DCOE fuel pooling in choke

[jturner]

I've been trying to dial in the idle circuit on my new DCOE 40s. The main circuit assemblies are removed to keep that out of the equation.

 

I synced the venturis with a manometer, set the mixture with my air/fuel gauge around 13. But I can't get it to idle below 1200 RPM, even with the idle stops backed out all the way.

 

My first though was fuel height. I checked it while the engine was running, and again shut off. Still 29mm. I checked for vacuum leaks with a can of carb spray.

 

So I took off my velocity stacks to investigate the throttle plate position, and noticed this fuel pooling around the bottom of the choke on venturi #2. It isn't happening with any of the other venturis.

 

Any ideas where this fuel is coming from? I assume I'm getting too much fuel in #2 and raising the idle.

 

 

 

Edited May 30, 2019 by jturner

[Simeon]

Don’t new DCOEs have idle air bypass screws now for help setting the idle?

 

What kind of manifolds are you using? Any chance that the carbs are not level front to back?

[jturner]

Just now, Simeon said:

Don’t new DCOEs have idle air bypass screws now for help setting the idle?

 

What kind of manifolds are you using? Any chance that the carbs are not level front to back?

 

They do have air bypass screws, but they're used (afaik) to balance airflow in the 4 venturis. So I opened 3 of them to match the weakest venturi (which has the bypass closed). I wouldn't be able to make any adjustments now and still have synced carbs.

 

The weakest venturi (with the bypass closed) is also the one pooling fuel.

 

I'm using BMW manifolds from a ti.

 

 

[MOJOJOY]

Make sure your Venturi is still in the right place? Is it being held by set screws on bottom of carb or the spring clip on the Venturi? I had a similar situation a few weeks back were it moved just enough to make a puddle on cylinder #3. The spring clip was damaged and compressed that allowed the Venturi to move 

[jturner]

2 minutes ago, MOJOJOY said:

Make sure your Venturi is still in the right place? Is it being held by set screws on bottom of carb or the spring clip on the Venturi?

 

I actually haven't been inside the carb since it's brand-new from Pierce. I tried to wiggle the aux venturi and it didn't move... the adjuster screw on the bottom of the carb body is locked down.

 

What would it look like if the aux venturi was in the wrong place?

[SaharaX2]

Recommend talking to Mike or Steven at Pierce Manifold since you bought the carbs from them.
Pierce Manifold is closed on Friday.

They were a big help to me with my 45 DCOE.



Sent from my iPad using Tapatalk

[Chris_B]

56 minutes ago, jturner said:

 

I actually haven't been inside the carb since it's brand-new from Pierce. I tried to wiggle the aux venturi and it didn't move... the adjuster screw on the bottom of the carb body is locked down.

 

What would it look like if the aux venturi was in the wrong place?

Your aux venturies appear in your pic to be properly placed. You said your fuel height is 29mm. Measured from where?

[jturner]

Measured through the emulsion tube well, using the tool below. I think the upper point is described as "top of carb body".

 

So I mean the fuel level is 29mm below the top of the emulsion tube well (top of carb body).

 

I've also seen a 25mm spec online, but 29mm seems to be recommended more often.

 

 

Edited May 30, 2019 by jturner

[Chris_B]

I think the 25mm spec puts the fuel a couple of MM below the opening to the aux venturi. From personal experience 29MM really pushes the limit. It depends on which barrel you are measuring, given the rearward tilt of the 02 motor mounting.

 

Another then to check is your needle valve in that carb, even though they are new carbs. I had a situation with pretty much new carbs (older, but not used much) where I had fuel pooling in one barrel. I checked fuel levels and concluded I had a bad needle valve. I picked up a couple of replacements from Pierce and when I pulled the valve, I found a tiny little piece of crud right in the sealing area of the valve. I replaced it anyway, and problem cured.

[jturner]

2 minutes ago, Chris_B said:

I think the 25mm spec puts the fuel a couple of MM below the opening to the aux venturi. From personal experience 29MM really pushes the limit. It depends on which barrel you are measuring, given the rearward tilt of the 02 motor mounting.

 

Another then to check is your needle valve in that carb, even though they are new carbs. I had a situation with pretty much new carbs (older, but not used much) where I had fuel pooling in one barrel. I checked fuel levels and concluded I had a bad needle valve. I picked up a couple of replacements from Pierce and when I pulled the valve, I found a tiny little piece of crud right in the sealing area of the valve. I replaced it anyway, and problem cured.

 

Yep, 25 is 2mm below, 29 is 6mm below. So you're saying my fuel level is too low? I've honestly seen both specs online and there doesn't seem to be much consensus.

 

Good idea with the needle valve.

[Chris_B]

No, I am saying it is too high. That causes fuel to spill into the port to the aux venturi when you don't want it to.

[jturner]

Just now, Chris_B said:

No, I am saying it is too high. That causes fuel to spill into the port to the aux venturi when you don't want it to.

 

I think we're crossing wires... or I really don't understand these carbs.

 

If Im measuring from the top of the carb to the fuel, and my measurement is larger than yours, the fuel has to be lower, no?

[Chris_B]

Right. I didn't understand what you were saying. I have used tools in the past that, although inserted from the top, expressed the fuel level in MM from the bottom. So, if your fuel level is 6 mm below the aux venturi port, that obviously can't be the cause of your excess fuel problem. No other adjustment on the carb could be causing fuel to pool in the barrel.

 

Regarding your idle speed, have you checked the position of your throttle plates WRT the first transition hole?

[jturner]

17 minutes ago, Chris_B said:

Regarding your idle speed, have you checked the position of your throttle plates WRT the first transition hole?

 

I did look through that plug after installation, but I couldn't get into a good position to see down there, so I gave up. 

 

On my bench, they were correct and in perfect sync between venturis that share a throttle rod, so I wasn't too worried about it then. I can check again to be 100%. The throttle lever is resting on the idle screw so I can't imagine they're any different than when they were on my bench.

[Son of Marty]

Check to see if the throttle arms have a air gap between the arms and the carb idle stop with the idle screw backed all the way off, I have come across jen-you-wine weber arms that have to be ground down a bit to give some clearance, the difference between a 900 rpm and a 1200 rpm idle is minuscule.