Carb jetting?, I got lots of top end, no bottom Options

[VaccaRabite]

So, ScottyB spent all of yesterday trying to get my carbs properly adjusted.

We can not get it to idle well below 1500 rpm. it sings around 3000, and screams above 4000. Even wthout load, we can tell the carbs are tuned for top end only.

Here is the deal. My motor is a 2056. The carbs are 44 webers. I KNOW that I will have an easier time with 40s. But I don't have 40s. And I know that folks around here have gotten 44s to work with a 2056. (I'm looking squarely at you here, OpaAndy).

So, engine particulars.
2056 motor.
compression test gives a range of 135 to 148psi on a warm engine
WebCam 494 grind
Valves are (freshly) adjusted to .006 in and ex (as per the cam card)
Deck deck height is .040
CR is 9.5 to 1 (calculated here: http://www.cprparts.com/ci_calc.html)
Exhaust is EuroRace header with a turbo muffler
My house sits at ~700feet elevation, but my driving area is between 100 and 1000 feet (I live around foothills)

How should I jet these carbs to work with this motor? What should my venturii size be?

I CAN NOT put my motor under load yet. The motor is in the car as of yesterday, but the car is NOT yet drivable.

Zach

[Kirmizi]

Zach, have you read Harney's Carburetor Clinic on tuning Weber IDF's?
I've got it bookmarked and seem to remember a description of jetting sizes/effects upon power bands and tuning.
Mike

[r_towle]

Your venturis are to large.
What size do you have?
32mm is (I think) the smallest vent for a stock 44mm carb.
Aircooled.net can have smaller ones made up...

On 40mm carbs, a 28mm vent is nice for low end grunt.

The 44mm is just the potential size...the vents make it smaller.
The problem is that the stock sized vents for the 44mm body are still to big IMHO....
Call aircooled.net...they are really cool and can help you out.
They have a large spreadsheet of carb jetting setups from customers that WORK...and they will actually SHARE this information.

The last time I did this, they swapped jets and vents with me till it ran perfect...I only ended up buying one set, paid for shipping (USPS cheapo box) each way, just twice.
I ended up with 31mm vents...it was a special motor though.

Rich

[Kirmizi]

http://www.carburetorclinic.com/weber_tech.htm
Mike

[rhodyguy]

bear with me a minute. with the linkage disconnected, you can not achive an idle around 900 with the idle adj screws only ? even if the screws are off the stops? 32mm on the vents.

[type11969]

Zach-

I have dell 40s on my 1.8 (equiv in flow to weber 44s) and I'm doing okay. Your 2056 will be fine with 44s. What vents size are you running right now? Sounds like it is too big. I've got 32s on my 1.8, 30s would be ideal but I couldn't find them. I'm pretty sure this is my approximate jetting setup:

55 idle jets
55 pump jets
140 main jets
180 air correctors

I run kind of rich so this may be an okay baseline for you.

-Chris

[VaccaRabite]

bear with me a minute. with the linkage disconnected, you can not achive an idle around 900 with the idle adj screws only ? even if the screws are off the stops? 32mm on the vents.

Oh, we could get it to idle at 900. But it was lumpy. At 700 it would lump, sputter, and start to die after a minute or so if we did not goose the throttle. It did not start to even out until around 1200, and really smoothed out around 1500.

Zach

[VaccaRabite]

Another wrinkle. I don't know my vent size. I can not figure out how to remove them from the carb. I can't find the set screw, and worry that they are staked some how, so I have not applied any force to remove them. Help in this area would be greatly appreciated.

[stepuptotheMike]

Zach,

Looking at the notes on my 2056 with Weber 44s... cam is WebCam 86A .435 x 290 deg.

Venturi Size: 36mm
Main Jets: 135
Idle Jets: 50
Air Correctors: 200
Emulsion: F11

-Mike

[rudedude]

I've go a similar 2056 with 33mm venturis in weber 40's and at 900 foot elevation has good low and top end. I cant remember jet sizes but could easily check.

Jule

[904svo]

Sounds like you have a vacumn leak, get starter fluid and check around carbs and then the intake manifold. On mine I found the intake manifold was not straight where it bolted up to the head.

[r_towle]

Another wrinkle. I don't know my vent size. I can not figure out how to remove them from the carb.

Are these webers?

The set screws are on the side, about halfway down the outside of each venturi.
Look on all three exposed sides...3, 6, and 9 oclock...

the upper vents, the ones with the round part in the middle are held in by a spring, but that spring is captured by the top cover of the carb...so you need to remove the top of the carb to get the top vent out.

It can be corroded and will take some gently persuasion to remove the top one.

Show a pic of all three sides of the carb and I can show you where the set screw is.

To find out what vents you have installed, you need to look down the throttle body and on the top edge of the main venturi is a number stamped into the vent.
If they are custom, you may not have this number.
Otherwise its on the top edge of the lower venturi.

I dont know your camshaft but think of it this way.
Higher HP numbers are only made in the upper RPM range.
One of the guys posted that he has 36mm vents...
That is great for a race application...WOT balls out driving, but it would suck around town...you would have slow air speed, and to much slow moving air.

If your camshaft has alot of overlap then it will run great at the upper RPM range and would be designed for bigger valves, large venturis, and will even out when the overlap is useful...high RPM.
At low RPM, camshafts with alot of overlap will run like a harley...very lumpy or loping...that is ok. They can be tuned.

The key is the amount of air you are allowing into the motor (its an airpump) and from there you figure out your jets to match...not the other way around.

Rich

[Joe Ricard]

Doesn't matter.

