I hate my Carbs Much Less, Chris Foley is a God! Options

[Mblizzard]

Well after much playing and changing I have to say I hate my carbs. I have done every jet size and I can't really get it to run well on anything but 70 idle jets and that is way to rich. With 60s it runs not quite as rich but the hesitation on the initial throttle is huge.

Have played with the adjustments and I think I have it running well but it never performs well. 2056 just built, 44 IDFs, 60 idle jets, 28 vents, 135 mains, F-11 emulsion tubs, 175 air correction jets. Timing at 27 to 30. SVDA Dizzy with electronic ignition. Valves recent set and rechecked. Synced at idle and 1500 rpm.

Runs well at higher rev and pulls strong but I can't get rid of that hesitation. I know there will always be some but at times from a dead stop it almost stalls.

What am I missing? (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/headbang.gif)

Gone through all of the Weber tech trouble shooting steps and I can't find anything that says I have something wrong. Is there an adjustment on the accelerator pump? Or do I need to up the accelerator jet?

I will be going back to FI at some point but these carbs should work better than they do. Taking it to Eurohaus tomorrow maybe they will have better luck.

Suggestions?

[rhodyguy]

did you ever try backing one of the throttle stop arm screws off contact?

[DBCooper]

You say "hesitation on the initial throttle is huge." What does that mean, exactly? Is it always from a "dead stop"? Meaning it falls on its face on the first touch of of the throttle? When you stab the throttle only from low RPM's, or only at high RPM's, or both? Or on a smooth application of the throttle it stumbles at some point as the RPM increases? All of those, or any of them more or less?

Are you using the Weber tech manual? It has (if I remember correctly) some values for the volume of gas from each full squirt of the accelerator pumps. Did you measure that? If not you can get a reasonable idea by watching the stream in each throat as you pump the carbs, but I guess you probably need to know what looks "right" first. to compare.

Oh, and another thing that can cause a low-RPM stumble is low float level and not enough fuel in the bowl.

[rhodyguy]

the carbs in the kit don't have a pump arm adj feature?

[7275914911]

I want to say too much Carb for a 2056(does it have a cam?). On my 2056(9550) I am running 40idf with 32 vent, .55 Idles and 1.35 Mains. I am also running big headers and performance muffler. And I am very happy with the performance. Cable Linkage also. Really money well spent on that item!

Good Luck, Mike....

[rhodyguy]

iirc his venturies have been sized to 32s.

[Cap'n Krusty]

Before we go any farther, what distributor are you running?

The Cap'n

[DBCooper]

Said it's a SVDA and 28 venturis on a 2056, but didn't say what cam.

[Cap'n Krusty]

Well, that's what I get for not reading the original post very well. Is the vacuum hooked up? Correctly? Is the timing set to what it should be with that distributor?

The Cap'n

[DBCooper]

Cap'n, he said he'd tried timing between 28 and 32, so I'm assuming with a light at full advance. Mike, were you getting timing movement with a light when you varied RPM's? And for curiosity do you know what the timing was at idle?

[Mblizzard]

Ok running through the list!

Stock FI cam.

Floats are set to the recommended spec.

Getting good movement of advance with rpm change. At idle the timing was just slightly advanced for TDC.

Dizzy says 28 to 34 BTDC so I am in that range.

The accelerator pumps seems to be putting out a good stream. Hesitation not present wit 70 idle jets.

Huge hesitation is only at low rpm or dead stop. In 3rd gear at 3000 rpm going to WOT is a slight hesitation that is barely noticeable.

Carbs to big? After consulting with numerous experts the consensus was 40 or 44 did not matter if the vents were sized correctly. Running 28s for more low end performance. Might try 32s but I just don't think that is the issue.

Did I miss anyone?

[r_towle]

I cant believe 60 idle jets on 44mm carbs would not run far to rich in the idle circuit.

The throttle plates are still 44mm regardless of the venture sizes.
It is a big carb for that motor.

Camshaft might make it work, but it would need plenty of overlap to speed up the A/F charge enough.

What happens when you run smaller idle jets?

