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> Whats wrong with my Carbs?, wants to stall leaving the traffic light.
Hans Jan
post Mar 25 2017, 09:12 PM
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Hello,

Not having much luck with the Search function.

The car: 1972, with 103mm cylinders (2.3l), aftermarket cam and larger valves with double springs.

Fuel supply: Dual EMPI HPMX 44 Carburetors,
Jets: .55 Idle, 1.55 main, Air 1.75.

History: After car-fire engine was out, heads taken off and some studs and springs replaced. Changed to quieter exhaust.
Had trouble with dialing in the carburetors and changed the jets to the recommendations from EMPI (see above). It runs a lot better now.

Remaining complaint;
The car runs pretty good (especially above 2,800) RPM.
However; It takes me a while to leave after each stop (stop signs traffic lights etc) because the car want to stall. When I push the accelerator to quickly the RPM dips down, and car will die. Only when I ease on the paddle very gently, it will increase in RPM, and I can lift clutch at above 1,500 RPM.

Anyone here understands this issue?



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exultant1
post Mar 25 2017, 09:33 PM
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What's your timing? What distributor are you using?
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Spoke
post Mar 25 2017, 09:37 PM
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Are your acceleration jets working? Sounds like it could be going lean when you first open the throttle.
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r_towle
post Mar 25 2017, 09:45 PM
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I would certainly check the distributor, advance weights and dwell/timing first .
I personally prefer 40 mm on that motor with the smaller ventures which makes off the line (your issue) more smooth with a faster air flow going into the motor.

You can do this two ways, both will cost the same.
1) bring it to a shop with a Dyno to tune the carbs.
2) throw smaller venturis in to increase the velocity of the charge...leave the rest as is. The increased velocity will draw in more fuel.

With smaller vents you will top out sooner, but you will increase lower rpm response.
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Keith914
post Mar 25 2017, 10:05 PM
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My 1.365 liter type IV has twin 44 Webers. It runs well at sea level with 55 idles, 150 mains, 200 air corrections and 34 venturys, along with vacuum advance distributor with timing at 32 degrees at 3000 rpm. I have an Innovative A/F gauge to help in tuning -- A/F's range between depending on: idling 12.5, accelerating 11 - 12.5, cruising above 2500 rpm 13.5, decelerating 14 - 15.
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Keith914
post Mar 25 2017, 10:08 PM
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Also, you need to be sure the "dormant" choke pistons are fully seated in the off position. PM me for more info if needed.
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PotterPorsche
post Mar 25 2017, 11:21 PM
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I'm with Keith your mains are a a little fat. You need to get an lm2 wiifeband to remove the guessing. Aircooled.net I believe rents one. Also timing . Sounds like your getting too much gas or not enough timing, when you step on the pedal. What do the spark plugs look like?
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Hans Jan
post Mar 26 2017, 11:03 AM
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Wow guys that is quite a response. Most of which I do not yet completely understand. I will look into all of your suggestions and let you know.

Exulant: Not sure what the timing is. Some lousy shop tried to dial in my car; $3,800 and twelve weeks later I picked it back up and start tinkering myself.

Spoke:: Not sure what acceleration jet is. Carbs come standard with 0.50 Acceleration pump (but honestly; I don't even know what I just said).

T-rowle: Will smaller venturis make the car slower?

Keith914: your engine is really only 1.365 liter? Not sure yet if my carbs have a "dormant" choke piston (will investigate).

PotterPorsche: Lm2 wideband, this is getting really technical. Give me some time to figure out if I understand how to use one of those.

Thanks y'all.
You have given me plenty of things to look at.

Br,
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r_towle
post Mar 26 2017, 11:12 AM
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Smaller venturis limit the overall amount of air, but only at peak rpm. You may sacrifice 2-300 Rpms by using smaller venturis but you will gain lower rpm performance.
With carbs it's always a sacrifice somewhere.
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r_towle
post Mar 26 2017, 11:16 AM
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You want a wide band air/fuel meter with a gauge.
I use one with an 02 sensor stuffed up the tailpipe for tuning only.
Others install them perminantly by welding a bung into the exhaust.
Still more granular is to use EGT temps to monitor the mixture on each cylinder.
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r_towle
post Mar 26 2017, 11:19 AM
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The nice part about carbs, at least our Weber's, is you can do these changes without opening up the carbs, so you could have a larger setup for racing, and a smaller setup for around town normal driving....swap takes minutes
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porschetub
post Mar 26 2017, 01:43 PM
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The smaller vents will lose some power right @ the top but this will be in a range you rarely drive in,what you will see is a big improvement in bottom end power and response,any small loss in power will be soon forgotten once you have improved drivability .
It was common knowledge earlier on with these carbs that they were not well setup ''out of the box'',this has been covered by aircooled.net and documented on theSamba.com.
When tuning carbs always carry out a full ignition tune up first,good leads, plugs,cap,etc and correct timing,otherwise its a waste of time.

