Extremely difficult problem or what??

[old grumpy]

My Minx 6 (with Zenith 34 IV carb.) has always been running as if the acc. jet had some dirt or blockage because it is hesitating a little when the pedal is pressed. On the other hand has the car has used surprisingly little petrol, so I didn't want to touch anything that would make it go back to original which means: Using a lot of petrol. Now the hesitating has became a problem, so I had to take a look inside the carb. Nothing could be seen however, blowing air in in jets to get dirt away and put the carb back again.

BUT now the engine did run, with what appears to be to much petrol. Hunting, black smoke, engine not running at idle, petrol is pouring out from the manifold "overflow pipe".
Float needle OK, the petrol level seem ok, As I said, nothing has been changed. Then I blocked the petrol to the carb. for a test. Just before the engine run out of petrol it did run OK.
Higher petrol pressure from the mechaical pump? Out of the blue? Unlikely. Trying another Zenith 34IV from the Commer K170 (same engine, same carb.) I took the upper part of the carb that have jets and everything and tried it. Same symptoms, as it's something else and not the carb?? But can there be anything else. This is not high tech. Just a simple carb. with basically one moving part.
When I was driving around with the Commer I was constantly fiddling with the
carb. to make it use less petrol, so I have taken this carb. apart hundreds of
times. Or does the engine get to little petrol?? That doesn't make sense either. The economy device with it's little membran that is only suppose to work on overrun?
Are the any area I haven thought of?

 

[Ken Ellis]

Maybe the floats are sinking? That would fill the bowl all the time, and essentially pressurize the carb at fuel pump pressure instead of letting fuel meter out as designed.

 

[old grumpy]

Maybe the floats are sinking? That would fill the bowl all the time, and essentially pressurize the carb at fuel pump pressure instead of letting fuel meter out as designed.

Thank you for the response.
No, I have tested this!
The petrol level is just below to the rubber ring where it is supposed to be.

 

[old grumpy]

Yes this is a hard one. Carb is OK, petrol petrol pump OK, everything is OK,...........as far as I can see
What have I missed. Can this be to difficult even for the Americans?

 

[Ken Ellis]

Well, I re-read your original post, and I didn't see where you dismantled the carb, immersed it in carb cleaner, and used a full parts kit to rebuild. Are there o-rings on valves that haven't been replaced? Seats uncleaned? Stuff like that? I'd start there, with all new parts, if you haven't.

When you said "No, I tested this" in response to possible float sinking -- just how did you test it? Did you remove the float assembly, immerse it, and watch for bubbles for a few minutes? Balance them at the midpoint of the bracket and look for level? Shake them and listen for sloshing? Or observe the unassembled carb for correct fuel level? Not sure what the test was.

In the Alpine manuals, there's a procedure for measuring and adjusting the fuel delivery volume from the mechanical fuel pump. Is there a similar test in your manual?

Can you arrange to safely feed the carb by gravity with an elevated fuel supply tank? That would remove the fuel pump as a variable.

Can't speak to the "economy device" that you mention. But if it's job includes metering fuel flow, it's a candidate for trouble. But that would be addressed in the "official" rebuild parts kit, I would think...

Whenever things "used to work, and now they don't", I look for sneaky causes... Things like re-tightening manifold-to-head bolts, which have the effect of removing a small air leak that the carb adjustment had been compensating for all along. What used to be just right to accommodate the leak now is way too rich, and floods out all the time. The carb suddenly was wacky -- but really, the change was somewhere else. Or there was an air leak in the throttle shaft area that was compensated for by carb adjustment. Then, the leak got gummed up by outside dirt, and now the carb runs rich all of a sudden. So maybe check for outlying causes.

And finally, when discussing carb problems, I always ask... is Weber an option?

Good luck!

 

[Bill Blue]

Maybe the carb was partially blocked, causing the engine to run lean. You raised the fuel level to compensate (flooding the carb) and now that the carb is unblocked, it is running rich. I suppose a critical question is when you say the fuel level is correct, is that by specification or your historical setting.

In any event, I think it is significant that blowing out the carb made it run rich. What are all the things that could have affected?

Bill

 

[John W]

Looks like the gasket's edge is touching the top of the float, but probably just the way it looks in a photo.

 

[Mike snyder]

I have run into similar problems with older carbs. Here is what I have found in the past: pin holes in brass floats, duel floats out of alignment, needle valve and seat worn so proper seating was not possible. Good Luck!
Mike

 

[old grumpy]

Maybe the carb was partially blocked, causing the engine to run lean. You raised the fuel level to compensate (flooding the carb) and now that the carb is unblocked, it is running rich. I suppose a critical question is when you say the fuel level is correct, is that by specification or your historical setting.

In any event, I think it is significant that blowing out the carb made it run rich. What are all the things that could have affected?

Bill

I did assume it did run lean = unusual good fuel economy. Dirt can have been blowing out. richer yes, but not that much!
No, havent rised the fuel level. Level is according to manual.
Made a test: making the main jet and the compesion jet smaller by insert a thin wire. result = as before. Isn't that odd??

 

[old grumpy]

Looks like the gasket's edge is touching the top of the float, but probably just the way it looks in a photo.

Does not matter, float don't go higher (on photo it's upside down.)

 

[old grumpy]

To test the puel pressure I used a "Filter King". ( adjustable pressure filter) Didn't help. When the pressure was lowered to much it didn't fill up the bowl and started going on less the 4 cylinders. All signs show the fuel level is OK.

 

[old grumpy]

And finally, when discussing carb problems, I always ask... is Weber an option?
Good luck!

This is the option. It's an iron head, have no inlet manifold for Weber DCD.

It will be very close to the hood (bonnet).
But as I am stubborn The original just has to work