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Discussion Starter · #1 ·
I made a good start at tuning

I made a good start at tuning in my 79 512BB today using the techiniques discussed by JRV and David Feinberg in prior threads. Timing was right on the money. The initial carb sync check was pretty good with no throat being off by more than 1/2 to 3/4 of a number. Actual numbers were 5 1/4 to a high of 6 (more on the 6 reading later). To make a long story short, everything synced in pretty good. I only had to make a few very minor adjustments carb to carb. So far so good.

I started adjusting idle mixture with cylinber 1, which is the right front most forward cylinder using the Gudson Colortune. For a novice like me this simplifies things quite a bit as my experience factor is zilch. (I have this impression that the Colortune is a good equalizer among novices like me but that the the ear and experience takes quite a while to become a good tuner).

Anyhow, I get to the left rear carb which comprises cylinders 7,8,9; Colortune will not show a color. I can see a spark, but no color.

OK, onward to to the left front, cylinders 10, 11, 12; no problem here. Basically aside from the left rear carb all the idle mixtures are within plus/minus 3/4 turns. They are all about 2 1/2 turns open.

Back to the left rear carb, cylinders 7,8,9. After a number of tries here is where I am. I opened the idle mixtures to 7, 8, 9 ANOTHER 2 or 3 turns. OK, some progress 7 and 8 are set however the idle mixture screws are now out about 4 to 5 turns. No matter what I do cylinder 6 will not not adjust to any color. I can see the spark, energy is getting there, the fuel mixture at idle is not.

Commander (wife) ordres all stop. It's time for dinner and miller lite.

Ok, guys, here is where I am and my thoughts.

I have a problem with my left rear carb. Cylinders 8, 9 have their idle mixture screws open way too far and cylinder 7, though I can see a spark with the colortune, appears not to have any "gas" at idle.

A couple piecies of additional of information. First, remember the high reading of 6 I had with the sychrometer? This occurred in cylinder 7, the one that is the problem. Second, when I examined all the plugs they all looked good except for cylinder 7, which looked "newer", not oily, not grayish but just newer. Third, when I rev the engine lightly to 3,000rpm with the colortune in the suspect cylinder 7 it goes blue suggesting that it is not a cylinder problem but an idle circuit carb problem. I have not done a compression check yet because I suspect a carb problem.

OK, here is what I think is happening. I think there is an idle circuit jet issue with the LR carb. When I look down the throats, the position of the throttle plates in all the carbs are dead on.

How do you clean the idle jets? Are there 3 per carb, Something isn't right here? Am I way off base?

Sorry about the length,

Drew
 
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Discussion Starter · #2 ·
Drew,

Glad to hear you made


Drew,

Glad to hear you made progress today with your carbs...

Let's address the idle mixtures issues on the one suspect carb. Believe it or not, in the 365BB owners manual cleaning the idle jets is part of a "normal service" interval...Oh, those crafty Italians!

There are three idle jets in each carb. These jet serve two important, but somewhat independent functions...The first being to provide fuel for idleing when the throttle plates are closed...and two, to provide "additional" fuel when the throttle plate are open...until the main circuits kick in. So, needless to say, there function and cleanliness is very important.

I find that these jets require semi-frequent periodic cleaning. The good news...very easy to do. Here's what they look like in the carbs...(The brass screw-one in each barrel)



Unscrew the jet holder...taking care not to loose the o-ring. This is what the assembly looks like removed.



The idle jet simply pulls out of the jet holder, as seen below:



Note that there are two holes in the idle jet...One in the end and one on the side. There should be no obstructions in either hole. I usually pull all the idle jets at the beginning of a driving season...and blow them all out with compressed air and replace the o-rings with new. A little silicon spray on the o-ring eases installation...Tighten them snug, but not too tight.

I suspect, based on your description, that this is the problem. It's a bit odd to have three pluged jets, on one carb...but who really knows why these things happen to these cars...

On the other hand, if all the spark plugs on one carb were extremely rich, that's another problem, all together...and what I'm dealing with today.