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rhodyguy
post Mar 26 2017, 01:48 PM
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Buy yourself a copy of the CBperformance weber manual. Read up and all of the suggestions will make sense. Don't go back to that shop.
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Keith914
post Mar 26 2017, 02:29 PM
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Oops, 2.365Liters!
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dyckster
post Mar 26 2017, 02:48 PM
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Hi Hans,
everyone is going to have an idea about what your problem is, myself included(accelerator adjustment)but you really need to educate yourself and learn how to fix it yourself.
Most mechanic nowadays are simply parts replacers, not diagnosing and problem solvers.
Buy the book, read it and understand it, then adjust stuff.
Make small adjustments, try it out between each adjustment. Its a great feeling when you figure it out yourself.
I'm not sure about the hpmx book, but I have the dellorto which is very much the same, and it has a section that says "if it does this then try this and this". that helped me immensely!
good luck
blair
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stugray
post Mar 27 2017, 11:51 AM
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My most recent weber challenges:
1 - My accel pump diaphragms did not match. One was barely pumping. I found a way to measure how much came out each and found them to be WAY off. Replaced both and it made a world of difference.

2 - If using pump gas (in the US) with ethanol: This WILL clog your jets. As the gas sits in the bowls the ethanol absorbs water, then the gas and ethanol evaporates leaving the water in the bowls to corrode the aluminum. This leads to white powdery deposits in the bowls which will clog the jets. FILTERS do NOT help. (the ethanol destroys the diaphragms in most of our fuel pressure regulators too - they will only last about 1 year in ethanol)

3 - Intake manifold leaks. Sometimes they would leak when hot, but not cold. Do the WD40, starting fluid, or water spray test AFTER the engine has warmed up. see if you can make the engine stumble spraying around the manifold bases, carb bases, and throttle shafts.
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Hans Jan
post Mar 27 2017, 01:48 PM
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From what I gather, it appears that I need to check the timing first before doing anything else. I have no clue how to do that, but will get a timing light and learn how to use it.

Distributor: Petronix (Flametrower) P/N D1867
Vacuum hose: No
Cam: Unknown (markings are "CWC")

How to determine what the timing should be set at, with this unknown cam?

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Racer Chris
post Mar 27 2017, 02:53 PM
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Use 28 degrees btdc @ 3500 rpm.

If I recall correctly, that engine has a pretty stout cam profile.
Between that and the large valves, you will probably never have good off-the-line performance without revving it up and dumping the clutch.
That said, try 170 mains and 220 air corr. jets.
Going bigger should shrink the flat spot.
You may also need to adjust the accelerator pump rods to squirt more fuel.
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forrestkhaag
post Mar 27 2017, 03:10 PM
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Also (Kieth) didn't we both notice exceptional improvments in my HPMX40's and your Weber 44's when we tapped and plugged the non-functional choke circuit ports?

Also / agree with the timing function needing to be right on the advance. Mine on the type 4 was 32-34 degrees...... otherwise power was suffering and I would experience lag on start off. (IMG:style_emoticons/default/beerchug.gif)
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Hans Jan
post Mar 29 2017, 09:53 PM
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Thanks for your input.
I'm a little short on time to work on the car.
Instead of learning about timing, I ordered #34 Venturi's (current size is #36). Just because that was something I could do while doing groceries.

Not sure if this is related, but.
The car also comes slow "off its RPM". Meaning when it runs at high RPM and I need to slow down (with foot of the accelerator and clutch pushed in, to downshift), or stop. The engine keeps spinning high for 2 or 3 more seconds.

During up-shifts it sounds like I'm pushing the accelerator between shifts (not the case).

Like I said: Not sure if its related, but worth noting.
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