Its an air velocity issue you have to sort out.
Smaller carbs, or more aggressive camshaft with headers and heads to match.

Smaller carbs will make you smile.

[Mblizzard]

I cant believe 60 idle jets on 44mm carbs would not run far to rich in the idle circuit.

The throttle plates are still 44mm regardless of the venture sizes.
It is a big carb for that motor.

Camshaft might make it work, but it would need plenty of overlap to speed up the A/F charge enough.

What happens when you run smaller idle jets?

Its an air velocity issue you have to sort out.
Smaller carbs, or more aggressive camshaft with headers and heads to match.

Smaller carbs will make you smile.

While I understand the thought on the butterfly valves, the information I got was that the valves could be 144 but the vent still determined the flow. A 28 vent in a 44 performs exactly the same as a 28 in a 40. Right or wrong that was the opinion of more than one person. I have seen 44s on smaller engines.

Going smaller on the jets to 45 makes it run so poorly that it is clear it is running very lean.

[Jetsetsurfshop]

Did you check the linkage. Working on my car today and had similar problems. The passenger carb was opening before the drivers. Basically running on 2 cylinders.

[r_towle]

Stock FI camshaft, jets to large, and throttle plates too large with a very slow port speed are clear factual evidence that the opinions you have listened to May not always be right.
40mm is good up to about 2.4 liter, but then you need custom vents to keep up.

How do you know it's running lean? Do you have an Air fuel gauge?
Running 50 idles is pretty typical on a 40 mm carb.
With the larger amount of air moving by the jet, you cannot help but suck in more fuel than a properly tuned 40mm carb, though at a lower speed.

It may be reality that in order to try and compensate for the larger throttle plates, and lower port speed, you may need more fuel to make up for it, but I have a really hard time believing that....

But what do I know.

[r_towle]

Did you port match the bottom of the carb to the manifolds?

carbs are all about port velocity, open times (duration) of the camshaft, and the overall sucking power of the engine...it's all a Venturi affect.

You might be able to get it right, or you may need to live with the bogging low speed of the 44 mm carbs on a stock camshaft motor...

Really the issue is the camshaft is really a low duration with little overlap, so the air speed is slowwwwwwww

This works fine with EFI when you can regulate the fuel with an on off switch, but when you regulate the fuel based upon port speed and air flow, you need smaller carbs...or a better air pump....or both.

[Bills914-4]

I'm guessing you balanced the carbs with a uni-sync of some type and that you adjusted the linkage so that they pull the same on each carb ,

when my carbs are out sync (one side getting more fuel there than the other side)
it stumbles and hesatates in the low RPM range & low rpm takeoff , Bill D.

you might want to invest in a weber book , I learned a lot form my dellorto book : )

[914_teener]

(IMG:style_emoticons/default/agree.gif)

Yup......stock camshaft.

[Cap'n Krusty]

Cap'n, he said he'd tried timing between 28 and 32, so I'm assuming with a light at full advance. Mike, were you getting timing movement with a light when you varied RPM's? And for curiosity do you know what the timing was at idle?

OK, I missed that, too. I'm a bit off today, sitting down a couple of minutes at a time between moving truckloads of stuff between storage sites for 3 people. Full advance with or without vacuum? The thing I'm getting to is whether there's enough initial advance when the throttle is cracked. Many systems accomplish this with a vacuum retard unit. As in, BAM, you have 10-12 degrees right now.

The Cap'n

[Mblizzard]

Cap'n, he said he'd tried timing between 28 and 32, so I'm assuming with a light at full advance. Mike, were you getting timing movement with a light when you varied RPM's? And for curiosity do you know what the timing was at idle?

OK, I missed that, too. I'm a bit off today, sitting down a couple of minutes at a time between moving truckloads of stuff between storage sites for 3 people. Full advance with or without vacuum? The thing I'm getting to is whether there's enough initial advance when the throttle is cracked. Many systems accomplish this with a vacuum retard unit. As in, BAM, you have 10-12 degrees right now.

The Cap'n

Without vacuum. I am going to run through everything again and check to be sure I have not missed anything and let you know.