engine and drivetrain Car Bogging Troubleshooting (Stumped!)

[darrinos]

I too, have had issues like this that seem to make no sense. I spent nearly 6 months trying to determine why I ran out of fuel. Changed pumps, filters, carbs, ALL the fuel line, looked in the tank, new coil, etc. I eventually found out that in the fuel line at the top of the sender/pick up....there was a fly stuck in the line. Yes, a FLY. No fly, no problem. But then, it started up again. This time, it was a bad spark plug. I've replaced the plugs, wires, cap, rotor, points and condensor and it ran great. For a week. Now, it's popping and sputtering again. I think it's fuel this time. Seems I can only get a few good weeks out of it and then she starts giving me trouble again. But during the good times, what a blast. Sounds like I'm talking about my ex wife here....that's a different subject. I'm guessing that like me, you probably have filter issues. I've also removed the top of the carb a few times and found a bit of rust/junk in the bowl of the Weber. Rust in tank is my suspicion on that. Best of luck!

[peterschop]

It don't sound like you are starving for fuel to me. Your video shows it cutting out at 3900 but as soon as the revs drop, it comes right back. Is your rotor the same as in Simeon's picture? Did you use the same rotor when you swapped distributors? The pop that you heard at 6000 rpm may have been the rotor breaking. Try a new rotor.

[percy]

I assumed that you were not using a rev limiting rotor.    I have seen limiters that target maximum rev speeds to as low as 4500.  As the spring gets old and loses tension, the rotor may actually limit speeds far less than expected.  Of course, this will not prevent over-revving by downshifting to the wrong gear at the wrong speed, in which case you might ulimately find your car behind a tow truck with a driver wearing a Jonny costume .

 

 

 

 

 

 

 

IF you use a standard rotor (rather than a rev limiting rotor) you could still get the rev limiting "feature."   All you need is a sloppy distributor with plenty of end play and/or a severely worn cap and/or a severely worn, corroded or damaged rotor.    In other words, at certain speeds the distributor and the sum of its components might prove incapable of delivering the necessary spark to each high tension terminal.  So, how about a photo of the distributor cap and rotor?  (It goes without saying that it is also possible to get defective parts or parts that are not intended for your application - that nonetheless fit or seem to fit. So, if you have the wrong parts, all diagnostic bets are off.  Come to think of it I recall a rough running M10 with a clear aftermarket distributor cap.  It was pretty enough, especially at night, but it was not until we swapped it out for a drab opaque black cap left in the bottom of the tool bin that the engine ran spectacularly.   )

 

 

 

 

 

 

Clear can be good and bad.

 

 

Mixing and matching parts leads to varying results.

 

 

 

 

 

 

3. 38/38 carb was too much. switched to weber 32/36 carb, no fix

 

 

 

Would you mind explaining what you meant by too much?  Was max engine speed (under load)  in any way different between the two carbs? 

 

 

 

How about a look-see down the throat of your 32/36 venturis?

 

 

Another thought as far fetched as my others is auxiliary venturi positioning.  I have been reluctant to suggest this since you swapped carburetors, and as I mentioned before, what are the odds that both carbs could be afflicted with the same malady?

 

From another thread asking about an Automatic and "Bogging."  http://www.bmw2002faq.com/topic/59384-automatic-and-carb-bogging-down/

 

 

I am going to go out on a limb and suggest that your jetting may not be the source of your problem. What you have described has happened to me on a couple of occasions involving that same carburettor. It is rather simple really, and involves a loose or rotated tube that is part of an auxiliary venturi. If you are familiar with what I am trying to describe, check to see that your's are fixed in the proper direction and stop reading now. If my description/explanation leaves you confused, keep reading and maybe it will make sense.

Looking at your carburettor from the top, with the choke open, you will notice that each carb barrel has an object/obstruction in the direct center of each barrel. I believe this part is labeled by Weber as an "auxiliary venturi." Going from memory, if you look at the dead center of that venturi, you will note a small brass tube sitting horizontally between the middle circle/ring. If your carb is new, the tube should appear to be shiny brass. If the carb has been exposed to the elements, including crankcase fumes, it will appear dark gray and may not be so obvious. These tubes contain a rectangular or slotted orifice that should be pointing downward. If you see either tube with an opening pointing towards the heavens or anywhere other than toward the ground, your engine will exhibit symptoms as you describe. Unfortunately, the Weber is not a Rolex and the tubes within the venturis are not always installed correctly or they have a tendency to rotate on their own. The fix is easy.

As I am sitting here now, I'm not sure if you need to remove the top cover of the carb to access the venturi tubes. The answer to that question probably turns on the size of your digits or instruments. In any event - IF you see one of the tubes is upside down, it is probably a good idea to remove the top of the carb (6 screws plus removal of 1 e/c clip from the choke assembly. The venturi's pull right up (they are secured by gravity). Rotate the tube to the appropriate position with your fingers or with a gentle application of some needlenose pliers. There is no obvious means of crimping the tube so that it remains in place for it is, I believe, a friction fit. But for our purposes, you might consider using a tooth pick and some fuel resistant adhesive on the edge between where the tube meets the body of the venturi. I think I have used Aviation Permatex but for all I know, one drop of crazy glue might do the trick.

Good luck and let us know if and how you cure your problem.

 

 

 

Auxiliary Venturi  (Notice brass tube.  You should see orifice in tube facing bottom - not the top. SImilar to this.)

 

 

 

 

[snowy]

Presuming you have good fuel to the carb from the fuel tank. I think the carb may have faulty floats. The hollow float can fill with fuel and  drag down both floats in the carb ( Im talking about the brass float here) opening the valve and enriching the mixture to the point of flooding . Replace the float unit as it cannot be fixed.

Leading up to this you get.

Fouled plugs, carbon and wet residue fuel.

Bogging at  two to three thousand RPM.

Blue smoke at exhaust pipe.

Difficult to start.

No amount of fiddling with the mixture screws help as they only work up to two full turns out.

You can check the jets but where you have been is still only using the idle jet, so if that's clean that's as far as you can go.

You change or clean the plugs , car runs great for 5 min then smoke and bogging returns.

Just my thoughts from recent experience.

[Dudeland]

Can you skip a tooth on the cam and still have the car run?  I did it on an old Camaro. 

[snowy]

Solved bogging. I opened the jetting hatch ( the round one on top)  and she ran normally. The ITG air filter attaching plate was blocking of the air inlet above the ram tubes. It's a great looking filter bit you need a spacer if fitting it to 40 DCOE. I wondered what that hole was for.......duh.

[zinz]

That would do it!!! Glad it was something simple...still, maddening. 

 

Glad you found it. 

 

Ed

[snowy]

Thanks Zinz

Attached is the image of the air holes. Carb1.Air hole above  No1 air trumpet. Carb2 Holes drilled in base plate.

[zinz]

Very nice. I'm a bit surprised ITG didn't have that hole predrilled. Very easy to overlook, for sure. 

 

How much gap do you have from the mouth of the stacks to the inside layer of foam filter? The more air space you can put in front of the stack, the better off you will be. 

[ray_]

Did ITG make that plate? I'd contact them if I were you...

 

Cheers,