Empi HMPX carbs

Paul

It just has to be able to idle.  As you turn your mixture screw out the RPM will increase slightly.  As you turn it in it will start to stumble.  If the carb is popping, it usually means it too lean.

Thank you Danny. I will try it tomorrow. Fingers crossed.

Paul ISAAC

OMG!  Danny's right and I totally forgot!

Today is Festivus!

Where's my Festivus Pole?

.

@Gordon Nichols posted:

...There's a bunch of people on here who have never had to tinker with a carburetor other than on a lawn mower or weed wacker.  To many people (my son, included), working on a carburetor is akin to lighting incense and tossing dried chicken bones onto a tanned alligator skin to unlock their celestial meaning.  There must be some sort of VooDoo involved with making a carburetor work right...

...Grab that file and store it on your hard drive...

Now, just a minute. This is from a guy who worked on his own carbs for a decade, trying to chase out the demons, fruitlessly applying logic and procedure, and finally gave in, sending them off to the High Shaman of carburetor Voodoo in his mountaintop Himalayan monastery.

Don't believe what these so-called experts are telling you. Unless you possess the right spiritual connections, no amount of logic and procedure will get your carbs running the way you imagine they should. You will get close, but the carburetor will always hold something back, just to taunt you. They can be so cruel that way.

There are only a handful of mortals left on the planet who have 'the touch'. Save yourself years of mental anguish and deliver your carbs to one of them. Take a vacation, or just get drunk for a week, and when you get the carbs back you can move on to joust with life's other dragons.

Once the Shaman has worked his magic, maintaining carbs is relatively simple. The dance of the mixture screws is easily mastered and takes just a few minutes to restore proper tune. And once or twice a year, a tweak of the idle stops will get you back in synch.

Life is too short to waste any of it setting up carbs. You'll need the time to work out which oil to buy.

.

Counterpoint: "No, You Can Master All The Things"

by An Idiot

I totally agree with Mitch and that's exactly what happened with me (he was subtly using me as an example, I'm sure).

And if you can't find a Shaman, find a Druid.   If the Druids don't happen to be in your neighborhood, get directions to Dr. Zook.

Okay Have followed everyone’s suggestions. Now starts and idles beautifully. If i start off easy and light throttle thru the gears no popping. As soon as I get a little aggressive on the throttle I get carb popping. Timing at 3K rpms approximately.28 to 30 after tdc.

any thoughts?

I feel I am close to getting it right.

Thank you

You may have to go up in size on main jet.  What size are you running now?

sold my last speedster due to carbs.....would only go Subi now...my P car is fine..no issues...

@Phisaac posted:

Okay Have followed everyone’s suggestions. Now starts and idles beautifully. If i start off easy and light throttle thru the gears no popping. As soon as I get a little aggressive on the throttle I get carb popping. Timing at 3K rpms approximately.28 to 30 after tdc.

any thoughts?

I feel I am close to getting it right.

Thank you

It's BTDC, BEFORE not after. The spark happens before, it takes time for the flame to burn across the top of the piston before it creates the pressure that slams the piston down.

Try a few more degrees, no more than 5, up to 32 or 33 degrees just to see if the popping goes away. If it does, pull it back to 32 degrees or 31. You don't want pinging, which sounds like marbles shaking around in a tin can. This can happen with too much timing.

What distributor do you have? If it's vacuum advance, disconnect the vacuum line from the distributor and plug it. Then rev up to 3k and reset your timing. With high vacuum, your timing can reach 38-40 degrees. But, under load, the vacuum advance will be zero. The vacuum advance only functions at light throttle.

No vacuum. Engine Mfg says no more than 28?

Paul ISAAC

Just try it, you can always pull the timing back. It's a test.

If that doesn't change anything, or makes the popping worse, it gives me a direction to send you.

Okay as usual thanks for your advice

Advance rather than retard ?

Yes, crank it up to 32 or 33 degrees at 3000 rpm. Then drive it. Make sure it's warmed up first, some engines don't like too much throttle cold, or full throttle below 2000 or even 2500 rpms.

Will try tomorrow

Paul ISAAC

Without changing springs or weights, I don't quite understanding how you can control what RPM level at which you reach maximum advance.

I rotate the distributor until it reaches maximum advance and the RPMs are whatever they are.

