SPITTING CARB - 914-6 all stock, Need assistance - please see latest post to this thread Options

[ctc911ctc]

Thank you all teeners for the replies, here are some answers to your questions

1) accelerator pump and volume: from one of you I received (borrowed) a Porsche certified calibration kit which included the sexy little high school chemistry glass vial - each carb is getting the correct volume per pump

2) procedure: this is not my first 914-6, I get the drill as to starting, absence of choke, hand throttle, etc

3) Timing: I set it at idle ( once started) and verified higher rpm’s- seems right

4) gaskets, pump diaphragm: carbs were recently rebuilt ( before me) all are new and in very good condition

I believe that after the accelerator-pump gas is expended the idle circuits (more than one) are not running so the engine dies

If I get it running using accel pump gas (pump the gas peddle) it will start to run after 10-15 tries - this is not normal operation

THEORY

The idle circuits are not priming, though the idles jets are clean (checked a few times) perhaps the circuits need to be completely flushed? (IMG:style_emoticons/default/dry.gif)

Or, is there another reason why the idles circuits are not priming?

Mystery……………or????? (IMG:style_emoticons/default/confused24.gif)

[930cabman]

Idle passageways plugged? drill/grind away the lead plugs and open them up??

When warm/hot does she idle?

[ctc911ctc]

Idle passageways plugged? drill/grind away the lead plugs and open them up??

When warm/hot does she idle?

yes, when warm/hot she does purrr, however getting there is a chore......

[930cabman]

Idle passageways plugged? drill/grind away the lead plugs and open them up??

When warm/hot does she idle?

yes, when warm/hot she does purrr, however getting there is a chore......

probably eliminates idle passageways plugged

What spark plugs are you running? I am considering going to BPR6ES from 7

[Ninja]

Not hard to flush the circuits but if the critter will idle after warm-up you shouldn't have plugged circuits.

If the idle circuits have any spots that could leak air into the circuit you might have too much "air correction" until the carbs heat up enough to close/minimize the leak.

So, all of those plugs referred to in the previous post might be a problem.

It might be possible to blow air into circuits while spraying plugs with soapy water to check for leakage.

I use an ultrasonic detector a bunch, but I don't think it would work very well on a running 6 as they are noisy.

Some carbs have an O-ring on the idle jet carrier, and I've seen many of those screw up and cause problems. However, the problems do not magically go away when warm.

Another thought is the base idle settings are on the lean end of things when warm and it just won't provide enough fuel for cold operation.

This might be exaggerated by stock carbs with stock jets running a physically larger engine or higher performance parameters.

If you cannot diagnose it, I might try 1 or 2 steps larger idle jets.

[Ninja]

Just re-read thread. You're stock so the original stuff should work fine.

The issue seems to have changed too. Thread started out with popping through the carbs and most of the replies were spot on for diagnosing that.

Backfire through carbs is caused by fire getting past intake valve and igniting the fuel in the venturi. It is more commonly a valve issue rather than a carb issue. Significant timing screw up might cause it as well, but the puppy would NEVER run properly.

Often, I'll see ITB carb setups with a "dirty" barrel and it's always the engine that did it...

You compression test looks GREAT, very close to each other.

Your leak down test numbers makes no sense to me but it may be my unfamiliarity with your equipment.

The leak down testers I've used have two gauges, the first for inlet and the second for what remains in the cylinder. Most have standard couplers and an air tip (blow gun) can be plugged into it. Blow gun not running should show 100% retention. Blow gun depressed will show a low number 20-30%. It will NEVER show zero so they are not as accurate as the technician would want.

Normal leak downs are shown as a percentage. As every gauge I've ever used had an initial setting of 100psi the numbers made sense.

I'm not sure what your numbers mean but they DO show loss. The Hawk's suggestion about finding out exactly where it's leaking are excellent.

My first 914 (a ratty 70 1.7L) would throw fireballs ten feet above the car on cold start then run like hammered shit for the first 30 seconds. It was set up with the center mounted progressive 2 bbl. (the set up everyone hates). This reduced performance but was very reliable and easy for beginners to understand/work on.

The hard starting/fireball BS was so bad it burned up a couple of air filters before I left the filter and engine cover off.

I set a friend's tree on fire one memorable night... (IMG:style_emoticons/default/ninja.gif)

I was 17 and didn't know then what I do now...

I'm positive I had poorly sealing intake valves that required heat before their sealing properties improved.

I traded that car off for my first 240Z (a straight trade 1983) and have always had a Z car since.

Look closely at the engine before damming the carbs.

Do a leak down on all cylinders the next time you have the carbs off. Spray a little WD/40 in the intake ports before each test. All will leak a little (small bubbles). When the leak down blows the WD out of the port you've found your puppy!

[Ninja]

Double post gremlin got me again!

