1835cc , 60 HP , single port heads, Zenith carb, hot oil box ( cools oil 20 degrees) with a Culver 60"x26" prop, 1200+ ROC and cruise at 80 mph at 2700 rpm.

Take off on a 900' grass strip with trees.

Pops

 

[eschrom]

I wonder if simply letting the carb draw cowling air instead of outside air would fix the problem?

Ed

 

[Pops]

You still have the incoming engine cooling air cooling the intake tubes on top of the engine condensing the charge. Also the Zenith carb ices up about like a Stromberg carb on a Cont A-65 engine. I don't think that small increase would help with both problems.
I know that using the hot oil box to help heat the carb enough where carb ice is not a constant problem. I still use my exhaust manifold heat as you normally use in a small cont engine for insurance, and get the normal RPM drop with used. Also no more problems with the charge condensing in the intakes causing engine roughness and loss of power.

 

[Darius Plank]

Looks like there is a mounting flange on both the top and bottom of the oil box with the intake charge flowing thru it?

 

[103]

You still have the incoming engine cooling air cooling the intake tubes on top of the engine condensing the charge. Also the Zenith carb ices up about like a Stromberg carb on a Cont A-65 engine. I don't think that small increase would help with both problems.
I know that using the hot oil box to help heat the carb enough where carb ice is not a constant problem. I still use my exhaust manifold heat as you normally use in a small cont engine for insurance, and get the normal RPM drop with used. Also no more problems with the charge condensing in the intakes causing engine roughness and loss of power.

Dan so good to see you on this list. Every VW can benafit from a heated intake manifold I may be able to omit my Oil cooler when done. If not I will add a remote one back in. Matt Naiva!

 

[Pops]

Looks like there is a mounting flange on both the top and bottom of the oil box with the intake charge flowing thru it?

Mounting flange on the bottom of the box for the Zenith up-draft carb and on top of the box there is a mount for a bracket on the bottom rear engine case bolt with a rubber cushion in between to support the intake manifold. Intake tube goes up through the hot oil box. There is about 1/8" / 3/16" clearance between the OD of the intake tube to the ID of the box that forces the flow of the oil to be close to the cooler intake tube.