Whatbs wrong with my BBQuiz 1

365 BB

Symptoms: Poor idle, poor low speed driveablity, excessive richness/smoke from RHS exhaust...Seems to run fine under full throttle conditions.

Preliminary diagnosis:
-As the smoke is from the RHS, and the BB exhaust crosses over...the problem appears to be on the LHS.
-Remove spark plugs on LHS
-Plugs 7,8,9 look fine
-Plugs 10,11,12 very, very rich...all equally black.

So, what's the most likely thing wrong with the car??

JRV...Sorry, but you can't take this quiz, yet.

Answer and solution posted on Sunday....


Regards to all,

David

Carb float level in respective carb?

Harry,

That's a great answer and likely the direction I might have pursued. However, on the 40 IF3C carbs that are used on the BB, there are two independent float chambers, with corresponding needle valves. One float chamber is used for one cylinder and the other float chamber is used for the two adjacent cylinders. Although possible, it is unlikely that both needle valves (controlling all three cylinders) failed simultaneously.

Additional information and clarification:

1-This problem came on suddenly...
2-Based on the spark plug readings (equally very black), all three adjacent cylinders were affected in the same manner.

Thank you....

Regards,
David

Throttle plate stuck open. Maybe due to a binding shaft, or broken throttle return spring.

Do these carbs have choke plates?.....if so then the corresponding choke plate may be affected.

Morning Hank,

Choke plates....Hmm, that too is a possiblity, but the 365BB does not utilize a choke plate...or for that matter, any choke mechanism what so ever.

Throttle plates and shafts are fine...and air flow through the suspected carb is identical to the others...

Thank you, as well.

Regards,
David

Hmmmmm....I had floats as first thought also fwiw.

I love this quiz idea !!!!

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Well, let's see. Since the problem is with all 3 barrels, it must be something common to, and effecting these simultaneously.......that is the reason for the throttle plate answer.

If these are OK, then I can only think of the 10-12 carbs sitting "loose" on the manifold....?

The solution to the problem lies in the sole fact that all three plugs, on the same carb, are equally near fouled. JRV, my initial diagnosis was the floats, as well, until I pulled the third plug...

>>then I can only think of the 10-12 carbs sitting "loose" on the manifold....?<<

good answer actually!

not that far fetched, I've seen a number of loose carbs over the years.....however air leaks, especially big ones cause Lean Running.

Hmmmm....

>>Since the problem is with all 3 barrels, it must be something common to all<<

agree....and at the moment I can only think of one other circuit that affects all 3 barrels, and I can see some possibilities there, but they seem remote.

Hmmmmmm....interesting.

Ahhhhh...something else just popped into my head...but surely that's not it....

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Hank,

I considered that thought, as well. However, air flow volume would have revealed leaky base gaskets...and the plugs would have indicated a lean, rather than rich running condition...

Thanks again for your thoughts and input.


Regards,
David