Whatbs wrong with my BBQuiz 1

Harry,

That's a great a

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

Morning Hank,

Choke plates.

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 firs

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

I love this quiz idea !!!!

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The solution to the problem li

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 thin

>>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 tho

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

Hank,

Without a doubt, you

Hank,

Without a doubt, you get the "funniest answer" award!! There's many a day that goes by that I do think I'm low on turn signal fluid...LOL.

However, there's a big storm coming this way today...and I'm going to try to get her back together and sneak in a little road test.

Till later...

David

>>and I'm going to

>>and I'm going to try to get her back together and sneak in a little road test.<<

Hmmmmmm....how could putting a load on the engine be neccesary to determine if the problem is solved?

1- Ignition works on the principal of 6 & 6 (not 3+3/3+3) by virtue of the Twin Pole Rotor. Beyond that it becomes seperated by individual cylinder condition.

2- Fuel Systems as a whole (pressure/volume)effect all cylinders or all on one side by and large.

3- Cam Timing effects an entire bank

4- Internal Engine components usually don't have issues related to 3's on a particular carb. Sometimes can be in pairs or sections...doesn't normally have anything to do with rich running though. And you won't be road testing to check cure in a day or two { }

Which brings us back to something that effects only 3 cylinders controlled by a single carb, and something about the individual carb that can cause issues on all 3 Barrells.

Hmmmmmm.....

>>Aren't these act

>>Aren't these actually 3 seperate carbs, that just happen to be in the same frame......with common shaft?<<

Henry,

Yes in one regard you can view them as 3 seperate carbs sharing some common components, but they are only 3 seperate carbs in a sense imo, they share the accelerator pump circuit, shaft & manifold and problems do 'seem to' effect "a carb" as a whole (more than one barrel at a time) when issues pop up, and because of that it is probably expedient when diagnoising Carb Issues to view each as one, and then seperate that whole into sections to focus in on perhaps specific problems. A throttle shaft leak, or base gaskit leak on one for example can migrate to other barrels of the same carb, but not effect surrounding carbs, so in trying to close in on the underlying cause it would seem easier imo to take one section (carb) as a whole, and then home in/disect from there.

Others mileage may vary, just giving an overview of how I try to rule out, then isolate & define, and then home in on the exact cause, in a mental step by step diagnostic procedure.

Good morning Gentlemen,

I m

Good morning Gentlemen,

I must say that I'm truly impressed with your thought processes expressed thus far. Hindsight is a wonderful thing and I only wish that I excercised the same logic when this problem first occured a few years back.

So, for a moment, let's highlight what we know so far:
-Problem is isolated to one carb
-All three plugs on the affected carb are rich
-Poor idle and low speed engine performance
-Seems "OK" at high engine speeds
-The problem came on suddenly

So, really....only one question remains:
What part of the suspected carb is utilized by all three cylinders and can cause rich running at idle...and poor low speed performance. By looking at the spark plugs, the problem would appear to be more than a simple mixture adjustment could compensate for....Agree?

Let's take a look at the accelerator pump circuit and the related components for its operation. There are three discharge nozzels, three screw-in check valves at the nozzels...and a dual diaphragm accelerator pump assembly which pumps fuel when needed.

Drew suggested that possibly the pump nozzel check valves were loose, hence allowing fuel to drip into the barrels. As these check valves loosen up over time, this certainly would cause the problem...but not this time, as the check valves were indeed tight.

So, what's left?
How does the accelerator pump circuit get its fuel supply? Here in this question lies the answer: In the bottom of one of the float chamber is the "pump discharge check valve" which supplies fuel to the accelerator pump circuit...only when fuel is needed. If this valve were to stick open, fuel would be drawn through the three dischage nozzels, at all times. Hence, at high engine speeds, the excessive richness would be masked by the fuel already passing through the carb.

Here's the culprit:


Hidden in the float chamber:



The "repair" is simple...Remove the check valve and shake. You should hear the check ball rattle. Nope...not this time! Clean valve with carb cleaner and compressed air...shake again.

Rattle...rattle. Reinstall valve, reassemble carb...Problem solved. But, let's take a look at these potential trouble areas, before putting that carb top cover on:



These "screws" which secure the pump discharge nozzels are check valves, as well. Although it is rare that these valves malfunction...they do become loose and allow fuel to seep from under the nozzles.

All back togther now....

Many thanks to all of you for your input...My goal, if you will...was to help up all with that sometimes, ever so challenging, diagnostic steps to determine what's wrong with my car.

Although this problem is pretty unique to the BB, I have other ideas for "quizs" that I'll be posting in the near future. Ideas are welcome...

Regards,
David