I read what you said but don’t understand? Do you mean let it idle and turn the distributor and the rpms increase with out using the throttle?

Paul ISAAC

The throttle is involved. I am by no means an expert but my understanding is that things like springs and weights inside the distributor determine at which RPM it reaches maximum advance.

The distributor mechanism will have some amount of advance, say 22 and then you add more, say 8, by rotating the distributor to reach 30 max.

The last time I set it, which was several years ago, I think I just reved the engine until it reached max. advance, whatever the RPMs were, and rotated the distributor until I had the total advance I wanted.

Maybe someone else can enlighten us. I probably should put a timing light on my engine to confirm what I have.

There are two advances the initial advance and the centrifugal advance.     The initial advance is set at idle say 10 degree BTDC.  The centrifugal advance is from the springs with lets say allow 20 degree of addition advance when spun by the engine.  When you add the two advances together, you get the total advance 10 + 20 = 30.

The weaker springs get to the 20 degrees faster than harder springs.  You probable don't need to change your springs.

Don't overthink this, Paul.  It's not that involved but it's different for vacuum advance and centrifugal advance distributors.  

The vacuum advance style has a small rubber vacuum hose going from one or both intake manifolds (or a port at the base of the carbs) over to the advance diaphragm on the side of the distributor - it looks like a small flying saucer attached to the disti side.  THAT is a vacuum advance system.  To set the advance on that you need to consult a stock VW service manual like Bentley's or Haynes for the proper base advance, but it is set at idle and is most often 6º - 8º advance at idle, set by loosening the hold-down clamp at the base of the disti, rotating the disti body until you get to that range and then re-tightening the clamp to keep it there.

For centrifugal advance:

For centrifugal advance we don't really care what the advance is at idle.  All we care about is advance at 3,000 rpm.

Slightly loosen the disti hold down clamp just enough to allow stiff movement.  Attach your timing light to #1 plug wire.  That is usually at around 4 o'clock when looking down onto the top of the disti cap and it runs to the front (towards the cockpit) passenger side spark plug.  

Have someone sit in the driver's seat, start the (previously warmed) engine and have your assistant run the engine up to 3,000 rpm and hold it there as best they can (yes, it makes a lot of noise).  Avoid the spinning fan belt and deftly rotate the disti while watching the timing with a timing light to get the advance up to 30º BTDC.

Turn off the engine and tighten the disti clamp without moving the disti body.  Re-start and do a check to make sure nothing moved and you're done.

Guys, you're confusing things a bit. Paul, yes, rev it up to 3000 rpms and hold it there. It really helps to have another person do this for you. Then set the timing by loosening and turning the distributor until you get the advance you want. I hope you have a degree wheel pulley, it makes it easier. Check what you have now, before you change it, I'd like to know what it's set to.

I know the engine builder said 28-30 degrees, and I agree with that. I'm just curious if you give it 32-33 degrees HOW IT RUNS. If you give it full throttle after you advance it a little and it stops spitting and sputtering that's good, it didn't have enough timing advance.

If it still spits and sputters, report back what you find.

@DannyP, when we say some advance amount at 3000 RPM, is that also maximum advance? Or if we have, say 30 degrees at 3000, would we have more advance at higher speeds?

Depends on your distributor, some don't have all the advance come in until 3500 or so, but most are all-in by 2500-2800, which is why most recommend 3000.

One of the coolest things about having Ed rebuild my German 009 (besides drooling on his Aetna Blue/Red Karman Coupe) was that he had a computer interface to his Sun distributor machine so he could map the advance curve to factory specs.

If I can find the printout, I'll scan it and post it up.

@DannyP, so, not knowing where it is all in, couldn't you do as I described above, rev it until it no longer advances and then rotate the distributor until you get the maximum advance you want whether it is 3000 RPM or not?

Absolutely.

Okay, stupid question. 12 degrees before tdc is at the 12 degrees mark just right of the tdc?
Hate to ask that elementary question but seems as I am chasing my tail.
Paul Isaac
Sent from my iPad

> On Dec 28, 2020, at 10:46 PM, SpeedsterOwners.com <alerts@crowdstack.com> wrote:
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Yes. The engine rotates clockwise, so you want it to fire BEFORE it gets to TDC.