[930cabman]

Not hard to flush the circuits but if the critter will idle after warm-up you shouldn't have plugged circuits.

If the idle circuits have any spots that could leak air into the circuit you might have too much "air correction" until the carbs heat up enough to close/minimize the leak.

So, all of those plugs referred to in the previous post might be a problem.

It might be possible to blow air into circuits while spraying plugs with soapy water to check for leakage.

I use an ultrasonic detector a bunch, but I don't think it would work very well on a running 6 as they are noisy.

Some carbs have an O-ring on the idle jet carrier, and I've seen many of those screw up and cause problems. However, the problems do not magically go away when warm.

Another thought is the base idle settings are on the lean end of things when warm and it just won't provide enough fuel for cold operation.

This might be exaggerated by stock carbs with stock jets running a physically larger engine or higher performance parameters.

If you cannot diagnose it, I might try 1 or 2 steps larger idle jets.

My /6 conversion has similar symptoms, difficult to start but purrs when warm. I have a set of 60 idle jets on the shelf, will find out when she comes out of the paint shop

[ctc911ctc]

Great notes Ninja, comments added within

Not hard to flush the circuits but if the critter will idle after warm-up you shouldn't have plugged circuits.


Got it - makes sense

If the idle circuits have any spots that could leak air into the circuit you might have too much "air correction" until the carbs heat up enough to close/minimize the leak.

So, all of those plugs referred to in the previous post might be a problem.


Understood


It might be possible to blow air into circuits while spraying plugs with soapy water to check for leakage.


Interesting - I did perform a smoke test - nothing leaked out of the control parts of the carbs nor from the manifold.



I use an ultrasonic detector a bunch, but I don't think it would work very well on a running 6 as they are noisy.


Out of my league - interesting!


Some carbs have an O-ring on the idle jet carrier, and I've seen many of those screw up and cause problems. However, the problems do not magically go away when warm.

Another thought is the base idle settings are on the lean end of things when warm and it just won't provide enough fuel for cold operation.


Larger idle jets?


This might be exaggerated by stock carbs with stock jets running a physically larger engine or higher performance parameters.

If you cannot diagnose it, I might try 1 or 2 steps larger idle jets.

THANK YOU NINJA!

[ctc911ctc]

Hi,

I came back to this car after a few major trips and family events……….

I took all of the plugs out and retested the compression – the engine is super cold (15 degrees out) garage is heated to 40 at all times.

Compression is about the same as listed above – 5lbs less for all cylinders.

I am declaring that compression is not the problem

Next, here are the plugs – the 1,2,3 plugs look good – the 4,5,6 are very heavy, rich

I am going to start over – my sense is that it should be possible to get this car to:

Prime sensibly – fuel pressure and then couple of pumps
Start with a couple of cranks
Sustain the running while in high manual idle until warming up
And then, can idle smooth and clean at 900

Here are some pics of the plugs – what would you do next? Ignition?

Plugs 1->6, L->R









Respectfully,
Cary Conrad

[Ninja]

Clean plugs, check float levels, run again.

If all of the jets/venturis are identical in all 6 barrels, then float level is most likely to cause richness difference between the two carbs.

Webers are super touchy about fuel pressure. I see 3.5 psi as the TOP limit. Check your fuel pressure with an ACCURATE gauge. A modern gauge for testing fuel injection will not read properly at low pressures.

[porschetub]

Hi,

I came back to this car after a few major trips and family events……….

I took all of the plugs out and retested the compression – the engine is super cold (15 degrees out) garage is heated to 40 at all times.

Compression is about the same as listed above – 5lbs less for all cylinders.

I am declaring that compression is not the problem

Next, here are the plugs – the 1,2,3 plugs look good – the 4,5,6 are very heavy, rich

I am going to start over – my sense is that it should be possible to get this car to:

Prime sensibly – fuel pressure and then couple of pumps
Start with a couple of cranks
Sustain the running while in high manual idle until warming up
And then, can idle smooth and clean at 900

Here are some pics of the plugs – what would you do next? Ignition?

Plugs 1->6, L->R









Respectfully,
Cary Conrad

Are those plugs any good they look old to me ? see they are Bosch ,looks like the worst 3 are fouling, have you checked for a good spark @ each cylinder ? ,is your CDI wiring good ? points set up right ?
Did you set the float heights correctly and what gauge did use ?,check to see if you have no spill over into the throat's under some throttle that will cause the very rich condition you have .
Don't for a minute think that previous work on the carbs has been done right ,pay to add the following ;
Vent size,
idle jets,
main jets,
air correctors,
emulsion tubes .
This would help a lot ,good luck and report back.

[Superhawk996]

here are the plugs – the 1,2,3 plugs look good – the 4,5,6 are very heavy, rich

None of those look good. All are too rich. 3 are way richer than the other 3.

Carbs are not tuned properly.