I will also bet on a vaccum leak. I use the grey RTV from permatex on each side of the phenolic gasket. no paper. Works good. CUZ of course that's what Jake said to use.

What size idle jets????

Are you able to lean out the idle adjustment screws to nearly shut off gas?

Um New engine??? timing set at what?

Ignition set up?
Spark plug gap?
Have the plugs fouled? Very possible as it sounds like a new motor.

Disconnect the linkage on one side and set idle speed. then tweak mixture screws re-set idle speed reconnect linkage and then synch carbs while engine runs at 2500 RPM off the idle stop screws.

[klink]

OK here's my two cents. Just got finished building my 1.7L to a 2.0L. 2.0L crank, rods, pistons barrels. Mild cam. Empi HPMX 44's. Weber knock-off carbs. Parts are interchangable. When I fired it up it ran and idled very well. It did however pop a little through the carbs. When I drove it, it had a serious low end bog but ran well mid range and top end. Got some advice from the local porsche repair shop as well as an off road shop. Both agreed the venturi size was too big. Carbs came with 36 mm veturies, 50 idle jets and 50 squirters. We went down to 34 mm venturies and the improvement was huge. Still had a touch of bog when I would give it gas at low RPMs. Rather than going smaller on the venturies they suggested going up on the idle jets. Went from 50s to 55s. Low end bog was gone. It responds very well anywhere at low end now. Does seem to idle a little rich though. The way it was explained to me is that if the venturies are too big there just isn't any vacuum being created in the motor, hence the popping back thruough the carbs and the inability to accept fuel. They also said you want the largest venturies that will run well. Too small of venturies will give great response in low RPMs but you will lose top end. So try reducing the venturies slowly. Put a smaller set in and try them. Stop when you get close and go to jetting. I am not an expert here, I just went on these peoples advice and it solved my problems. Word to the wise, when you take off the tops of the carbs if they are still on the motor put something down the carb throats to catch parts. I don't know if webers do it but when I took the tops off the Empi's a couple of spring loaded somethings held in by a crush washers took off on me. They are supposed to stay in the carb body on one side right in the middle and there are two per carb. Hope this is helpful...again just my two cents.

[904svo]

OK here's my two cents. Just got finished building my 1.7L to a 2.0L. 2.0L crank, rods, pistons barrels. Mild cam. Empi HPMX 44's. Weber knock-off carbs. Parts are interchangable. When I fired it up it ran and idled very well. It did however pop a little through the carbs. When I drove it, it had a serious low end bog but ran well mid range and top end. Got some advice from the local porsche repair shop as well as an off road shop. Both agreed the venturi size was too big. Carbs came with 36 mm veturies, 50 idle jets and 50 squirters. We went down to 34 mm venturies and the improvement was huge. Still had a touch of bog when I would give it gas at low RPMs. Rather than going smaller on the venturies they suggested going up on the idle jets. Went from 50s to 55s. Low end bog was gone. It responds very well anywhere at low end now. Does seem to idle a little rich though. The way it was explained to me is that if the venturies are too big there just isn't any vacuum being created in the motor, hence the popping back thruough the carbs and the inability to accept fuel. They also said you want the largest venturies that will run well. Too small of venturies will give great response in low RPMs but you will lose top end. So try reducing the venturies slowly. Put a smaller set in and try them. Stop when you get close and go to jetting. I am not an expert here, I just went on these peoples advice and it solved my problems. Word to the wise, when you take off the tops of the carbs if they are still on the motor put something down the carb throats to catch parts. I don't know if webers do it but when I took the tops off the Empi's a couple of spring loaded somethings held in by a crush washers took off on me. They are supposed to stay in the carb body on one side right in the middle and there are two per carb. Hope this is helpful...again just my two cents.

Hope you put the springs and washer back, there for the choke with out them your
engine will run rich.

[klink]

So that's what those are....one of them went half way accross the garage and I had to take the battery out to get another but I found them and re installed them. Seems like the lock washer looking keepers that seat into the top of the carb body should hold them down better. I got the springs and parts back down the bore and gently tapped the keepers in. I was thinking that if I take them apart again I might put just a dab of RTV glue on top of them and make sure it's smooth and flat. Any other ideas on how to control these little suckers?

[VaccaRabite]

I just pulled a carb and took stock of what I had. Many thinks to those that have helped this far, I have learned a lot.

Here is what is in the carb:

Venturi: 32mm (not stamped anywhere as far as I could see, so I measured 1.258 inches (31.95mm))
Aux Vent: 4.5
pump jets: 50
Main jet: 125
Emulsion tube: F11
Air Correction 200
Idle Jet: 55
Inlet Valve: 55

Thanks

Zach

[904svo]

Change the mains to 135 that should help the low end and the idle. The book says
the main are used above 2800 rpm's but the idle circuit gets its gas through the mains.

[r_towle]

bigger main jets is compensating for the low air speed created by using a venturi that is to large.

Drop the vents to 28-30...both custom sized but you need to increase the velocity of the intake charge.

Your camshaft, what is it, who made it etc?

Rich

[VaccaRabite]

I have been emailing with the guy at Aircooled.net. He seems to think that for my cam (Webcam 494 grind) my vents and jetting is "darned near perfect."

He thinks my issue is either float level or air leaks. I know my 3/4 float is good, and I am pretty sure my 1/2 float is good. So, air leaks.

Now that the motor is in the car, I actually have a lot of hooking up to do before I can start it for more testing. The gas tank went in tonight. Though I may need to fiddle with the fuel lines under it, I am not happy with how they are running.

Zach