Well set at 32degrees as you suggested and not as much but still had carb popping ?

Paul Isaac
Sent from my iPad

> On Dec 28, 2020, at 11:17 PM, SpeedsterOwners.com <alerts@crowdstack.com> wrote:
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I have the CB Perfomance Magnaspark

Paul Isaac
Sent from my iPad

> On Dec 28, 2020, at 10:24 PM, SpeedsterOwners.com <alerts@crowdstack.com> wrote:
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The builder also best luck with idle mixture set at 2.5 turns? Seem really rich. Still some popping? not as a good of an idle as,when it was set with the tach at approximately 1.5 turns but less popping on acceleration?

Paul Isaac
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> On Dec 28, 2020, at 10:07 PM, SpeedsterOwners.com <alerts@crowdstack.com> wrote:
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Lots of good advice here. We want to help. Almost impossible to fix anything via email.

One last thing.

If you don't know how a properly set up and adjusted engine will run you definitely have a disadvantage. If the carburetors are correctly adjusted at idle. the engine will be running very smoothly. No shaking at all. When you reconnect the linkage nothing should change.

Check your accelerator pump linkage. There should be 1/8 to 3/16" of the threaded rod unless you have 150hp or something like. Weber gives a specification for the volume the pumps are to deliver, it's a starting place not an absolute. This was a major problem for me. I have gone thru the same problem and after everything else this was the fix.

Back off the adjustment nut. Both carbs should be the same.

Idle mixture is between 1/2 and 1 turn if you have the correct idle jets.

Jim
You are correct very difficult by email,but everyone’s comments have helped. Difficult to measure accelator pump rod since carbs on the engine and as you know very little room.
Thank you

Paul Isaac
Sent from my iPad

> On Dec 29, 2020, at 8:14 AM, SpeedsterOwners.com <alerts@crowdstack.com> wrote:
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Difficult or not you better have a look. Very likely you have 1/2" sticking out. It will flood every time you get on the gas.

At 2 1/2 turns on the idle jet screws will have you wasting more gas than you can afford to buy.

I have a 911 shroud on my engine and turned the carbs around to have access to the adjustment screws. If you have the VW shroud you may not be able to do that. As much time as I spent working on the carbs it was worth the effort.

Jim, good advice, except that very last one. First, they're actually VOLUME screws, not mixture. The mixture(ratio of fuel to air) is set by the jets, and we merely adjust how much of that mixture the idle circuit receives. Think about it, the fuel and air ratio is determined by the jets, not the screws.

I've found the correct range is somewhere between 1 and 1.5 turns out from(very carefully and softly) closed. If you end up with peak idle speed at less than 1 turn, the jets are too rich. More than 1.5 turns, the jets are too lean.

2.5 turns is the STARTING POINT for Dellortos, they have a finer thread screw.

1.5 turns out is the STARTING POINT for Webers and clones.

From there, you screw them in until idle speed drops off, then turn them out to peak speed, and maybe 1/8 turn more(NO MORE THAN THAT). I have good luck with exactly at peak speed.

Follow my procedure.

Jim is right though, that the acceleration pump circuit can be problematic and make you think it's the idles or mains. If steady state cruise is OK(no pops, no gas smell, and smooth running) and WOT(wide open throttle) is good(except for initial throttle application) you're probably looking at the accelerator circuit.

But remember, 90% of carburetor problems are ignition.

@Jim Gilbert - Madison, Mississippi posted:

Idle mixture is between 1/2 and 1 turn if you have the correct idle jets.

This is the last post I was speaking of. Sorry if there's any confusion. I guess Jim ad I were typing at the same time.

I'm quoting the WEBER guide. All I can tell you is what worked on my car.

Phisaac,

I don't know if it is possible on Weber/Empi, but on Dellorto one can install the auxiliary venturi upside down.  Perhaps on re-assembly?  On the 1-2 side?

I know (don't ask how) that when the aux vent is upside down, you can have perfect balance and idle, and it runs well with gentle acceleration up to about 2000.  But if you tromp it or try to accelerate past 2000ish you will be rewarded with truly attention-getting snarly backfiring.

It is not the kind of thing one would normally look for, but it is east to spot if you do.

Like I said, that may not even be possible; just a thought - - - -