Regards,
David
 
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Discussion Starter · #3 ·
Drew,

There's another p


Drew,

There's another possibility for the apparent lack of fuel that I hadn't considered. If I'm remembering correctly, the 512BB has idle cut-off solenoids on the carbs (which the 365 does not have.) These solenoids are engaged when the ignition is on...and allow fuel to flow to the idle circuit of each carb. Conversely, when the key is turned off, fuel is cut off to the idle circuit...hence preventing the engine from "running on". If the solenoid, on the carb in quesion, is not functioning properly, or does not have power when the engine is running, you will have the symptoms you previously described.

A quick test for power would be to unplug, then plug-in the wire on the solenoid. You should hear/feel it click...The solenoid is mounted on the carb and has a single wire connected to it...(Looks like a small cylinder .50" diameter and 1.00" deep)

Let me know what you find...and we'll go from there.

Regards,
David
 
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Discussion Starter · #4 ·
>>the 512BB has idle c

>>the 512BB has idle cut-off solenoids on the carbs (which the 365 does not have.) These solenoids are engaged when the ignition is on...and allow fuel to flow to the idle circuit of each carb.<<

good call and a definate must check when an entire carb is off line.

JRV
 
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Discussion Starter · #5 ·
Thanks JRV...

I don't h


Thanks JRV...

I don't have all that "high-tech" stuff on the 365 carbs...LOL. It did/would seem a bit odd to have all three idle jets plugged...

David
 
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Discussion Starter · #6 ·
Yea David, my Miura doesn'

Yea David, my Miura doesn't have those new fangled gadgets either {
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Discussion Starter · #7 ·
Don't you guys ever sleep.

Don't you guys ever sleep. Jeeezesh, but thanks a lot. This information is priceless.

A couple of things. First I can visualize the cylinders you are talking about. I always thought they were part of the electric choke mechanism. In fact, the wires got in my way on some of the carbs when I was using the colortune and I may have left them unplugged on the left rear carb. But now I know how to check.

It's raining here in the Southeast and will be all day. I think tonight I'm going to clean all the idle jets this evening after work and check the function of the cutoff solenoids.

Drew
 
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Discussion Starter · #8 ·
Geez Drew,

Your BB has all


Geez Drew,

Your BB has all the modern convienences of home...Electric choke, cut-off solenoids...

My BB only came with the "pump and pray" chokes...

Time for lunch.


David
 
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Discussion Starter · #9 ·
OK, some success.

At lunch


OK, some success.

At lunch I ran home to check out a few things. First, the small cylinder .50" diameter and 1.00" deep is for the choke. No power with ignition on or off. When the choke electrical switch is thrown power is applied and you can hear them click. I left the choke switch on and removed the connection to the cylinders and you can hear them click.

I pulled the offending idle jet on cylinder 7, blew it out, reinstalled it and presto I have ignition mixture at idle. I went to the auto parts store and got 12 O rings. I intend to blow out all the idle jets tonight and start over from scratch later in the week. I presume my measurements and adjustments will change al little.

Live and learn,

Drew
 
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Discussion Starter · #10 ·
I took a vacation day on Frida

I took a vacation day on Friday to tune the Boxer (carbed). After about 6 hours of balancing carbs and adjusting mixture with colortune it was test time. I had all cylinders within about 1/2 Kg/H reading 5. The colortune was a bunson blue on all cylinders; this time I had blown out all the idle jets with compressed air. Timing was on and had re-adjusted idle downward to just below 1000rpm as it had crepted up as the car was tuned.

Took it out, what a rocket. The small progression "stall" upon take off is just about completely gone. You can tell it feels much peppier.

JRV and David Feinberg, thank you very much for all your help. I could never have done this and proabaly would not have attempted it without it.

Drew Altemara
 
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Discussion Starter · #11 ·
A rocket, eh? (Big smile o

A rocket, eh? (Big smile on my face..) Excellent!

Drew,
This is very good to hear...I sure hope you're basking in the glow of your significant accomplishment. Regardless of the help, to diagnose and repair a carb problem on a BB is no small task.

Best regards,
David
 
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Discussion Starter · #12 ·
>>This is very good to

>>This is very good to hear...I sure hope you're basking in the glow of your significant accomplishment. Regardless of the help, to diagnose and repair a carb problem on a BB is no small task. <<

I certianly Second That and BRAVO on the success, patience and determination to accomplish a quite difficult operation!!!

{
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Regards, JRV
 
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